Background: Exercise-induced enhancement of the force-frequency and relaxation-frequency relations has been studied in conscious animals but not in intact diseased human hearts. Methods and Results: We evaluated left ventricular (LV) isovolumic contraction (dP/dt(max)) and relaxation (τ) during atrial pacing and dynamic exercise in 13 patients with nonobstructive hypertrophic cardiomyopathy (HCM) and 7 control subjects to investigate the influence of exercise on the force-frequency and relaxation-frequency relations. Group A consisted of 6 patients in whom the heart rate (HR)- dP/d(max) relation was markedly enhanced during exercise (88±30%) compared with during pacing (34±15%). Group B consisted of 7 patients in whom the HR- dP/dt(max) relation showed similar enhancement during exercise (28±7%) and atrial pacing (28±11%). There was no difference in the HR-τ (derivative method [TD] and pressure half-time method [T( 1/4 )) relation between pacing and exercise in groups A and B. Both the mean maximal wall thickness and the hypertrophy score in group B were greater than in group A (27±5 versus 19±2 mm and 7±1 versus 5±1 points, respectively; both P<.01). There was no difference in the LV peak systolic pressure, end-diastolic pressure, or the plasma level of catecholamines at baseline, at 50 W of exercise, and at peak pacing between groups A and B. The HR-dP/dt(max) relation in the control group was markedly enhanced during exercise (80±27%) compared with during pacing (32±14%). The HR-τ relation in the control group was enhanced during exercise (TD, 35±9%; T( 1/4 ), 34±8%) compared with during pacing (TD, 12±7%; T( 1/4 ), 14±7%). Conclusions: Exercise-induced enhancement of the relaxation- frequency relation was inhibited in all HCM patients, regardless of the degree of LV hypertrophy. The patients without exercise-induced enhancement of the force-frequency relation had more severe LV hypertrophy than the patients with the enhancement, indicating that the adrenergic control of the force-frequency relation may, at least in part, depend on the severity of LV hypertrophy or the stage of HCM.
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