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 the 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.