The electrocardiogram, vectorcardiogram, and ventricular gradient in the tetralogy of Fallot.

THERE HAS BEEN inereasinog interest in the physiologic rather than the anatomic disturbances in tetralogy of Fallot." 2 Accordingly, the degree of pulmonary stenosis and the size of the ventricular septal defect are the factors of physiologic importance in this congenital anomaly. The dextroposition of the aorta is functional due to the high ventricular septal defect, and the right ventricular hypertrophy is secondary to the pulmonary stenosis. Thus, tetralogy of Fallot embraces a spectrum of hemodynamic possibilities depending upon the relative degree of pulmonary stenosis and the size of the interventricular septal defect. At one extreme is the patient with complete pulmonary atresia and a large interventricular septal defect (pseudotruneus arteriosus) and, at the other, minimal pulmonary stenosis with a small interventrieular septal defect. Between the extremes many physiologic possibilities exist, depending upon the relative severity of the two defects. There are, however, three distinct hemodynamic possibilities: (1) right-toleft intracardiac shunt at rest, (2) no right-to-left intracardiac shunt at rest but a right-to-left shunt upon exercise, and (3) a left-to-right intracardiac shunt but no rightto-left shunt either at rest or with exercise. In the first two instances a small left-to-right shunt may exist which is usually less than systemic blood flow. A fourth, exceedingly rare possibility exists which includes patients with pulmonary stenosis and interventricular septal defect but no intracardiac shunt either right-to-left or left-to-right at rest or upon exercise. Such a classification obviates such terms as acyanotic tetralogy of Fallot or "balanced tetralogy." The present study was undertaken to determine if the electrocardio-