ESTIMATION OF SUBENDOCARDIAL ISCHEMIA IN VALVAR AORTIC STENOSIS IN CHILDREN

Abstract

Eighty-four cardiac catheterizations were reviewed in infants and children with isolated valvar aortic stenosis to evaluate the presence of subendocardial ischemia. An index of myocardial oxygen supply/demand was calculated from the left ventricular(LV) and aortic (Ao) pressure pulses. Supply was estimated by multiplying the area between Ao and LV pressures during diastole, i.e. Diastolic Pressure Time Index(DPTI), by arterial oxygen content(C). Demand was estimated by the systolic pressure time index(SPTI) from the area under the LV tracing during systole. 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 a reduction in the LV subendocardial/subepicardial flow ratio. With severe stenosis (AVA<7cm2/m2) an increasing number of patients develop supply/demand ratios<10. Patients with AVA<.7cm2/m2 but heart rates (HR)<100/min maintain adequate ratios>10, whereas patients with severe stenosis and HR>100/min all have ratios<10 consistent with subendocardial ischemia. It is concluded that HR is a critical factor in the production of a reduced myocardial oxygen supply/demand ratio in patients with severe valvar aortic stenosis. This ratio is easily calculated from data obtained at cardiac catheterization and appears to be useful in identifying possible subendocardial ischemia in patients with aortic stenosis.