Hearts with biventricular connections and deficient atrioventricular septation are readily recognizable from their characteristic morphology.1 As yet, however, there is still no consensus on precisely what to call them,2 how to categorize them, and, perhaps most importantly, how to approach their surgical repair.

Recent studies on the development of the heart6 have increased markedly our appreciation of the disposition of the specialized conduction tissues, showing how some rests of tissues in unexpected locations are remnants of a well organized system found throughout avian and mammalian species. These studies also help us to account more logically for the distribution of the conduction tissues in congenitally malformed hearts. On the basis of our overall studies, therefore, combined with these recent advances, we are able to understand the normal and abnormal disposition of the conduction tissues. These understandings then permit us to offer explanations for those arrhythmias which have a “natural” basis, such as the grossly abnormal patterns found in hearts with isomerism of the atrial appendages or univentricular atrioventricular connection, and the accessory pathways found in the setting of ventricular preexcitation. We are also able to understand the changes affecting these tissues as part of acquired disease, such as the fibrosis of the long atrioventricular bundles found in atrioventricular septal defect and corrected transposition and the immunologic damage underscoring congenitally complete heart block in infants of mothers with collagen disease. We are only beginning to explore the possibility that abnormalities of the myocardiutn itself, or the fibrous tissue matrix, can also underscore the existence of abnormal rhythms. With all this knowledge, it is to be hoped that, in the future, we will see far fewer of those arrhythmias which have an “unnatural” basis, such as those related to direct surgical damage to the conduction tissues and their arterial supply, or those produced by abnormal loading conditions which are themselves the consequence of congenital malformations. Although we have learned, and applied, a great deal, there is still much to be done before we unravel all the secrets of the causes of arrhythmias in childhood.

A historical review highlights an interest in the etiology of birth defects over the course of several centuries and recalls specific hypotheses on the origin of cardiovascular defects postulated 60 years ago. The “State of the Art” of the epidemiology of cardiovascular malformations is characterized by an expanding base of knowledge which holds promise for eventual preventive interventions. Epidemiologic investigations conducted in the past decade have led to an increased understanding of the benefits and problems of studies of populations and of methodologic issues in surveillance of disease and study of risk factors. Comparative evaluations of reported studies to an ongoing population-based case-control investigation (the Baltimore-Washington Infant Study) demonstrate variations in prevalence by time and place, evidence for a strong genetic predisposition to cardiac maldevelopment and new hypotheses regarding environmental risks in the home and place of occupation.

Prevalence of atrioventricular septal defect in liveborn infants at birth was calculated in Bohemia (population of 6.3 million). Of 664,208 liveborn infants, 4,409 had a congenital malformation of the heart and in 126 of them (0.19/1,000 live births, 2.9% of all heart defects) this was found to be an atrioventricular septal defect. The ratio between those with a common valvar orifice (complete form) versus those with separate right and left atrioventricular valvar orifices (incomplete form) was 1.14:1. The ratio of girls to boys was 1.17:1. Children born in March, July and October were more likely to have the defect (0.26/1,000 live births) than those born in May (0.10/ 1,000 live births). The defect was the eighth most frequent critical congenital cardiac malformation. Eight in each 100,000 liveborn children, and 3.56% of all patients with congenital cardiac disease, are at high risk of dying due to deficient atrioventricular septation, which in 82.5% resulted in the presence of a common atrioventricular valve (complete form). Unconditional death rate was studied in 1,008 liveborn children who died with a cardiac malformation before the age of 15 before the advent of cardiac surgery. Of these, 64 (6.35%) died with an atrioventricular septal defect which was complete in 5.95% and incomplete in 0.40%. All but one of 60 children with the complete form (common atrioventricular valve) died in the first year of life. The last child died between the age of 2 and 5 years. The estimate for natural survival was calculated using our own data on the prevalence and age distribution of mortality. Of all the liveborn children with atrioventricular septal defect, 91% are expected to survive the first month, 81% (78−85) the first trimester, 63% (56−69) six months, and 49% (35−54) the first year. The survival curve remains stable thereafter.

Sudden death occurs in patients after repair of congenital heart disease. In those with tetralogy of Fallot, or a similar lesion, ventricular tachycardia has been hypothesized as the major arrhythmic mechanism for sudden death. It would be desirable to identify individuals at risk for sudden death, to determine which arrhythmia would be likely to cause sudden death, and to treat those individuals with an appropriate antiarrhythmic to prevent sudden death. For the last 10 years, physicians have been treating patients with antiarrhythmic drugs, based on a number of criteria, the most common of which is the presence of premature ventricular contractions.1,2 The practice has recently been called into question by the CAST trial. It is the purpose of this paper to review the evidence that repair causes ventricular arrhythmias, that ventricular arrhythmias cause sudden death, and that ventricular arrhythmias should be treated prophylactically.

Atresia of the outflow tract of the right ventricle in the presence of an intact ventricular septum poses major problems for surgical management. In the light of known problems, 43 autopsied hearts with this congenital abnormality were evaluated to note the arrangement of the myocardium and the cavity of the right ventricle, the state of the tricuspid valve, the precise substrate for pulmonary atresia, and the presence offistulous communications between the ventricular cavity and the coronary arteries. The specimens could be divided into two groups. The first group (38 hearts) had hypoplasia of the cavity of the right ventricle with mural hypertrophy while the second group (5 hearts) had a dilated right ventricular cavity with thinning of the wall. The larger group could be divided into two subgroups on the basis of the substrate for pulmonary atresia. Twenty hearts had muscular atresia of the right ventricular outflow tract and 18 had a potentially patent outflow tract blocked by an imperforate pulmonary valve. A comparison of these two subgroups revealed that mural hypertrophy and cavitary hypoplasia were more severe in hearts with muscular atresia. The tricuspid valve was hypoplastic and its leaflets were not dysplastic in this group but the leaflets were dysplastic in hearts with valvar pulmonary atresia. Fistulous communications between the ventricular cavity and the coronary arteries were only seen in the cases with muscular atresia. In this series, recognition of muscular pulmonary atresia would have identified those patients with the worst surgical prognosis.

In this review, we discuss and describe those features which distinguish hearts with abnormal atrioventricular septation from the normal heart. The hearts, best described as atrioventricular septal defects, are unified by having a common atrioventricular junction guarded by a valve having five leaflets. The left component has three leaflets and cannot be interpreted in terms of a cleft in a normal mitral valve. The papillary muscles supporting this valve are also markedly dissimilar from the arrangement seen in normal hearts. The subaortic outflow tract is displaced superiorly compared to the normal heart, and is no longer wedged between the left valve and the septum. There is marked discrepancy in the inlet and outlet lengths of the ventricular mass, these dimensions being equal in hearts with normal atrioventricular septation. Although having the above features in common, atrioventricular septal defects show anatomic variations related to the arrangement of the bridging leaflets and their relationship to the septal structures. There may be a common valvar orifice or separate right and left orifices. The anatomic potential for shunting may be at atrial or ventricular levels, or both. Rarely, the septal structures may be intact. Other important features include ventricular dominance, the left ventricular outflow tract, and the disposition of the atrioventricular conduction tissues.

Although uncertainty exists, in some situations, as to the optimal type of operation and a true cure may not always be possible, the outlook for patients with all types of complete transposition is poor without surgical treatment. With surgery, and in spite of current uncertainties as to the optimal type of repair, most patients can be greatly benefited, and many given a long and happy life. Even more should be possible in the future.

Defects of the atrioventricular septum impose changes in the septal architecture, atrioventricular valves, and conduction system that must be well understood for optimal repair. The atrioventricular node and bundles are shifted to more posterior and inferior positions that can be anticipated by the surgeon so as to maintain the integrity of atrioventricular conduction. The atrioventricular valve is a five leaflet structure that possesses a common orifice or separate orifices depending on characteristics of the superior and inferior bridging leaflets. These features are demonstrated by intraoperative photographs viewed from the surgeon's position.

We used pulsed Doppler echocardiography to study the right ventricular diastolic function of29 normal babies and 12 neonates with pulmonary atresia and intact ventricular septum. Eleven patients underwent staged operations of closed pulmonaryvalvotomy followed by either rightventricular outflow reconstruction (n=5) or balloon angioplasty of the pulmonary valve (n=3). In normal babies, the Doppler wave form showed dominant early (E) and separate late active (A) waves of activity, when the heart rate was slow (<100/min). The two waves gradually merged with increasing heart rate, to form a monophasic active wave. Prior to any intervention, all except one of our patients had only a monophasic active right ventricular filling wave over the entire range of heart rates recorded. To quantitate these differences in ventricular filling, we derived 4 diastolic indices from the ratio of: the peak velocity of the early versus the late active wave (EIA); the integral with time of these waves (E/Aarea); the time of diastolic filling relative to the cardiac cycle (TIRR); and the peak diastolic filling velocity relative to the mean filling velocity over the cardiac cycle (Velocity Index). Profiles of the indices against heart rate for both normal controls and patients indicated that only the index of the time of diastolic filling (T/RR) and the Velocity Index were appropriate for our serial comparisons. Thus, for neonates with pulmonary atresia, the index of the time (TIRR) was significantly lower (0.29±0.03 vs 0.43±0.04, p<0.01) and the Velocity Index higher (5.98±0.79 vs 3.98 ±0.31, p<0.001) than those of normal. After valvotomy, but with a poor surgical result, babies continued to have a predominantly monophasic right ventricular filling pattern without significant improvement (p>0.05) of the index of time (T/RR=0.29±0.05) or velocity (5.88±1.17). Babies who underwent a second stage procedure and achieved a final good result had predominantly biphasic right ventricular diastolic filling waves with significant progression (p<0.001) in the index of time (T/RR=0.42±0.03) and velocity (4.09±0.49).