Variations within the fibrous skeleton and ventricular outflow tracts in tetralogy of Fallot.

We studied 20 hearts with tetralogy of Fallot with particular reference to the morphology of the fibrous continuity between the aortic and atrioventricular valves and of the ventricular outflow tracts. The extent of valvar fibrous continuity varied with the degree of aortic override, with the extent of the perimembranous ventricular septal defect opening between the ventricular inlets, and with the development of the ventriculoinfundibular fold. This, when fused with the septomarginal trabeculation, produced discontinuity between the leaflets of the tricuspid valve and the continuous leaflets of the aortic and mitral valves, as well as a muscular posteroinferior rim to the defect. Rotation of the aortic root ranged through 119 degrees. Aortic override varied from 33% to 94%, with 35% of these hearts having more than half of the aortic circumference connected to the right ventricle. The pulmonary valves had three leaflets in 50%, two leaflets in 45%, and four leaflets in one (5%). All hearts had two main coronary arterial orifices, 45% of which were atypical in location. One heart displayed a transmural course of the left coronary artery arising from the nonfacing sinus. By measurement, the subpulmonary length was, on average, roughly 50% greater than the subaortic length, and, when the selected hearts were sectioned, much of the subpulmonary infundibulum was found to be composed of free-standing musculature rather than true outlet septum. The proportion of total right ventricular length represented by the infundibulum was 0.31 +/- 0.07, confirming that, compared with that of normal hearts, the narrowed infundibulum in tetralogy is longer rather than shorter.