Conal Septum Research Articles

Mitral atresia with a large left ventricle and an underdeveloped or absent right ventricular sinus: Clinical profile, anatomic data and surgical considerations

In mitral atresia with a large left ventricle, the tricuspid valve is either straddling and biventricular or entirely left ventricular. To learn how to assess the identity of the tricuspid valve in such cases 15 heart specimens were examined as well as the echocardiograms of 10 living patients. When the right ventricular sinus was underdeveloped (11 cases), a straddling tricuspid valve was present; when it was absent (14 cases), the tricuspid valve was entirely left ventricular.Regardless of biventricular or exclusively left ventricular attachments, the tricuspid valve was tricommissural (at postmortem examination or on echocardiography) in 22 cases (88%). Its chordal attachments showed considerable variations but were usually paraseptal or on the ventricular septal crest or conal septum. When biventricular, the tricuspid valve straddled through an inlet ventricular septal defect. Clinical or anatomic evidence, or both, of tricuspid regurgitation was present in 14 cases (56%).It is concluded that 1) the identity of the atrioventricular valves is reflected in their chordal attachments more accurately than in their leaflet morphology and depends primarily on the type of ventricular loop present; 2) as a rule, the tricuspid valve is right-sided in D-looped and left-sided in L-looped ventricles; 3) valve identity expressed as the number and position of the papillary muscle attachments is generally recognizable echocardiographically and can be used to diagnose the type of ventricular loop that is present; and 4) the presence and degree of tricuspid regurgitation deserve attention when choosing optimal palliative surgery.

Infundibular septal defect with severe aortic regurgitation: A new surgical approach

Aortic regurgitation associated with prolapse of an aortic cusp and an infundibular septal defect is caused by the lack of anatomical support for the aortic annulus by the conal septum. This fact is taken into consideration in the new surgical approach that we performed in 5 children 3 to 16 years of age with infundibular ventricular septal defect and severe aortic regurgitation. The ventricular septal defect is closed by a patch anchored to another patch through the prolapsed cusp. This second patch is pulled up with the prolapsed cusp and is then fixed in the aortic wall. In all 5 patients, all clinical signs of aortic insufficiency disappeared, and only minimal aortic regurgitation could be demonstrated by color Doppler mapping.

Transposition of the great arteries, ventricular septal defect, and pulmonary outflow tract obstruction

During a 10-year period (1980 to 1990), 62 patients underwent complete repair for transposition of the great arteries, ventricular septal defect, and pulmonary outflow tract obstruction. Twenty-two patients (35%) (mean age 8.1 +/- 7.2 years) underwent the Rastelli operation: The ventricular septal defect was enlarged anteriorly in eight patients, and right ventricular-pulmonary artery continuity was established with an extracardiac valved (9/22) or nonvalved (13/22) conduit. Forty patients (65%) (mean age 3.3 +/- 3.2 years) underwent the Lecompte modifications: The conal septum was extensively excised when present (30/40), anterior translocation of the pulmonary bifurcation was performed in 32 patients, and right ventricular-pulmonary artery continuity was established by direct anastomosis without a prosthetic conduit. There were seven early deaths (11%; 70% confidence limits, 7% to 17%): two after the Rastelli procedure (9%; 70% confidence limits, 3% to 20%) and five after the Lecompte operation (12.5%; 70% confidence limits, 7% to 20%). Four patients were lost to follow-up, yielding a 93% complete follow-up (mean follow-up 55 months). There were two late deaths (one in each group). Actuarial probability of survival (+/- standard error) at 5 years was 83% +/- 9% after the Rastelli operation and 84% +/- 6% after the Lecompte procedure. All long-term survivors (except one in the Rastelli group) were in functional class I. Five patients in the Rastelli group underwent late reoperation for obstruction of the extracardiac conduit (28%; 70% confidence limits, 16% to 42%). Three late reoperations (10%; 70% confidence limits, 4% to 19%) were required after the Lecompte operation (one for residual ventricular septal defect and two for residual pulmonary outflow tract obstruction). At most recent examination, residual pulmonary outflow tract obstruction was present in seven patients of the Rastelli group (39%; 70% confidence limits, 26% to 53%) and in six patients of the Lecompte group (19%; 70% confidence limits, 12% to 29%). The combined likelihood of reoperation for pulmonary outflow tract obstruction and residual pulmonary outflow tract obstruction was significantly higher in the Rastelli group (67% versus 26%; p = 0.005). Both procedures provide satisfactory early and late results. The Lecompte operation allows complete repair in infancy, is feasible in patients with anatomic contraindications to the Rastelli operation, and may reduce the need for reoperation and the prevalence of residual pulmonary outflow tract obstruction.

Surgical management of the conal (supracristal) ventricular septal defect

Surgical management of the conal (supracristal) ventricular septal defect differs significantly from the management of the perimembranous (infracristal) ventricular septal defect. The absence of a portion of the conal septum can lead to prolapse of the right cusp of the aortic valve, which predisposes these patients to aortic insufficiency. Between January 1980 and December 1989, 36 children with conal ventricular septal defect underwent intracardiac repair. Diagnosis was by echocardiography, cardiac catheterization, and intraoperative exploration. Preoperative evaluation showed that 26 patients (72%) had aortic valve prolapse and 16 (44%) had aortic insufficiency. Pulmonary-to-systemic flow ratios ranged from 1:1 to 3.5:1 (mean 2.0:1.0). Ten patients (27%) were believed to have clinical congestive heart failure. Age at the time of operation ranged from 2 weeks to 18 years (mean 5.5 years). Operative exposure was through the pulmonary artery (26), aorta (4), right ventricle (3), or right atrium (3). Simultaneous aortic valve suspension for aortic insufficiency was performed in four patients. Operative survival was 100%. Follow-up is complete in all patients and ranges from 0.5 to 9 years (mean 4.3 years). All patients are in normal sinus rhythm. No residual ventricular septal defects have been identified. Twenty-three of 36 patients (64%) have no evidence of aortic insufficiency; 12 of 36 (33%) have trivial or mild aortic insufficiency. One patient with initial severe aortic insufficiency underwent repeat aortic valvuloplasty 3 years after ventricular septal defect closure and aortic valve suspension. No patients have required aortic valve replacement. Surgical management of the conal ventricular septal defect differs from that of the perimembranous ventricular septal defect in two critical aspects. The operative approach should be through the pulmonary artery. This allows the best exposure of the remaining conal septum and the pulmonary and aortic valve leaflets, facilitating closure of the defect without injury to the valves or conduction system. Conal ventricular septal defects should undergo early closure, regardless of shunt volume, to prevent progressive aortic insufficiency.

Anatomic correction of transposition of the great arteries with ventricular septal defect: Experience with 118 cases

One hundred eighteen patients, 100 with transposition of the great arteries plus ventricular septal defect and 18 with double-outlet right ventricle and subpulmonary ventricular septal defect have undergone arterial switch and patch closure of the ventricular septal defect since February 1983. In transposition of the great arteries the ventricular septal defect was perimembranous in 70 cases, trabecular in 28, and infundibular in 10. Eleven patients had multiple ventricular septal defects. In addition to 18 patients with double-outlet right ventricle, malalignment of the conal septum was present in 19 cases. Coronary type A distribution was recognized in 79 cases, type C in one, type D in 24, and type E in 14. Great arteries were side by side in 19% of cases. Aortic coarctation was present in 31 cases, and subaortic obstruction in 9. Age at operation ranged from 4 days to 4 years (mean, 3.5 +/- 8.3 months), and mean weight was 4.0 +/- 1.6 kg. Thirty-seven infants were younger than age 1 month. Thirty-six patients underwent previous operations: pulmonary artery banding alone (n = 13), pulmonary artery banding and coarctation repair (n = 13), and coarctation repair alone (n = 10). Mean time between the first procedure and the switch was 2.2 months. Six patients with aortic coarctation underwent one-stage repair, through median sternotomy, aortic reconstruction, closure of the ventricular septal defect, and arterial switch. Perioperative mortality was 13.5% (70% confidence limit 10% to 17.6%, n = 16). It was directly related to coronary artery kinking in 50% of deaths and to anatomy and size discrepancy of the great arteries in the remaining deaths. Univariate analysis could not find any significant risk factor of in-hospital mortality. Mean follow-up of 30.3 +/- 23.5 months was achieved in all but 2 survivors. There was one late death. Ten patients underwent 11 reoperations for recoarctation (n = 1), pulmonary stenosis (n = 7), residual ventricular septal defect (n = 2), and stenosis of superior vena cava (n = 1). Two patients needed a permanent pacemaker. Actuarial survival and freedom from reoperation at 5 years were 84.5% +/- 3.6% and 85.7% +/- 4.6%, respectively. We conclude that anatomic correction of complex transposition is a safe method that offers good early and midterm results.

Ventricular septal defect closure without aortic valve plication in patients with aortic valve prolapse

Ventricular septal defect (VSD) with associated aortic regurgitation (AR) secondary to prolapse of an aortic valve cusp into the VSD poses a significant problem as to the appropriate timing and type of surgical intervention. Various centers have advocated surgical plication of the redundant aortic cusp tissue at the time of VSD closure. 1–3 Results of aortic valve plication have been varied, both in our center and others. 1–4 A major pathophysiologic factor in the development of aortic valve prolapse and subsequent AR in these patients is believed to be insufficiency in the conal septum, which should serve to support the aortic valve “anulus” from below. 5,6 This lack of support allows the valve cusp to sag into the VSD and to be further distorted by hemodynamic factors. 7 In an attempt to avoid the need for aortic valve plication in these patients, we have elected to close their VSDs at the earliest sign of AR or aortic valve prolapse, as determined by physical examination, echocardiography or angiography. We present our experience with patients undergoing early closure of a VSD with associated aortic valve prolapse.

Lectin histochemistry of the embryonic heart: fucose-specific lectin binding sites in developing rats and chicks.

Glycoconjugates, particularly their sugar side chains, play important roles in embryonic development. Changes in cell-surface-associated glycoconjugates are known to affect cell differentiation, cellular interactions, and other developmental phenomena during embryogenesis. The embryonic heart goes through a series of complicated morphologic events during development. Of particular interest is morphogenesis of the outflow tract. This region of the embryonic heart originates from more than one cell population and undergoes a complex process of septation during formation of the great vessels. Histochemical analysis with a series of fucose-specific lectins conjugated to horseradish peroxidase has revealed the presence of a fucosylated glycoconjugate in the outflow tract of the developing heart. The results reveal further that the expression of the fucosylated glycoconjugate is stage-dependent and thus probably genetically regulated. The timing and distribution of staining with the lectin OFA suggest that this fucosylated glycoconjugate may play a role in directing the migration of neural crest cells into the heart and subsequent formation of the conus septum.

Surgical Management of Patients with Interrupted Aortic Arch and Severe Subaortic Stenosis

Ten patients underwent palliative surgery for interrupted aortic arch and severe subaortic obstruction due to posterior displacement of the conal septum. Their ages ranged between 4 and 28 days (mean, 11.0 ± 7.7 days) and their weights, between 2.1 and 4.2 kg (mean, 2.85 ± 0.6 kg). Preoperative echocardiography and cardiac catheterization were performed on all patients. The ratios of the left ventricular outflow tract diameters and the ascending aortic diameters to the descending aortic diameters were 0.56 ± 0.03 and 0.56 ± 0.06, respectively, compared with 0.81 ± 0.12 and 0.95 ± 0.17, respectively, in 20 patients with interrupted aortic arch but without obstruction ( p < 0.001). Four of the 10 patients underwent pulmonary artery banding and insertion of a bypass graft between the ascending and the descending aorta. All 4 died of low cardiac output soon after operation (100% operative mortality). The remaining 6 patients underwent banding and insertion of a graft between the main pulmonary artery proximal to the band, and the descending aorta. All of these patients survived, and all except 1 are doing well 3 months to 4 years postoperatively. The use of a pulmonary artery-descending aorta conduit and of distal pulmonary artery banding provides good palliation for patients with interrupted aortic arch and major subaortic stenosis.

Rastelli operation as one stage anatomical correction for infants with complete transposition of the great arteries and ventricular septal defect.

We recently adopted the Rastelli operation as a one stage anatomical correction for three infants with transposition of the great arteries and associated with ventricular septal defect (TGA + VSD). In all, ventricular septal defect was enlarged by excision of the conus septum to avoid obstruction of intraventricular tunnel and Hancock valved conduits of 18 mm in diameter were used for reconstruction of pulmonary trunk. The postoperative function of the left ventricule proved to be better than that of the right ventricle, as the systemic ventricle, after the Mustard procedure for TGA + VSD. Our results show that the Rastelli operation is effective as a one stage anatomical correction in infants with TGA + VSD.

Anatomic correction of the Taussig-Bing anomaly

Anatomic correction of the Taussig-Bing anomaly depends on thorough understanding of the variable interrelations between the atrioventricular valves, ventricular septal defect, infundibular muscle bands, and aortic and pulmonary outflows and the resulting haemodynamic changes. Depending on the relative position of the great arteries, two clinicopathological types have been identified. In the two patients with side-by-side relationship of the great arteries, the conal septum was well developed, so that there were various degrees of subaortic stenosis. Associated coarctation of the aorta was present in both patients. Coronary anatomy was identical (Type E) to that present in complete transposition with side-by-side great arteries. In these patients, anatomic correction was achieved by wide excision of the conal septum and intraventricular repair. In contrast, two patients with anteroposterior relationship of the great arteries had a poorly developed conal septum and no subaortic stenosis or coarctation of the aorta. In these patients, repair was achieved by diverting blood from the ventricular septal defect to the adjoining pulmonary artery combined with switching of the great arteries and coronary transfer. There were no early or late deaths associated with either method of repair, and there was evidence of good correction of the hemodynamic abnormalities. It is concluded that anatomic correction is possible in all patients with the Taussig-Bing anomaly and that the method of repair depends on the relative position of the great arteries.

A successful procedure for correction of the Taussig-Bing malformation

We report upon a successful procedure for surgical correction of the Taussig-Bing malformation. This procedure consisted of resection of the aortic conal septum and direction of left ventricular blood flow through the ventricular septal defect to the aorta by use of a nonvalved conduit (14 mm in diameter) in the right ventricle. The patient survived the operation and postoperative hemodynamics were excellent 10 months postoperatively.

Cardiovascular malformations associated with administration of prenalterol to young chick embryos.

Prenalterol (levo-1-[4-hydroxyphenoxy]-3-isopropyl-amino-2-propanol), a new stimulant of cardiac beta-adrenergic receptors in man, induces cardiovascular malformations when topically administered to 2 1/2- through 5 1/2-day chick embryos (Hamburger-Hamilton stages 17-27). Ventricular septal defects (VSD) located in the middle portion of the conal septum and classified as the simple, punched-out type VSD without septal malalignment were the predominant malformations observed throughout the developmental period tested. Arch malformations of the aortic circulation were also observed throughout the test interval, while anomalies of the pulmonary system were observed only at Hamburger-Hamilton stages 17 and 26-27. At stage 25 prenalterol demonstrated an acute toxicity significantly less than (1/50-1/20) epinephrine (P = .035 at concentrations of 8-10 mM) but was relatively equipotent with epinephrine in producing cardiovascular malformations. The effective median concentrations of the two agents were comparable (0.5-1.0 mM). The spectra of malformations induced by prenalterol and epinephrine were qualitatively similar. Malformations included absence of the right and/or left third aortic arch (innominate arteries), persistent remnant of the left fourth aortic arch, and VSD. These results support a previously proposed theory by these investigators that hyperstimulation of cardiac beta-adrenergic receptors in the chick embryo produces cardiovascular malformations.

A computer graphic study of cardiac truncal septation

AbstractSeptation of the cardiac truncus arteriosus in the normal rat embryo was described and illustrated by three‐dimensional reconstruction from serial sections through the developing outflow tract. Tracings of selected structures were digitized on an Apple II‐plus microcomputer, relayed through a central computer facility, and displayed on a Hewlett‐Packard 9845C graphics computer. Rotation and dissection of the color images allowed a kinetic description of the principal features of truncal septation and comparison with analogous events in the chick.A complex of tissue structures appeared in the downstream, distal truncus at 13 days of gestation and moved toward the ventricle(s) through the following day. As in the chick, the forming semilunar valves remained within 200 μm of the cephalic margin of the myocardial sleeve as they rotated and descended toward their definitive position against the heart. Mesenchymal condensations formed within the intervening aorticopulmonary (AP) septum and remained in close association with the principal bifurcation of the spiralling blood lumens, passing between the valves and descending along the conus septum. As the conus septum fused at 15 days of gestation, three outlets for cardiac outflow were seen: the major left and right streams to the aortic and pulmonary valves, respectively, and an apparently dwindling stream which crossed from the right ventricle behind the conus septum to exit through the aorta. In the chick, but not in the rat, nerve bundles invaded the distal truncus during septation to form the cardiac plexus.

Two-dimensional echocardiographic features of interruption of the aortic arch

The 2-dimensional echocardiographic features of interruption of the aortic arch are presented based on analysis of the echocardiograms and angiograms from 8 infants: 2 with type A and 6 with type B interruption. Each infant had a patent ductus arteriosus, 6 had a conoventricular septal defect with leftward deviation of the conal septum, 1 had truncus arteriosus with truncal valve stenosis, and 1 had a distal aortopulmonary septal defect with an intact ventricular septum. Echocardiographic images obtained from the suprasternal notch or from a high parasternal approach demonstrated the interruption of the aortic arch and continuation of the patent ductus arteriosus into the descending aorta. These findings were compared with those in infants with aortic atresia and a hypoplastic ascending aorta or discrete coarctation of the aorta with tubular hypoplasia of the aortic arch. Types A and B interruption of the aortic arch were easily differentiated and the caliber of the patent ductus arteriosus was assessed. The characteristic conoventricular septal defect was readily visualized from an apex 2-chamber view or from a subcostal sagittal plane view. With this information subsequent angiography can be more expeditiously performed in this group of critically ill infants.

Conal anatomy in aortic atresia, ventricular septal defect, and normally developed left ventricle

Although aortic valve atresia is usually associated with severe underdevelopment of the mitral apparatus and left ventricle in rare cases of aortic atresia, the left ventricle may be of normal size, or even enlarged. This occurrence seems related to the presence of a significant ventricular septal defect. We have presented the morphologic findings in seven patients with aortic atresia and normally developed left ventricle, (six necropsied patients, and one studied angiocardiographically). Four autopsied patients had conal type ventricular septal defects, characterized in three by conoventricular malalignment. Subaortic atresia in these patients resulted from leftward deviation of the conal septum. One patient with aortic atresia and well-developed left ventricle had a membranous defect, and one patient had a complete A-V canal. The ventricular septal defect in the patients with conoventricular malalignment are very similar to the conal VSD observed in patients with aortic arch interruptions. Although ultimate survival with these uncommon groupings of anomalies necessitates patency of the ductus arteriosus, clinical recognition rests on (1) awareness of its existence, (2) ultrasonography, and (3) selective biventricular and aortic angiography. It is possible that some of these patients might be candidates for ventriculo-aortic reconstitiution.

Ventricular septal defect in interruption of aortic arch

A necroscopy study of 34 patients with interruption of the aortic arch was carried out to characterize more fully the ventricular septal defect and the anatomic basis of subaortic obstruction. In 21 patients (61.8 percent) the site of interruption was between the left common carotid artery and the left subclavian artery; in 13 (38.2 percent) it was distal to the left subclavian artery; no case of interruption just distal to the innominate artery was found. A ventricular septal defect was present in all but two patients, both with large aortopulmonary fenestrations. All patients had visceroatrial situs solitus and D-ventricular loop. The great arteries were normally related in 33 patients and D-transposition was found in one patient. Twenty-one patients had a ventricular septal defect involving the conal septum. Conoventricular malalignment resulted in a typical subpulmonary ventricular defect. The malignant was characteristically in a leftward direction allowing for potential muscular narrowing of the left ventricular outflow tract. In some patients, the conal ventricular septal defect was characterized by a deficiency of a the conal septum without malalignment. In 4 of 21 patients with a ventricular septal defect involving the conal septum, the defect was immediately adjacent to the pulmonary.value. Typical infracristal membranous ventricular defects five patients), cushion defects (3 patients) and muscular defects (3 patients), were also found. The potential for subaortic narrowing was present in some of these patients as well. No relation between position of ventricular septal defect and type of arch interruption could be discerned. The presence or absence of subaortic obstruction was not predictive of a specific type of interruption. Similarly, although deformity of the aortic valve was not uncommon in this series, it was not associated with any specific type of interruption.

Anatomical study of truncus arteriousus communis with embryological and surgical considerations.

Twelve specimens of truncus arteriosus communis have been studied anatomically, with special reference to the conal anatomy and to the associated cardiac anomalies which can create additional problems if surgical repair is planned. A wide spectrum of conal morphology has been observed, suggesting that differential conal absorption is a developmental characteristic of truncus arteriousus as well as of transposition complexes. The invariable absence of septation of the ventricular infundibula and semilunar valves, in spite of the variable anatomy of the free wall of the conus, indicates that all types of truncus arteriosus, ontogenetically, should be considered as a single undivided conotruncus. Various types of ventircular septal defect were found: (a) ventricular septal defect with absent crista, in which no remnants of conal septum are present; (b) supracristal ventricular septal defect, in which vestigial conal septum is seen in front of the membranous septum; (c) bulloventricular foramen, associated with univentricular origin of the truncus from the right ventricle. Frequent associated anomalies are underdevelopment of the aortic arch, truncal valve malformations, and obstructive ventricular septal defect. The AV conduction system studied in one case showed an arrangement similar to Fallot's tetralogy with the His bundle and the left bundle-branch in a safe position behind the posteroinferior rim of the defect. The postoperative fate of the frequently abnormal truncal valve and the theoretical indications for total repair for Type IV truncus are also discussed.

Variations in clinical presentation of Fallot's tetralogy in infancy. Angiographic and pathogenetic implications.

Striking variability has been observed in the presenting features in infancy of patients subsequently shown to have tetralogy of Fallot. Some patients presented with severe cyanosis in the neonatal period while others had a systolic murmur and cyanosis only on crying. In these latter patients cyanosis became present at rest over the subsequent months. Yet others presented with episodic attacks of unconsciousness, and a final group presented with dyspnoea and heart failure, accompanying a left-to-right shunt. Angiography demonstrates corresponding variations in the anatomy of the ventricular outflow tracts. In the severely cyanosed patients, the conus septum was deviated so as to obstruct the pulmonary outflow tract, and was best visualized in the lateral projection. In the patients with increasing cyanosis or episodic attacks of unconsciousness, the conus septum again obstructed the pulmonary infundibulum, but was obliquely orientated, not being seen clearly on either lateral or frontal projections. The episodic attacks were considered to be related to infundibular spasm, as previously shown to occur in Fallot's tetralogy. In contrast, increasing cyanosis was believed to be related to hypertrophy of infundibular musculature. In the patients with an initial left-to-right shunt, the arteries were orientated side-by-side so that the conus septum was observed in the frontal projection. Again, subsequent cyanosis was related to ventricular hypertrophy producing outflow tract obstruction. These findings are interpreted in the setting of a recent study, indicating that Fallot's tetralogy is produced by rotation of the embryonic conus together with sinistro-anterior deviation of the conus septum.

Tetralogy of fallot: A morphometric and geometric study

Fourteen examples of tetralogy of Fallot were studied by morphometric and geometric methods, and the findings compared with results from 10 normal hearts. The data show that in Fallot's tetralogy the conal septum is deviated anteriorly. The infundibulum, although narrow, is similar to, or of greater length than, that of the normal heart. This finding is not in agreement with recent observations suggesting that the anomaly represents lack of growth of the pulmonary conus. Our results further demonstrate that the aorta is dextroposed in Fallot's tetralogy and that in the majority of cases absorption of the right extremity of the conoventricular flange has led to aortic-tricuspid fibrous continuity. The overall findings indicate that conal rotation has occurred in addition to anterior deviation. The data are interpreted as supporting a hypothesis of “lack of conal inversion” and conal malseptation as the morphogenetic mechanisms in tetralogy of Fallot.

Uncommon Conal Pathology in Complete Dextrotransposition of the Great Arteries with Ventricular Septal Defect

The anatomic and clinical findings are reported in five cases of complete dextrotransposition of the great arteries with an uncommon and varied conal pathology, different from the usual conal architecture of classic complete dextrotransposition of the great arteries. The following points summarize the most important findings: (1) The ventricular septal defect was due to a positional anomaly or a deficiency of the conal septum in all of these cases. (2) The conal free wall distribution was different from that designated as characteristic of classic complete dextrotransposition of the great arteries, ie, in three cases, a persistence of the subpulmonary conal free wall preventing the pulmonary-mitral fibrous continuity. (3) A positional deviation of the conal septum inside the conus resulted in obstructive anomalies of the subpulmonary outflow tract in two cases and of the subaortic in another. (4) There was overriding of the conal septum of the ventricular septum in two cases. (5) In keeping with item 4, the observation of the pulmonary outflow tract of three additional cases of classic complete dextrotransposition of the great arteries with intact ventricular septum suggests a possible origin of the fibromuscular subpulmonary stenosis in these patients: the abnormal fusion line between the ventricular septum and a malorientated conal septum. Some important angiocardiographic characteristics of these cases are also shown. The surgical Implications of these particular anatomic characteristics are discussed.