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We studied the influence of active coronary vasomotion on transmural myocardial perfusion during tachycardia.Regional myocardial blood flow was estimated in chronically prepared awake dogs by injecting radioactive microspheres (7-10 /xm in diameter) into the left atrium.Studies were performed during ventricular pacing at 100, 150, 200, and 250 beats/min under control conditions with intact coronary vasomotor tone, and during maximal coronary vasodilation induced by intravenous infusion of adenosine.During control conditions, mean myocardial blood flow was 1.27 ± 0.12 ml/min per g of myocardium at a heart rate of 100 beats/min, and increased regularly with increasing heart rates.Transmural myocardial perfusion remained essentially uniform as heart rates were increased from 100 to 250 beats/min.During administration of adenosine, mean myocardial blood flow increased to 5.49 ± 0.39 ml/min per g at a heart rate of 100 beats/min, and transmural myocardial perfusion was uniform.As heart rates were increased, flow to the subendocardium decreased as a linear function of heart rate while subepicardial flow was maintained so that the ratio of subendocardial-subepicardial flow fell from 1.00 at a heart rate of 100 beats/min to 0.40 at a heart rate of 250 beats/min.The reduction of subendocardial perfusion with increasing heart rate was most marked in the deepest myocardial layers.This rate-dependent decrease in subendocardial blood flow resulted in a decrease in mean myocardial blood flow with increasing heart rates (mean change at 250 beats/min = -18%; P < 0.05).These data indicate that active coronary vasomotion is necessary for maintenance of uniform transmural myocardial perfusion during tachycardia.
Bache et al. (Tue,) studied this question.