The pathogenesis of tetralogy of Fallot.

A pathogenetic mechanism for the formation of tetralogy of Fallot is postulated. We propose that the right ventricular ejection stream is divided into a transseptal aortic stream and an infundibular pulmonary stream during embryonic life before the ventricular septum is closed. The surgically unaltered hearts from 77 cases of tetralogy of Fallot were examined, and measurements made of certain morphologic features. A malformed, stenotic pulmonary valve was found in most all cases and accounts for a divided ejection stream. Infundibular stenosis is shown to be a postnatally acquired, progressive lesion. The detailed anatomic features of the heart and great vessels in tetralogy of Fallot are explained as a response of the developing heart and great vessels to the abnormal blood flow pattern of a divided right ventricular ejection stream. This pathogenetic mechanism, compared to previously proposed hypotheses, appears better able to account for the malformation complex of tetralogy of Fallot.