Two Dimensional Echocardiographic Recognition of the Descending Thoracic Aorta GARY S. MINTZ, MD MORRIS N. KOTLER, MD, FACC BERNARD L. SEGAL, MD, FACC WAYNE R. PARRY Philadelphia,
Pennsylvania
Two dimensional echocardiography was used to identity the descending thoracic aorta in 106 subjects. In 12 of these subjects, contrast injection techniques were used to identify this structure as it descended posteriorly adjacent to the atrfoventrtcular groove. The course of the descending thoracic aorta was mapped using both the long axis and transverse axis views. The normal descending thoracic aorta (26 subjects) measures 10 f 1.4 mm/m2 during diastole. Unusual M mode echocardiographic patterns of the descending aorta may be confused with other disease states; they are clarified with the two dimensional study. The size and appearance of the descending aorta in different types of cardiovascular disease, including aortic aneurysm, in 80 patients are described. It is anticipated that two dimensional echocardiography will prove to be a useful method of studying patlents with aortic disease.
The pericardium, the coronary sinus, the pulmonary veins, and the descending aorta are posterior cardiac structures that are situated adjacent to the posterior atrioventricular (A-V) groove. In normal persons M mode echocardiographic study of the posterior cardiac surface is limited. A discrete pericardial echo is seen only in the presence of a pericardial effusion or with sufficient attenuation of the intensity of the ultrasonic beam. The coronary sinus is visualized as a separate structure only in patients with anomalous pulmonary venous drainage, persistent left superior vena cava or tricuspid insufficiency.’ The descending aorta has not been recognized as a separate structure. Two dimensional echocardiography facilitates study of cardiac structures because of improved spatial orientation. Preliminary two dimensional studies have demonstrated in the long axis view a circular echo-free structure posterior to the A-V groove. Although the identity of this structure has not been established conclusively, some authors have suggested that it may represent the coronary sinus2 or a pulmonary vein.” The purpose of this report is fourfold: (1) to prove that this circular structure represents the descending thoracic aorta, (2) to establish normal values for this view of the descending thoracic aorta, (3) to demonstrate the ability of two dimensional echocardiography to recognize pathologic changes in the descending thoracic aorta, and (4) to correlate two dimensional echocardiographic findings with M mode echocardiographic studies of the posterior cardiac surface. Met hods From the William Likoff Cardiovascular Institute, Hahnemann Medical College and Hospital, Philadelphia, Pennsylvania. Manuscript received January 29, 1979; revised manuscript received March 20, 1979, accepted April 2, 1979. Address for reprints: Gary S. Mintz, MD, Likoff Cardiovascular Institute. Hahnemann Medical College and Hospital, 230 North Broad Street, Philadelphia. Pennsylvania 19102.
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Echocardiography: M mode echocardiographic studies were performed in the supine or left lateral decubitus position using either a Smith-Kline Ekoline 20A ultrasonascope interfaced with an Irex 101 Continutrace recorder or an Irex System II ultrasonascope. Two dimensional echocardiographic studies were performed in the supine or left lateral decubitus position using either a Varian WI000 or a Grumman RT400 phased-array sector scanner. In some patients simultaneous M mode and two dimensional echocardiographic studies were also performed. The M mode echocardiographic study consisted of a standard lon-
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gitudinal sweep from the aorta to below the level of the mitral valve leaflets. The two dimensional echocardiographic study consisted of the long axis view and a series of continuous transverse views from the ascending aorta at the level of the aortic leaflets to the left ventricular apex. During both M mode and two dimensional studies, gain and reject settings were adjusted for maximal far field resolution and definition. Patients: Three groups of patients were studied. Twelve patients (Group I) were studied immediately after transfemoral diagnostic cardiac catheterization. Simultaneous M mode and two dimensional echocardiographic studies were performed using a Varian V3000 phased-array sector scanner; during two dimensional study, 1 of the 32 sector scan transducer elements was selected to provide an M mode record. The catheter tip was positioned within the ascending aorta and 10 cc of saline solution was rapidly injected. Visualization of the microbubbles from the injection or of the catheter within the echo-free space identified the descending aorta. Twenty-six volunteer normal persons (Group II) were studied to define the normal size of the aorta. Eighty patients with a variety of cardiovascular disorders (Group III) were also studied; 12 patients had coronary artery disease, 10 had mitral insufficiency secondary to mitral valve prolapse, lOhad mitral insufficiency from a cause other than mitral prolapse, 25 had aortic insufficiency (including 5 who also had aortic stenosis), 15 had chronic hypertension and left ventricular hypertrophy and 8 had primary disease of the aorta. Measurements: With use of the two dimensional long axis view, diastolic internal ascending aortic dimensions were measured at the level of the aortic valve and above the sinus of Valsalva; anteroposterior diastolic internal descending aortic dimensions were measured from the recording of the descending aorta behind the A-V groove. The record was damped to the point at which the pericardium became a single line in order to appreciate the true descending aortic lumen. All measurements were normalized for body surface area and reported as mean f 1 standard deviation. was performed using Student’s t Statistical analysis
ET AL.
appeared as a pulsatile echo-free space in the posterior A-V groove (Fig. 1 and 2). Systolic pulsations were only seen with proper record damping. In the transverse views the course of the descending thoracic aorta could be followed (Fig. 5). At the level of the left ventricular apex below the papillary muscles, the descending thoracic aorta was not seen normally. At the level of the tips of the mitral leaflets or of the
.
test.
Results In all 12 patients in Group I the descending aorta was recognized during simultaneous M mode and two dimensional echocardiographic study. The aorta was identified by contrast injection in six patients (Fig. 1) and during catheter manipulation and withdrawal in six patients (Fig. 2). M mode echocardiographic findings: The descending thoracic aorta usually appeared as an echo-free space behind the left atrium, A-V groove, or left ventricular posterior wall (Fig. 3). This pattern was typically recorded only during maximal or near maximal decrease in far gain. However, occasional atypical findings occurred in patients in whom this posterior echo-free space was recorded with normal far gain and damping settings. The appearance of an additional posterior echo-free space occasionally led to an erroneous identification of structures and a diagnosis of mitral anular calcification or posterior pericardial effusion (Fig. 4) or left atria1 enlargement. Conversely, a dilated descending aorta occasionally caused left atria1 compression. Two dimensional echocardiographic findings: In the long axis view the descending thoracic aorta usually
FIGURE 1. Top panels, still frames of a two dimensional echocardiographic study of the descending thoracic aorta (Desc. Ao). The long axis view was recorded before and after injection of saline solution; each frame is accompanied by a labeled idealized diagram. The descending aorta appears as a circular echo-free space posterior to the atrioventricular groove. After saline injection, this echo-free space is obliterated by the contrast effect. Bottom panel, same patient. M mode echocardiographic study of the descending thoracic aorta recorded simultaneously with the two dimensional echocardiogram of Panel A. An echo-free space appears behind the left ventricular posterior wall (LPW). After contrast injection (open arrow), a cloud of echoes is recorded within this echo-free space. A = anterior: Ao = aorta; ECG = electrocardiogram; IVS = interventricular septum; Inject = injection of contrast medium; LA = left atrium; LV = left ventricle: MV = mitral valve; P = posterior: RV = right ventricle.
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FIGURE 2. Still frames of a two dimensional echocardiographic study of the descending thoracic aorta. The long axis view was recorded before and after withdrawal of the descending aortic catheter. The catheter (C.) is identified as a blob of echoes within the descending aorta before withdrawal. Abbreviations as in Figure 1.
papillary muscle, the descending aorta first appeared as a circular or oval echo-free space. At the level of the mitral leaflets, the aorta was located directly behind the left ventricle. At the level of the left atrium, the descending aorta was seen lateral to and behind the left atrium. At the level of the pulmonary arterial bifurcation, the descending thoracic aorta appeared directly posterior to the bifurcation.
ET AL.
In normal persons in the long axis view, the descending aorta was seen in the posterior A-V groove. By contrast, in patients with left atrial enlargement, it was displaced 1 to 4 cm superior to the A-V groove and was visualized behind the left atrium. In patients with left ventricular hypertrophy, it was occasionally displaced inferiorly and visualized behind the left ventricular posterior wall. Aortic measurements (Table I): In normal persons, the ascending aortic lumen during diastole measured 27 f 4.5 mm (16 f 1.8 mm/m2) at the level of the aortic valve and 22 f 4.0 mm (13 f 1.4 mm/m2) above the sinus of Valsalva. The descending aortic lumen during diastole measured 17 f 3.3 mm (10 f 1.4 mm/m2). In patients with abnormal aortic measurements, the descending aorta was larger than normal in patients with coronary artery disease, hypertension and aortic valve disease. The ascending aorta was statistically larger than normal in patients with mitral valve prolapse and aortic valve disease. Nine patients had primary disease of the aorta: one had a hypoplastic descending aorta (Fig. 6), two had an aneurysm of only the ascending aorta (Fig. 7), one had an aneurysm of both the ascending and the descending aorta, four had an aneurysm of only the descending thoracic aorta (Fig. 8), and two had aneurysms of the abdominal aorta without involvement of the thoracic aorta. The findings in the patients with aortic aneurysms were confirmed with aortography. In the patient with a hypoplastic aorta, the ascending aortic measurements were normal, but the descending aortic measurement was 2 standard deviations smaller than normal. These findings were confirmed at surgery and necropsy. In patients with aortic aneurysm (Table II) the involved segment was at least 2 standard deviations larger than normal or larger than the aortic measurements in patients with other forms of cardiac disease; the uninvolved segments were within normal limits.
TABLE I Two Dimenslonal Measurements of Ascending and Descending Aorta Clinical Diagnosis
Ascending Aorta (mm/m*) At Aortic Above Sinus Valve of Valsalva
Age (yr)
Normal
26
32 f 20
16 f 1.8 (10-19)
13 f 1.4 (9-17)
10 f 1.4 (8-16)
Co;ro,“;;eartery
12
63f
11
16 f 2.1 (13-20)
14 f 2.9 (10-20)
11 f 1.7’ (9-14)
Mitral insufficiency without prolapse
10
51 f 20
16 f 1.8 (14-19)
13 f 1.4 (10-14)
10 f 2.2 (7-14)
Mitral insufficiency secondary to prolapse
10
39%
19
18 f 2.5 (14-22)
15 f 2.0’ (13-18)
10 f 1.4 (9-13)
Hypertension and ventricular hypettrophy
15
49f
18
16 f 3.2 (1 l-23)
14 f 2.5 (9-18)
11 f 1.4’ (9-13)
Aortic valve disease
25
46f
16
19 f 4.4 (11-23)
17 f 3.7’ (9-24)
12 f 2.6’ (8-16)
Statistically larger than normal. Data are presented as mean f 1 standard deviation with ranges in parentheses. l
234
Descending Aorta (mm/m2)
Patients (no.)
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FIGURE 3. Typical M mode echocardiographic sweep from the body of the left ventricle up to the aorta (Ao). The descending aorta (Desc Ao) appears as an echo-free space behind the atrioventricular junction, the transition point from the left atrial posterior wall (LAPW) to the left ventricular posterior wall (LVPW). Unidentified abbreviations as in Figure 1.
FIGURE 4. Echocardiograms of a patient whose descending thoracic aorta was displaced inferiorly behind the left ventricular posterior wall (LPW). Top, M mode study was variously interpreted as showing a small posterior pericardial effusion or mitral anular calcification. Len, the two dimensional study indicated that this posterior echo-free space represented the descending thoracic aorta (Desc. Ao). Unidentified abbreviations as in Figure 1.
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/“I
ET AL.
Arch
FIGURE 5. Left, schematic diam of transducer angulatttns that permit study of the descending thoracic aorta. Position 1 corresponds to the standard long axis view shown in Figures 2 and 4. Positions 2 through 5 correspond to the series of transverse views shown at bottom. In the latter panels. transverse views of the descending thoracic aorta are recorded as the two dimensional echocardiographic beam passes through (in sequence from left to right) the left ventricle at the level of the papillary muscles (position 2) the left ventricle at the level of the mitral valve (position 3). the aorta and the left atrium (position 4) and the aorta and the pulmonary artery (position 5). The descending aorta (Desc Ao) first appears as the transducer beam passes through the papillary muscles (PM) or the tips of the mitral valve (MV); the descending aorta appears as a circular or oval echo-free space posterior (P) and to the right (R) of the left ventricle (LV). If the heart is more vertical the aorta appears as a circle; if the heart is more horizontal the aorta appears as an oval. At the level of the mitral valve (position 3) the descending aorta lies directly behind the left ventricle. At the level of the aorta (Ao) and left atrium (LA), it appears to the left and posterior to the left atrium. At the level of the aorta and pulmonary arterial (PA) bifurcation, it is posterior to the pulmonary arterial bifurcation. Asc. Ao. = ascending aorta; L = left; LPA = left pulmonary artery; MPA = main pulmonary artery; R = right; RPA = right pulmonary artery; other abbreviations as in Figure 1.
Discussion In vivo echocardiographic identification of intracardiac structures is aided by intravascular contrast injection and detection of intravascular catheters. Rapid intravascular injection of indocyanine green or saline solution produces a cloud of echoes; a combination of factors including differential acoustical impedance, microcavitation and turbulence account for the echocardiographic contrast effect. The contrast is seen downstream as well as at the injection site. This technique may be used to identify structures seen with M mode4 and two-dimensional echocardiography,s to detect and localize right to left and left to right shunts and
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to document tricuspid insufficiency.6 Similarly, pulmonary arterial catheters and transvenous pacemakers7 have been recognized in the right ventricle, right ventricular outflow tract and pulmonary artery; and the intraaortic balloon has been detected echocardiographically.8 Using both of these techniques, we have identified the descending aorta as it crosses the posterior A-V groove. On M mode echocardiographic examination the descending aorta may appear as an additional echo-free space behind the left atrium. On two dimensional study, its course may be followed from the level of the bifurcation of the pulmonary artery to below the left ventricle. Additionally, the abdominal aorta may
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-mse
FIGURE 6. Two dimensional echocardiographic study of a patient with a hypoplastic descending thoracic aorta (Desc Ao) proved at surgery and necropsy. The single frame of the long axis view is accompanied by a labeled idealized diagram. The descending aorta is positioned normally in the posterior atrioventricular groove but measures only 5 mm/m*. AML = anterior mitral leaflet; Asc. Ao = ascending aorta; PML = posterior mitral leaflet; other abbreviations as in Figure 1.
Base
FIGURE 6. Two dimensional echocardiographic study of a patient with an angiographically proved type Ill dissection of the thoracic aorta. The single frame of the long axis view is accompanied by a labeled idealized diagram. The ascending aorta (Ao) is normal in size. The descending aorta (Desc Ao) is enlarged, and an intimal flap (whife arrow) separates the true from the false lumen. Abbreviations as in Figure 1.
FIGURE 7. Two dimensional echocardiographic study of a patient with an angiographically proved aneurysm of the ascending thoracic aorta. The single frame of the long axis view is accompanied by a labeled idealized diagram. The ascending aorta (Asc. Ao.) is markedly dilated (39 mm/m*); the descending thoracic aorta (Desc Ao) is normal (11 mm/m*). Abbreviations as in Figure 1.
be studied using standard abdominal ultrasonic techniques. The superior aortic arch may be studied by the suprasternal notch echocardiographic window. Differentiation of descending aorta from other posterior cardiac structures: Until now, it was usually thought that the descending aorta could not be recognized in either the standard M mode echocardiographic sweep or the two dimensional echocardiographic long axis view. At normal gain levels needed to identify the endocardium, the pericardial echoes are usually so strong that the descending aorta is obscured. The M mode echocardiographic study of posterior cardiac structures is particularly difficult. Numerous studies discuss pitfalls in the diagnosis of pericardial effusion9 difficulty in differentiation of a pericardial from a pleural effusion, and errors in measurement of left atria1 size.‘O Our studies show that the descending aorta can be seen on M mode echocardiography as a linear echofree space behind the left atrium. In retrospect, this structure can be visualized in many patients. Because it is usually assumed that the descending aorta is not recorded during routine M mode study, the presence of another posterior echo-free structure may cause confusion in structure identification, leading to the erroneous diagnosis of pericardial effusion, mitral anular calcification or left atria1 enlargement. A double line in
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ET AL
TABLE II Two Dimensional Echocardiographic Measurements of the Ascending and Descending Aorta in Eight Patients With an Aortic Aneurysm Ascending Aorta (mm/m*) Case no.
Site of Aneurysm
At Aortic Valve
Above Sinus of Valsalva
Descending Aorta (mm/m*)
1
Abdominal
17
15
12
2 3
Abdominal Descending thoracic Descending thoracic Descending thoracic’ Descending thoracic Ascending thoracic Ascending thoracic
:s
:::
;s
20
19
22
-
-
36
18
16
18
22
39
11
19
29
11
4 5 6 7 8
In patient 5, the heart was displaced lo the right so that the ascending aorta was not recordable. l
the region of the left atria1 posterior wall is a common finding. It has been stated that the anterior line is either an artifact or an intraatrial reflection.ll In reality, the anterior line represents the true left atria1 posterior wall (or its interface with the descending aorta), and the space behind it represents the descending aorta. Two dimensional versus M mode echocardiography: Two dimensional echocardiography is better suited to the study of the posterior cardiac structures. The spatial interrelations and relative positions of these structures can be readily identified. In the long axis view the left atrium is circular, the pericardium is a linear structure that usually bridges the A-V junction and the aorta is a circular pulsatile echo-free space behind the pericardium. (Others have suggested, but never proved, that this echo-free space is the coronary sinus2 or pulmonary veins). Similarly, the course of the aorta can be
mapped using the transverse views. Because it is easier to recognize the descending aorta with two dimensional echocardiography, this technique is invaluable in the interpretation of unusual M mode echocardiographic patterns of posterior cardiac structures. Normal aortic measurements: We have attempted to establish normal values for the size of the descending aorta. In normal persons the diastolic diameter of the lumen of this segment of the descending aorta measures 10 f 1.4 mm/m2. This compares with ascending aortic luminal diameters of 16 f 1.8 mm/m2 at the level of the aortic valve and 13 f 1.4 mm/m2 above the level of sinus of Valsalva. In our patients with mitral insufficiency exclusive of mitral valve prolapse (cardiomyopathy, flail leaflet, pure rheumatic mitral disease or endocarditis), aortic measurements were similar to those of the younger patients in our control group. Because the older patients had no cause for aortic disease, their aortic measurements substantiate our view that the values of the control population were normal. Abnormal aortic measurements: Patients with coronary artery disease, chronic hypertension or aortic valve disease with aortic insufficiency also had an enlarged descending aorta; although the mean enlargement was small, individual variations were significant. The pattern of enlargement of the ascending aorta varied in each of these patient populations. Lastly, we also studied a small group of patients with intrinsic aortic disease. In one patient with a hypoplastic aorta, the aorta was 2 standard deviations smaller than normal. In six patients with a thoracic aortic aneurysm, the involved segment was larger than that seen in any patient with other forms of cardiovascular disease. In two patients with an abdominal aortic aneurysm, the thoracic aortic measurements were normal. These data suggest that two dimensional echocardiography is a useful technique for studying the entire aorta and detecting localized or diffuse aortic aneurysms. This technique should also allow the clinician to follow up patients with aneurysm of the aorta and to document changes in size that might be useful clinically.
References 1. Orsmond GS, Rultenberg HD, Besslnger FB, Moller JH: Echocardiographic features of total anomalous pulmonary venous connection to the coronary sinus. Am J Cardiol 41597-601, 1978 2. Tajik Al, Seward JB, H@r DTJ, Malr DD, Lie TT:Twodirnsnsional real-time ultrasonic imaging of the heart and great vessels: technique. image orientation, structure identification, and validation. Mayo Clin Proc 53:271-303, 1978 3. Nanda NC, Gramlak R: Clinical Echocardiography. Saint Louis, CV Mosby, 1978, p 383 4. Gramlak R, Shah PM, Kramer DH: Ultrasound cardiography: contrast studies in anatomy and function. Radiology 92:939-948, 1969 5. Tajik Al, Seward JB: Contrast echocardiography. In, Clinical
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6.
7.
8. 9. 10.
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Echocardiography (Kotler MN, Segal BS, ed). Philadelphia, FA Davis, 1978, p 317-342 Lieppe W, Behar VS. Scallfon R, Klsslo JA: Detection of tricuspid regurgitation with two-dimensional echocardiography and peripheral vein injections. Circulation 57:128-133. 1978 Charuzi Y, Kruas R, Swan HX: Echocardiographic interpretation in the oresence of Swan-C&z intracardiac catheters. Am J Cardiol 40:98b-994, 1977 Weir I, Yacoub M, Prldie RB: Echocardiography of the intra-aortic balloon. Br Heart J 37:1045-1048, 1975 Kotler MN, Segal BL. Mintz G, Parry WR: Pitfalls and limitations of M-mode echocardiography. Am Heart J 94:227-249, 1977 Feigenbaum H: Echocardiography. Philadelphia, Lea & Febiger, 1976, p 237-245
Pennsylvania
Two dimensional echocardiography was used to identity the descending thoracic aorta in 106 subjects. In 12 of these subjects, contrast injection techniques were used to identify this structure as it descended posteriorly adjacent to the atrfoventrtcular groove. The course of the descending thoracic aorta was mapped using both the long axis and transverse axis views. The normal descending thoracic aorta (26 subjects) measures 10 f 1.4 mm/m2 during diastole. Unusual M mode echocardiographic patterns of the descending aorta may be confused with other disease states; they are clarified with the two dimensional study. The size and appearance of the descending aorta in different types of cardiovascular disease, including aortic aneurysm, in 80 patients are described. It is anticipated that two dimensional echocardiography will prove to be a useful method of studying patlents with aortic disease.
The pericardium, the coronary sinus, the pulmonary veins, and the descending aorta are posterior cardiac structures that are situated adjacent to the posterior atrioventricular (A-V) groove. In normal persons M mode echocardiographic study of the posterior cardiac surface is limited. A discrete pericardial echo is seen only in the presence of a pericardial effusion or with sufficient attenuation of the intensity of the ultrasonic beam. The coronary sinus is visualized as a separate structure only in patients with anomalous pulmonary venous drainage, persistent left superior vena cava or tricuspid insufficiency.’ The descending aorta has not been recognized as a separate structure. Two dimensional echocardiography facilitates study of cardiac structures because of improved spatial orientation. Preliminary two dimensional studies have demonstrated in the long axis view a circular echo-free structure posterior to the A-V groove. Although the identity of this structure has not been established conclusively, some authors have suggested that it may represent the coronary sinus2 or a pulmonary vein.” The purpose of this report is fourfold: (1) to prove that this circular structure represents the descending thoracic aorta, (2) to establish normal values for this view of the descending thoracic aorta, (3) to demonstrate the ability of two dimensional echocardiography to recognize pathologic changes in the descending thoracic aorta, and (4) to correlate two dimensional echocardiographic findings with M mode echocardiographic studies of the posterior cardiac surface. Met hods From the William Likoff Cardiovascular Institute, Hahnemann Medical College and Hospital, Philadelphia, Pennsylvania. Manuscript received January 29, 1979; revised manuscript received March 20, 1979, accepted April 2, 1979. Address for reprints: Gary S. Mintz, MD, Likoff Cardiovascular Institute. Hahnemann Medical College and Hospital, 230 North Broad Street, Philadelphia. Pennsylvania 19102.
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Echocardiography: M mode echocardiographic studies were performed in the supine or left lateral decubitus position using either a Smith-Kline Ekoline 20A ultrasonascope interfaced with an Irex 101 Continutrace recorder or an Irex System II ultrasonascope. Two dimensional echocardiographic studies were performed in the supine or left lateral decubitus position using either a Varian WI000 or a Grumman RT400 phased-array sector scanner. In some patients simultaneous M mode and two dimensional echocardiographic studies were also performed. The M mode echocardiographic study consisted of a standard lon-
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gitudinal sweep from the aorta to below the level of the mitral valve leaflets. The two dimensional echocardiographic study consisted of the long axis view and a series of continuous transverse views from the ascending aorta at the level of the aortic leaflets to the left ventricular apex. During both M mode and two dimensional studies, gain and reject settings were adjusted for maximal far field resolution and definition. Patients: Three groups of patients were studied. Twelve patients (Group I) were studied immediately after transfemoral diagnostic cardiac catheterization. Simultaneous M mode and two dimensional echocardiographic studies were performed using a Varian V3000 phased-array sector scanner; during two dimensional study, 1 of the 32 sector scan transducer elements was selected to provide an M mode record. The catheter tip was positioned within the ascending aorta and 10 cc of saline solution was rapidly injected. Visualization of the microbubbles from the injection or of the catheter within the echo-free space identified the descending aorta. Twenty-six volunteer normal persons (Group II) were studied to define the normal size of the aorta. Eighty patients with a variety of cardiovascular disorders (Group III) were also studied; 12 patients had coronary artery disease, 10 had mitral insufficiency secondary to mitral valve prolapse, lOhad mitral insufficiency from a cause other than mitral prolapse, 25 had aortic insufficiency (including 5 who also had aortic stenosis), 15 had chronic hypertension and left ventricular hypertrophy and 8 had primary disease of the aorta. Measurements: With use of the two dimensional long axis view, diastolic internal ascending aortic dimensions were measured at the level of the aortic valve and above the sinus of Valsalva; anteroposterior diastolic internal descending aortic dimensions were measured from the recording of the descending aorta behind the A-V groove. The record was damped to the point at which the pericardium became a single line in order to appreciate the true descending aortic lumen. All measurements were normalized for body surface area and reported as mean f 1 standard deviation. was performed using Student’s t Statistical analysis
ET AL.
appeared as a pulsatile echo-free space in the posterior A-V groove (Fig. 1 and 2). Systolic pulsations were only seen with proper record damping. In the transverse views the course of the descending thoracic aorta could be followed (Fig. 5). At the level of the left ventricular apex below the papillary muscles, the descending thoracic aorta was not seen normally. At the level of the tips of the mitral leaflets or of the
.
test.
Results In all 12 patients in Group I the descending aorta was recognized during simultaneous M mode and two dimensional echocardiographic study. The aorta was identified by contrast injection in six patients (Fig. 1) and during catheter manipulation and withdrawal in six patients (Fig. 2). M mode echocardiographic findings: The descending thoracic aorta usually appeared as an echo-free space behind the left atrium, A-V groove, or left ventricular posterior wall (Fig. 3). This pattern was typically recorded only during maximal or near maximal decrease in far gain. However, occasional atypical findings occurred in patients in whom this posterior echo-free space was recorded with normal far gain and damping settings. The appearance of an additional posterior echo-free space occasionally led to an erroneous identification of structures and a diagnosis of mitral anular calcification or posterior pericardial effusion (Fig. 4) or left atria1 enlargement. Conversely, a dilated descending aorta occasionally caused left atria1 compression. Two dimensional echocardiographic findings: In the long axis view the descending thoracic aorta usually
FIGURE 1. Top panels, still frames of a two dimensional echocardiographic study of the descending thoracic aorta (Desc. Ao). The long axis view was recorded before and after injection of saline solution; each frame is accompanied by a labeled idealized diagram. The descending aorta appears as a circular echo-free space posterior to the atrioventricular groove. After saline injection, this echo-free space is obliterated by the contrast effect. Bottom panel, same patient. M mode echocardiographic study of the descending thoracic aorta recorded simultaneously with the two dimensional echocardiogram of Panel A. An echo-free space appears behind the left ventricular posterior wall (LPW). After contrast injection (open arrow), a cloud of echoes is recorded within this echo-free space. A = anterior: Ao = aorta; ECG = electrocardiogram; IVS = interventricular septum; Inject = injection of contrast medium; LA = left atrium; LV = left ventricle: MV = mitral valve; P = posterior: RV = right ventricle.
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FIGURE 2. Still frames of a two dimensional echocardiographic study of the descending thoracic aorta. The long axis view was recorded before and after withdrawal of the descending aortic catheter. The catheter (C.) is identified as a blob of echoes within the descending aorta before withdrawal. Abbreviations as in Figure 1.
papillary muscle, the descending aorta first appeared as a circular or oval echo-free space. At the level of the mitral leaflets, the aorta was located directly behind the left ventricle. At the level of the left atrium, the descending aorta was seen lateral to and behind the left atrium. At the level of the pulmonary arterial bifurcation, the descending thoracic aorta appeared directly posterior to the bifurcation.
ET AL.
In normal persons in the long axis view, the descending aorta was seen in the posterior A-V groove. By contrast, in patients with left atrial enlargement, it was displaced 1 to 4 cm superior to the A-V groove and was visualized behind the left atrium. In patients with left ventricular hypertrophy, it was occasionally displaced inferiorly and visualized behind the left ventricular posterior wall. Aortic measurements (Table I): In normal persons, the ascending aortic lumen during diastole measured 27 f 4.5 mm (16 f 1.8 mm/m2) at the level of the aortic valve and 22 f 4.0 mm (13 f 1.4 mm/m2) above the sinus of Valsalva. The descending aortic lumen during diastole measured 17 f 3.3 mm (10 f 1.4 mm/m2). In patients with abnormal aortic measurements, the descending aorta was larger than normal in patients with coronary artery disease, hypertension and aortic valve disease. The ascending aorta was statistically larger than normal in patients with mitral valve prolapse and aortic valve disease. Nine patients had primary disease of the aorta: one had a hypoplastic descending aorta (Fig. 6), two had an aneurysm of only the ascending aorta (Fig. 7), one had an aneurysm of both the ascending and the descending aorta, four had an aneurysm of only the descending thoracic aorta (Fig. 8), and two had aneurysms of the abdominal aorta without involvement of the thoracic aorta. The findings in the patients with aortic aneurysms were confirmed with aortography. In the patient with a hypoplastic aorta, the ascending aortic measurements were normal, but the descending aortic measurement was 2 standard deviations smaller than normal. These findings were confirmed at surgery and necropsy. In patients with aortic aneurysm (Table II) the involved segment was at least 2 standard deviations larger than normal or larger than the aortic measurements in patients with other forms of cardiac disease; the uninvolved segments were within normal limits.
TABLE I Two Dimenslonal Measurements of Ascending and Descending Aorta Clinical Diagnosis
Ascending Aorta (mm/m*) At Aortic Above Sinus Valve of Valsalva
Age (yr)
Normal
26
32 f 20
16 f 1.8 (10-19)
13 f 1.4 (9-17)
10 f 1.4 (8-16)
Co;ro,“;;eartery
12
63f
11
16 f 2.1 (13-20)
14 f 2.9 (10-20)
11 f 1.7’ (9-14)
Mitral insufficiency without prolapse
10
51 f 20
16 f 1.8 (14-19)
13 f 1.4 (10-14)
10 f 2.2 (7-14)
Mitral insufficiency secondary to prolapse
10
39%
19
18 f 2.5 (14-22)
15 f 2.0’ (13-18)
10 f 1.4 (9-13)
Hypertension and ventricular hypettrophy
15
49f
18
16 f 3.2 (1 l-23)
14 f 2.5 (9-18)
11 f 1.4’ (9-13)
Aortic valve disease
25
46f
16
19 f 4.4 (11-23)
17 f 3.7’ (9-24)
12 f 2.6’ (8-16)
Statistically larger than normal. Data are presented as mean f 1 standard deviation with ranges in parentheses. l
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Descending Aorta (mm/m2)
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FIGURE 3. Typical M mode echocardiographic sweep from the body of the left ventricle up to the aorta (Ao). The descending aorta (Desc Ao) appears as an echo-free space behind the atrioventricular junction, the transition point from the left atrial posterior wall (LAPW) to the left ventricular posterior wall (LVPW). Unidentified abbreviations as in Figure 1.
FIGURE 4. Echocardiograms of a patient whose descending thoracic aorta was displaced inferiorly behind the left ventricular posterior wall (LPW). Top, M mode study was variously interpreted as showing a small posterior pericardial effusion or mitral anular calcification. Len, the two dimensional study indicated that this posterior echo-free space represented the descending thoracic aorta (Desc. Ao). Unidentified abbreviations as in Figure 1.
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Arch
FIGURE 5. Left, schematic diam of transducer angulatttns that permit study of the descending thoracic aorta. Position 1 corresponds to the standard long axis view shown in Figures 2 and 4. Positions 2 through 5 correspond to the series of transverse views shown at bottom. In the latter panels. transverse views of the descending thoracic aorta are recorded as the two dimensional echocardiographic beam passes through (in sequence from left to right) the left ventricle at the level of the papillary muscles (position 2) the left ventricle at the level of the mitral valve (position 3). the aorta and the left atrium (position 4) and the aorta and the pulmonary artery (position 5). The descending aorta (Desc Ao) first appears as the transducer beam passes through the papillary muscles (PM) or the tips of the mitral valve (MV); the descending aorta appears as a circular or oval echo-free space posterior (P) and to the right (R) of the left ventricle (LV). If the heart is more vertical the aorta appears as a circle; if the heart is more horizontal the aorta appears as an oval. At the level of the mitral valve (position 3) the descending aorta lies directly behind the left ventricle. At the level of the aorta (Ao) and left atrium (LA), it appears to the left and posterior to the left atrium. At the level of the aorta and pulmonary arterial (PA) bifurcation, it is posterior to the pulmonary arterial bifurcation. Asc. Ao. = ascending aorta; L = left; LPA = left pulmonary artery; MPA = main pulmonary artery; R = right; RPA = right pulmonary artery; other abbreviations as in Figure 1.
Discussion In vivo echocardiographic identification of intracardiac structures is aided by intravascular contrast injection and detection of intravascular catheters. Rapid intravascular injection of indocyanine green or saline solution produces a cloud of echoes; a combination of factors including differential acoustical impedance, microcavitation and turbulence account for the echocardiographic contrast effect. The contrast is seen downstream as well as at the injection site. This technique may be used to identify structures seen with M mode4 and two-dimensional echocardiography,s to detect and localize right to left and left to right shunts and
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to document tricuspid insufficiency.6 Similarly, pulmonary arterial catheters and transvenous pacemakers7 have been recognized in the right ventricle, right ventricular outflow tract and pulmonary artery; and the intraaortic balloon has been detected echocardiographically.8 Using both of these techniques, we have identified the descending aorta as it crosses the posterior A-V groove. On M mode echocardiographic examination the descending aorta may appear as an additional echo-free space behind the left atrium. On two dimensional study, its course may be followed from the level of the bifurcation of the pulmonary artery to below the left ventricle. Additionally, the abdominal aorta may
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FIGURE 6. Two dimensional echocardiographic study of a patient with a hypoplastic descending thoracic aorta (Desc Ao) proved at surgery and necropsy. The single frame of the long axis view is accompanied by a labeled idealized diagram. The descending aorta is positioned normally in the posterior atrioventricular groove but measures only 5 mm/m*. AML = anterior mitral leaflet; Asc. Ao = ascending aorta; PML = posterior mitral leaflet; other abbreviations as in Figure 1.
Base
FIGURE 6. Two dimensional echocardiographic study of a patient with an angiographically proved type Ill dissection of the thoracic aorta. The single frame of the long axis view is accompanied by a labeled idealized diagram. The ascending aorta (Ao) is normal in size. The descending aorta (Desc Ao) is enlarged, and an intimal flap (whife arrow) separates the true from the false lumen. Abbreviations as in Figure 1.
FIGURE 7. Two dimensional echocardiographic study of a patient with an angiographically proved aneurysm of the ascending thoracic aorta. The single frame of the long axis view is accompanied by a labeled idealized diagram. The ascending aorta (Asc. Ao.) is markedly dilated (39 mm/m*); the descending thoracic aorta (Desc Ao) is normal (11 mm/m*). Abbreviations as in Figure 1.
be studied using standard abdominal ultrasonic techniques. The superior aortic arch may be studied by the suprasternal notch echocardiographic window. Differentiation of descending aorta from other posterior cardiac structures: Until now, it was usually thought that the descending aorta could not be recognized in either the standard M mode echocardiographic sweep or the two dimensional echocardiographic long axis view. At normal gain levels needed to identify the endocardium, the pericardial echoes are usually so strong that the descending aorta is obscured. The M mode echocardiographic study of posterior cardiac structures is particularly difficult. Numerous studies discuss pitfalls in the diagnosis of pericardial effusion9 difficulty in differentiation of a pericardial from a pleural effusion, and errors in measurement of left atria1 size.‘O Our studies show that the descending aorta can be seen on M mode echocardiography as a linear echofree space behind the left atrium. In retrospect, this structure can be visualized in many patients. Because it is usually assumed that the descending aorta is not recorded during routine M mode study, the presence of another posterior echo-free structure may cause confusion in structure identification, leading to the erroneous diagnosis of pericardial effusion, mitral anular calcification or left atria1 enlargement. A double line in
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TABLE II Two Dimensional Echocardiographic Measurements of the Ascending and Descending Aorta in Eight Patients With an Aortic Aneurysm Ascending Aorta (mm/m*) Case no.
Site of Aneurysm
At Aortic Valve
Above Sinus of Valsalva
Descending Aorta (mm/m*)
1
Abdominal
17
15
12
2 3
Abdominal Descending thoracic Descending thoracic Descending thoracic’ Descending thoracic Ascending thoracic Ascending thoracic
:s
:::
;s
20
19
22
-
-
36
18
16
18
22
39
11
19
29
11
4 5 6 7 8
In patient 5, the heart was displaced lo the right so that the ascending aorta was not recordable. l
the region of the left atria1 posterior wall is a common finding. It has been stated that the anterior line is either an artifact or an intraatrial reflection.ll In reality, the anterior line represents the true left atria1 posterior wall (or its interface with the descending aorta), and the space behind it represents the descending aorta. Two dimensional versus M mode echocardiography: Two dimensional echocardiography is better suited to the study of the posterior cardiac structures. The spatial interrelations and relative positions of these structures can be readily identified. In the long axis view the left atrium is circular, the pericardium is a linear structure that usually bridges the A-V junction and the aorta is a circular pulsatile echo-free space behind the pericardium. (Others have suggested, but never proved, that this echo-free space is the coronary sinus2 or pulmonary veins). Similarly, the course of the aorta can be
mapped using the transverse views. Because it is easier to recognize the descending aorta with two dimensional echocardiography, this technique is invaluable in the interpretation of unusual M mode echocardiographic patterns of posterior cardiac structures. Normal aortic measurements: We have attempted to establish normal values for the size of the descending aorta. In normal persons the diastolic diameter of the lumen of this segment of the descending aorta measures 10 f 1.4 mm/m2. This compares with ascending aortic luminal diameters of 16 f 1.8 mm/m2 at the level of the aortic valve and 13 f 1.4 mm/m2 above the level of sinus of Valsalva. In our patients with mitral insufficiency exclusive of mitral valve prolapse (cardiomyopathy, flail leaflet, pure rheumatic mitral disease or endocarditis), aortic measurements were similar to those of the younger patients in our control group. Because the older patients had no cause for aortic disease, their aortic measurements substantiate our view that the values of the control population were normal. Abnormal aortic measurements: Patients with coronary artery disease, chronic hypertension or aortic valve disease with aortic insufficiency also had an enlarged descending aorta; although the mean enlargement was small, individual variations were significant. The pattern of enlargement of the ascending aorta varied in each of these patient populations. Lastly, we also studied a small group of patients with intrinsic aortic disease. In one patient with a hypoplastic aorta, the aorta was 2 standard deviations smaller than normal. In six patients with a thoracic aortic aneurysm, the involved segment was larger than that seen in any patient with other forms of cardiovascular disease. In two patients with an abdominal aortic aneurysm, the thoracic aortic measurements were normal. These data suggest that two dimensional echocardiography is a useful technique for studying the entire aorta and detecting localized or diffuse aortic aneurysms. This technique should also allow the clinician to follow up patients with aneurysm of the aorta and to document changes in size that might be useful clinically.
References 1. Orsmond GS, Rultenberg HD, Besslnger FB, Moller JH: Echocardiographic features of total anomalous pulmonary venous connection to the coronary sinus. Am J Cardiol 41597-601, 1978 2. Tajik Al, Seward JB, H@r DTJ, Malr DD, Lie TT:Twodirnsnsional real-time ultrasonic imaging of the heart and great vessels: technique. image orientation, structure identification, and validation. Mayo Clin Proc 53:271-303, 1978 3. Nanda NC, Gramlak R: Clinical Echocardiography. Saint Louis, CV Mosby, 1978, p 383 4. Gramlak R, Shah PM, Kramer DH: Ultrasound cardiography: contrast studies in anatomy and function. Radiology 92:939-948, 1969 5. Tajik Al, Seward JB: Contrast echocardiography. In, Clinical
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6.
7.
8. 9. 10.
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Echocardiography (Kotler MN, Segal BS, ed). Philadelphia, FA Davis, 1978, p 317-342 Lieppe W, Behar VS. Scallfon R, Klsslo JA: Detection of tricuspid regurgitation with two-dimensional echocardiography and peripheral vein injections. Circulation 57:128-133. 1978 Charuzi Y, Kruas R, Swan HX: Echocardiographic interpretation in the oresence of Swan-C&z intracardiac catheters. Am J Cardiol 40:98b-994, 1977 Weir I, Yacoub M, Prldie RB: Echocardiography of the intra-aortic balloon. Br Heart J 37:1045-1048, 1975 Kotler MN, Segal BL. Mintz G, Parry WR: Pitfalls and limitations of M-mode echocardiography. Am Heart J 94:227-249, 1977 Feigenbaum H: Echocardiography. Philadelphia, Lea & Febiger, 1976, p 237-245
