An analysis of 35 cases of the complete form of persistent common atrioventricular canal.

SUMMARY Thirty-five hearts with the complete form of persistent common atrioventricular canal were classified according to the morphology of the common anterior leaflet. The ratio of specimens with a free-floating undivided common anterior leaflet (Type I) to those with a divided common anterior leaflet attached to the septum (Type II) was 1:2. Type I cases had a high incidence of other cardiac (90 percent) and noncardiac (80 percent) malformations. These were primarily conotruncal anomalies (80 percent), left ventricular outflow obstructions (66 percent), aortic arch hypoplasia (30 percent), and abnormalities of organ position or symmetry including the polysplenia and asplenia syndromes. In contrast, Type II canals exhibited a high incidence of Down's syndrome (40 percent), other cardiac and noncardiac anomalies being less common. The associated anomalies suggest that Type I lesions reflect an earlier interference during embryo-genesis than Type II lesions. A clockwise QRS loop and a normal or right axis on the electrocardiogram in four cases were associated with a left ventricular inflow tract of normal length, suggesting that conduction system displacement and a deficient base of the heart may be interrelated. Postmortem double contrast radiography confirmed the angiographic differences between Type I and II lesions, and in Type I lesions clarified the alterations in the angiographic profile occurring with variations in the fullness of the common anterior leaflet.