Objectives. We investigated the effect of adrenergic stimulation on left ventricular relaxation in patients with hypertrophic cardiomyopathy. Background. Exercise-induced decreases in acceleration of left ventricular relaxation have been observed in patients with hypertrophic cardiomyopathy. However, data on sequential changes in left ventricular relaxation during exercise are limited. Methods. We measured right (fluid filled) and left (high fidelity micromanometer) ventricular pressures during moderate supine ergometer exercise and during rapid right atrial pacing in four groups of patients: 9 with severe hypertrophic cardiomyopathy, 9 with moderate hypertrophic cardiomyopathy, 10 with hypertension and moderate hypertrophy and 5 control subjects. Results. There was a curvilinear relation between the time constant of relaxation (tau) and heart rate in all groups during exercise. There was no difference in the slope of this relation between the two hypertrophic cardiomyopathy subgroups. Although the slope of this relation between tau and heart rate was steeper in the hypertensive than the moderate hypertrophic cardiomyopathy group (p < 0.001, analysis of covariance), the decrease in tau during right atrial pacing was similar in both groups. There were no significant differences in plasma levels of catecholamines at rest or at peak exercise among groups or in maximal heart rate during pacing. Conclusions. Pacing-induced changes in tau in hypertrophic cardiomyopathy were similar to those in hypertensive hypertrophy, but remarkable decreases in exercise-induced acceleration of tau were observed only in hypertrophic cardiomyopathy. Our results may indicate a depressed left ventricular relaxation response to exercise-induced adrenergic stimulation in hypertrophic cardiomyopathy.
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