Ventricular septal defect in interruption of aortic arch

Ventricular Septal Defect in Interruption of Aortic Arch

ROBERT M. FREEDOM, MD, FRCP (C), FACC

HUGH H. BAIN, MB, ChB, MRCP (UK) ENRIQUE ESPLUGAS, MD RENATE DISCHE, PhD, MD RICHARD D. ROWE, MB, FRCP (Edin)

Toronto, Ontario, Canada

A necropsy 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. Co- noventricular malalignment resulted in a typical subpulmonary ventricular defect. The malalignment 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 the conal septum without malalignment. In 4 of the 21 patients with a ventricular septal defect involving the conal septum, the defect was immediately adjacent to the pulmonary valve. 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.

From the Departments of Paediatric Cardiology and Pathology, The Hospital for Sick Children, and the Department of Paediatrics and Pathology, The University of Toronto, Toronto, Ontario, Canada. Manuscript received July 9, 1976, revised manuscript received September 30, 1976, accepted October 6, 1976.

Address for reprints: Robert M. Freedom, MD, The Hospital for Sick Children, 555 University Ave., Toronto, Ontario, Canada M5G 1X8.

Interruption of the aortic arch is a rare cardiac anomaly, constituting probably less than 1 percent of all congenital heart disease. 1 In this condition, the ascending and descending portions of the aorta are not continuous, and blood flow to the descending aorta occurs through a patent ductus arteriosus. Interruption of the aortic arch rarely occurs in isolation, 2 and almost any cardiovascular malformation can coexist. 1 A ventricular septal defect is usually present. In 1971, Van Praagh et al.1 presented the anatomic findings in 10 autopsy cases of interrupted aortic arch, and suggested that a leftward shift of the crista supraventricularis, resulting in a large subpulmonary ventricular septal defect and muscular subaortic stenosis, was highly characteristic of this disorder. Before their report, little emphasis had been placed on the conal morphology in the patient with interruption of the aortic arch. 2,4

If untreated, interruption of the aortic arch is usually lethal in the neonate; the reported mean age of death is only 10 days. ~ In the past few years, reconstitution of the aortic arch has been accomplished success-

572 April 1977 The American Journal of CARDIOLOGY Volume 39

INTERRUPTION OF AORTIC ARCH--FREEDOM ET AL.

fully in the neonate, s-ll Because of the recent emphasis on pr imary surgical correct ion (when possible) of symptomat ic congenital hear t defects, in this paper we characterize more fully the spec t rum of ventr icular septal defect in respect to conal ana tomy in 34 pat ients with interrupt ion of the aortic arch, the largest number of such pat ients s tudied from any single inst i tut ion.

Definitions

Aortic arch interruptions: These are classified according to the method of Celoria and Patton 12 (types A, B and C), but we add subcategories to A and B:

Type A interruption: interruption distal to the left subclavian artery.

Type A1 interruption: interruption just distal to the left subclavian artery with an aberrant right subclavian artery.

Type B interruption: interruption distal to the left common carotid artery.

Type B1 interruption: interruption distal to the left common carotid artery with an aberrant right subclavian artery.

Type C interruption: interruption distal to the innominate artery.

Conal structures: Because there are considerable differ- ences regarding the terminology of conal structures,~,~:~- ~ we will be using the definition of terms as suggested by Anderson and Becker and their associates. 16,17

1. Conal septum: This represents the embryonic septum between the aortic and pulmonary conuses. It can be considered to possess two components: (a) that portion between the aortic and pulmonary valves, forming part of the ventricular septum; (b) the segment extending from this septal compo- nent to the parietal wall of the right ventricle and forming an integral part of the crista supraventricularis. Septal defects in the conal septum are termed conal or infundibular.

2. Crista supraventricularis: Becker et al. 17 use this term to describe a structure in the normal heart. As such, it is considered to be that muscle mass that separates the pulmonary valve from the tricuspid valve.

3. Trabecula septomarginalis: This describes the septal trabecula that extends from beneath the pulmonary valve toward the ventricular apex and continues as the moderator band. The trabecula septomarginalis has anterior and posterior limbs at its superior extent. The septal part of the conal septum is inserted between these limbs in the normal heart.

Case Material

The computer files of the Cardiac Records Division of The Hospital for Sick Children, Toronto, were reviewed for the

T A B L E I

Type and Incidence of Aortic Arch Interruption*

T y p e Number % o f To ta l

A 12 35 .3 } 38.2 A~ 1 2.9 B 18 5 2 . 9 } 61.7 B~ 3 8.8 C 0 0

To ta l 34 100

* Proved at necropsy at The Hospi ta l f o r Sick Chi ldren• This s tudy excludes pat ients w i t h arch atresia ( that is, those w i t h a f ib rous strand connecting the ascending and descending aor ta) .

diagnosis of interruption of the aortic arch. In 50 recorded cases, with this diagnosis, 34 necropsy specimens from our cardiac registry were available for study. Of the 34 patients, 22 were male and 12 female; their median age of death was 8 days (range less than 1 day to 10 years).

Results

Types of aortic arch interruption (Table I): In 21 of 34 pat ients (61.8 percent) , the aorta had type B interrupt ion, with an aber ran t right subclavian ar tery in 3. Thi r teen patients had aortic arch interruption distal to the left subclavian ar tery (type A, 38.2 percent), with only one pat ient having an aberrant r ight subclavian artery. Ty p e C in ter rupt ion (distal to the innominate artery) was not found.

All pat ients had visceroatrial situs solitus and a D- ventr icular loop. The great arteries were normally related in 33 of the 34 patients. One pat ient had D- t ransposi t ion of the great arteries, ventr icular septal defect and type B in ter rupt ion of the aortic arch. Two of the 34 pat ients (5.9 percent) each with a type B interrupt ion, had type I t runcus arteriosus. Of the 31 remaining patients, 12 had type A interruption, including one with an aberrant right subclavian artery, and 19 had type B interruption, including 3 with an aberrant right subclavian artery.

Ventricular septal defect (Table II): All but two pat ients (93.8 percent) had a defect of the ventr icular septum; the remaining two had a large aort icopulmonary fenestrat ion (Fig. 1). The ventr icular defect involved the conal septum in 21 patients, and in 7 of these, the membranous septum was also involved. In 14 patients, the conal defect resulted from malal ignment (and, hence, lack of fusion) between the c.onal septum and anter ior and posterior limbs of the t rabecula septomarginalis (Fig. 2 to 4). This malal ignment of the conal septum was characterist ical ly in a leftward direction, allowing actual or potential narrowing of the left ventr icular outflow tract, above the level of the yentricular septal defect (Fig. 2B). Fur thermore , the malalignment of the conal septum usually resulted in a large subpulmonary ventricular septal defect (from the right ventr icular aspect) and subaortic defect (from the left ventr icular aspect) (Fig. 2 to 4). Although the majori ty of conal defects resulted from conoventr icular mal-

T A B L E II

Correlation of Ventricular Septal Defect With Type of Aortic Arch Interruption

Type o f In te r rup t ion

Posit ion o f VSD Tota l A A~ B B~ C

Conal 14 4 8 2 Conal and membranous 7 1 " i " 4 1 Membranous 5 1 . . . 4 . . Cushion type or A-V 3 2 . . . 1 . .

canal Muscular 3 3 . . . . . . . Intact vent r icu la r septum 2 . . . . . . 2 . .

. ° .

A-V = a t r ioven t r i cu la r ; VSD = vent r icu lar septal defect .

April 1977 The American Journal of CARDIOLOGY Volume 39 573


P

FIGURE 1 (left). Right ventricle in a patient with a large aorticopulmonary fenestration (AP). The pulmonary artery (PA) originates normally above the right ventricular infundibulum. The conal septum (cs) and trabecula septomarginalis (ts) are shown. The raphe (lower arrows) at the junction of the conal septum with the anterior and posterior limbs of the trabecula septomarginalis is evident. The patients whose hearts are shown in Figures 1 to 11 all had interruption of the aortic arch.

FIGURE 2 (below). Right and left ventricles in a patient with conoventricular malalignment. A, right ventricle (RV). The pulmonary artery (PA) originates above the morphologic right ventricle, and there is pulmonary valve--tricuspid valve (tv) discontinuity. The conal septum (cs) is deviated leftward, leaving a substantial ventricular septal defect (arrow) in the "arms" of the trabecula septomarginalis (ts). B, left ventricle (LV). The leftward deviated conal septum is seen protruding through the ventricular septal defect, resulting in muscular subaortic stenosis. The aortic valve (AoV) is thickened and mildly stenotic as well.

-1



FIGURE 3 (right). Right ventricle in a patient with ventricular septal defect and muscular subaortic stenosis resulting from conoventricular malalignment. The conal septum is malal- igned (curved arrow), resulting in a large ventricular septal defect (straight arrow) between the "arms" of the trabecula septomarginalis (ts).

FIGURE 4 ( lower left). Right ventricle in a patient with membranous ventricular septal defect (arrow) and perhaps mild malalignment of conal septum (cs) and trabecular septum. PA = pulmonary artery.

FIGURE 5 ( lower right). Right ventricular view in a patient with a large supracristal ventricular septal defect (arrows). The aortic valve (AoV) obviously lacks support, the conal septum (cs) and trabecula septomarginalis (ts) are clearly seen, and there is no evidence of conoventricular malalignment. PA = pulmonary artery; RVW = right ventricular wall; tv = tricuspid valve.



FIGURE 6 (left). Right ventricle in a patient with type I common aorticopulmonary trunk. A slightly larger ventricular septal defect is present (arrow). The distal infundibulum is absent. Note the similarity to "supracristal" ventricular septal defect. TR = truncus arteriosus; ts = trabecula septomarginalis.

FIGURE 7 (lower left). Close-up v iew of right ventricular conal anatomy in a patient with two ventricular defects. The upper curved arrow shows an intraconal ventricular septal defect, and the lower curved arrow points to an infracristal defect, cs = conal septum; PV = pulmonary valve; tv = tricuspid valve.

FIGURE 8 (lower right). Right ventricle in a patient with large ventricular septal defect (ar row) resulting from deficiency of inferior and mid-portion of conal septum (cs), without significant conoventricular malalignment. PA = pulmonary artery; ts = trabecula septomarginalis.

!_



alignment, this was not invariably so. In four patients, the ventricular septal defect could be characterized as "supracristal" (actually intraconal, involving the most cephalad portion of the conal septum), lying immediately adjacent to the left and right pulmonary cusps and separated from the membranous ventricular septum by various amounts of conal septum (Fig. 5). In both patients with interruption of the aortic arch and common aorticopulmonary trunk, the septal defect was indis- tinguishable from that observed in isolated truncus arteriosus (Fig. 6 to 9). The conal ventricular septal defect was not restrictive, and a muscular "subtruncal" stenosis was not seen in these two patients. Thus, in 14 (67 percent) of 21 patients with a ventricular defect involving a conal structure, the defect resulted from conoventricular malalignment; in the two patients with truncus arteriosus, there was virtual absence of the conal septum and parietal conus with absence of the truncal septum; and in four patients (19 percent), the defects were intraconal and immediately adjacent to the pulmonary valve ("supracristal" type). In some patients, the defect involved the inferior or mid-portion of the conal septum, but there was no associated conoventricular malalignment (Fig. 7 and 8).

A typical infracristal membranous ventricular septal defect was present in five patients (14.7 percent) (Fig. 9A and 10). Two patients had an atrioventricular (A-V) communis defect (Fig. 11), and one patient with D- transposition had a ventricular septal defect in the "canal" position. Three patients had a large muscular ventricular communication. Common or single ventricle was not identified in any patient.

Subaor t ic obs t ruc t ion (Table III): The anatomic potential for subaortic obstruction is most evident in patients with a ventricular septal defect resulting from conoventricular malalignment (Table III). In our study, the anatomic potential for subaortic obstruction was based on (1) unequivocal anatomic narrowing of the systemic outflow tract when compared with that of a matched normal subject, or (2) documentation of a pressure gradient of at least 10 mm Hg across the systemic outflow tract. Using these criteria, we probably excluded some patients with mild subaortic obstruction. These patients have a large subpulmonary (conal) ventricular septal defect and a leftward deviated conal septum. Thirteen of 21 patients with a ventricular septal defect of the conoventricular malalignment type had anatomic evidence of subaortic obstruction resulting from the abnormally positioned conal septum. This group included patients whose defect resulted from isolated conoventricular malalignment and those who had associated contiguous membranous defects. Pa- tients with an isolated membranous, muscular cushion type defect may also exhibit subaortic obstruction, usually related to mitral valve abnormality of deposits of accessory endocardial cushion tissue, or both {Fig. 9B).

The aortic valve was tricuspid in 22 patients and was grossly deformed and stenotic in only 1 of these (Table IV). A bicuspid aortic valve was evident in 10 patients, and was stenotic in 3 of these. Both truncal valves were

tricuspid and the free valve margins were mildly thickened. Truncal valve stenosis was not present in either patient. There was clearly the potential for aortic valve prolapse in the patient with high, intraconal ventricular defect.

There was no obvious relation between the position of the ventricular septal defect and the type of aortic interruption (Table III) in our small study group, and the presence or absence of subaortic obstruction did not predispose to any specific type of interruption.

Significant underdevelopment of the left ventricle was found in only one patient who had a very small conal defect, partly occluded by both mitral and tricuspid valve tissue, and severe subaortic obstruction.

Discussion

Distortion of conal anatomy is responsible for a wide spectrum of congenital heart defects, is In our study, we demonstrated that defects of the conal septum are common in patients with interruption of the aortic arch, occurring in 21 of 34 patients. Conoventricular malalignment, as Van Praagh et al.1 observed, is responsible for the presence of a large subpulmonary ventricular septal defect and for the anatomic basis of the subaortic obstruction often evident in these patients. Conal maldevelopment in some of these patients is manifested as absence of the conal septum in its inferior, middle or superior portion. These defects can be considered in- tracristal and are not invariably characterized by conoventricular malalignment. Indeed, the raphe at the line of insertion of the conal septum with the anterior and posterior limbs of the trabecula septomarginalis has been preserved in these patients. In the patient with conoventricular malalignment, this bulbar raphe is not evident, and the ventricular communication lies "in the arms" of the trabecula septomarginalis.

Fac tors de te rmin ing type of ven t r i eu la r septal defect: conoven t r i cu la r development and alignment . There are considerable variations in the ap- pearance of the conal ventricular septal defect, and this is related in part, to its embryogenesis. Goor et al. 14,19 presented a classification of ventricular septal defect based on developmental characteristics of the septum. In their classification, the infundibular ventricular septal defect represents a significant category of defect, and was found in 33 of 112 isolated defects. They suggested that the common denominator anatomically for the infundibular ventricular septal defect is the involvement of the crista supraventricularis from the right ventricular aspect, the anterior margin of such defects is placed anteriorly to the so-called infundibulo-ventricular line. What Goor et al. characterized as infundibular ventricular septal defect encompasses what we and others term conal ventricular septal defect. Ven- tricular defects of the infundibular or conal type have at least four subtypes: (1) ventricular septal defect of the membranous septum cutting into the adjacent inferior aspect of the conal septum; (2) mid-conal ventricular septal defect; (3) "supracristal" ventricular septal defect, lying adjacent to the left and right pul-

Ai)rll 1977 The American Journal of CARDIOLOGY Volume 39 577


FIGURE 9 (above). Right and left ventricles in a patient with a moderately large infracristal membranous ventricular septal defect. A, right ventricle. Arrow points to the septai defect. There is no conoventricular malalignment. B, left ventricle (LV). There is significant narrowing of the left ventricular outflow tract (Ivot) by accessory endocardial cushion tissue (ac) attached to the aortic leaflet of the mitral valve (amv). The aortic valve (AO) is bicuspid. PA = pulmonary artery.

FIGURE 10 (left). Right ventricle in a patient with mild deficiency of the inferior portion of the conal septum (cs) adjacent to the posterior arm of the trabecula septomarginalis (ts). Conoventricular malalignment is not present, and the ventricular septal defect (arrow) involves both the membranous and adjacent oonal septum. PA = pulmonary artery.



FIGURE 11. Left ventricle in a patient with complete common A-V canal. The left ventricular (LV) outflow tract is not appreciably narrowed. The aort ic valve (AO) is tricuspid•

monary cusps; and (4) ventricular septal defect characterized by complete absence of the conal septum. Indeed, the ventricular defects observed in the present study encompass this spectrum of conal defect.

It is difficult to ascertain the incidence of conal versus nonconal ventricular septal defect because relatively little attention has been focused on this finding in the patient with interruption of the aortic arch. Ventricular septal defect was very common in our patients but can be absent. Eight (80 percent) of 10 patients with aortic arch interruption studied by Van Praagh et al. I had muscular subaortic stenosis, a finding that suggests the presence of a conal ventricular septal defect in these patients. Of 32 patients with ventricular septal defect in our study, the conal septum was involved in 21 (66 percent). Immagoulou et al. 2° stated that muscular subaortic stenosis above the ventricular septal defect was present in 6 of their 18 necropsy cases (33 percent). In these three series involving 64 patients, 35 probably had involvement of the conal septum (incidence rate 55 percent).

Ventricular septal defect in tetralogy of Fal lo t versus aortic arch interruption: The ventricular septal defect in tetralogy of Fallot and that in interruption of the aortic arch are caused by conoventricular malalignment. Van Praagh et al. 21 have suggested that

TABLE II I

Correlation of Position of Ventricular Septal Defect and Subaortic Obstruction*

Subaortic Obstruction

Position of VSD Number no, %

Conal 14 9 64.2 Conal and membranous 7 4 57.1 Membranous 5 2 40 "Cushion" type 2 1 50 Muscular 3 1 33 Other . . . . . . . . .

* Excluding the patient w i th D-transposition of the great arteries.

the essence of tetralogy of Fallot resides in subpulmonary conal underdevelopment and in failure of the subpulmonary conus to be carried in a posterior, inferior and rightward direction. This is thought to result in a subpulmonary infundibulum that is too small in all di- rections. Furthermore, the conoventricular malalignment results in a defect posterior to the conus and in the limbs of the trabecula septomarginalis.

Rosenquist et al. 22 suggested that tetralogy of Fallot comprises a spectrum of anomalies in which a variable portion of the conal septum remains in its usual position, forming the inferior and posterior margins of the ventricular septal defect. The remainder of the conal septum is deviated anteriorly, partitioning off a stenotic outflow tract and forming the anterior border of the ventricular septal defect. Becker et al., 17 in their mor- phometric and geometric study of tetralogy of Fallot, concluded that lack of conal inversion and conal mal- septation are the morphogenetic mechanisms responsible for tetralogy of Fallot. Despite various interpre- tations of the embryologic events, disturbances of conal growth, maturation and geometry are obviously implicit to the pathogenesis of Fallot's tetralogy. Similarly, in the patient with interruption of the aortic arch, conal ventricular septal defect and subaortic stenosis, disturbances of conoventricular development and alignment result in these features. Furthermore, the leftward deviation of the conal septum may interfere with ade- quate antegrade flow of blood through the left ventricular outflow tract during the critical embryonic stages

T A B L E I V

M o r p h o l o g i c Features of Aort ic Valve and Type of Interruption of Aort ic A r c h *

Type of Aort ic Arch Interrupt ion

Aort ic Valve A A I B BI C

1. Tricuspid, normal ly formed 9 1 9 2 2. Tricuspid, stenotic 1 . . . . . 3. Bicuspid, not stenotic 1 . . . "6 ' 4. Bicuspid, stenotic 1 . . . 1 " i

• . •

* Excluding the two patients wi th common aort icopulmonary trunk.



in the morphogenesis of the aortic arch and may be responsible for the frequent associations with severe anomalies of the aortic arch. 1,23

Yentricular septal defec t in t r un cus a r t e r iosus versus aor t ic a r ch in te r rupt ion : The ventricular septal defect in common aorticopulmonary trunk (truncus arteriosus) results from conal maldevelopment, and superficially there is a resemblance between the ventricular septal defect in truncus arteriosus and interrupted aortic arch. Van Praagh and Van Praagh 24 suggested that the ventricular septal defect in truncus arteriosus results from virtual absence of the distal pulmonary infundibulum (conus), with the ventricular septal defect lying between the anterior and posterior limbs of the septal band (trabecula septomarginalis). Recently, Rosenquist et al. 25 called attention to a spectrum of conal and truncal septal defects in patients with truncus arteriosus, and mentioned patients with small or diminutive conal septal defects. Angelini and Leachman 26 have described the spectrum of truncoconal septal defects and proposed a classification based on the degree of absence of the truncoconal septum. 26 It is of interest that the two patients with truncus arteriosus and interruption of the aortic arch in our study both had conal defects typical of truncus, not Of aortic arch interruption (Fig. 8 to 10). To our knowledge, truncus arteriosus has not been complicated by a "subtruncal" stenosis, although a restrictive conal ventricular septal defect would result in obstruction to flow from both ventricles into the truncus.

Single or common ventr ic le: This was not an associated cardiovascular malformation in our study, although this association has been sporadically docu- mented. 1 In the compilation by Van Praagh et al. of patients with aortic arch interruption through October 1969, 4 of 184 cases (2 percent) had single ventricle. This association was not observed in the 20 patients described by Immagoulou et al. 2° However, Collins et al. 9 recently reported that 3 of 29 patients (10 percent) with interruption of the aortic arch had single ventricle. 9 In necropsy and angiocardiographic reviews of patients with single or common ventricle culled from six series of patients, 27-32 aortic arch interruption was noted in 2 of 261 patients (although Van Praagh et al.32 recorded 3 patients with aortic arch atresia among 60 patients with single or common ventricle).

Subaor t i c obs t ruc t i on - - su rg i ca l implications: Subaortic obstruction, or at least the anatomic potential for subaortic obstruction, is noted commonly in the patient with interruption of the aortic arch. Van Praagh et al. 2 attributed this anatomic substrate to a characteristic leftward shift of the crista supraventricularis which results in a muscular subaortic stenosis. 1 Sub- aortic obstruction in these patients is not invariably the result of conoventricular malalignment. Accessory endocardial cushion tissue or anomalous mitral attach- ment may also result in subaortic narrowing. 33,34

Recently, Moulaert and Oppenheimer-Dekker 35 described the anterolateral muscle bundle of the left ventricle. This bundle, which is found between the left coronary aortic semilunar cusp and the anterior leaflet of the mitral valve, was reported to be present in ap-

proximately 40 percent of normal hearts. This tissue is thought to be derived embryologically from the left extremity of the bulboatrioventricular flange. These authors comment that when a ventricular septal defect is present it is frequently associated with severe anomalies of the aortic arch, including interruption, atresia, coarctation and tubular hypoplasia. Both conoventricular malalignment and the anterolateral muscle bundle of the left ventricle may result in anatomic subaortic stenosis.

It is difficult to state with any precision the incidence of subaortic stenosis in patients with interruption of the aortic arch. Fifty percent in the present series had anatomic evidence of a potential for left ventricular outflow tract narrowing. Moller and Edwards 36 reported that 8 of 105 patients (8 percent) with interruption of the aortic arch had subaortic stenosis. In a recent clinical and pathologic study of interruption of the aortic arch, 2° muscular subaortic stenosis above the ventricular septal defect was found in 6 of 18 necropsy cases (33 percent). It is our impression that at least 25 to 30 percent of patients, possibly more in symptomatic neonates, might be anticipated to have subaortic obstruction. According to Tyson et al. 6 when there is evidence of ventriculoaortic obstruction, thoughts of arch reconstruction in the neonate should be abandoned, and pulmonary arterial banding should be employed. It is possible, however, that pulmonary arterial banding might aggravate and intensify the subaortic obstruction in at least some of these patients. Freed et al. 37,3s doc- umented the development of subaortic obstruction after pulmonary arterial banding for ventricular septal defect and suggested that a leftward deviated conal septum that hypertrophied in response to the banding might be responsible for this complication. There is not enough experience with the surgical management of patients with arch interruption and subaortic obstruction to provide firm guidelines. It is possible that this subaortic muscular obstruction, in some of these patients, could be surgically approached through the ventricular septal defect.

Hypoplas t ic lef t ventr ic le: Gross underdevelopment of the left ventricle occurred only once in our series. Collins et al., 1° summarizing the experience of the New England regional infant cardiac program, stated that 8 of 29 patients had hypoplasia of the left heart chambers 9. None of the 10 cases personally studied by Van Praagh 1 were characterized as having a grossly underdeveloped left heart, and this was not mentiond in the study of Immagoulou et al. 2° Angiocardiogra- phically, and at necropsy, the morphologic left ventricle appears relatively small when compared with the usually significantly hypertrophied and dilated morphologic right ventricle. It has been our experience based on our large necropsy series, on selective left ventricu- lograms in nearly 50 patients with interruption of the aortic arch, and on diagnostic ultrasonic studies in 10 patients that left ventricular dimensions are usually normal when compared with the normal values of Rowlatt et al. 39

The aortic valve was bicuspid in 10 of our 34 patients, and in 5 of the 10 cases studied by Van Praagh et al)



Clinical Implications and Speculations 1. In the patient with interruption of the aortic arch,

one must be cognizant of the frequency of conal ventricular septal defect and conal-ventricular malalignment, the latter resulting in the anatomic potential for subaortic narrowing. It is therefore desirable to obtain a pressure recording across the left ventricular outflow tract. Selective left ventricular angiocardiograms should demonstrate both the high conal position of the van- tricular septal defect and the subaortic narrowing.

2. In some patients with ventricular septal defect secondary to conoventricular malalignment, although the leftward deviated conal septum may encroach on the left ventricular outflow tract, no pressure gradient can be demonstrated across the aortic valve at cardiac catheterization. Partial correction with reconstitution of the aortic arch and pulmonary arterial banding may set the stage for acquired subaortic obstruction after banding for the ventricular septal defect. 38,39 In these patients, it was suggested that an abnormally deviated conal septum becomes hypertrophied in response to the pulmonary arterial band, thus narrowing the left ventricular outflow tract. These observations indicate that aggressive at tempt at total repair using the technique of profound hypothermia may help to avoid certain difficulties.

3. Gross underdevelopment of the left ventricle occurred only once and was associated with a restrictive ventricular septal defect.

4. Although aortic valve abnormalities were not uncommon, severe aortic valve stenosis was unusual. Recognition of aortic valve stenosis in the patient with interruption of the aortic arch requires pressure re- cordings across the aortic valve and retrograde aortog- raphy.

5. The patient with muscular and "cushion" ventricular septal defects may have left ventricular outflow tract obstruction. The patient with A-V communis and interruption of the aortic arch undoubtably has a se- verely distorted mitral valve (or common A-V valve), and both the valve leaflet and accessory endocardial cushion tissue conjointly narrow the left ventricular outflow tract. This combination of defects may prove inoperable. Mechanisms for subaortic obstruction in the patient with muscular ventricular septal defect include muscular, fibrous and cushion tissue deposits.

6. Interruption of the aortic arch is distinctly rare in the patient with situs inversus totalis, L-ventricular loop, the heterotaxy syndrome or the syndrome of jux- taposition of the atrial appendages.

7. When interruption of the aortic arch occurs in double outlet right ventricle with L-transposition of the great arteries, there must be gross underexpansion of the subaortic conus.

8. Aorticopulmonary fenestration occurs rarely with interruption of the aortic arch. 1,2°,4° The ventricular septum is usually intact, but the aorticopulmonary septum is virtually absent.

9. The patient who survives surgical reconstitution of the aortic arch and palliative pulmonary arterial banding (leaving the ventricular septal defect open) is at risk for the development of aortic regurgitation. An important pathogenetic mechanism for aortic valve prolapse and subsequent regurgitation is lack of anatomic support for the aortic valve structure. 41-44 Ob- viously, the patient with a conal ventricular septal defect, especially with an immediate subpulmonary ventricular septal defect, lacks sufficient support for the right coronary sinus and anulus and is predisposed to aortic regurgitation. Although aortic regurgitation secondary to a prolapse mechanism is uncommon in the first year of life, it is conceivable that the timing and severity of aortic runoff will be aggravated by restenosis at the site of arch reconstruction. 45,48 One might therefore conclude that total primary repair of the arch and ventricular septal defect would present these complications.

10. Interruption of the aortic arch rarely occurs as an isolated anomaly, and almost any cardiovascular malformation can be coexistent. As Van Praagh et al. 1 stated, interruption of the aortic arch is indicative of a significant intracardiac anomaly. Moulaert et al. 47 recently presented evidence in a small group of patients that certain ventricular defects may influence prenatal patterns of intracardiac flow, potentially resulting in reduced aortic flow and predisposing to anomalies of the aortic arch. Although our study expands the observations of both Van Praagh and Moulaert and their col- leagues, it defines a considerably wider anatomic spectrum of ventricular septal defect than that pre- viously reported. Indeed, our observations suggest that at least in some patients (particularly those with an isolated membranous or muscular ventricular defect, typical truncal ventricular defect or intact ventricular septum), there is no obvious intracardiac anomaly that predisposes to a reduced aortic flow.

Acknowledgment We acknowledge the photographic assistance of Mr. Mi-

chael Starr, and the secretarial assistance of Miss Kathy Forde.

References 1. Van Praagh R, Bernard WF, Rosenthal A, et ah Interrupted aortic

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Ventricular septal defect in interruption of aortic arch

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