Miguel Zabakoitia, M.D., received his medical degree from the University of Guadalajara, Mezico, in 1976. Afier 3 years of residence training in internal medicine at the Instituto National de la Nutrition in Mexico City, he completed 3 years of cardiology fellowship at the University of Ottawa Heart Institute. After 1 year of research fellowship in echocardiography at Northwestern University Medical School, he joined their faculty as Director of the Noninvasive Laboratory Veterans Administration Lakeside Hospital). He has been on the faculty at The University of TeFas Health Science Center at San Antonio since 1966 and is currently Assistant Professor of Medicine and Director of the Non-invasive Laboratories. His research interests include the assessment of valvular heart disease with the use of Doppler echocardiography, particularly through the epicardial and transesophageal approach, and the pacing-induced segmental wall motion response during transesophageal stress echocardiography. 270

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ECHOCARDIOGRAPHIC ASSESSMENT OF PROSTHETIC HEART VALVES

INTRODUCTION

It has been more than 30 years since the first artificial valves for the treatment of severe valvular heart disease were implanted sucReplacement with cessfully in the aortic’ and mitral’ positions. prosthetic valves has become the standard of patient care for hemodynamically significant lesions. The first valves used in clinical practice in the early 1960s were the ball-in-cage valves. Soon after, several disc-in-cage valves were introduced, but over a decade they were abandoned because of severe hemodynamic and thrombotic complications. The tilting disc design continued with numerous ingenious modifications. In the 197Os, broad use of biological prostheses started, mainly because long-term anticoagulation was not necessary. In the early 1980s the decreased durability of bioprostheses became obvious, and most cardiac surgeons shifted back to mechanical valves. Clinical results with a particular artificial heart valve vary widely among different patient populations around the world. However, patient-related variables, the type of surgery, and the time factor (patients operated on at different periods) have the greatest impact on the results of valvular replacement.3-8 Despite substantial improvements in design and manufacturing, dysfunction due to loss of structural integrity, thrombosis, infection, degeneration, dehiscence, fibrous ingrowth, hemolysis, and embolization continue to challenge the skills of practicing cardiologists and cardiac surgeons. Thus it is not surprising that, after so many years of clinical experience, the search for the “ideal” artificial heart valve continues with increasing interest. The optimal management of patients with prosthetic cardiac valves requires serial assessment of both valve function and left ventricular performance. Doppler echocardiography has become the mode of choice in making this serial assessment because of its noninvasive nature.s-20 More recently, transesophageal echocardiograCurr

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phy has provided superb imaging resolution of prosthetic valves and adjacent structures.21-25 To fully appreciate the value and limitations of Doppler echocardiography in assessing prosthetic valve dysfunction, a brief review of the several types of artificial heart valves and the most common complications associated with them is in order. TYPES OF PROSTHETIC

VALVES

Over the last 30 years, a multiplicity of prosthetic valves has been utilized. Artificial heart valves can be divided according to their constituents into biological and mechanical. Biological (tissue) prostheses can be separated according to their species source into homografts krllografts) and heterografts (xenografts). The mechanical prostheses, in turn, can be subdivided according to their structural mechanism into ball-in-cage, single-tilting disc, and double-tilting disc. For the purpose of completeness, atrioventricular annular rings are considered within this group (Table 1). Most prosthetic devices have a base ring, circular in shape, that is surrounded by a fabric sewing ring that permits the device to be fastened to the annulus. b P.M. SHAH:To the list provided in Table 1 might be added the Ionescu Shiley valve, which although discontinued at present, was inserted in several thousand patients in the early and mid-1980s. This is a pericardial xenograft, and its failure or malfunction is similar to that described for other biological valves. Simi-

TABLE 1. Types of Prosthetic Heart Currently Approved for

Valves

Clinical Use

in the United States Biological Aortic homogrd Porcine hetemgraft Hancock Carpentier-Edwards Mechanical BaII-in-cage Starr-Edwards Single-tilting disc Medtmnic-Hall Omniscience Double-tilting disc St. Jude Medical Annular ring Carpentier-Edwards Duran Puig Massana-Shiley

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larly, the Bjork-Shiley tilting disc has been inserted in a large number of patients. It has been discontinued.

Several new valves, biological and mechanical, are currently under clinical investigation. Most of the results with these new devices are either incomplete or not yet published. Therefore, this monograph will focus on those artificial heart valves that are approved by the Food and Drug Administration (FDA) for commercial use in this country. b S.H. RAHIMTDCM: Annular rings strictly are not prosthetic heart valves. However, their inclusion in this report is useful.

BIOLOGICAL

The antibiotic-sterilized, cryogenically preserved homograft, sewn freehand in the aortic position, is an alternative for patients with significant valvular disease.26-zs The major advantages of the aortic homografts are relative resistance to infection and preservation of good hemodynamics even with the use of a very small size?” 3o These features make them particularly attractive in patients with native or prosthetic aortic valve endocarditis and patients with small aortic root diameter. The absence of signiticant echo-producing artifacts is an additional benefit from the echocardiographic point of view. However, because of the increased technical difficulties involved in the preparation and insertion of aortic homografts, and concerns regarding their durability, relatively few centers continue to use homografts on a routine basis. The Hancock prosthesis is obtained from young porcine aortic valves mounted on a semi-flexible stent made from polypropylene that is covered with Dacron cloth (Fig 1). In the late 197Os, the hemodynamic performance of this bioprosthesis was improved by replacing the muscular-based septal leaflet with a larger noncoronary leaflet.3l The Carpentier-Edwards porcine valve is mounted onto an asymmetric, totally flexible metal stent made from Elgiloy (an alloy of cobalt and nickel). The reasons for the flexible stent are to reduce stress forces at the commissures and the base of the cusps, and to improve the hemodynamics.32 A further development has been the supra-annular valve design, which provides a 20% to 30% increase in the orifice area.33 MECHANICAL The mechanical prostheses currently available in the United States are the Starr-Edwards models 1260 (aortic) and 6120 (mitral), the Curr

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FIG 1. Hancock prosthesis.

Medtronic-Hall, the Omniscience, and the St. Jude Medical. The atrioventricular annular rings are the Carpentier-Edwards (rigid),34 the Duran (flexible),35 and the Puig Massana-Shiley (adjustable) .36 The Starr-Edwards is a ball-in-cage prosthesis with a bariumimpregnated Silastic ball inside a stellite cage to which is attached a seamless cloth sewing ring (Fig 2). The Medtronic-Hall is a single-tilting disc prosthesis. The circular disc, coated with pyrolytic carbon, pivots over a central strut inside a housing machined from one solid piece of titanium attached to a rotatable Teflon sewing ring (Fig 3). The open-disc angle of the aortic valve is 79, and that of the mitral valve is 70’. The close-disc angle is 0’ in both aortic and mitral positions. The disc of this prosthesis does not have a fixed opening angle, but in the open position it rests on a hook-shaped stent out of the orifice. As a result, the flow velocities can be recorded across the entire valve orifice. Both opening and closing clicks are normally heard. Absence of either click is indicative of dysfunction.37 The Omniscience, a second-generation of the Lillehei-Kaster, is a single-tilting disc prosthesis. The pyrolytic carbon disc moves inside a titanium housing attached to a seamless Teflon sewing ring (Fig 4). 274

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FIG 2. Starr-Edwards

prosthesis.

This valve has an open-disc angle of 80” and a close-disc angle of 12”. Similar to the Medtronic-Hall, the Omniscience normally has Fpening and closing clicks, the latter being louder than the former. The St. Jude Medical is a split disc (bileaflet) prosthesis whose pyrolytic carbon discs pivot inside a pyrolytic carbon housing attached to a Dacron sewing ring (Fig 5). The two leaflets have an opening angle of 85’ and a closing angle of 30’ to 35’, depending on valve size. Flow is relatively laminar across the entire valve orifice and can be recorded well at almost any point in the open position.3s Normally, the valve opening is silent but the valve closing is heard as a loud click. However, contrary to the single-disc prosthesis, significant dysfunction of the St. Jude Medical can occur even in the presence of an audible closing click originating from one of the two leaflets.38 The atrioventricular ring used most extensively around the world is the Carpentier-EdwardsW Thus, the discussion regarding annular rings will focus on this particular device unless otherwise specified. This prosthetic ring is constructed of titanium alloy and has a sewing ring of silicone rubber covered with a polyester knit fabric. Design objectives include retention of the natural valve apparatus and prevention of secondary distention of the annulus. The mitral ring has a kidney-shaped configuration, whereas the tricuspid ring has an oval configuration. The feasibility of mitral valve repair and ring insertion now extends to approximately 95% of patients with degenerative disease, 70% with rheumatic disease, and 75% with ischemic disease .40 b P.M. SHAH: The Duran annular ring is a flexible ring and thus offers, at least hi theory, the advantage of being able to adapt to changes in shape and size that the annulus may be subjected to during the cardiac cycle. The complication of Curr Probl

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275

FIG 3. Medtronic-Hall

aortic and mitral prostheses.

FIG 4. Omniscience valve,

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FIG 5. St. Jude Medical valve.

systolic anterior motion and left ventricular outflow tract gradient described with the Carpentier-Edwards ring has not been reported with the Duran ring. COMPLICATIONS

ASSOCIATED

WITH

PROSTHETIC

VALVES

One must realize that insertion of any type of artificial heart valve is not a cure for that specific valvular lesion. All prosthetic valves have common and particular complications that characterize their “natural history.” Thus, when a patient receives a prosthetic device, he or she is exchanging one disease state for another. In general, significantly elevated aortic transvalvular gradients, reduced mitral valve orifice, and moderate to severe prosthetic valve re rgitation, am pathognomonic of prosthetic valve dysfunction.41- PO However, biological and mechanical prostheses differ in the mechanism that produces such abnormalities. BIOLOGICAL

With homografts, the freehand insertion technique of these unstented valves is technically demanding. Aortic insufficiency has been reported to be a significant problem, with an incidence of 27.3% .” However, most cases (23.2%) have been mild or moderate, and only 4.1% have been severe. Aortic homograft insufficiency has a Curr

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variety of mechanisms: (1) slow leaflet degeneration, which may lead to cusp rupture; (2) spontaneous cusp rupture, particularly in patients with uncontrolled hypertension; and (3) infective endocarditis with associated cusp destruction.zg The probability of freedom from homograft failure is not different from that reported with porcine xenografts at 5 years (97% vs 94% 1.2s,51 However, at 10 years, the 85% actuarial probability of valve survival with homografts is considerably superior to the 63% reported for the Hancock xenograft.52 Significant aortic homograft stenosis is not a problem.5” Leaflet calcification is uncommon, and, when present, occurs as discrete, small, bony, cauliflower-like spicules that have only a minor effect on leaflet movement.30 The two major complications of biological porcine heterograit valves are infective endocarditis and calcific degeneration.54-70 Endocarditis can affect both the valve sewing area, which may lead to valvular dehiscence as evidenced by a “rocking” motion of the suture may lead to fi%J60’ 61 and the tissue leatlets.62 Calcific degeneration significant stenosis due to restricted cusp motion, or to regurgitation valve failure indue to torn CUS~(S).‘~-~~ The rate of bioprosthetic creases slowly until the sixth year,76 and then more rapidly because of tissue degeneration with disruption of collagen, lipid deposition, platelet aggregation, erosion, and loss of elastic fiber crimp.67, 77 Failure of bioprosthetic valves is usually gradual. The patient is likely to present with a new murmur or with symptoms of congestive heart failure. In most cases, there is time to establish not only the severity of the valve lesion but also a preoperative etiologic diagnosis (ie, flail cusp(s), vegetation, calcification, etc). Thus it is not surprising that the rate of reoperation with bioprostheses is higher than with mechanical prostheses.78’ 7s The effect of the anatomic position on xenograft valve durability is controversial. Craver et a151 did not find significant differences. However, Lakier and associatesa showed that xenografts in the aortic position degenerated earlier than in the mitral position. Similar results were found by other investigators.81,82 In marked contrast, a recent study by Bloomfield and co-workers7’ reported that failure of the porcine prosthesis occurred more frequently in the mitral position, and when reoperation for valve failure was required in patients with both aortic and mitral porcine valves, the mitral prosthesis was found to have failed twice as often as the aortic prosthesis. These findings have been supported by other rep0rts.8~-~~ The durability of the standard Carpentier-Edwards xenograft porcine valve has been similar to that of the Hancock biopmsthesis. Recently, Jamieson and co-workers,‘” in a study of 1,303 CarpentierEdwards prostheses in 1,190 patients, reported freedom at 10 years from thromboembolism of 64% for aortic and 77% for mitral; struc278

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tural valve deterioration of 79% for aortic and 72% for mitral; and all valve-related complications of 59% for aortic and 47% for mitral valve replacements. The heniodynamic performance of the modified orifice Hancock and the standard Carpentier-Edwards bioprostheses has been recently compared in a randomized study of 100 patients.87 Pressure gradients were lower and Gorlin valve areas larger for the modified orifice Hancock valve than for the standard Carpentier-Edwards valve, but the differences were significant only for the smaller valve sizes. Compared with the standard Carpentier-Edwards, the mean pressure gradients were significantly lower for the Hancock 19 mm valves (16.9 vs 31.7 mm Hg, p < 0.04), for the 21 mm valves 05.2 vs 22.4 mm Hg, p < 0.0031, and for the 23 mm valve (9.2 vs 13.8 mm Hg, p < 0.04). The Gorlin areas were also significantly larger for the Hancock 19 mm valve (0.85 vs 0.77 cm2, p < 0.004) and the 21 mm valve (1.11 vs 0.89 cm2, p < 0.0009), but not for the 23 mm valve (1.59 vs 1.14 cm’, p < 0.08). Mean gradients and valve areas were not different from any of the larger valve sizes. The magnitude of these differences is small; however, their clinical importance is unknown.” In the mitral position, the Hancock bioprosthetic resting gradients have ranged from 3.6 mm Hg to 6 mm Hg.s8S8s The Carpentier-Edwards valve has received substantial hemodynamic evaluation by Pelletier et aLso In the aortic position (standard and supra-annular combined data), the peak aortic gradients for rest/exercise were 12.5/19 mm Hg for 21 to 23 mm valves; 11.5/18 mm Hg for 25 to 27 mm valves; and 7.5/U mm Hg for 29 to 31 mm valves. The effective orifice areas at rest/exercise were 1211.25 cm2 for 21 to 23 mm valves; 1.4A.6 cm2 for 25 to 27 mm valves; and 1.912.45 cm2 for 29 to 31 mm valves. In the mitral prosthesis, the average mean gradients at rest/exercise were 6.5114 mm Hg for 27 to 29 mm valves and 5/12 mm Hg for 31 to 33 mm valves. The mean effective orifice areas at rest/exercise for 27 to 29 mm and 31 to 33 mm valves were 2.W2.8 and 2.5/3.0 cm’, respectively. These studies were performed with satisfactory cardiac output at both rest and exercise.” The single most attractive advantage of bioprosthesis is that in most cases anticoagulation is not needed. Low thrombogenicity rates have been consistently reported in most series.‘(j, “, 8’Sa’, s1 However, the increased risk of reoperation is a high price to pay for the reduced risk of bleeding through avoidance of the use of anticoagulants. S.H. RAHIMTOOLA: It is important to remember that reoperation is not the same severity of complication as bleeding, particularly as many bleeding episodes leave no sequelae. Furthermore, many patients with bioprosthetic mitral valves need long-term anticoagulation for other reasons, most frequently atrial fibrillation. Thus, I agree with the author that the increased risk of reoperation is a high price to pay for the reduced overall risk of bleeding.

b

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b P.M. SHAH:It was a common practice to insert tissue valve in patients over the age of 6.5 or 70 years, with the thought that the prosthesis in most instances would outlast the expected longevity. However, with increasing life expectancy in the United States, it is not uncommon to see patients in their late 70s and early 80s leading useful lives and returning for reoperation. Hence, selection of a biological valve based merely on age is being tempered with considerations of increased longevity.

MECHANICAL

The most common complications of mechanical prostheses are thrombosis and thromboembolism.g2’ s3 These can occur gradually or as sudden catastrophic events. Thrombosis with fibrosis of the atrial side of a disc-type prosthesis in the mitral position can be an insidious complication. Thrombosis can produce varying degrees of both stenosis (by obstructing the valve orifice) and regurgitation (by preventing complete valve closure).~ The pattern of thrombotic occlusion with tilting-disc valves usually starts in the minor oritlce and can progress rapidly to interfere with its excursion. In the mitral position, the incidence of thromboembolism is lowest for the Medtronic-Hall, followed by the St. Jude Medical, the Starr-Edwards, and the Omniscience, respectively.94-103 Ten-year actuarial data are available only for the Starr-Edwards.1o1 Thromboembolism in the aortic position is lowest for the St. Jude Medical and the Medtronic-Hall, somewhat higher for the Starr-Edwards, and highest for the Omniscience, the follow-up of which is quite limited.s6’ 104-10g Similar to data for the mitral position, the actuarial event-free data at 10 years for the aortic position are available only for the Starr-Edwards.‘og The incidence of thrombosis is identical for the Starr-Edwards, the Medtronic-Hall, and the St. Jude Medical, and mildly increased for the Omniscience, the follow-up of which is markedly limited. The incidence of thrombosis of mechanical prostheses in the tricuspid position is disturbing. The tricuspid valve is particularly vulnerable, probably because of lower pressure on the right side of the heart with slower blood flow across the prosthesis and more stagnant zones.1’o The incidence of thrombosis in this location has been higher with the tilting disc valves compared with the ball-in-cage prosthesis (20% vs 4% 1?l” There is a continuing risk of this complication, which can be present many years after implantation. The choice of prosthesis in this location should be a ring or a bioprosthesis. It is important to remember that anticoagulants do not eliminate the risk of thromboembolic complications. Without anticoagulants, significant thromboembolic events occur at a rate of 15% to 20% per patient per year, and with them, the rate is reduced to 2% to 4% per 280

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patient per year. However, anticoagulation per se carries a 3% to 5% risk per patient per year of bleeding, which should be taken into consideration when deciding the type of prosthesis to insert. The incidence of endocarditis is similar for the Starr-Edwards, the Medtronic-Hall, and the St. Jude Medical, and somewhat higher for the Omniscience, with a small sample size.96,10*,103~‘Oatlo9 The St. Jude Medical has the lowest grofile for any given annulus size among all mechanical prostheses.’ 4, 111-113 The Medtronic-Hall and the Omniscience have a lower profile than the Starr-Edwards, because the narrow disc offers less obstruction to blood flo~.‘~, ~6,‘14, *15 The main advantage of the ball-in-cage prosthesis has been its proven long-term durability, now exceeding 25 years?16’ ‘17 However, because of its high protile and central occluder, this valve, although durable, has not proven ideal for all uses. The hemodynamic properties of the St. Jude Medical and the Medtronic-Hall, in terms of clinical gradient relief and regurgitation, are similar. There have been no cases of structural failure of the Starr-Edwards (models 1260 and 61201, the Medtronic-Hall, or the Omniscience valves; however, there have been approximately 10 cases of disc escape or fracture in St. Jude Medical valves.1o6 Regarding annular devices, Deloche et ala recently published results of the long-term (10 to 17 years) follow-up of 206 consecutive patients > 18 years of age who underwent mitral valve repair with Carpentier techniques. The predictability of the technique was demonstrated by the low incidence (4%) of early reoperation. The most common cause of reoperation was residual prolapse of the mitral leaflets, which either was not recognized or was underestimated at operation. In this series, the incidence of prosthetic ring dehiscence was 0.5%. Chauvaud and colleagues118 found a similar incidence of reoperation (73 of 1,705, 4.28%) after valve reconstructions with the Carpentier ring within a follow-up period of 3 to 18 years. On the other hand, reports on the use of flexible rings showed a higher incidence of early reoperation (8.6%) and ring dehiscence (2.8%).35 Systolic anterior motion of the mitral valve has been described after prosthetic ring annuloplasty~1s-121 This is an infrequent but real problem. These cases may behave hemodynamically as obstructive hypertrophic cardiomyopathy. The left ventricular outflow tract obstruction is variable and can occasionally lead to deleterious consequences.‘21 After ring insertion, systolic anterior motion can occur as a spontaneous phenomenon or be induced by certain pharmacologic interventions (eg, nitroglycerin), indicating its dynamic behavior. The predisposing factors for the development of systolic anterior motion after mitral ring insertion are: 1. Excess leaflet tissue (myxomatous degeneration) 2. Small left ventricular outflow tract Curr

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281

3. 4. 5. 6.

Hyperkinetic heart Extensive posterior leaflet resection Excess nanowing of the annulus Intravenous isoproterenol

b P.M. SHAH:It appears that, among the factors predisposing to the development of systolic anterior motion, a rigid or nonflexible ring should be added, since the complication is either nonexistent or especially rare with use of the Duran rina.

ECHOCARDIOGR4PHIC

EVALUATION

OF PROSTHETIC

VALVES

The initial attempts at using echocardiography in assessing prosthetic valve function used combined M-mode and phonocardiography.49, 122-125 The interval between the aortic second sound (A,) and the mitral valve opening (M,) was used as an indicator of malfunction of the mitral prosthesis. A shortened AZ-M, interval would have the same significance as a short AZ-opening snap interval in native mitral stenosis. However, this interval may also be shortened in patients with poor left ventricular function, significant perivalvular regurgitation, and first-degree atrioventricular block.125 Similarly, the extent of ball excursion and the opening and closing velocities derived by M-mode were thought to represent indexes of valve function.lz3 However, a variety of factors, including heart rate, left ventricular loading conditions, and the force of ventricular contraction, can affect these variables.lz5 Furthermore, the A, was not clearly recorded in some patients, and the presence of associated arrhythmias could further confuse the interpretation of these time interval recordings. Because of these reasons and with the confirmation of the accuracy of Doppler ultrasound in predicting valve gradients and areas, the use of phonoechocardiography in the assessment of prosthetic valve dysfunction has been largely abandoned. Two-dimensional (2-D) echocardiography has been used extensively to assess prosthetic valve function.58-65’126-140 Reduced disc! leaflet excursion may be observed in the presence of thrombosis or tissue ingrowth. However, cinefluoroscopy is often more helpful than echocardiography in detecting abnormalities of disc/leaflet motion. 137,141 A major obstacle of both tissue and mechanical valves is their nonbiological material, which often causes significant reverberation and other types of artifacts that impede the passage of the ultrasound beam and obscure or shadow the structures lying behind.‘42 In this situation, the differentiation between artifact and true cardiac structures may be difficult, or impossible, even by the well trained echocardiographer. Evaluation of bio rostheses is somewhat easier, particularly in the mitral position. B ’ 6o Increased cusp thickness, a focal mass or masses of echoes attached to the 2.82

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leaflets,143 rocking motion of the valves,6o’ 61 and prolapse or flail of the CUSPS~‘-~ all suggest tissue valve dysfunction. In general, however, because of excessive reverberations and beam width artifacts, precordial 2-D imaging has been disappointing in its ability to clearly define the extent of mechanical leaflet, disc, or poppet excursion, and to differentiate distinctly between a true echo-dense mass originating from a vegetation or thrombus and that produced by an artifact. Some of these problems have been overcome with the use of transesophageal echocardiography (see below). During the past decade, strong evidence has been accumulated suggesting that Doppler ultrasound provides a noninvasive, accurate, and reproducible means to evaluate qualitatively and quantitatively stenotic and regurgitant lesions of native and prosthetic heart v&,es.9-20,47-50,144-155 The Doppler velocities are converted into pressure gradients by the modified Bernoulli equation: pressure gradient

(A P) = 4 V”

This equation assumes that the viscous and frictional forces are negligible, which may not be true in the case of prosthesesl’ Also, it assumes that the flow velocity proximal to the valve is so low that it can be ignored. However, this velocity may be high, particularly in the aortic position. Lastly, the Bernoulli equation assumes that the angle between Doppler beam and flow direction is near Oos5’This is not always the case with prostheses where multiple and eccentric jets can be generated. Despite these theoretical limitations, excellent correlations have been obtained when continuous wave Doppler and catheterizationderived gradients are recorded simultaneously (Fig 61.144-‘50 The largest series of patients studied by this combined technique was reported by Burstow et al.146 The calibrated catheter pressures were superimposed to the Doppler signals in 36 patients with 42 prosthetic valves in various anatomical positions. In this series, Doppler accurately estimated transprosthetic pressure gradients irrespective of valve type or position. Both maximal and mean pressure gradients determined by continuous-wave Doppler correlated closely with the corresponding simultaneous catheter-derived gradients. Lack of simultaneity between the two techniques is the primary reason when an apparent discrepancy is seen. On the basis of this study, the authors concluded that continuous-wave Doppler could be safely substituted for cardiac catheterization in the measurement of prosthetic valve gradients.146 b S.H. RAHIMTOOLA: When one compares two techniques, it is essential to know not only the correlation (r value) but also the regression equation and the two standard errors of the regression equation. Also, it is important to study a conCurr

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FIG 6. Panel A corresponds to simultaneous Doppler-catheter pressure recordings in a patient with a stenotic mitral Hancock prosthesis. Pressure gradient between left atrium (LA) and left ventricle (LV) is seen. Panel B displays the digitization of Doppler flow velocity, and left ventricular plus left atrial pressure wave forms shown in Panel A at IO-msec intervals. The phase delay of catheter (cath) gradient compared with Doppler gradient is related to fluidfilled catheter system. (From Burstow DJ, Nishimura RA, Bailey KR, et al: Continuous wave Doppler echocardiographic measurement of prosthetic valve gradients. A simultaneous Doppler-catheter correlative study. Circulation 1989; 80504-514. Reproduced with permission.) secutive group of patients number of patients.

in a blinded

fashion

and to study a sufficiently

large

b P.M. SHAH:Some discrepancies between the Doppler-derived peak gradients, especially for mechanical prosthetic valves in the a&tic position, and those obtained at cardiac catheterization have been reported. These have also been extensively investigated in in vitro models. The discrepancies are explained largely on the basis of rapid pressure recovery observed with the prosthesis, so that the pressure measured 3 to 5 cm distal to the valve in the ascending aorta does not reflect the precise gradients in the immediate vicinity of the valve. It is therefore recommended that mean gradients be used for decision making; more importantly, comparisons with early postoperative study in the same patient would help determine significance of a high peak velocity. Peak aortic velocities of between 4.0 and 5.5 msec have been reported across smaller sizes of normally functioning mechanical valves in the presence of a vigorously contracting left ventricle.

The recent introduction of transesophageal echocardiography into the clinical arena opens a new window for the reliable assessment of prosthetic valve dysfunction. There are several practical advantages in using transesophageal echocardiography for the assessment of prosthetic valve dysfunction. Imaging resolution of the prosthesis 284

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and adjacent structures is substantially enhanced because of the close proximity with the esophageal probe and the use of higher frequency transducers~56 Artifacts originating from the synthetic materials of the prosthesis are. a lesser problem than when imaging is obtained from the transthoracic approach.14’ Consequently, flow masking is no longer a limitation in prostheses located in the mitral position.15’ Thus, it is not surprising that the transesophageal technique has significantly improved the ability of echocardiography to detect prosthetic valve complications such as vegetations (Color Figs lA and lB1, abscesses, mycotic aneurysms, dehiscence, and thrombi (Fig 7) -157,158 b P.M. SHAH: Transesophageal echocardiography has assumed an important diagnostic role in any patient suspected with prosthetic valve malfunction or infection. The information obtained can help with making management decisions in most patients, without the need for additional invasive testing.

Before describing -the specific characteristics of prosthetic valve dysfunction, it is important to appreciate that the echocardiographic

FIG 7. Transesophageal echocardiographic image of left atrium (LA) and left atrial appendage (LAA) in patient with Bjork-Shiley prosthesis in mitral position. A thrombus is identified within the left atrial appendage. A0 = aorta; RVOT = right ventricular outflow tract. (From Chaudhry FA, Herrera C, DeFrino PF, et al: Pathologic and angiographic correlations of transesophageal echocardiography in prosthetic heart valve dysfunction. Am Heart J 1991; 122:1057-1064. Reproduced with permission.) Curr

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assessment of these patients should be complete and meticulous. Particular attention should be focused on the native valves, and the systolic and diastolic function of the left ventricle. Cardiac failure in patients with normally functioning prostheses may be caused by: 1. 2. 3. 4. 5.

Left ventricular dysfunction, either systolic or diastolic Native valve stenosis or regurgitation Ischemic heart disease Constrictive pericarditis Pulmonary embolism 6. Pericardial effusion 7. Arrhythmias

However, it is essential that prosthetic valve dysfunction from the list before any other cause is entertained.

be excluded

MITRAL POSITION

In general, all prosthetic mitral valves offer some degree of obstruction to flow, which resembles mild mitral stenosis on a Doppler tracing. Biological prostheses are designed to perform like native valves, that is, flow occurs centrally and is relatively undisturbed. However, mild stenosis is present as a result of the relatively large size of the stent and sewing ring, which reduces the effective orifice area.36 The echocardiographic technique used for imaging mitral prostheses is similar to the technique used for the native valve. The leaflet or disc excursion of mechanical devices is better seen from the parasternal long-axis and the apical four- and two-chamber views, whereas the porcine xenograft cusps are better seen from the parasternal short-axis view. The apical window is also helpful in biological prostheses to detect flail cusps. With the use of Doppler echocardiography, the severity of obstruction is expressed as the mean transprosthetic diastolic gradient, the pressure half-time, and the effective prosthetic mitral valve area. Normal values for biological prostheses are listed in Table 2 and those for mechanical prostheses in Table 3. A useful clinical practice is to perform a postoperative baseline study. In this regard, the patient serves as his or her own control on subsequent examinations. b S.H. RAHIMTOOLXIt needs to be emphasized that the gradients measured will also vary with the size of the prosthesis, the flow per beat across the valve, and the diastolic filling period. The ideal time to perform the baseline study is not known. The first outpatient visit after discharge from hospital, that is, at 2 to 6 weeks, is probably the most practical time.

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TABLE 2. Normal

DoDuler

Values

for Biolotical

Mitral

Prostheses* Valve Area

Prosthesis

Peak Velocity Wsec)

Mean Gradient (mm Hg)

Pn?ssure Half-time (msec)

Hancock Carpentier-Edwards

1.5 t 0.3 1.8 ? 0.2

4.3 f

123 t

‘Individual variability ular co”wactility.

in valve gradients

2.1

6.5 2 2.1

may be seen depending

Mean (cm?

Ran%e (cm 1

31

1.7

1.3-2.7

SO 2 25

2.5

1.6-3.5

on valve size, position,

and left ventric-

The pressure gradient across a prosthetic mitral valve is calculated by Doppler using the simplified Bernoulli equation (A P = 4 V”). The reliability of Doppler measurements across prosthetic mitral valves has been validated during simultaneous,144’14” and nonsimultaneouss-l” cardiac catheterization. In the series by Burstow et al,146 20 patients with mitral prostheses underwent catheterization and Doppler recordings simultaneously (Fig 8). The catheter-derived gradients were obtained from both direct (transseptal technique) and indirect (pulmonary capillary wedge pressure) measurements of left atrial pressure. The results were analyzed separately according to the catheterization technique. In the 12 patients with direct left atrial pressure measurement, the correlation coefficient for maximal Doppler and catheter gradients was 0.96 (SEE = 21, and that for mean gradients was 0.97 (SEE = 1.2). For the group of eight patients with indirect left atrial pressure measurement, the correlation coefficient for maximal gradients was 0.67 (SEE = 5.21, and that for mean gradients was 0.44 (SEE = 2.2). TABLE 3. Normal

Doppler

Values

for Mechanical

Mitral

Prostheses* Valve Area

Peak Velocity Wsecl

Prosthesis Starr-Edwards Bjork-Shiley St. Jude Medical Medtronic-Hall Omniscience Carpentier-Edwards Duran (ring) *Individual variability ular contractili~.

Cur-r Probl

Cardiol,

1.8 f 1.6 f

0.4 0.3

1.5 2 0.3 1.7 f 1.8 f

(ring)

1.4 2 0.3 1.3 -c 0.3

in valve gradients

May

0.3 0.3

18%~

Mean Gradient (mm Hg)

Pmssure Half-time (msec)

4.6 2.3 3.5 3.1 3.3

110 so 77 83 125

2 k -c rt +

2.4 1.6 1.3 0.3 0.3

3.8 ” 0.4 3.8 2 1.1

may be seen depending

” * 2 ” ‘_

Mean (cm’)

Range (cm 1

27 22 17 13 23

2.1 2.4 2.3 2.4 1.9

1.2-2.5 1.6-3.7 1.8-4.4 1.5-3.3 1.6-3.1

38 + 16 83 2 13

2.6 2.8

1.8-3.8 1.3-3.3

on valve size, position,

and left ventric-

287

FIG 8. Panel A corresponds to left atrial pressure (LA) measured directly using the Vans-septal technique. Doppler and catheter gradients are closely correlated. Panel B corresponds to left atrial pressure measured indirectly using pulmonary capillary wedge pressure (PCW). Curr

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The inaccuracy of the transmitral valve gradients, and thus of the mitral valve areas, in prosthetic valves using pulmonary capillary wedge pressure indirectly as left atrial pressure has been shown previously by Schoenfeld and co-workers.‘5s This inaccuracy is caused by (1) phase delay of the pulmonary wedge V wave relative to the transseptal V wave, resulting in a higher mean diastolic pressure gradient, and (2) lack of fidelity of the pulmonary wedge pressure for rapid acceleration and deceleration.14 ’ 1’S b P.M. SIWE: Contraction of blood volume and low flow state resulting from excessive use of diuretics may result in a low transvalvular gradient despite significant obstruction. This may be unmasked by continuous-wave Doppler recorded during or immediately after exercise.

Because valve gradient is proportional to volume, the presence of prosthetic regurgitation may incorporate additional flow velocity to the already increased transprosthetic valve gradient.16’ A useful sign suggesting the presence of signitlcant mitral regurgitation is the recording of a high forward peak E-wave velocity across the prosthesis. This sign is particularly helpful in the case of mechanical prostheses, where interrogation within the left atrium from the apex may be difficult or impossible. However, the greatest value of this sign is realized whenever we have the opportunity to compare the currently increased peak E-wave flow velocity with previously recorded examinations. The effective prosthetic mitral valve area is calculated by the pressure half-time method in a manner identical to that used for native mitral stenosis”: mitral valve area (cm? =

220 pressure half-time

(msec)

Normal values are listed in Tables 2 and 3. The peak E-wave velocity is elevated in both prosthetic mitral stenosis and regurgitation? 5o However, the pressure half-time will be abnormally prolonged only if stenosis is present. Color flow imaging provides a means for spatial identification of flows through the mitral-prosthesis if the proper transducer orientations and limitations are kept in mind?61 The porcine xenograft has a high-velocity, turbulent, eccentric, forward diastolic jet, usually di-

Note phase delay in pulmonary wedge V wave which overestimated catheter-derived maximal (max) and mean gradients compared with corresponding Doppler-derived gradients. (From Burstow DJ, Nishimura RA, Bailey KR, et al: Continuous wave Doppler echocardiographic measurement of prosthetic valve gradients. A simultaneous Doppler-catheter correlative study. Circulation 1989; 80:504-514. Reproduced with permission.) Curr

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289

rected toward the septum. The jet takes on a “candle-flame” appearance similar to that of mitral stenosis, with central abasing. Flow through a ball-in-cage valve has turbulent, high-velocity peripheral jets. Areas of jets adjacent to the outflow tract appear larger than those adjacent to the free wall. There are regions of flow reversal just distal to the cage during mid- and late-diastole. Turbulence displayed as a green/yellow mosaic is detected along the edges of the forward flow jets. Flow imaging of tilting disc valves has two highvelocity jets. The flow area through the major orifice is at least twice as large as that through the minor orifice. Greater intraventricular turbulence occurs when the major orifice is oriented toward the septum than when it is oriented toward the left ventricular free Wtlll.161 This finding indicates that single-tilting disc valves in the mitral position have better velocity profiles when the major orifice is oriented toward the left ventricular free wall. Forward flow imaging through a bileaflet mitral valve is characterized by three regions. The two jets from the lateral orifices are directed toward the septum and free ~all.1~~ Compared with the other mechanical valve designs, the bileaflet valve creates a lower level of turbulence.“3P 161 Color flow imaging may help in distinguishing transvalmlar from perivalvular regurgitation and physiologic backflow from mild regurgitation However, when color flow imaging is used through the transthoracic approach, this differentiation is not alwa s possible, particularly when a mechanical prosthesis is in place.’ Y’ In sharp contrast, when color flow imaging is used through the transesophageal window (Color Fig 21, this differentiation can be readily made in most cases irrespective of the type and position of the prosthesis.157, 162 At The University of Texas Health Science Center at San Antonio, echocardiography plays an essential role before, during, and after mitral ring insertion. Before surgery, echocardiography can predict the probability of repair and establish the functional type of mitral valve incompetence (degenerative, infective, rheumatic, or ischemic) that will serve as a guide for reconstruction. In addition, the left ventricular dimensions and the presence of preoperative wall motion abnormalities can also be detected. During surgery, epicardial and transesophageal echocardiography can detect any degree of residual mitral regurgitation. It is important to appreciate that transesophageal echocardiography is extremely sensitive for the detection of mitral regurgitation and, therefore, assessment of its degree should be established in a common decision among the cardiologist, surgeon, and anesthesiologist. In general, 2 2+ residual mitral regurgitation is unacceptable, and further repair or replacement is necessary. In addition, intraoperative echocardiography plays an essential role in detecting perivalvular leak, residual leaflet prolapse, systolic anterior motion of the mitral valve, and new wall motion abnormali290

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ties. After surgery (3 to 6 months), echocardiography is helpful in assessing stability of the ring, worsening of residual mitral regurgitation, if any, and reassessment of systolic anterior motion of the mitral valve and segmental wall motion abnormalities. b P.M. SHAH:Intraoperative assessment of surgical correction of mitral regurgitation should be made after achieving a baseline hemodynamic state. For instance, blood pressure and volume status would influence size of the regurgitation jet. Hence, severity of residual regurgitation should only be made following restitution of volume and pressure.

AORTIC POSITION

The criteria for evaluation of aortic valve prostheses are the degree of the transprosthetic pressure gradient” ‘, lo, so8‘4~ and the effective prosthetic aortic valve area.‘63-165 Prosthetic aortic valve hemodynamics are similar to those of mild aortic stenosis. By using the modified Bernoulli equation, continuous-wave Doppler interrogation across any type of aortic prosthesis accurately predicts the systolic pressure gradients. Normal values for biological prostheses are listed in Table 4, and those for mechanical prostheses in Table 5. The use of continuous-wave Doppler for assessing aortic valve prostheses is irreplaceable. All the standard aortic Doppler windows should be routinely interrogated. These include apical (patient in left lateral decubitus position), right parasternal (patient in right lateral decubitus position), and suprasternal (patient in decubitus position and head extended). The subcostal view can be used alternatively if the Doppler signal obtained from the above-mentioned windows is suboptimal. In my experience, careful interrogation through the three standard aortic Doppler windows has resulted in satisfactory Doppler signals in virtually all cases. When interrogating the aortic flow velocity of a mechanical valve from the apical position, the jet will be displayed on the opposite side of the prosthesis. Artifacts originating from the prosthesis may interfere with the Doppler TABLE 4. Normal

Doppler

Values

for Biological

Aortic

Prostheses’ Valve Area

Prosthesis Aortic Homograft Hancock Carpentier-Edwards ‘Individual variability oh- conhmXiIily.

Curr

Pmbl

Cardiol,

Peak Velocity Wsec)

Mean Gradient (mm HR)

Mean (cm-7

E3e

1.8 f 0.4 2.4 k 0.4

7.1 s 3 11 r 2

22 1.8

1.7-3.1 1.4-2.3

2.4 k 0.5

14 *

1.8

in valve gradients

May

1992

may be seen depending

6

on valve size, position,

1.2-3.1 and left venttic-

a91

TABLE 5. Normal

Doppler

Values

for Mechanical

Aortic

Prostheses’ V& Mean Gradient (mm Hg)

pey;;&pity Prosthesis Starr-Edwards Bjork-Shiley

St. Jude

Medical

Medtrunic-Hall Omniscience

3.1 f 0.5 1.9 ” 0.2 to 2.8 ” 0.9 22 f 0.5 to 3.0 2 0.8 2.6 ” 0.3 2.8 f 0.4

*Individual variability in valve @adients tricular contractility. tInsufficient data available

24rt4 14 + to 31 rf: 22 f to 11 r+ 12 2 14 2

may be seen depending

Areat

Mean (cm’)

EY7

3 2 11 6 3 3

on valve size, position,

and left ven-

signal. Under these circumstances, the right parasternal window is particularly useful because the prosthetic valve itself and the artifacts generated from its nonbiological constituents no longer interpose between the systolic aortic flow and the continuous-wave Doppler ultrasound beam. The accuracy of Doppler ultrasound to predict the transprosthetic aortic gradients has been clearly demonstrated by Burstow et al’& in simultaneous catheterization and continuous-wave Doppler recordings (Fig 9). In 15 of their 20 patients with aortic prostheses, the left ventricular pressure was recorded by the transseptal technique, and in five by the percutaneous left ventricular puncture because of additional mitral prostheses. The correlation coefficient for maximal Doppler and catheter gradients was 0.94 (SEE = 6) and that for mean gradients was 0.94 (SEE = 3). The mean gradients derived by either technique should correspond very closely to each other. However, it is important to remember that the maximal gradient derived by Doppler corresponds to the maximal gradient derived by cardiac catheterization (maximal separation between the left ventricular and the aortic pressure tracings) in as much as both are instantaneous pressure measurements. The Doppler maximal gradient should not be matched to the peak-to-peak gradient (difference between the peak left ventricular and the peak aortic pressure tracings), which is not an instantaneous event. Because the catheterization maximal gradient is not a routine measurement, only the mean transprosthetic gradient by either technique should be considered when making a clinical judgment. 292

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FIG 9. Simultaneous Doppler-catheter pressure recordings from three patients with StarrEdwards (Panel A), Hancock (Panel B), and Bjork-Shiley (Panel C) prostheses in the aortic position. Close correlation between Doppler- and catheter-derived maximal (max) and mean gradients is noted. The peak-to-peak (p-p) gradients are lower than both the maximal and mean gradients. (From Burstow DJ, Nishimura RA, Bailey KR, et al: Continuous wave Doppler echocardiographic measurement of prosthetic valve gradients. A simultaneous Doppler-catheter correlative study. Circulation 1989; 80504-514. Reproduced with permission.) b P.M. SHAH: It is important to emphasize that maximum gradient by Doppler of 100 mm Hg may be seen with a normally functioning, smaller size prosthetic valve in the presence of good left ventricular function. Thus, only the mean gradient should be considered, and comparison with the baseline recording in the same patient is exceedingly useful in determining the relevance of high gradients.

In general, all but the smallest aortic valves have Doppler mean gradients < 40 mm Hg. A decrease in mean pressure drop is seen as the valve increases in size. Individual variability in the Doppler gradients is seen in patients with normally functioning prosthetic valves secondary to valve size and position as well as to left ventricular function. The time course of the pressure drop is also useful in relation to the severity of prosthetic aortic valve function, ie, the more severe the obstruction, the more prolonged the appearance of the systolic peak gradient?’ CUIT Pmbl

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293

TRICUSPID POSITION

Tricuspid valve disease, either stenosis or regurgitation, is much less common than diseases of the left-sided heart. Thus, information and experience with tricuspid valve replacement is relatively limited. Mild or moderate tricuspid regurgitation secondary to advanced aortic or mitral valve disease is a relatively common finding. In general, however, mild to moderate degrees of regurgitation diminish or even disappear after correction of the primary lesion, such as severe mitral stenosis. Evaluation of a tricuspid valve prosthesis by Doppler echocardiography is identical to the methods used for a native tricuspid valve. The tricuspid pressure half-time, however, has not been as thoroughly investigated as its mitral counterpart. It does seem to offer comparable ability to differentiate an abnormally high transtricuspid gradient due to regurgitation from one due to obstruction!’ Similar to mitral prostheses, while interrogating mechanical tricuspid prostheses from the apical position, large amounts of reverberations may obscure the region of interest for assessing regurgitation. Fortunately, the right atrium can be visualized from different echocardiographic windows such as the parasternal long-axis view of the right ventricle, parasternal short-axis view, and subcostal view. It is important to remember that flow across the right-sided chambers changes according to the respiratory cycle, ie, increases during inspiration and decreases during expiration. Thus, analysis should average five beats in sinus rhythm and seven representative beats in atrial fibrillation. Tricuspid annuloplasty is a much more common procedure for alleviation of significant regurgitation than is valve replacement. The antegrade flow through the annuloplasty ring can be analyzed by measuring the mean transvalvular gradient in the same manner as for any other type of tricuspid prosthesis. Tricuspid valve repair with ring insertion is extremely effective in alleviating severe tricuspid insufficiency either as an isolated finding or in association with aortic or mitral valve disease. However, it is not indicated in cases of tricuspid insufficiency associated with stenosis. PUZMONZC POSITION

Prosthetic valves of any kind are extremely rare in the pulmonic position. This is partly because nonoperative interventions such as balloon valvuloplasty have been proven to be highly effective in relief, at least temporarily, of hemodynamically significant pulmonic valvular stenosis.166 In addition, the mean pulmonary artery pressure and pulmonary vascular resistance are approximately one-sixth of systemic, the pulmonary artery pulse pressure is lower, and the 294

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pulmonary arterial distensibility is higher.16’ As a result, most surgeons approach the pulmonic valve with valvulotomy or valvectomy instead of inserting a prosthetic device. I have followed several relatively young individuals with either valvulotomy or valvectomy of the pulmonic valve as treatment for pulmonic restenosis after balloon valvuloplasty or recurrent endocarditis. In a short-term follow-up of 3 to 5 years, they seem to tolerate the pulmonic regurgitation fairly well. The long-term results of the hemodynamic burden on right ventricular function remain to be seen. The Doppler envelope of pulmanic insufficiency in all these patients is characterized by an early peak flow velocity followed by a rapid diastolic deceleration slope, consistent with an early diastolic equalization between the right ventricle and the pulmonary artery pressures. When dealing with a patient with a pulmonic valve prosthesis, the parasternal and the subcostal transducer positions are conventional. As with any other prosthetic device, a mild degree of stenosis is expected as evidence of mild elevation of the transpmsthetic valve velocity. Accordingly, peak flow velocities below 2.5 m/set should be consistent with a normally functioning pulmonic valve prosthesis. ROLE OF ECHOCARDIOGRAPHY CLINICAL SITUATIONS ASSESSMENT

IN SPECIFIC

OF STENOSES

The normal aortic valve area is 3 to 4 cm’, and the mitral valve area is 4 to 5 cm’. These values are rarely reached with prosthetic devices. All prosthetic valves produce a certain degree of obstruction across the valve annulus .‘, 11-15P” This inherent stenosis is caused by the ring or cage, and the leaflet, disc or poppet. The degree of this obstruction increases with the passage of time because of tissue ingrowth and endothelialization. The gradient across the prosthetic valve critically depends on the type and the size of the prosthesis and the amount of blood flow across that prosthesis, ie, the larger the flow, the higher the gradient. Thus, in those patients with high cardiac output or with prosthetic regurgitation, higher-than-normal gradients will be expected. Therefore, the same type and size of prosthetic device can produce widely varying gradients in different patients. The key to assessment of prosthetic function, therefore, is a careful Doppler examination in the immediate postoperative period. This serves as a baseline study, and the gradients obtained are normal for that particular patient. Any further gradient that is obtained should be compared with this baseline study. If very high gradients are obtained in the immediate postoperative evaluation, then the possibility of patient-prosthesis mismatch should be raised. The decreased prosthetic valve area is usually mild to moderate in Curr

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295

COLOR FIG 1A. Transesophageal echocardiographic image of left atrium (LA) and bioprosthesis (p) in mitral position. A small echo-dense structure (solid arrow) suggestive of a vegetation is attached to a flail cusp (open arrow). In addition, a large, color-coded regurgitant jet is noted within the left atrium.

COLOR FIG 18. Bioprosthesis excised from patient illustrated in Color Figure 1A, showing one cusp partially disrupted and vegetation (arrow). (From Chaudhry FA, Herrera C, DeFrino PF, et al: Pathologic and angiographic correlations of transesophageal echocardiography in prosthetic heart valve dysfunction. Am Heart J 1991; 122:1057-1064. Reproduced with permission) 296

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COLOR RG 2. Systolic frame from longitudinal plane of transesophageal echocardiography in a patient with mechanical disc prosthesis in mitral position. Transvalvular and perivalvular regurgitant jets are clearly identified. (Used with permission of William J. Stewart, MD, Cleveland Clinic.)

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297

severity and often of no immediate clinical significance. However, occasionally it can be a severe problem because the patient may be hemodynamically and symptomatically worse after valve replacement. Under these circumstances, the concept of patient-prosthesis mismatch is applicable. The mismatch is primarily because the annulus size is relatively small compared with the body surface area of the patient.168 The long-term effects of this residual stenosis have not been fully studied, and it may account for the unexplained lack of improvement seen in some patients after valve replacement, Another important concept emphasized previously by Rahimtoola’68 is that, in patients with valvular stenosis, the annulus into which the prosthesis has to be inserted is usually smaller than that in patients with valvular regurgitation. As a result, the prosthetic valve areas tend to be smaller in patients who have undergone valve replacement for a stenotic valve. Thus, in assessing patients with prosthetic devices, it is important to investigate the predominant valve lesion that justified the valve replacement. Prosthetic Valve Areas Because the transprosthetic gradient is dependent on the type and size of the valve, the diastolic filling period, and the left ventricular loading conditions, a high pressure gradient does not necessarily mean prosthetic stenosis. Conversely, a mildly elevated gradient may be indicative of signiilcant stenosis in a patient with severe left ventricular dysfunction and low cardiac output. Thus, calculation of valve areas provides a more accurate assessment of prosthetic valve function than measurement of transprosthetic gradients. However, Doppler-derived valve areas are difficult to confirm because no gold standard is available. Calculation of prosthetic valve areas by cardiac catheterization is subject to error because of the inherent inaccuracies of the Gorlin formula.16g This equation was derived for valves with a specific size and shape, constant flow rates, and fixed oriilce. However, as we have reviewed previously in this monograph, prosthetic valves vary widely in their size and shape and have pulsatile flow. “On “’ In addition, the Gorlin constant is both flow and pressure dependent.“” 173 Mitral Valve Area Despite the above-mentioned limitations, good correlations (r = 0.83~’ and 0.9713) have been reported between the valve area estimated by Doppler (pressure half-time formula) and that derived by catheterization (Gorlin formula). Using color flow to aid alignment of the Doppler beam parallel to the flow, prosthetic mitral valve areas were compared with those derived by catheterization.18 The correlation for bioprostheses was 0.94 and for mechanical was 0.79. In the 298

Corr

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1992

same study, bioprosthetic valve areas of < 1.1 cm2 were surgically confmned to be stenotic. In the case of mechanical prostheses, all nonobstructed valves had areas > 1.3 cm”.” b S.H. RMIIMTWLXThe limitations of assessing accurately the severity of valve stenosis in the operating room must be kept in mind.

The use of transesophageal echocardiography in assessing patients with prosthetic mitral valve stenosis is relatively limited. Ideally, these patients have already had the severity of mitral stenosis calculated by means of a meticulous transthoracic examination. The 2-D images obtained through the transesophageal approach may help in better delineating the morphological characteristics of the prosthesis and surrounding structures in order to define the possible cause of stenosis (Fig 10). In addition, the possibility of an associated intracavitary thrombus within the left atrium (or left atrial appendage) can be clearly identified through this technique and may help in the surgical approach. Aortic Valve Area Prosthetic aortic valve area is calculated by the continuity tion in a manner similar to that used with the native valveso:

equa-

-%xo~*hook

AVA km2) = v

TRANSPROSTHETIC

where AVA is aortic valve area, CSA is cross-sectional area, LVOT is left ventricular outflow tract, and V is velocity. The inner left ventricular outflow diameter is measured from the parasternal long-axis view immediately proximal to the prosthesis, and the cross-sectional area is estimated by the formula: CSA (cm’? = 7~ (l/2 DJ2 where r is 3.14 and D is diameter. The left ventricular outflow tract velocity is obtained with the use of pulsed Doppler by placing the sample volume immediately proximal to the aortic prosthesis from the apical five-chamber view. The transprosthetic velocity is obtained with the use of continuous-wave Doppler from any of the conventional aortic windows (apical, suprasternal, or right parasternal) wherever the highest velocity is displayed. In a recent study by Kapur et al,l’ prosthetic aortic valve areas calculated by color-guided continuous-wave Doppler correlated well with those obtained by cardiac catheterization (bioprostheses r = 0.87, mechanical r = 0.76). For bioprosthesis, areas < 1.0 cm” were surgically confirmed to be stenosed. For mechanical valves, areas > 1.0 cm2 were free of significant obstruction, Curr

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299

FIG 10. Transesophageal echocardiographic image in a patient with St. Jude Medical prostheses in the mitral and tricuspid positions. A large vegetation (veg) and a thrombus (th) are clearly identified within the left atrium (LA). LV = left ventricle; RA = right atrium; RV = right ventricle.

Although it is tempting to perform the so-called angle correction, whereby blood flow as seen by color flow imaging may supposedly be in a closer alignment with the ultrasound beam, it has been my experience that angle correction is not necessary to guide the continuous-wave Doppler beam in either native or prosthetic valves. It must be emphasized that blood flow is a three-dimensional concept, and attempting to reduce the ultrasound-flow angle into a twodimensional plane may introduce an unaccountable variable. In addition, as we have previously discussed, mechanical devices may have multiple and eccentric jets, which further complicate the theoretical advantages of angle correction. As with the mitral valve, the role of transesophageal echocardiography in patients with aortic valve stenosis is limited. The ultrasound beam through the transesophageal approach encounters the prosthetic aortic valve in an oblique position. This precludes a proper alignment between the ultrasound beam and the forward flow across the prosthetic valve. Therefore, the main purpose of performing a transesophageal examination in this circumstance is to better delineate the morphological aspects of the prosthetic valve and the surrounding structures in order to identify the possible 300

Cut-r

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1932

cause of the prosthetic stenosis, such as a vegetation, cific degeneration, etc. ASSESSMENT

thrombus,

cal-

OF REGURGITATION

It should be appreciated that not all prosthetic leaks are necessarily pathologic. The physiologic backflow, that is, the blood flow that leaks before the occluder seals the valve orifice, is negligible with the Medtronic-Hall, the Omniscience, and the St. Jude Medical because they close very rapidly. However, the inertia with a Starr-Edward ball slows its closure, and a minimal amount of backflow is seen with this valve. The built-in regurgitation is an intrinsic leak that occurs after the occluder seals the valve orifice. According to the manufacturers, this “built-in” regurgitation helps in avoiding thrombus formation at and around the valve by preventing blood stasis. The highest frequency of built-in leak occurs with the St. Jude Medical, is slightly lower with the Medtronic-Hall and the Omniscience, and is virtually absent with the Starr-Edwards. b P.M. SHAH:The physiologic backflow associated with mechanical prostheses tends to have low-velocity, nonturbulent characteristics on color flow imaging. In contrast, perivalvular or pathologic regurgitation results in a turbulent jet identified with mosaic coloration of the jet.

In patients with aortic insufficiency, the use of continuous-wave Doppler may provide useful information regarding severity.5o The rate of decrease of the aortic-left ventricular pressure difference obtained from the regurgitant flow may be helpful in differentiating severe aortic regurgitation from mild or moderate. A pressure half-time < 300 msec indicates significant regurgitation.” A low velocity of regurgitation at end-diastole indicates a high left ventricular endthis technique, although highly diastolic press~re.~~ Unfortunately, specific to identify patients with significant aortic insufficiency, is poorly sensitive. The rate of decrease of the aortic-left ventricular pressure difference is a reflection of diastolic interplay among different factors, including severity of aortic insufficiency, diastolic aortic orifice size, left ventricular stiifness, left ventricular dimensions, left ventricular end-diastolic pressure, heart rate and rhythm, and perhaps more importantly, chronic@ of the aortic insufficiency. Thus, patients with severe chronic aortic insufficiency and adequate left ventricular compliance tend to have an aortic-left ventricular diastolic pressure slope similar to those patients with mild or moderate aortic insufficiency.174 From the transthoracic approach, the Doppler grading of mitral and aortic rosthetic valve regurgitation is similar to that for native valves.1759’ 7t This is possible in most cases of bioprostheses and Cur-r

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301

atrioventricular rings. However, in patients with mechanical prostheses, accurate grading of its severity is very difficult. The use of alternative views such as the parasternal short- and long-axis and the subcostal transducer positions may occasionally help. However, several studies have reported a significant underestimation of the degree of regurgitation by transthoracic Doppler echocardiography as compared with that obtained by angiography.“’ As discussed earlier in this monograph, both tissue and mechanical prostheses contain nonbiological materials that can reflect or attenuate (absorb) the ultrasound waves. The Starr-Edwards and the St. Jude Medical produce the largest artifacts (reverberations), whereas the aortic homografts, the porcine heterografts, and the annular rings produce the least. It may be impossible to detect any flow on the opposite side of a prosthesis when the valve is interposed between the transducer and the region of interest. A typical example is in the evaluation of prosthetic mitral regurgitation from the apical view, where most of the left atrium may be masked by the ‘acoustic shadow” that extends into the far field and prevents effective insonation of the region of interest. This may result in the incorrect conclusion that mitral regurgitation is not present. The problem can be minimized when the left atrium is interrogated using the parasternal view. However, the mitral regurgitant jet is not ideally displayed from this transducer position. In addition, when mitral and aortic mechanical prostheses are present in the same patient, the aortic valve shadows part of the left atrium, again precluding an adequate interrogation of the mitral prosthesis. The origin of prosthetic regurgitation, that is, valvular versus perivalvular, may have important implications. In a symptomatic patient with significant regurgitation, transvalvular origin will necessitate replacement of the prosthesis, whereas perivalvular origin may be solved by repair. This differentiation is difticult through the transthoracic approach. The use of color flow imaging from multiple transthoracic windows may help; however, in some instances, combined valvular and perivalvular regurgitation might be present in the same prosthesis making the correct identification practically impossible. Transesophageal echocardiography may overcome the limitations encountered by the transthoracic approach. The transesophageal window provides excellent imaging resolution because of the proximity between the esophagus and the cardiac valves, and the ability to use high-frequency transducem.156 Differentiation between valvular versus perivalvular origin of the regurgitation is frequently possible. At The University of Texas Health Science Center at San Antonio, we quantified the severity of prosthetic valve regurgitation by transesophageal echocardiography with the use of a global visual assessment. The presence of a short (< 10 mm) and narrow (10 mm) sys302

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1992

tolic jet or jets, predominantly encoded in red, seen on the atrial aspect of the prosthesis, is considered a physiologic backflow. Mitral regurgitation is considered mild if the regurgitant jet reaches up to the mid-left atrium; moderate if the regurgitant jet passes beyond the mid-left atrium but does not enter into the pulmonary veins or fill the atrial appendage; and severe if the regurgitant jet enters into the pulmonary veins, producing reversal of systolic flow or filling the atrial appendage. Aortic regurgitation is considered mild when a narrow jet is restricted to the left ventricular outflow tract, and moderate or severe when a wide regurgitant jet passes this level. b P.M. SHAH:Quantitation of regurgitation is extremely difticult and often imprecise. The criteria stated above may be used when a central jet exists. However, the eccentric jet is often poorly quantitated on the basis of its size. The systolic jet filling the atrial appendage or pulmonary vein may be used as additional evidence of severe regurgitation.

Recently, we reported the comparative value of transesophageal vs. transthoracic echocardiography, and the value of both against angiography, in assessing patients with aortic or mitral prosthetic valve regurgitation.162 Using this system, we found a good agreement between transesophageal color imaging grading and that obtained by angiography. Our study also demonstrated the superiority of the transesophageal over the transthoracic approach in assessing the severity of valvular regurgitation and the structural abnormalities leading to prosthetic dysfunction. In this series, 10 patients had evidence of bioprosthetic flail cusp(s) (Fig 11). All these cases had associated severe regurgitation. In selected patients, transesophageal echocardiography avoided the need for angiography and facilitated optimal timing for reoperation.162 b S.H. F~AHIMTOOLA: I agree that transesophageal echocardiography often provides substantial useful information compared to that obtained by transthoracic echocardiography.

INFECTNE

ENDOCARDZTZS

Prosthetic valve endocarditis continues to be a substantial cause of primary valve failure, particularly for biological prostheses?” 157J178 However, the incidence of perivalvular abscesses, valvular dehiscence, and perivalvular regurgitation is higher when infective endocarditis affects mechanical valves than when it involves biological valves .157JIs8 The leaflets of bioprosthetic valve endocarditis may have areas of thickening or thinning with otherwise normal function, loss of pliability with redominant stenosis, or retraction and tears causing regurgitation. t!i This heterogeneity in the pathologic anatomy of bioprosthetic valves leads to a wide variation of echocardiographic apCur-r Probl

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1992

303

FIG 11. Panel A corresponds to a transesophageal echocardiographic image of left atrium (LA), right atrium (RA), and bioprosthesis (p) in mitral position. Two flail cusps prolapsing into the left atrium are identified (arrows). Panel B illustrates the bioprosthesis (Hancock) excised from this patient. The two flail cusps (FC) are clearly seen. (From Chaudhry FA, Her304

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pearance and a paucity of fully sensitive or specific signs. The ability of transthoracic echocardiography to distinguish between tissue degeneration and vegetations is limited. Thickened cusps as seen by transthoracic 2-D echocardiography is an insensitive finding because it may be present in old but otherwise normally functioning valves or in grossly abnormal valves.55-57 b S.H. RAI-IIMTOOLA: The results of the Edinburgh Trial and the VA Cooperative trial showed no significant difference in the incidence of prosthetic endocarditis between the mechanical and the bioprosthetic valves.

The clinical significance of echocardiographic identification of valvular vegetations in patients with native and prosthetic valve endocarditis is controversial.56-58’ 64S17s However, most series favor a worse prognosis when vegetations are present. For example, the incidence of thromboembolic events has been found to be higher in patients with vegetations that are large (2 10 mm), mobile, and located on the mitral valve.‘” The transthoracic approach is useful in patients with infective endocarditis and detects vegetations in approximately two-thirds of the patients. However, the transesophageal technique has increased the ability to identify valvular vegetations on the mitral, aortic, and tricuspid valves with a sensitivity over 90% 17s,180 and to distinguish them from thickened cusps in both native17s-182 and prosthetic valves.157SX628ls3 Another important contribution of transesophageal echocardiography in prosthetic valve endocarditis has been the documentation of flail cusps and perivalvular abscesses.157, 158,181 A flail cusp is a devastating complication of bioprostheses in both mitral (Fig 12) and aortic positions (Fig 13). This echocardiographic finding is frequently associated with severe regurgitation and the need for an emergent operation. We recently reported the diagnostic accuracy of transesophageal echocardiography in detecting this complication.‘57 In this series, transesophageal echocardiography detected 90% of surgically confirmed flail cusps, whereas precordial echocardiography detected only 40% ?57 Early identification of perivalvular abscesses complicating infective endocarditis is particularly important because antibiotic therapy may not be able to penetrate the areas within the active infection. In addition, because the most common location is between the two left-sided annular rings, the conduction system might be involved. Thus, development of ring abscesses should always be suspected in

rera C, DeFrino PF, et al: Pathologic and angiographic correlations of transesophageal echocardiography in prosthetic heart valve dysfunction. Am Heart J 1991; 122:10571064. Reproduced with permission.) Curr

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FIG 12 Pane IA

corresponds to a transesophageal echocardiographic in the mitral position. An echo-dense structure is seen within the left atrium (LA). Bright dense echoes OS thesis

W 306

image in a patic snt with a consistent with a flail cusp are also seen with in tl le bio-

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patients with infective endocarditis with a poor response to appropriate antibiotics, or in the presence of new conduction abnormalities such as complete heart block or bundle branch block. Reports of perivalvular abscesses complicating native or prosthetic valve endocarditis using transthoracic echocardiography are few and incomplete .184-1188The value of transesophageal echocardiography in the detection of abscesses complicating endocarditis in native and prosthetic devices was recently reported by Daniel and colleagues.158 The sensitivity and specificity for detection of abscesses were 28.3% and 98.6%, respectively, for transthoracic, and 87.0% and 94.6% for transesophageal echocardiography; positive and negative predictive values were 92.9% and 68.9%, respectively, for the transthoracic approach, and 90.9% and 92.1% for the transesophageal approach. This report strongly confirms that transesophageal echocardiography is the method of choice for detection of valvular vegetations and abscesses complicating the course of native and prosthetic valve endocarditis. It is important to emphasize that the role of echocardiography in the diagnosis of prosthetic valve endocarditis should be based on clinical grounds. If the clinical suspicion is reasonably high, a negative echocardiographic study, even from the transesophageal approach, should not exclude the diagnosis or obviate the need for antibiotic therapy. INTRAOPERATACE ASSESSMENT

Intraoperative 2-D and Doppler echocardiography have emerged as important tools for the cardiac surgeon and anesthesiologist. The use of epicardial or transesophageal echocardiography permits realtime visualization of ventricular function, chamber volume, valvular anatomy, and flow dynamics. These techniques help in making decisions about the type of surgical plan and the immediate assessment of the results of the rocedure. In 1972, Johnson et al” i: first described intraoperative epicardial M-mode echocardiograms to assess results of mitral valve operations. Since then, many investigators have used epicardial 2-D imaging in different types of cardiac operations.1so-1g4 In epicardial echocardiography, the transducer is placed in a sterile plastic sleeve. Ultrasonic gel is placed between the transducer surface and the inside of the sleeve to provide the acoustic interface between the outer sur-

prosthesis consistent with degenerative calcification on the remaining cusps. LV = left ventricle; RV = right ventricle. Panel 6 illustrates the bioprosthesis (lonescu-Shiley) excised from this patient. The partially destroyed flail cusp (FC) is clearly evident.

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FIG 13. Panel A corresonds to a transesophageai echocardiographic image in a patient with a bioprosthesis in the aortic position. A large and irregular echo-dense structure is noted (arrow) within the outflow tract in diastole. Because of its appearance (two distinct echodense structures), the initial interpretation was a flail cusp with a vegetation. Significant 30.3

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face of the sleeve and the epicardium. In our experience and that of others, this method has resulted in no infections or serious complications. The pamsternal long-axis view is obtained with the transducer applied over the anterior surface of the right ventricle. This view provides a tomographic plane of the anterior and posterior mitral valve leaflets, mitral annulus, and chordae tendineae. When the transducer is rotated 90°, a short-axis view is obtained. The aortasuperior vena cava window is especially useful for visualizing the aortic and left ventricular outflow tract anatomy. The right ventricular four-chamber view is obtained by placing the transducer on the inferior aspect of the right ventricle. The advantages of epicardial over transesophageal echocardiography include more flexibility for transducer positions, which increases the ability to obtain more tomographic planes, and better imaging resolution of structures located distal from the esophagus, such as the right ventricle and pulmonary artery. Thus, particularly for the intraoperative assessment of complex congenital heart disease, epicardial imaging is particularly useful.‘78, ~3’ However, in most adult cardiac operations involving the left ventricle and leftsided valves, the transesophageal window provides superb image quality without interrupting the operative procedure. Previously employed intraoperative methods to assess regurgitation were often crude, providing only gross assessment of valve integrity. Injecting fluid into the arrested ventricle to check for valvular leakage into an upstream chamber is inaccurate because of altered, nonphysiological chamber geometry and pressure in the nonbeating heart. Measurement of left atrial pressure and height of V waves after discontinuation of cardiopulmonary bypass is often misleading, as these variables are dependent on atrial size and compliance as well as on ventricular loading conditions. Early experience with freehand allograft aortic replacement suggested that long-term results depended on careful p$;ement and matching of the donor valve to the recipient annulus. ) Intraoperative 2-D echocardiography in combination with color flow mapping provides an excellent tool to assess aortic ring size and perivalvular anatomy. This information can be obtained quickly, with minimal delay to the surgical team and with no prolongation of cardiopulmonary bypass or aortic cross-clamp time.lg5 At The University of Texas Health Science Center at San Antonio, we utilize epicardial and

aortic insufficiency was present. LA = left atrium; LV = left ventricle; RA = right atrium; RV = right ventricle. Panel 6 illustrates the bioprosthesis (Hancock) excised from this patient. A fenestrated flail cusp is noted. There was no vegetation on the pathologic specimen. It is possible, but not proven, that a vegetation could be dislodged during surgical manipulation or processing of the specimen. Curr

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303

transesophageal echocardiography to monitor aortic homograft insertion. The primary reason is to assess the presence and severity of aortic insufficiency that can result from the freehand insertion. Additionally, immediate postcardiopulmonary bypass assessment of the allograft by echocardiography should reveal normal leaflet motion, unrestricted outflow tract, and proper positioning of the aortic valve. Prior to discharge from the hospital, we routinely perform transthoracic and transesophageal echocardiographic examinations on these patients. This allows us an excellent opportunity to evaluate the aortic valve, particularly for any degree of residual aortic regurgitation. Transthoracic follow-up can be performed every 2 years unless otherwise indicated. Doppler color flow imaging has been established as an accurate technique to assess intraoperative mitral regurgitation at the time of coronary revascularization or mitral valve reconstruction.‘g2’ 1s6400 After aortic unclamping, color flow imaging is useful in evaluating the effect of the operation on the structure and function of the mitral apparatus. The introduction of color Doppler echocardiography offered several advantages over the previously used contrast echocardiography in the assessment of mitral regurgitation. This new technique did not necessitate the insertion of intracardiac needles or the injection of contrast agents. In addition, echocardiographic analysis can be performed without interruption of the operation, Beat-by-beat analysis is now possible, and long-term follow-up studies can be performed using similar methods of evaluation. In our institution, we rely heavily on transesophageal echocardiography for monitoring mitral valve repairs and insertion of annular rings. There are three specific features we look at in those cases. Residual mitral regurgitation is perhaps the most important. We only accept a mild degree of residual regurgitation, which is characterized by a relatively small and narrow jet that does not reach the posterior aspect of the left atrium. If a larger amount of residual regurgitation is present, further repair or replacement is usually recommended. Systolic anterior motion of the mitral valve is a real and potentially serious problem. Significant left ventricular outflow tract obstruction (>70 mm Hg) can occasionally develop and complicate the intra- or immediate postoperative management. It is important to recognize this complication because it usually gets worse with the administration of catecholamines. It is also important to diiferentiate systolic anterior motion at the level of the mitral leaflets (leaflet SAM) from systolic anterior motion at the level of the chordal apparatus (chordal SAM), inasmuch as the latter does not produce left ventricular outflow tract obstruction (unpublished data). Wall motion abnormalities have been observed after mitral ring insertion, particularly over the posterobasal aspect of the left ventricle. It is possible that left ventricular “remodeling,” as a mechanism of adap310

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tation to the new mechanical device, is the main reason for these apparent wall motion abnormalities. This remodeling does not seem to be related to the rigidity of the ring because it tends to disappear over time. In the presence of significant mitral valve disease, tricuspid regurgitation is a relatively common finding?01 During mitral valve repair or replacement, significant tricuspid regurgitation should be corrected, otherwise a potentially serious problem may arise.202 Right ventricular angiography is usually not performed preoperatively because of a low degree of clinical suspicion or a false impression that the surgeon will correct the tricuspid regurgitation during surgery if necessary. At the time of operation, the surgeon traditionally assesses the severity of tricuspid regurgitation by unreliable methods such as palpation of a regurgitant thrill and height of the right atrial V wave. Recently, Czer and colleagueszo3 performed intraoperative echocardiography and color flow Doppler in 51 patients to evaluate the severity of tricuspid regurgitation. In this study, it was demonstrated that tricuspid regurgitation can be evaluated intraoperatively by Doppler color flow mapping in a reliable and reproducible manner. The authors also compared the accuracy of color flow Doppler against the height of the right atrial V wave either before or after cardiopulmonary bypass and found that the latter method did not clearly differentiate all patients with 3+ or 4+ tricuspid regurgitation from those with less severe regurgitation. In this study, tricuspid regurgitation was demonstrated by prepump color Doppler mapping in 87% of the patients and was moderate or severe (3+ or 4+) in 40% of them. All patients who required tricuspid annuloplasty had 3+ or 4+ tricuspid regurgitation, whereas most patients without tricuspid valve repair had 2+ regurgitation or less. Tricuspid annuloplasty provided a significant reduction in regurgitation (two grades or greater) in 94% of the cases. Given the high operative mortality associated with r;;perations for tricuspid regurgitation afand the highly effective reduction in ter mitral valve operations tricuspid regurgitation by ring annuloplasty, advanced 13+ or 4+) tricuspid regurgitation should be identified and surgically corrected at the time of the initial operation. Intraoperative Doppler color flow mapping provides the most accurate means of identifying such patients. As with any new technique, intraoperative echocardiography, either epicardial or transesophageal, has a learning cmve. This learning period requires active participation among the echocardiographer, the surgeon, and the anesthesiologist. It is not uncommon that, at the beginning, some operating room statf may feel that echocardiography is invading their very close niche. However, as their understanding of cardiac anatomy and color flow dynamics as seen on 2-D imaging broadens, their interest in intraoperative echocardiCum

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ography increases. Intraoperative echocardiography is a safe and useful tool that should be performed in most patients undergoing valvular heart operations. b P.M. SHAH: I fully concur with the recommendation that the cardiologist, cardiac surgeon, and cardiac anesthesiologist work closely in order to utilize the information available by intraoperative transesophageal echocardiography for improved care of the patient. I would personally be hesitant to refer a patient for valve surgery to an institution that does not utilize intraoperative echocardiographic monitoring.

GUIDELINES FOR PERFORMING PROSTHETIC VALVES

DOPPLER ECHOCABDIOGBA?‘HY

IN

Guidelines for performing echocardiographic studies in patients with prosthetic valves are summarized in Table 6. All patients undergoing prosthetic valve replacement should have Doppler echocardiographic studies before they leave the hospital. This provides an TABLE 6. Guidelines Prosthetic Patient

for Performing Valves*

Doppler

Echocardiographic

Category

Early postoperative Biological and mechanical valves Long-term follow-up Bioprosthetic valves Adults Patient-prosthesis mismatch Chronic renal failure or other metabolic abnormality of calcium Mechanical valves Adults Patient-prosthesis mismatch Chronic renal failure or other metabolic abnormality of calcium Clinical suspicion dysfunction Mitral position Aortic

‘Arbitrary tlmplies

312

of prosthetic

in Patients

Doppler

Echocardiography

Baseline

in all patients

Every 2 every Once a Once a

with Follow-upt

years for the first 6 years, year year or every other year year

Every 2 or 3 Once a year Every 3 or 4 increased mechanical

and

years or every other year years. There is no evidence early degeneration on valves.

then

of

valve Both transthoracic and transesophageal echocardiography Transthoracic first; if results are suboptimal or clinically inconsistent, recommend transesophageal echocardiography.

position

author’s recommendation transthoracic studies unless

Studies

otherwise

specified

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important baseline to compare with future examinations. The fiequency of serial Doppler echocardiographic examination must be tailored to each patient. Careful clinical follow-up has no substitute. The clicks of an abnormally functioning prosthesis are usually crisp and high-pitched. Dull (low-pitched), soft, or absent valve clicks may be indicative of mechanical dysfunction due to thrombosis and/or tissue ingrowth. If no abnormality is suspected, there is no need for routine serial Doppler examinations. On the other hand, if the gradient is already high at the time of the baseline postoperative study, and a patient-prosthesis mismatch is entertained, serial Doppler examinations are critically important for detection of any further increase in the gradient due to superimposition of an intrinsic valve dysfunction. Since the incidence of porcine bioprosthetic valve failure is >25% at 10 years, > 42% at 12 years, and > 60% at 15 years,76’ a’ careful follow-up of these patients is clearly indicated. In selected patients, the Doppler echocardiographic findings are sufficiently diagnostic so that corrective surgery can be performed without preoperative cardiac catheterization. In assessing patients with prosthetic valves by Doppler echocardiography, it is important to keep in mind three clinically relevant concepts. First, valve areas, in addition to mean gradients, should be routinely calculated. Second, studies performed under less than optimal conditions, such as in patients with a rapid heart or respiratory rate, with arrhythmias tie, atrial fibrillation with rapid ventricular response), on mechanical ventilators, or in any situation that precludes obtaining all standard views, should be interpreted very cautiously. If possible, the examination should be repeated under better conditions. Third, whenever the information provided by the conventional transthoracic study is markedly limited or inconsistent with the clinical suspicion, a transesophageal examination should be performed. Table 7 describes useful recommendations for “things to be done” and “lesions to be looked at” during transesophageal echocardiographic examination in patients with prosthetic valves. b S.H. RAHIMTOOLA:This review by Dr. Zabalgoitia is balanced, thorough, and careful. It is a very good review. I would like to emphasize that, in our experlence and that of others, in an occasional patient with prosthetic heart valve, Doppler echocardiography wlll give a very high false gradient. Therefore, clinical judgment is, as always, extremely important. b P.M. SHAH:Dr. Zabalgoitia is to be complimented for providing this excellent mvlew and bibliography on the important subject of prosthetic heart valves. The approaches and recommendations are balanced and reflect the considerable experience that the author has acquired in this field. Curr

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TABLE 7. Recommendations Patient

During

Condition

I. Prosthetic stenosis

a TEE Examination

valve

A. B. C.

D. II. Prosthetic regurgitation

valve

A. B. C.

D.

III. Prosthetic endocarditis

valve

A. B.

C.

IV. Source

in Patients

with

Prosthetic

Valves

Recommendations

of emboli

A. B.

C.

D. ASA = atrial septal aneurysm; PFO = patent foramen wale;

Iook for possible cause, ie, thmmbus, vegetation, calcification Restricted ball excursion or disc motion may be apparent, particularly in the mitral position Look for thrombus within the LA&LA In addition, for mitral stenosis: 1) calculate mean gradient and valve area Look for possible cause, ie, vegetation, dehiscence, flail cl.lsp(sl Differentiate valvular vs perivalvular (preferably with biplane probe) Assess severity (preferably with biplane probe) In addition, for mitral regurgitation: 11 color and pulse Doppler within LAA and pulmonary veins in search of ‘systolic flow reversal” indicative of severe regurgitation 2) using the TEE horizontal plane, gradually advance and withdraw the pmbe to obtain multiple tomographic cuts of the LA in search of the best regurgitant jet display Look for vegetations in the prosthetic and in the native valves Look for perivalvular abscesses (the pertaortic area and the space between the aortic and the mitral annuli am the most common sites) Look for indirect evidence of infection, ie, flail cusp(s.1, valve dehiscence Look for thmmbus in I&L&A Look for thmmbus attached to the prosthesis; restricted ball excursion or disc motion may suggest thmmbus formation Look for causes of ‘paradoxical embolization,” ie, ASD, ABA, PFO; perform contrast study unless an ASD is obvious by Z-D and color Doppler Look for ascending aorta debris using the longitudinal plane

ASD = atrial septal defect; IA = let3 atrium; TEE = transesophageal echocardiography

L4A = left atrial appendage;

ACKNOWLEDGMENTS The author deeply appreciates the constructive criticism of Dr. L. J. Rosado, cardiothoracic surgeon at the University of Arizona Health Sciences Center, Tucson, and the secretarial assistance of Phyllis Faschingbauer. 314

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Echocardiographic assessment of prosthetic heart valves.

Miguel Zabakoitia, M.D., received his medical degree from the University of Guadalajara, Mezico, in 1976. Afier 3 years of residence training in inter...
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