Depressed High-energy Phosphate Content in Hypertrophied Ventricles of Animal and Man

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Abstract
It is frequently stated that hypertrophied ventricles tolerate ischemia less well than nonhypertrophied ventricles. The authors' earlier studies in a rat supravalvular aortic stenosis model and canine valvular aortic stenosis model, both with concentric left ventricular hypertrophy, disclosed accelerated rates of ischemic contracture and diminished basal myocardial high energy phosphate stores. These studies have been extended to ten patients with severe left ventricular hypertrophy caused by valvular aortic stenosis and normal coronary arteries. ATP (endocardial and epicardial) from transmural left ventricular biopsies taken at operation before aorta cross-clamping, and frozen immediately in liquid nitrogen, were compared with similar biopsies from patients with nonhypertrophied myocardium supplied by normal coronary arteries. The subendocardial high energy phosphate levels in the nonhypertrophied myocardium was greater than high energy phosphate levels in the subepicardium of nonhypertrophied ventricles (ATP-micromoles/gram-protein, epi = 36.8 +/- 3.3, endo = 37.7 +/- 3.3) (p = NS). However, in the hypertrophied myocardium the subendocardium consistently showed significantly depressed high-energy phosphate levels when compared with subepicardial levels (ATP-hypertrophied myocardium, epi = 31.5 +/- 1.6, endo = 25.9 +/- 1.7) (p less than 0.05). This uniform depression of ATP stores, greatest in the subendocardium, in left ventricular hypertrophy suggests a common biologic mechanism for the enhanced sensitivity to ischemia. Of importance for patients may be the prior observation in rats that repletion of ATP( stores before ischemia eliminates the accelerated rate to ischemic contracture. Diminished subendocardial ATP stores appear to be an intrinsic property of severely hypertrophied myocardium and probably contribute to its enhanced sensitivity to ischemia.