What is the relationship between heart rate, aortic valve area, and subendocardial ischemia (estimated by oxygen supply/demand ratio) in children with valvar aortic stenosis?
In children with severe valvar aortic stenosis, tachycardia significantly reduces the myocardial oxygen supply/demand ratio, suggesting exercise-induced tachycardia could help identify borderline ischemia.
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 100/minute and severe stenosis all have ratios consistent with subendocardial ischemia. Supply/demand 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.
Lewis et al. (1974) studied this question.