ESTIMATION OF SUBENDOCARDIAL ISCHEMIA IN VALVAR AORTIC STENOSIS IN CHILDREN

Abstract

An index of myocardial oxygen supply/demand was calculated from the left ventricular and aortic pressure tracings in 80 infants and children with isolated valvar aortic stenosis. Supply was estimated by multiplying the area between aortic and left ventricular pressures during diastole (DPTI) by arterial oxygen content (C). Demand was estimated from the area under the left ventricular tracing during systole (SPTI). The oxygen supply/demand ratio was expressed as: DPTI X C/SPTI. A ratio <10 has been shown experimentally in animals to be associated with reduced subendocardial flow. With severe stenosis, i.e., aortic valve area (AVA) <10. Patients with AVA <100/minute maintain adequate ratios whereas patients with heart rates >100/minute and severe stenosis all have ratios consistent with subendocardial ischemia. Supply/demand ratios <10 are usually associated with significant T wave abnormalities on the ECG while patients with normal T waves generally have ratios >10. It is concluded that in severe valvar aortic stenosis heart rate is a critical factor in the development of a reduction in the oxygen supply/demand ratio consistent with subendocardial ischemia. Exercise induced tachycardia may be useful in identifying patients with severe valvar aortic stenosis and borderline ischemia who have normal T waves at rest.