Fractional gradients along the outflow tract of the right ventricle in tetralogy of Fallot: anatomic and hemodynamic correlative study.

In 16 patients undergoing surgical correction of tetralogy of Fallot, attempts were made to determine where, in the outflow tract, the most critical preoperative obstruction was located. In the open chest, pressures were taken in the right ventricle, proximal conus, distal conus, and pulmonary artery. Pressure gradients between these levels were indicative of stenosis at the infundibular ostium (Ost.), conus (C), and pulmonary valve (PV), respectively. Total delta P = delta P Ost. + delta P C + delta P PV, where delta P is the pressure gradient between the right ventricle and the pulmonary artery. In order to evaluate the contribution of each obstructive segment to the overall obstruction, we introduced a new term, the fractional gradient (FG). The FG is defined by the following formula: FG = (delta P segmental/delta P total). The average total pressure gradient in this series was 7 mm Hg. The average segmental gradients were 15.5, 39.0, and 17.0 mm Hg for the infundibular ostium, conus, and pulmonary valve, respectively. The FGs across segments were 0.20, 0.54, and 0.26, indicating that only 20% of the average obstruction was located in the infundibular ostium. The remaining obstruction is distal and unrelated to the infundibular ostium. Analysis of the FGs in the various types of conus indicated, from an anatomic viewpoint, that in 80% of patients with tetralogy the infundibulectomy does not have to be radical.