Reoperation for Left Ventricular Outflow Tract Obstruction After Repair of Atrioventricular Septal David M. Overman Left ventricular outflow tract obstruction (LVOTO) is an important source of morbidity and mortality after repair of atrioventricular septal defect (AVSD). The intrinsic anatomy of the left ventricular outflow tract in AVSD is complex and predisposes to the development of LVOTO. LVOTO after repair of AVSD usually involves multiple levels and sources of obstruction, and surgical intervention must address each component of the obstruction. This includes fibromuscular obstruction, septal hypertrophy, and valve related sources of obstruction. Special attention is also directed to the anterolateral muscle bundle of the left ventricle, a well defined but under recognized feature of the left ventricular outflow tract in AVSD. It is present in all patients with AVSD, and resection of a hypertrophic anterolateral muscle bundle of the left ventricle should be incorporated in all operations for LVOTO after repair of AVSD. LVOTO after repair of AVSD has several unique features that must be taken into consideration to maximize outcome after surgical intervention. These include anatomic factors, technical aspects of surgical intervention, and proper selection of the operation used for relief of LVOTO. Semin Thorac Cardiovasc Surg Pediatr Card Surg Ann 17:43-47 C 2014 Elsevier Inc. All rights reserved.
Introduction
Morphology of the LVOT in AVSD
L
The anatomy of the LVOT in AVSD has been extensively detailed.11–14 Its main features are “unwedging” of the aortic root (anterior and rightward), disparate inlet and outlet septum lengths (short inlet, long outlet), and deficiency of the muscular interventricular septum (septal “scoop”) Figs. 2 and 3).15,16 The normal LVOT is quite short, measuring only a few millimeters. The aorta sits “wedged” between the mitral and tricuspid valves. In AVSD, the aortic valve is anterior and rightward, no longer positioned between the two normally formed AV valves. Vacating of the distal LVOT by the aortic root collapses the anteroposterior dimension of the LVOT. In addition, the unwedged position of the aortic root creates length at the distal end of the LVOT that is not present in normal hearts and results in discrepant inlet and outlet septal lengths. The muscular septal deficiency underlying the AV valves causes the leaflets to form a convexity toward the ventricular apex rather than toward the atria, as is normal, and this convexity measurably narrows the LVOT. These various intrinsic anatomic abnormalities combine to create a narrow and elongated LVOT with an abnormal outlet angle, classically described angiographically as the “goose neck” deformity. LVOT geometry in AVSD is also significantly impacted by the anatomy of the AV valve and the subvalvar apparatus. Specifically, the superior bridging leaflet may be closely applied
eft ventricular outflow tract obstruction (LVOTO) is a well-described sequelae of repair of atrioventricular septal defect (AVSD). Indeed, a narrow left ventricular outflow tract (LVOT) has long been recognized as an intrinsic feature of hearts with AVSD.1 LVOTO is second only to left atrioventricular (AV) valve regurgitation as an indication for reoperation after repair of AVSD. The reported incidence of LVOTO requiring reintervention after primary repair of AVSD varies from 0.5% to 4.5%.2–7 Duration of follow-up is an important determinant of the observed incidence, as reoperation for LVOTO generally occurs at a mean interval of 5 to 7 years after primary repair.2,8–10 The need for reoperation for LVOTO after AVSD repair has a significant impact on late survival (Fig. 1). LVOTO after repair of AVSD has several unique features that must be taken into consideration to maximize outcome after surgical intervention. These include anatomic factors, technical aspects of surgical intervention, and proper selection of the operation used for relief of LVOTO. Division of Cardiovascular Surgery, The Children’s Heart Clinic, Children’s Hospitals and Clinics of Minnesota, Minneapolis, MN. Address correspondence to David M. Overman, Chief, Division of Cardiovascular Surgery, The Children’s Heart Clinic, 2530 Chicago Ave. South, Suite 500, Minneapolis, MN 55404. E-mail: [email protected]
http://dx.doi.org/10.1053/j.pcsu.2014.01.008 1092-9126/& 2014 Elsevier Inc. All rights reserved.
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44
Figure 1 Actuarial survival after reoperation for LVOTO after repair of AVSD. A significant difference (P o.001) is observed as compare with age and gender matched population.
to the “scooped out” interventricular septum (as in some hearts with Rastelli Type A common AV valve configuration), or free floating (Rastelli Type C common AV valve). When closely adherent, the superior leaflet and associated primary and anomalous chordae may significantly crowd the distal LVOT. The papillary muscles of the left AV valve are rotated counterclockwise and are more closely spaced in AVSD compared with the normal heart. The anterolateral papillary muscle may have an abnormally high insertion, creating proximal LVOT narrowing. While closely spaced or parachute type arrangements of the papillary muscles are typically the substrate of left ventricular inflow obstruction, their abnormal positioning in AVSD brings the subvalvar and chordal apparatus toward the “center” of the proximal LVOT, where they may be a source of outflow tract turbulence. Accessory papillary muscles are frequently present in AVSD, as are anomalous chordal insertions and accessory fibrous bands. Thus, valvar and
D.M. Overman
Figure 3 Ratios of the inlet and outlet septal dimensions in partial AVSD, complete AVSD, and in normal hearts. There is no significant difference in the ratios of partial and complete AVSD (P 4 .05). The difference is highly significant (P o .01) when hearts with AVSD (any form) are compared with normal hearts.
subvalvar abnormalities are critical features of LVOTO in AVSD (Fig. 5).17
Special Emphasis: Anterolateral Muscle Bundle of the Left Ventricle This unfavorable geometry is further compromised by the known occurrence of encroachment on the LVOT by the anterolateral muscle bundle of the left ventricle (AML; Fig 4). In the surgical literature, the presence and importance of the AML in the setting of LVOTO after repair of AVSD has been largely unrecognized. The AML is a horizontal muscle bundle located between the left coronary cusp and the aortic leaflet of the mitral valve. Initially described by Moulaert and Oppenheimer-Decker,18 it is present in roughly 40% of normal hearts. In a study of 77 hearts with AVSD, Draulans-Noe and Wenink19 showed that the AML is present in 100% of AVSD specimens, and frequently bulged into the LVOT. In this morphometric analysis and in a corroborating echocardiographic and magnetic resonance imaging study, the authors noted that the AML alone did not create significant subaortic stenosis.20 Nevertheless, operations for LVOTO that do not address encroachment by a hypertrophic AML almost certainly increase the risk of recurrence.
Predictors of LVOTO after AVSD Repair
Figure 2 Illustration of measurements of the inlet and outlet septa from the left ventricular side in normal hearts (top) and hearts with atrioventricular septal defect (bottom).
Investigators have attempted to identify clinical and echocardiographic predictors of LVOTO after AVSD repair. Historically, patients without Trisomy 21 have been identified as being at increased risk for LVOTO, but more recent series refute this notion.8,21 Likewise, evidence is mixed with regard to the impact of subtype of AVSD (partial, transitional, or complete) on the incidence of LVOTO after repair. Most recent series report similar reoperation rates amongst AVSD subtype.3,6,8 Similarly, Rastelli Type A configuration of the common AV valve has been widely understood to predispose
Reoperation for LVOT obstruction after ASD repair
45 that, by design, seats the AV valve on the crest of the septal “scoop” would seem to create an anatomic substrate for LVOTO. However, while one recent series found a weak association with need for reoperation for LVOTO after modified single-patch repair,8 several other large series found no association.5,30,31 Most reported series have used the modified single-patch technique selectively, choosing to use the two-patch or traditional single-patch technique when the ventricular septal defect is large and the septal “scoop” deep, although Nunn and colleagues use the modified single patch irrespective of ventricular septal defect morphology.30 It may be that VSD patch placement may not be as protective against development of LVOTO as is commonly believed. In normal hearts, the interventricular septum describes a concavity toward the LVOT. Placement of a straight patch to close a large VSD may unfavorably alter the geometry and flow dynamics within the distal LVOT. It is conceivable that the stiff materials usually used to “reconstruct” the distal LVOT may provide a substrate for LVOTO. Longer follow-up will be needed to definitively answer the concerns of use of the modified single-patch technique in the setting of a large and deep VSD.
Surgical Approaches to LVOTO After AVSD Repair
Figure 4 Cross sectional view from the left ventricular apex of a normal heart (top) and a heart with atrioventricular septal defect (bottom). In the normal heart there is wide egress to the left ventricular outlet. In AVSD, the aortic valve is bounded laterally by the anterolateral muscle bundle, inferiorly by the superior bridging leaflet, and medially by the subaortic portion of the interventricular septum.
to LVOTO after AVSD repair compared with Types B and C, but data from the recent literature does not support this view.3,8,22,23 Echocardiographic predictors of LVOTO after AVSD repair that have been proposed include amount of displacement of the AV valve leaflet tips into the left ventricle, the presence of fixed or thick chords in the LVOT, an acute aortoseptal angle, high insertion of the anterolateral papillary muscle, and an abnormal aorta to subaortic ratio.24–26 The clinical utility of these retrospectively established measures, however, has not been established. Primary surgical repair technique has been extensively examined as a causative agent in the development of LVOTO after AVSD repair. Specifically, the “modified single-patch” repair technique originally described by Lillehei and reintroduced by Wilcox as a simpler repair technique than the traditional one patch or two patch methods,27 is considered by some to predispose to the development of LVOTO.28,29 This concern is based on the morphologic observations described above. In particular, when the superior bridging leaflet is closely applied to the “scooped out” interventricular septum, the distal LVOT dimension is compromised. An operation
In light of the complex anatomy of the LVOT in AVSD and the various components that may provide a substrate for outflow tract obstruction, effective surgical therapy mandates a versatile armamentarium. Adequate relief of LVOTO after AVSD repair can usually be accomplished using a standard transaortic approach. However, to maximize the efficacy of operations for LVOTO after AVSD repair, surgical attention to all components of the LVOTO substrate is required. It is typical that repair of LVOTO after AVSD repair involves therapy directed at more than one level or type of obstruction.8,32
Figure 5 Intraoperative photograph demonstrating chordal apparatus that may serve as a substrate for future LVOTO. The VSD patch is tipped anteriorly, and the angled clamp encircles chordae inserting at the left ventricular side of the interventricular septum in the distal LVOT.
D.M. Overman
46 As pointed out by Van Arsdell et al,32 when intervention for LVOTO is limited to standard fibromyectomy, recurrence rates are high. There are three critical elements of a thorough operation for LVOTO after AVSD repair: 1) Careful attention to complete removal of all fibromuscular material, including that found on the mitral and aortic valves. 2) Aggressive muscular resection that addresses the abnormal geometry of the LVOT in AVSD (such as incision and partial resection of an encroaching anterolateral muscle bundle and adequate proximal extension of muscular resection to address “tunnel” obstruction). 3) Removal of anomalous secondary and tertiary left AV valve chordae that reside within the LVOT. Fibromuscular stenosis of the distal LVOT is the most common element of LVOTO after AVSD repair. As in fixed subaortic stenosis in normal hearts, extensive involvement of the aortic valve cusps and the undersurface of the mitral apparatus are common. The fibrotic elements diminish the natural expansive properties of the LVOT. All visible deposits must be debrided to restore the dynamic properties of the LVOT. Resection of hypertrophic interventricular septum is frequently required. The AML is found leftward and anterior in the distal LVOT. This can be entirely removed safely and resection will substantially increase the distal LVOT diameter in a measurable fraction of patients. Anomalous chords are frequently present. While they rarely are substantial enough to cause important gradients, such chords create proximal turbulence and predispose to recurrence of, in particular, fibromuscular obstruction. Careful attention must be paid, of course, that primary chords important to AV valve competence are not resected. In a small number of cases, where chordal abnormalities are extensive and important contributors to LVOTO, valve replacement may be necessary. Despite complete relief of LVOTO at first intervention, however, obstruction may recur in anywhere from 15% to 25% of patients (37% in one series). Repeat transaortic resection may be undertaken with acceptable results in such patients, particularly if there is evidence to suggest that important sources of obstruction were inadequately addressed at the prior operation. In patients with recalcitrant and complex LVOTO, the modified Konno procedure is a useful alternative strategy. This operation is well suited for application in AVSD with complex LVOTO. Its advantages include substantial expansion of the whole of the LVOT, thus reducing the need to resect or manipulate structures within the LVOT, and low risk of complete heart block.33 This is particularly attractive in AVSD, with its complex AV valve anatomy and the difficulties inherent to valve repair in that setting. Septoplasty provides wide access to the subvalvar space while providing expansion of the outflow tract well away from the valve apparatus. In patients with tunnel obstruction, the procedure provides reliable relief of obstruction throughout the length of the LVOT.
Potential issues with use of a modified Konno include residual VSD, inadequate visualization of the distal LVOT, and therefore incomplete relief of LVOTO that is immediately subaortic in nature, and the need to perform a right ventriculotomy. In light of the extensive nature of the operation the aforementioned limitations, the modified Konno should rarely be used as a first-line operation for LVOTO after AVSD repair. However, it is an ideal choice when standard transaortic resection has failed. Some investigators have advocated resuspension of the AV valve as an ancillary technique to address LVOTO in the setting of AVSD, particularly in patients with absent or restrictive VSD. Van Son and colleagues34 reported on three patients who had undergone repair of complete ASVD with absent or restrictive VSD for which this technique was used. This concept had been articulated several years before by Chang and Becker,13 and was championed by Van Arsdell and colleagues,32 who extended the concept to conversion of Rastelli Type A anatomies to that of Rastelli Type C by detaching chordal insertions and augmenting the superior bridging leaflet. While this procedure has theoretical appeal, there are no reports of long-term follow-up information upon which to make a judgment regarding its utility. Finally, apical aortic conduit placement has rarely been used in extremely difficult cases of complex LVOTO. Brown et al35 have the largest experience with this operation. Reoperation rates are high after this procedure, and it has a very circumscribed role in the current era.
Conclusions LVOTO is an important source of morbidity and mortality after repair of AVSD. The intrinsic anatomy of the LVOT in AVSD is complex and predisposes to the development of LVOTO. A thorough knowledge of the morphology of the LVOT in AVSD is required to properly choose and apply the appropriate procedure for the each individual patient. LVOTO after repair of AVSD usually involves multiple levels and sources of obstruction, and surgical intervention must address each component of the obstruction. This includes fibromuscular obstruction, septal hypertrophy, and valve related sources of obstruction. Special attention is also directed to the AML, a well-defined but underrecognized feature of the LVOT in AVSD. It is present in all patients with AVSD, and resection of a hypertrophic AML should be incorporated in all operations for LVOTO after repair of AVSD. Adequate relief of LVOTO can usually be gained using a transaortic approach. When LVOTO recurs, particularly if there is not an identifiable reason for failure of the initial intervention, the modified Konno procedure is an appropriate alternative. AV valve leaflet augmentation and resuspension may have a role in patients with restrictive or absent interventricular communication, or in patients with Rastelli Type A valves that are closely applied to the septal crest. There is, however, scant information regarding late outcomes in the small number of patients described in the literature who have
Reoperation for LVOT obstruction after ASD repair undergone this procedure. Its role in addressing LVOTO after repair of AVSD, therefore, is presently not well understood. Left ventricular apical aortic conduits have rarely been used in children for particularly complex forms of LVOT. They are associated with high reoperation rates because of conduit or prosthetic valve failure and are not recommended.
References 1. Van Mierop LHS, Alley RD, Kausel HW, et al: The anatomy and embryology of endocardial cushion defects. J Thorac Cardiovasc Surg 1962;43:71-83 2. Najm HK, Coles JG, Endo M, et al: Complete atrioventricular septal defects: results of repair, risk factors, and freedom from reoperation. Circulation 1997;96(suppl 9); [II-311–II-315] 3. Vohra HA, Chia AXF, Yuen HN, et al: Primary biventricular repair of atrioventricular septal defects: an analysis of reoperations. Ann Thorac Surg 2010;90:830-838 4. Bakhtiary F, Takacs J, Cho MY, et al: Long-term results after repair of complete atrioventricular septal defect with two patch technique. Ann Thorac Surg 2010;89:1239-1243 5. Backer CL, Stewart RD, Bailliard F, et al: Complete atrioventricular canal: comparison of modified single-patch technique with two-patch technique. Ann Thorac Surg 2007;84:2038-2046 6. Birim O, van Gameren M, de Jong PL, et al: Outcome after reoperation for atrioventricular septal defect repair. Interact Cardiovasc Thorac Surg 2009;9:83-87 7. Gunther T, Mazzitelli D, Haehnel CJ, et al: Long-term results after repair of complete atrioventricular septal defect: analysis of risk factors. Ann Thorac Surg 1998;65:754-760 8. Myers PO, del Nido PJ, Marx GR, et al: Improving left ventricular outflow tract obstruction repair in common atrioventricular canal defects. Ann Thorac Surg 2012;94:599-605 9. Gurbuz AT, Novick WM, Pierce CA, et al: Left ventricular outflow tract obstruction after partial atrioventricular septal defect repair. Ann Thorac Surg 1999;68:1723-1726 10. Overman DM, Moga FX, Finkelstein MJ, et al. Twenty-seven years of repair of complete atrioventricular septal defect: repair technique does not influence incidence of post-operative left ventricular outflow tract obstruction. Presented at the Fortieth Annual Meeting of the Society of Thoracic Surgeons, January 26-28, San Antonio, TX. 11. Piccoli GP, Gerlis LM, Wilkinson JL, et al: Morphology and classification of atrioventricular septal defects. Br Heart J 1979;42:621-632 12. Ebels T, Ho SY, Anderson RH, et al: The surgical anatomy of the left ventricular outflow tract in atrioventricular septal defect. Ann Thorac Surg 1986;41:483-488 13. Chang CI, Becker AE: Surgical anatomy of left ventricular outflow tract obstruction in complete atrioventricular septal defect: a concept for operative repair. J Thorac Cardiovasc Surg 1987;94:897-903 14. Shiokawa Y, Becker AE: The left ventricular outflow tract in atrioventricular septal defect revisited: surgical considerations regarding preservation of the aortic valve integrity in the perspective of anatomic observations. J Thorac Cardiovasc Surg 1997;114:586-593 15. Penkoske PA, Neches WH, Anderson RH, et al: Further observations on the morphology of atrioventricular septal defects. J Thorac Cardiovasc Surg 1985;90:611-622 16. Gallo P, Formigari R, Hokayem NJ, et al: Left ventricular outflow tract obstruction in atrioventricular septal defect: a pathologic and morphometric evaluation. Clin Cardiol 1991;14:513-521
47 17. Piccoli GP, Ho SY, Wilkinson JL, et al: Left-sided obstructive lesions in atrioventricular septal defects: an anatomic study. J Thorac Cardiovasc Surg 1982;83:453-460 18. Moulaert AJ, Oppenheimer-Decker A: Anterolateral muscle bundle of the left ventricle, bulboventricular flange and subaortic stenosis. Am J Cardiol 1976;37:78-81 19. Draulans-Noe HAY, Wenink ACG: Anterolateral muscle bundle of the left ventricle in atrioventricular septal defect: left ventricular outflow tract and subaortic stenosis. Pediatr Cardiol 1991;12:83-88 20. Wenink ACG, Ottenkamp J, Guit GL, et al: Correlation of morphology of the left ventricle outflow tract with two-dimensional Doppler echocardiography and magnetic resonance imaging in atrioventricular septal defect. Cardiology 1989;63:1137-1140 21. De Biase L, Di Commo V, Ballerini L, et al: Prevalence of left-sided obstructive lesions in patients with atrioventricular canal without Down’s syndrome. J Thorac Cardiovasc Surg 1986;91:467-469 22. Suzuki K, Ho SY, Anderson RH, et al: Morphometric analysis of atrioventricular septal defect with common valve orifice. J Am Coll Cardiol 1998;31:217-223 23. Hoohenkerk GJF, Bruggemans MS, Rijlaarsdam M: More than thirty years’ experience with surgical correction of atrioventricular septal defects. Ann Thorac Surg 2010;90:1554-1562 24. Lim DS, Ensing GJ, Ludomirsky A, et al: Echocardiographic predictors for the development of subaortic stenosis after repair of atrioventricular septal defect. Am J Cardiol 2003;91:900-903 25. Sittiwangkul R, Ma RY, McCrindle BW, et al: Echocardiographic assessment of obstructive lesions in atrioventricular septal defects. J Am Coll Cardiol 2001;38:253-261 26. Smallhorn JF: Cross-sectional echocardiographic assessment of atrioventricular septal defect: basic morphology and preoperative risk factors. Echocardiography 2001;18:415-431 27. Wilcox BR, Jones DR, Frantz EG, et al: Anatomically sound, simplified approach to repair of “complete” atrioventricular septal defect. Ann Thorac Surg 1997;64:487-493 28. Lacour-Gayet F, Campbell DN, Mitchell M, et al: Surgical repair of atrioventricular septal defect with common atrioventricular valve in early infancy. Cardiol Young 2006;16(suppl 3):52-58 29. Adachi I, Ho SY, McCarthy KP, et al: Ventricular scoop in atrioventricular septal defect: relevance to simplified single-patch method. Ann Thorac Surg 2009;87:198-203 30. Nunn GR: Atrioventricular canal: modified single patch technique. Semin Thorac Cardiovasc Surg Pediatr Card Surg Ann 2007;10:28-31 31. Jonas RA, Mora B: Individualized approach to repair of complete atrioventricular canal: selective use of the traditional single patch technique versus the Australian technique. World J Pediatr Congenit Heart Surg 2010;1:78-86 32. Van Arsdell GS, Williams WG, Boutin C, et al: Subaortic stenosis in the spectrum of atrioventricular septal defects: Solutions may be complex and palliative. J Thorac Cardiovasc Surg 1995;110:1534-1541; [discussion, 1541-1542] 33. Caldarone CA, Van Natta TL, Frazer JR, et al: The modified Konno procedure for complex left ventricular outflow tract obstruction. Ann Thorac Surg 2003;75:147-151; [discussion, 151-152] 34. Van Son JAM, Schneider P, Falk V: Repair of subaortic stenosis in atrioventricular canal with absent or restrictive interventricular communication by patch augmentation of ventricular septum, resuspension of atrioventricular valves, and septal myomectomy. Mayo Clin Proc 1997;72:220-224 35. Brown JW, Ruzmetov M, Fiore AC, et al: Long term results of apical aortic conduits in children with complex left ventricular outflow tract obstruction. Ann Thorac Surg 2005;80:2301-2308
Introduction
Morphology of the LVOT in AVSD
L
The anatomy of the LVOT in AVSD has been extensively detailed.11–14 Its main features are “unwedging” of the aortic root (anterior and rightward), disparate inlet and outlet septum lengths (short inlet, long outlet), and deficiency of the muscular interventricular septum (septal “scoop”) Figs. 2 and 3).15,16 The normal LVOT is quite short, measuring only a few millimeters. The aorta sits “wedged” between the mitral and tricuspid valves. In AVSD, the aortic valve is anterior and rightward, no longer positioned between the two normally formed AV valves. Vacating of the distal LVOT by the aortic root collapses the anteroposterior dimension of the LVOT. In addition, the unwedged position of the aortic root creates length at the distal end of the LVOT that is not present in normal hearts and results in discrepant inlet and outlet septal lengths. The muscular septal deficiency underlying the AV valves causes the leaflets to form a convexity toward the ventricular apex rather than toward the atria, as is normal, and this convexity measurably narrows the LVOT. These various intrinsic anatomic abnormalities combine to create a narrow and elongated LVOT with an abnormal outlet angle, classically described angiographically as the “goose neck” deformity. LVOT geometry in AVSD is also significantly impacted by the anatomy of the AV valve and the subvalvar apparatus. Specifically, the superior bridging leaflet may be closely applied
eft ventricular outflow tract obstruction (LVOTO) is a well-described sequelae of repair of atrioventricular septal defect (AVSD). Indeed, a narrow left ventricular outflow tract (LVOT) has long been recognized as an intrinsic feature of hearts with AVSD.1 LVOTO is second only to left atrioventricular (AV) valve regurgitation as an indication for reoperation after repair of AVSD. The reported incidence of LVOTO requiring reintervention after primary repair of AVSD varies from 0.5% to 4.5%.2–7 Duration of follow-up is an important determinant of the observed incidence, as reoperation for LVOTO generally occurs at a mean interval of 5 to 7 years after primary repair.2,8–10 The need for reoperation for LVOTO after AVSD repair has a significant impact on late survival (Fig. 1). LVOTO after repair of AVSD has several unique features that must be taken into consideration to maximize outcome after surgical intervention. These include anatomic factors, technical aspects of surgical intervention, and proper selection of the operation used for relief of LVOTO. Division of Cardiovascular Surgery, The Children’s Heart Clinic, Children’s Hospitals and Clinics of Minnesota, Minneapolis, MN. Address correspondence to David M. Overman, Chief, Division of Cardiovascular Surgery, The Children’s Heart Clinic, 2530 Chicago Ave. South, Suite 500, Minneapolis, MN 55404. E-mail: [email protected]
http://dx.doi.org/10.1053/j.pcsu.2014.01.008 1092-9126/& 2014 Elsevier Inc. All rights reserved.
43
44
Figure 1 Actuarial survival after reoperation for LVOTO after repair of AVSD. A significant difference (P o.001) is observed as compare with age and gender matched population.
to the “scooped out” interventricular septum (as in some hearts with Rastelli Type A common AV valve configuration), or free floating (Rastelli Type C common AV valve). When closely adherent, the superior leaflet and associated primary and anomalous chordae may significantly crowd the distal LVOT. The papillary muscles of the left AV valve are rotated counterclockwise and are more closely spaced in AVSD compared with the normal heart. The anterolateral papillary muscle may have an abnormally high insertion, creating proximal LVOT narrowing. While closely spaced or parachute type arrangements of the papillary muscles are typically the substrate of left ventricular inflow obstruction, their abnormal positioning in AVSD brings the subvalvar and chordal apparatus toward the “center” of the proximal LVOT, where they may be a source of outflow tract turbulence. Accessory papillary muscles are frequently present in AVSD, as are anomalous chordal insertions and accessory fibrous bands. Thus, valvar and
D.M. Overman
Figure 3 Ratios of the inlet and outlet septal dimensions in partial AVSD, complete AVSD, and in normal hearts. There is no significant difference in the ratios of partial and complete AVSD (P 4 .05). The difference is highly significant (P o .01) when hearts with AVSD (any form) are compared with normal hearts.
subvalvar abnormalities are critical features of LVOTO in AVSD (Fig. 5).17
Special Emphasis: Anterolateral Muscle Bundle of the Left Ventricle This unfavorable geometry is further compromised by the known occurrence of encroachment on the LVOT by the anterolateral muscle bundle of the left ventricle (AML; Fig 4). In the surgical literature, the presence and importance of the AML in the setting of LVOTO after repair of AVSD has been largely unrecognized. The AML is a horizontal muscle bundle located between the left coronary cusp and the aortic leaflet of the mitral valve. Initially described by Moulaert and Oppenheimer-Decker,18 it is present in roughly 40% of normal hearts. In a study of 77 hearts with AVSD, Draulans-Noe and Wenink19 showed that the AML is present in 100% of AVSD specimens, and frequently bulged into the LVOT. In this morphometric analysis and in a corroborating echocardiographic and magnetic resonance imaging study, the authors noted that the AML alone did not create significant subaortic stenosis.20 Nevertheless, operations for LVOTO that do not address encroachment by a hypertrophic AML almost certainly increase the risk of recurrence.
Predictors of LVOTO after AVSD Repair
Figure 2 Illustration of measurements of the inlet and outlet septa from the left ventricular side in normal hearts (top) and hearts with atrioventricular septal defect (bottom).
Investigators have attempted to identify clinical and echocardiographic predictors of LVOTO after AVSD repair. Historically, patients without Trisomy 21 have been identified as being at increased risk for LVOTO, but more recent series refute this notion.8,21 Likewise, evidence is mixed with regard to the impact of subtype of AVSD (partial, transitional, or complete) on the incidence of LVOTO after repair. Most recent series report similar reoperation rates amongst AVSD subtype.3,6,8 Similarly, Rastelli Type A configuration of the common AV valve has been widely understood to predispose
Reoperation for LVOT obstruction after ASD repair
45 that, by design, seats the AV valve on the crest of the septal “scoop” would seem to create an anatomic substrate for LVOTO. However, while one recent series found a weak association with need for reoperation for LVOTO after modified single-patch repair,8 several other large series found no association.5,30,31 Most reported series have used the modified single-patch technique selectively, choosing to use the two-patch or traditional single-patch technique when the ventricular septal defect is large and the septal “scoop” deep, although Nunn and colleagues use the modified single patch irrespective of ventricular septal defect morphology.30 It may be that VSD patch placement may not be as protective against development of LVOTO as is commonly believed. In normal hearts, the interventricular septum describes a concavity toward the LVOT. Placement of a straight patch to close a large VSD may unfavorably alter the geometry and flow dynamics within the distal LVOT. It is conceivable that the stiff materials usually used to “reconstruct” the distal LVOT may provide a substrate for LVOTO. Longer follow-up will be needed to definitively answer the concerns of use of the modified single-patch technique in the setting of a large and deep VSD.
Surgical Approaches to LVOTO After AVSD Repair
Figure 4 Cross sectional view from the left ventricular apex of a normal heart (top) and a heart with atrioventricular septal defect (bottom). In the normal heart there is wide egress to the left ventricular outlet. In AVSD, the aortic valve is bounded laterally by the anterolateral muscle bundle, inferiorly by the superior bridging leaflet, and medially by the subaortic portion of the interventricular septum.
to LVOTO after AVSD repair compared with Types B and C, but data from the recent literature does not support this view.3,8,22,23 Echocardiographic predictors of LVOTO after AVSD repair that have been proposed include amount of displacement of the AV valve leaflet tips into the left ventricle, the presence of fixed or thick chords in the LVOT, an acute aortoseptal angle, high insertion of the anterolateral papillary muscle, and an abnormal aorta to subaortic ratio.24–26 The clinical utility of these retrospectively established measures, however, has not been established. Primary surgical repair technique has been extensively examined as a causative agent in the development of LVOTO after AVSD repair. Specifically, the “modified single-patch” repair technique originally described by Lillehei and reintroduced by Wilcox as a simpler repair technique than the traditional one patch or two patch methods,27 is considered by some to predispose to the development of LVOTO.28,29 This concern is based on the morphologic observations described above. In particular, when the superior bridging leaflet is closely applied to the “scooped out” interventricular septum, the distal LVOT dimension is compromised. An operation
In light of the complex anatomy of the LVOT in AVSD and the various components that may provide a substrate for outflow tract obstruction, effective surgical therapy mandates a versatile armamentarium. Adequate relief of LVOTO after AVSD repair can usually be accomplished using a standard transaortic approach. However, to maximize the efficacy of operations for LVOTO after AVSD repair, surgical attention to all components of the LVOTO substrate is required. It is typical that repair of LVOTO after AVSD repair involves therapy directed at more than one level or type of obstruction.8,32
Figure 5 Intraoperative photograph demonstrating chordal apparatus that may serve as a substrate for future LVOTO. The VSD patch is tipped anteriorly, and the angled clamp encircles chordae inserting at the left ventricular side of the interventricular septum in the distal LVOT.
D.M. Overman
46 As pointed out by Van Arsdell et al,32 when intervention for LVOTO is limited to standard fibromyectomy, recurrence rates are high. There are three critical elements of a thorough operation for LVOTO after AVSD repair: 1) Careful attention to complete removal of all fibromuscular material, including that found on the mitral and aortic valves. 2) Aggressive muscular resection that addresses the abnormal geometry of the LVOT in AVSD (such as incision and partial resection of an encroaching anterolateral muscle bundle and adequate proximal extension of muscular resection to address “tunnel” obstruction). 3) Removal of anomalous secondary and tertiary left AV valve chordae that reside within the LVOT. Fibromuscular stenosis of the distal LVOT is the most common element of LVOTO after AVSD repair. As in fixed subaortic stenosis in normal hearts, extensive involvement of the aortic valve cusps and the undersurface of the mitral apparatus are common. The fibrotic elements diminish the natural expansive properties of the LVOT. All visible deposits must be debrided to restore the dynamic properties of the LVOT. Resection of hypertrophic interventricular septum is frequently required. The AML is found leftward and anterior in the distal LVOT. This can be entirely removed safely and resection will substantially increase the distal LVOT diameter in a measurable fraction of patients. Anomalous chords are frequently present. While they rarely are substantial enough to cause important gradients, such chords create proximal turbulence and predispose to recurrence of, in particular, fibromuscular obstruction. Careful attention must be paid, of course, that primary chords important to AV valve competence are not resected. In a small number of cases, where chordal abnormalities are extensive and important contributors to LVOTO, valve replacement may be necessary. Despite complete relief of LVOTO at first intervention, however, obstruction may recur in anywhere from 15% to 25% of patients (37% in one series). Repeat transaortic resection may be undertaken with acceptable results in such patients, particularly if there is evidence to suggest that important sources of obstruction were inadequately addressed at the prior operation. In patients with recalcitrant and complex LVOTO, the modified Konno procedure is a useful alternative strategy. This operation is well suited for application in AVSD with complex LVOTO. Its advantages include substantial expansion of the whole of the LVOT, thus reducing the need to resect or manipulate structures within the LVOT, and low risk of complete heart block.33 This is particularly attractive in AVSD, with its complex AV valve anatomy and the difficulties inherent to valve repair in that setting. Septoplasty provides wide access to the subvalvar space while providing expansion of the outflow tract well away from the valve apparatus. In patients with tunnel obstruction, the procedure provides reliable relief of obstruction throughout the length of the LVOT.
Potential issues with use of a modified Konno include residual VSD, inadequate visualization of the distal LVOT, and therefore incomplete relief of LVOTO that is immediately subaortic in nature, and the need to perform a right ventriculotomy. In light of the extensive nature of the operation the aforementioned limitations, the modified Konno should rarely be used as a first-line operation for LVOTO after AVSD repair. However, it is an ideal choice when standard transaortic resection has failed. Some investigators have advocated resuspension of the AV valve as an ancillary technique to address LVOTO in the setting of AVSD, particularly in patients with absent or restrictive VSD. Van Son and colleagues34 reported on three patients who had undergone repair of complete ASVD with absent or restrictive VSD for which this technique was used. This concept had been articulated several years before by Chang and Becker,13 and was championed by Van Arsdell and colleagues,32 who extended the concept to conversion of Rastelli Type A anatomies to that of Rastelli Type C by detaching chordal insertions and augmenting the superior bridging leaflet. While this procedure has theoretical appeal, there are no reports of long-term follow-up information upon which to make a judgment regarding its utility. Finally, apical aortic conduit placement has rarely been used in extremely difficult cases of complex LVOTO. Brown et al35 have the largest experience with this operation. Reoperation rates are high after this procedure, and it has a very circumscribed role in the current era.
Conclusions LVOTO is an important source of morbidity and mortality after repair of AVSD. The intrinsic anatomy of the LVOT in AVSD is complex and predisposes to the development of LVOTO. A thorough knowledge of the morphology of the LVOT in AVSD is required to properly choose and apply the appropriate procedure for the each individual patient. LVOTO after repair of AVSD usually involves multiple levels and sources of obstruction, and surgical intervention must address each component of the obstruction. This includes fibromuscular obstruction, septal hypertrophy, and valve related sources of obstruction. Special attention is also directed to the AML, a well-defined but underrecognized feature of the LVOT in AVSD. It is present in all patients with AVSD, and resection of a hypertrophic AML should be incorporated in all operations for LVOTO after repair of AVSD. Adequate relief of LVOTO can usually be gained using a transaortic approach. When LVOTO recurs, particularly if there is not an identifiable reason for failure of the initial intervention, the modified Konno procedure is an appropriate alternative. AV valve leaflet augmentation and resuspension may have a role in patients with restrictive or absent interventricular communication, or in patients with Rastelli Type A valves that are closely applied to the septal crest. There is, however, scant information regarding late outcomes in the small number of patients described in the literature who have
Reoperation for LVOT obstruction after ASD repair undergone this procedure. Its role in addressing LVOTO after repair of AVSD, therefore, is presently not well understood. Left ventricular apical aortic conduits have rarely been used in children for particularly complex forms of LVOT. They are associated with high reoperation rates because of conduit or prosthetic valve failure and are not recommended.
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