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Is there an anatomic basis for subvalvular right ventricular outflow tract obstruction after an arterial switch repair for complete transposition?
Is there an anatomic basis for subvalvular right ventricular outflow tract obstruction after an arterial switch repair for complete transposition? A morphometric study and review The study was initiated by reports on right ventricular outflow tract obstruction in complete transposition of the great arteries after an arterial switch repair. We investigated 39 heart specimens with native, unoperated transposition of the great arteries. Of these, 14 hearts had a ventricular septal defect; 25 had an intact ventricular septum. In each heart specimen the narrowest site of the subaortic outflow tract was measured and compared with the circumference of the aortic orifice. Obstruction was considered to be present if the outflow tract circumference was less than that of the aortic orifice. In addition, the diameter of the ascending aorta immediately above the level of the valve orifices was measured and compared with that of the pulmonary trunk. An obstruction was present in the subaortic right ventricular outflow tract of two hearts (5.1 %): one of the obstructions, in a neonatal heart with intact ventricular septum, was caused by a prominent supraventricular crest and anterior trabeculations; the other obstruction was an additional extensive muscular hypertrophy, in the heart of a 13-year-old patient with a similar anatomy, and a septal defect. A mismatch between the diameters of the ascending aorta and the pulmonary trunk was present in 15 of 32 hearts measured. Our observations and a review of the literature confirm that subvalvular right ventricular outflow tract obstruction in hearts with native transposition of the great arteries is infrequent. Nevertheless, the anatomic characteristics of the right ventricular outflow tract are such that the tract is intrinsically narrow and muscular hypertrophy may easily lead to obstruction. After an arterial switch operation, subvalvular obstruction could be caused by dynamic processes analogous to those observed after relief of isolated pulmonary valve stenosis. Anatomic subvalvular obstruction could be due to either an obstruction that was not identified before operation or (a purely speculative hypothesis) subtle degrees of mismatch in size between the proximal aorta and the pulmonary trunk, which may be considered irrelevant at time of operation but may also set into pace a process of ongoing adaptive infundibular hypertrophy. (J 'fHORAC CARDIOVASC SURG 1993;105:142-6)
Tomoharu Akiba, MD,* Rodolfo Neirotti, MD, and Anton E. Becker, MD,
Amsterdam, The Netherlands
From the Departments of Cardiovascular Pathology and Pediatric Cardiac Surgery, University of Amsterdam, Academic Medical Center, Amsterdam, The Netherlands. Received for publication Feb. 4, 1992. Accepted for publication June 3, 1992. Address for reprints: Anton E. Becker, MD, Department of Cardiovascular Pathology, Academic Medical Center, Meibergdreef 9, 1105 AZ Amsterdam-ZO, The Netherlands. *Research fellow,Yamagata University School of Medicine, Yamagata, Japan.
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In many centers the arterial switch operation has become the procedure of choice in caring for infants with either complete transposition of the great arteries (TGA) or double-outlet right ventricle with subpulmonary defect (Taussig-Bing malformation). Right ventricular (RV) outflow tract obstruction is presently considered one of the most significant complications after anatomic correction.' A recent review of 118 patients, including an evaluation of their midterm results after anatomic correction, revealed that 10 patients needed another operation, 7
0022-5223/93/$1.00/+ 0.10
Volume 105 Number 1 January 1993
because of R V outflow obstruction' The stenosis was caused by insufficient resection of preoperative subaortic stenosis in only 1 of the 7 patients. In the remaining patients, the obstruction was located chiefly at the site of anastomosis between a small aortic root and a large pulmonary artery. Subvalvular RV outflow tract obstruction thus appears rarely, but nevertheless has been documented. Indeed Kanter.' Klautz," and their associates reported a prevalence of approximately 23%.3,4The obstruction was most prevalent among patients who underwent operations for Taussig-Bing malformation-three of seven (42.9%)3 and two of four (50%),4 These disappointing results almost certainly relate to the fact that a narrow muscular subaortic outflow tract is frequently observed in the heart with Taussig-Bing malformation, whereas its clinical severity is often difficult to ascertain before operation. 5, 6 However, the same authors also report that subvalvular R V outflow tract obstruction is prevalent after the switch operation in TGA, calculated as 17.4%3 and 17.6%4. This is somewhat surprising since clinically significant R V outflow tract obstruction in native TGA is generally considered to be rare; the figures vary from 0.4%,7 through 4.7%,8 to 6.9%.9 On the other hand, a recent survey of 96 patients with TGA who underwent arterial switch repair reported resection of the obstructive myocardium in 13 (13.6%),10 whereas an anatomic study documented potential obstruction in 11 (22%) of 50 heart specimens with complete TGA. 1[ However, no reports thus far have provided an explanation of why or how subvalvular R V outflow tract obstruction could develop after an arterial switch operation, if it was not present before the procedure. For this reason, the available reports have been reviewed and put into the perspective of a morphometric study of the R V outflow tract of heart specimens with complete TGA.
Patients and methods Thirty-nine heart specimens with native, unoperated, completeTGA were investigated. The study was limited to hearts withnormally arranged atrial chambersand a concordantatrioventricular connection. Hearts with the Taussig-Bing configuration wereexcluded. Hearts with a ventricularseptal defect (VSD) wereseparatedfromthosewithan intactventricularseptum;the formerwere classified according to Sotoand associates. 12 The morphology of the subaorticright ventricularoutflow tract was analyzed, with a focus on the outflow tract musculature in each heart. The smallest internaldiametersof boththe RVoutflow tract and the aortic valve orifice were measured. The outflow tract diameter wasexpressed as a percentageof that of the aortic valve orifice. Obstruction wasconsidered to be presentif the diameter of the outflow tract was smaller than that of the aortic valve orifice.
Outflow tract obstruction after arterial switch repair
14 3
The diameters of the ascending aorta and the pulmonary trunk weremeasuredfrom the arterial side,immediatelyabove the level of the valveorifices, and expressed as a ratio (pulmonaryjaortic). Seven hearts had pulmonary valve stenosis and thereforecouldnotbe measuredreliably. The relationshipof the great arteries was categorized as either anteroposterioror side byside,with the aortic valve to the right of and slightlyanterior to the pulmonary valve. Other associated congenital abnormalitiessuchas aorticarch anomalies were also noted.
Results Of the 39 hearts, 25 had an intact ventricular septum and 14 showed a VSD. Thirteen of the latter had a single defect: a perimembranous outlet in eight, a perimembranous inlet in two, a muscular outlet in two, and a muscular trabecular defect in one; the remaining heart had two muscular trabecular defects. Displacement of the outlet septum was present in eight hearts, each of which had a perimembranous defect. Anterior deviation was present in six and posterior displacement in two. An anteroposterior relationship of the aorta and pulmonary trunk was present in 32 heart specimens (22 with an intact septum; 10 with a septal defect). The ratio between the diameter of the pulmonary trunk and that of the ascending aorta (measured in 28 cases) averaged 0.99 ± 0.11, varying between 0.83 and 1.20. Such a mismatch occurred in 11 of the 28 hearts. A side-by-side relationship was present in seven hearts (three with an intact septum; four with a septal defect). The pulmonary/ aortic ratio in these instances (four hearts) averaged 1.38 ± 0.11, varying between 1.20 and 1.50. Subvalvular R V outflow tract obstruction was found in two hearts (5.1%). In one heart with an anterosuperior relationship of the great arteries and an intact septum (in a neonate aged 9 days at the time of death), the obstruction was caused by a pronounced supraventricular crest, largely the result of marked accentuation of the ventriculoinfundibular fold and prominent anterior trabeculations (Fig. 1). The diameter of the outflow tract was 57% of that of the aortic valve orifice. In the second case, a 14-year-old child exhibited an anterosuperior relationship of the great arteries and a perimembranous outlet septal defect; the outflow tract anatomy was somewhat similar to that of the first case, but it was accentuated by excessive hypertrophy. Hence hypertrophic anterior trabeculations aggravated circumferential hypertrophy of the infundibular musculature and caused obstruction (Fig. 2). In this specimen, the outflow tract diameter was 43% of that of the aortic valve orifice. No coexisting subpulmonary anomalies were present. Coarctation of the aorta was found in three hearts (two
I 44
Akiba, Neirotti, Becker
The Journal of Thoracic and Cardiovascular Surgery
Fig. 1. RV outflow tract in a heart with completeTGA and intact ventricular septum (9 days). A, Obstruction caused by pronounced supraventricular crest (SC) and prominentanterior trabeculations. B, The latter are best seen (arrow) once the infundibulum is wide open. TV, Tricuspidvalve.
Fig. 2. Wide-open RV outflow tract in a heart withcompleteTGA and VSD (14 years). RV outflow tract obstruction caused by marked hypertrophyof muscular infundibulum, accentuated by anterior trabeculations (asterisks). VSD, ventricular septal defect.
with a VSD, one with an intact septum), one of which (case 2) had subaortic obstruction. All associated anomalies are summarized in Table I. Discussion After an arterial switch repair for complete TGA, the appearance of subvalvular RV outflow tract obstruction is rare/ but nevertheless has been documented and is worthy of study.': 4 Kanter and coworkers- described 4 of 23 patients (17.4%) with complete TGA in whom RV outflow tract obstruction occurred during the operation,
per their diagnosis. They made this diagnosis on the basis of inability to successfully wean the patient from cardiopulmonary bypass, in the presence of systemic or suprasystemic R V pressures and normal or low proximal pulmonary arterial pressures. However, such intraoperative observations do not necessarily relate to anatomic obstruction. For instance, it is known that after valvotomy for isolated pulmonary valve stenosis the muscular infundibulum may acquire a hypercontractile state, which may cause severe obstruction in the postoperative period
Volume 105 Number 1 January 1993
despite an adequate valvotomy. 13 This phenomenon could explain the intraoperative assessment ofRV outflow tract obstruction after an arterial switch repair and could also apply to cases reported by Klautz and associates." They reported that 6 of 34 patients (17.6%) had a posteroperative R V-pulmonary artery peak systolic gradient of 20 mm Hg or more. The infundibular pressure gradients were evaluated within 2 weeks after repair, however, and this is too short a time lapse to rule out dynamic R V outflow obstruction. Thus the figures produced by these authors may well appear to be grossly overstated. Nevertheless, these findings may apply in rare instances and may relate to the mechanism of anatomic obstruction. First, subvalvular R V outflow tract obstruction could have been present before the operation, although unnoticed clinically. The present study was tailored to evaluate the occurrence of potential obstruction in the R V outflow by measuring the narrowest diameter of the R V outflow tract and by comparing it with the diameter of the aortic orifice. On that basis, 2 of 39 hearts with complete TGA showed obstruction. The prevalence of 5.1%, in itself, is less relevant than the confirmation that muscular obstruction within the R V outflow tract in hearts with native, unoperated, complete TGA is infrequent. However, additional circumstances such as a VSD and rightward deviation of the outlet septum may induce muscular hypertrophy and eventual obstruction in an outflow tract, which is intrinsically narrow.?" Second, some degree of mismatch between the two great arteries could playa role, although this hypothesis is purely speculative. Serraf and colleagues/ recently presented a study of 118 patients who had undergone an arterial switch procedure; in 100 of these patients the pulmonary trunk was larger than the aorta. Urban and Brecher!" stated that two thirds of their patients had such a mismatch. Our own findings are very much in accord with these observations. In 15 of 32 hearts measured, the diameter of the aortic anulus was smaller than that of the pulmonary trunk. In case of a distinct mismatch, the operative technique is adjusted by incision of the aorta and insertion of a patch of pericardium. I However, subtle degrees of mismatch almost certainly will occur but may not necessarily be considered important at the time of operation. One could hypothesize, therefore, that, once "switched," the RV in such instances will have to cope with a persistent narrow outflow, irrespective of the wide size of the distal pulmonary trunk. The RV, transformed to a volume-loaded ventricle rather than a pressure-loaded ventricle, will attempt to compensate for the obstruction at the junction between the mismatched ascending aorta and the pulmonary trunk. Hence, ongoing R V hypertrophy may ensue
Outflow tract obstruction after arterial switch repair
14 5
Table I. Associated anomalies in 39 hearts with complete TGA I. Subaortic right ventricular outflow tract obstruction (2 hearts)
Pronounced ventriculoinfundiI (IVS) bular fold and anterior trabeculations I (VSD) Circumferential hypertrophy of the infundibulum; hypertrophic anterior trabeculations 3 (VSD, 2; IVS, I) 2. Coarctation of the aorta (3 hearts; I with subaortic obstruction) 3. Subpulmonary left ventricular outflow tract obstruction (4 hearts) Septal hypertrophy 2 (VSD, I; IVS, I) Deviated outlet septum 2 (VSD, 2) 4. Pulmonary valve stenosis (7 hearts; 2 with subpulmonary obstruction) 5 (VSD, 4; IVS, I) Bicuspid I (VSD) Dysplastic I (VSD) Bicuspid + dysplastic 5. Dysplastic mitral valve (I I (IVS) heart) I (VSD) 6. Straddling mitral valve (I heart) I (IVS) 7. Mitral valve bridging (I heart) 8. Anomalous attachment of the 3 (VSD) tricuspid valve tension apparatus to the outlet septum (3 hearts) 18 (VSD, I; IVS, 17) 9. Patent ductus arteriosus (18 hearts) I (IVS) 10. Left juxtaposition of the right atrial appendage (I heart) II. Persistent left superior vena 3 (VSD, 2; IVS, I) cava (3 hearts) IVS, Intact ventricular septum; VSD, ventricular septal defect.
and exacerbate the intrinsic anatomic potential of R V outflow tract obstruction. This study, though tentative, could stimulate a prospective study to evaluate the potential of such mechanisms in patients with complete TGA selected for an arterial switch operation. We thank Mr. W. P. Meun for the photography and Ms. M.
1. Schenker for secretarial assistance.
REFERENCES 1. Quaegebeur JM, Rohmer J, Ottenkamp J, et al. The arterial switch operation: an eight-year experience.J THORAC CARDIOVASC SURG 1986;92:361-84. 2. Serraf A, Bruniaux J, Lacour-Gayet F, et al. Anatomic correction of transposition of the great arteries with ventricular septal defect:experiencewith 118cases.J THORAC CARDIOVASC SURG 1991;102:140-7.
1 46
The Journal of Thoracic and Cardiovascular Surgery
Akiba, Neirotti, Becker
3. Kanter KR, Anderson RH, Lincoln C, Rigby ML, Shinebourne EA. Anatomic correction for complete transposition and double-outlet right ventricle. J THORAC CARDIOVASC SURG 1985;90:690-9. 4. Klautz RJM, Ottenkamp J, Quaegebeur JM, Buis-Liem TN, Rohmer J. Anatomic correction for transposition of the great arteries: first follow-up (38 patients). Pediatr CardioI1989;10:1-9. 5. Yacoub MH, Radley-Smith R. Anatomic correction of the Taussig-Bing anomaly. J THORAC CARDIOVASC SURG 1984;88:380-8. 6. Stellin G, Zuberbuhler JR, Anderson RH, Siewers RD. The surgical anatomy of the Taussig- Bing malformation. J THORAC CARDIOVASC SURG 1987;93:560-9. 7. Trusler GA, Castaneda AR, Rosenthal A, et al. Current results of management in transposition of the great arteries, with special emphasis on patients with associated ventricular septal defect. J Am Coll Cardiol1987; I0:106171. 8. Waldman JD, Schneeweiss A, Edwards WD, Lamberti JJ,
9.
10.
II.
12.
13.
Shem-Tov A, Neufeld HN. The obstructive subaortic conus. Circulation 1984;70:339-44. Schneeweiss A, Motro M, Shem-Tov A, Neufeld HN. Subaortic stenosis: an unrecognized problem in transposition of the great arteries. Am J Cardiol 1981;48:336-9. Urban AE, Brecher AM. The arterial switch repair and the obstructive right ventricular outflow tract: Does it matter? Thorac Cardiovasc Surg 1991;39(suppl): 170-5. Boyadjiev K, Ho SY, Anderson RH, Lincoln C. The potential for subpulmonary obstruction in complete transposition after the arterial switch procedure. Eur J Cardiothorac Surg 1990;4:214-8. Soto B, Becker AE, Moulaert AJ, Lie JT, Anderson RH. Classification of ventricular septal defects. Br Heart J 1980;43:332-43. Griffith BP, Hardesty RL, Siewers RD, Lerberg DB, Ferson PF, Bahnson HT. Pulmonary valvulotomy alone for pulmonary stenosis: results in children with and without muscular infundibular hypertrophy. J THORAC CARDIOVASC SURG 1983;83:577-83.
Tomoharu Akiba, MD,* Rodolfo Neirotti, MD, and Anton E. Becker, MD,
Amsterdam, The Netherlands
From the Departments of Cardiovascular Pathology and Pediatric Cardiac Surgery, University of Amsterdam, Academic Medical Center, Amsterdam, The Netherlands. Received for publication Feb. 4, 1992. Accepted for publication June 3, 1992. Address for reprints: Anton E. Becker, MD, Department of Cardiovascular Pathology, Academic Medical Center, Meibergdreef 9, 1105 AZ Amsterdam-ZO, The Netherlands. *Research fellow,Yamagata University School of Medicine, Yamagata, Japan.
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In many centers the arterial switch operation has become the procedure of choice in caring for infants with either complete transposition of the great arteries (TGA) or double-outlet right ventricle with subpulmonary defect (Taussig-Bing malformation). Right ventricular (RV) outflow tract obstruction is presently considered one of the most significant complications after anatomic correction.' A recent review of 118 patients, including an evaluation of their midterm results after anatomic correction, revealed that 10 patients needed another operation, 7
0022-5223/93/$1.00/+ 0.10
Volume 105 Number 1 January 1993
because of R V outflow obstruction' The stenosis was caused by insufficient resection of preoperative subaortic stenosis in only 1 of the 7 patients. In the remaining patients, the obstruction was located chiefly at the site of anastomosis between a small aortic root and a large pulmonary artery. Subvalvular RV outflow tract obstruction thus appears rarely, but nevertheless has been documented. Indeed Kanter.' Klautz," and their associates reported a prevalence of approximately 23%.3,4The obstruction was most prevalent among patients who underwent operations for Taussig-Bing malformation-three of seven (42.9%)3 and two of four (50%),4 These disappointing results almost certainly relate to the fact that a narrow muscular subaortic outflow tract is frequently observed in the heart with Taussig-Bing malformation, whereas its clinical severity is often difficult to ascertain before operation. 5, 6 However, the same authors also report that subvalvular R V outflow tract obstruction is prevalent after the switch operation in TGA, calculated as 17.4%3 and 17.6%4. This is somewhat surprising since clinically significant R V outflow tract obstruction in native TGA is generally considered to be rare; the figures vary from 0.4%,7 through 4.7%,8 to 6.9%.9 On the other hand, a recent survey of 96 patients with TGA who underwent arterial switch repair reported resection of the obstructive myocardium in 13 (13.6%),10 whereas an anatomic study documented potential obstruction in 11 (22%) of 50 heart specimens with complete TGA. 1[ However, no reports thus far have provided an explanation of why or how subvalvular R V outflow tract obstruction could develop after an arterial switch operation, if it was not present before the procedure. For this reason, the available reports have been reviewed and put into the perspective of a morphometric study of the R V outflow tract of heart specimens with complete TGA.
Patients and methods Thirty-nine heart specimens with native, unoperated, completeTGA were investigated. The study was limited to hearts withnormally arranged atrial chambersand a concordantatrioventricular connection. Hearts with the Taussig-Bing configuration wereexcluded. Hearts with a ventricularseptal defect (VSD) wereseparatedfromthosewithan intactventricularseptum;the formerwere classified according to Sotoand associates. 12 The morphology of the subaorticright ventricularoutflow tract was analyzed, with a focus on the outflow tract musculature in each heart. The smallest internaldiametersof boththe RVoutflow tract and the aortic valve orifice were measured. The outflow tract diameter wasexpressed as a percentageof that of the aortic valve orifice. Obstruction wasconsidered to be presentif the diameter of the outflow tract was smaller than that of the aortic valve orifice.
Outflow tract obstruction after arterial switch repair
14 3
The diameters of the ascending aorta and the pulmonary trunk weremeasuredfrom the arterial side,immediatelyabove the level of the valveorifices, and expressed as a ratio (pulmonaryjaortic). Seven hearts had pulmonary valve stenosis and thereforecouldnotbe measuredreliably. The relationshipof the great arteries was categorized as either anteroposterioror side byside,with the aortic valve to the right of and slightlyanterior to the pulmonary valve. Other associated congenital abnormalitiessuchas aorticarch anomalies were also noted.
Results Of the 39 hearts, 25 had an intact ventricular septum and 14 showed a VSD. Thirteen of the latter had a single defect: a perimembranous outlet in eight, a perimembranous inlet in two, a muscular outlet in two, and a muscular trabecular defect in one; the remaining heart had two muscular trabecular defects. Displacement of the outlet septum was present in eight hearts, each of which had a perimembranous defect. Anterior deviation was present in six and posterior displacement in two. An anteroposterior relationship of the aorta and pulmonary trunk was present in 32 heart specimens (22 with an intact septum; 10 with a septal defect). The ratio between the diameter of the pulmonary trunk and that of the ascending aorta (measured in 28 cases) averaged 0.99 ± 0.11, varying between 0.83 and 1.20. Such a mismatch occurred in 11 of the 28 hearts. A side-by-side relationship was present in seven hearts (three with an intact septum; four with a septal defect). The pulmonary/ aortic ratio in these instances (four hearts) averaged 1.38 ± 0.11, varying between 1.20 and 1.50. Subvalvular R V outflow tract obstruction was found in two hearts (5.1%). In one heart with an anterosuperior relationship of the great arteries and an intact septum (in a neonate aged 9 days at the time of death), the obstruction was caused by a pronounced supraventricular crest, largely the result of marked accentuation of the ventriculoinfundibular fold and prominent anterior trabeculations (Fig. 1). The diameter of the outflow tract was 57% of that of the aortic valve orifice. In the second case, a 14-year-old child exhibited an anterosuperior relationship of the great arteries and a perimembranous outlet septal defect; the outflow tract anatomy was somewhat similar to that of the first case, but it was accentuated by excessive hypertrophy. Hence hypertrophic anterior trabeculations aggravated circumferential hypertrophy of the infundibular musculature and caused obstruction (Fig. 2). In this specimen, the outflow tract diameter was 43% of that of the aortic valve orifice. No coexisting subpulmonary anomalies were present. Coarctation of the aorta was found in three hearts (two
I 44
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The Journal of Thoracic and Cardiovascular Surgery
Fig. 1. RV outflow tract in a heart with completeTGA and intact ventricular septum (9 days). A, Obstruction caused by pronounced supraventricular crest (SC) and prominentanterior trabeculations. B, The latter are best seen (arrow) once the infundibulum is wide open. TV, Tricuspidvalve.
Fig. 2. Wide-open RV outflow tract in a heart withcompleteTGA and VSD (14 years). RV outflow tract obstruction caused by marked hypertrophyof muscular infundibulum, accentuated by anterior trabeculations (asterisks). VSD, ventricular septal defect.
with a VSD, one with an intact septum), one of which (case 2) had subaortic obstruction. All associated anomalies are summarized in Table I. Discussion After an arterial switch repair for complete TGA, the appearance of subvalvular RV outflow tract obstruction is rare/ but nevertheless has been documented and is worthy of study.': 4 Kanter and coworkers- described 4 of 23 patients (17.4%) with complete TGA in whom RV outflow tract obstruction occurred during the operation,
per their diagnosis. They made this diagnosis on the basis of inability to successfully wean the patient from cardiopulmonary bypass, in the presence of systemic or suprasystemic R V pressures and normal or low proximal pulmonary arterial pressures. However, such intraoperative observations do not necessarily relate to anatomic obstruction. For instance, it is known that after valvotomy for isolated pulmonary valve stenosis the muscular infundibulum may acquire a hypercontractile state, which may cause severe obstruction in the postoperative period
Volume 105 Number 1 January 1993
despite an adequate valvotomy. 13 This phenomenon could explain the intraoperative assessment ofRV outflow tract obstruction after an arterial switch repair and could also apply to cases reported by Klautz and associates." They reported that 6 of 34 patients (17.6%) had a posteroperative R V-pulmonary artery peak systolic gradient of 20 mm Hg or more. The infundibular pressure gradients were evaluated within 2 weeks after repair, however, and this is too short a time lapse to rule out dynamic R V outflow obstruction. Thus the figures produced by these authors may well appear to be grossly overstated. Nevertheless, these findings may apply in rare instances and may relate to the mechanism of anatomic obstruction. First, subvalvular R V outflow tract obstruction could have been present before the operation, although unnoticed clinically. The present study was tailored to evaluate the occurrence of potential obstruction in the R V outflow by measuring the narrowest diameter of the R V outflow tract and by comparing it with the diameter of the aortic orifice. On that basis, 2 of 39 hearts with complete TGA showed obstruction. The prevalence of 5.1%, in itself, is less relevant than the confirmation that muscular obstruction within the R V outflow tract in hearts with native, unoperated, complete TGA is infrequent. However, additional circumstances such as a VSD and rightward deviation of the outlet septum may induce muscular hypertrophy and eventual obstruction in an outflow tract, which is intrinsically narrow.?" Second, some degree of mismatch between the two great arteries could playa role, although this hypothesis is purely speculative. Serraf and colleagues/ recently presented a study of 118 patients who had undergone an arterial switch procedure; in 100 of these patients the pulmonary trunk was larger than the aorta. Urban and Brecher!" stated that two thirds of their patients had such a mismatch. Our own findings are very much in accord with these observations. In 15 of 32 hearts measured, the diameter of the aortic anulus was smaller than that of the pulmonary trunk. In case of a distinct mismatch, the operative technique is adjusted by incision of the aorta and insertion of a patch of pericardium. I However, subtle degrees of mismatch almost certainly will occur but may not necessarily be considered important at the time of operation. One could hypothesize, therefore, that, once "switched," the RV in such instances will have to cope with a persistent narrow outflow, irrespective of the wide size of the distal pulmonary trunk. The RV, transformed to a volume-loaded ventricle rather than a pressure-loaded ventricle, will attempt to compensate for the obstruction at the junction between the mismatched ascending aorta and the pulmonary trunk. Hence, ongoing R V hypertrophy may ensue
Outflow tract obstruction after arterial switch repair
14 5
Table I. Associated anomalies in 39 hearts with complete TGA I. Subaortic right ventricular outflow tract obstruction (2 hearts)
Pronounced ventriculoinfundiI (IVS) bular fold and anterior trabeculations I (VSD) Circumferential hypertrophy of the infundibulum; hypertrophic anterior trabeculations 3 (VSD, 2; IVS, I) 2. Coarctation of the aorta (3 hearts; I with subaortic obstruction) 3. Subpulmonary left ventricular outflow tract obstruction (4 hearts) Septal hypertrophy 2 (VSD, I; IVS, I) Deviated outlet septum 2 (VSD, 2) 4. Pulmonary valve stenosis (7 hearts; 2 with subpulmonary obstruction) 5 (VSD, 4; IVS, I) Bicuspid I (VSD) Dysplastic I (VSD) Bicuspid + dysplastic 5. Dysplastic mitral valve (I I (IVS) heart) I (VSD) 6. Straddling mitral valve (I heart) I (IVS) 7. Mitral valve bridging (I heart) 8. Anomalous attachment of the 3 (VSD) tricuspid valve tension apparatus to the outlet septum (3 hearts) 18 (VSD, I; IVS, 17) 9. Patent ductus arteriosus (18 hearts) I (IVS) 10. Left juxtaposition of the right atrial appendage (I heart) II. Persistent left superior vena 3 (VSD, 2; IVS, I) cava (3 hearts) IVS, Intact ventricular septum; VSD, ventricular septal defect.
and exacerbate the intrinsic anatomic potential of R V outflow tract obstruction. This study, though tentative, could stimulate a prospective study to evaluate the potential of such mechanisms in patients with complete TGA selected for an arterial switch operation. We thank Mr. W. P. Meun for the photography and Ms. M.
1. Schenker for secretarial assistance.
REFERENCES 1. Quaegebeur JM, Rohmer J, Ottenkamp J, et al. The arterial switch operation: an eight-year experience.J THORAC CARDIOVASC SURG 1986;92:361-84. 2. Serraf A, Bruniaux J, Lacour-Gayet F, et al. Anatomic correction of transposition of the great arteries with ventricular septal defect:experiencewith 118cases.J THORAC CARDIOVASC SURG 1991;102:140-7.
1 46
The Journal of Thoracic and Cardiovascular Surgery
Akiba, Neirotti, Becker
3. Kanter KR, Anderson RH, Lincoln C, Rigby ML, Shinebourne EA. Anatomic correction for complete transposition and double-outlet right ventricle. J THORAC CARDIOVASC SURG 1985;90:690-9. 4. Klautz RJM, Ottenkamp J, Quaegebeur JM, Buis-Liem TN, Rohmer J. Anatomic correction for transposition of the great arteries: first follow-up (38 patients). Pediatr CardioI1989;10:1-9. 5. Yacoub MH, Radley-Smith R. Anatomic correction of the Taussig-Bing anomaly. J THORAC CARDIOVASC SURG 1984;88:380-8. 6. Stellin G, Zuberbuhler JR, Anderson RH, Siewers RD. The surgical anatomy of the Taussig- Bing malformation. J THORAC CARDIOVASC SURG 1987;93:560-9. 7. Trusler GA, Castaneda AR, Rosenthal A, et al. Current results of management in transposition of the great arteries, with special emphasis on patients with associated ventricular septal defect. J Am Coll Cardiol1987; I0:106171. 8. Waldman JD, Schneeweiss A, Edwards WD, Lamberti JJ,
9.
10.
II.
12.
13.
Shem-Tov A, Neufeld HN. The obstructive subaortic conus. Circulation 1984;70:339-44. Schneeweiss A, Motro M, Shem-Tov A, Neufeld HN. Subaortic stenosis: an unrecognized problem in transposition of the great arteries. Am J Cardiol 1981;48:336-9. Urban AE, Brecher AM. The arterial switch repair and the obstructive right ventricular outflow tract: Does it matter? Thorac Cardiovasc Surg 1991;39(suppl): 170-5. Boyadjiev K, Ho SY, Anderson RH, Lincoln C. The potential for subpulmonary obstruction in complete transposition after the arterial switch procedure. Eur J Cardiothorac Surg 1990;4:214-8. Soto B, Becker AE, Moulaert AJ, Lie JT, Anderson RH. Classification of ventricular septal defects. Br Heart J 1980;43:332-43. Griffith BP, Hardesty RL, Siewers RD, Lerberg DB, Ferson PF, Bahnson HT. Pulmonary valvulotomy alone for pulmonary stenosis: results in children with and without muscular infundibular hypertrophy. J THORAC CARDIOVASC SURG 1983;83:577-83.