ADRENERGIC CONTROL OF THE FORCE-FREQUENCY AND RELAXATION-FREQUENCY RELATIONS IN PATIENTS WITH HYPERTROPHIC CARDIOMYOPATHY

Background Exercise-induced enhancement of the force frequency and rel axation-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 relaxati on (tau) during atrial pacing and dynamic exercise in 13 patients with nonobstructive hypertrophic cardiomyopathy (HCM) and 7 control subjec ts to investigate the influence of exercise on the force-frequency and relaxation-frequency relations. Group A consisted of 6 patients in wh om the heart rate (HR)-dP/dt(max) relation was markedly enhanced durin g exercise (88+/-30%) compared with during pacing (34+/-15%). Group B consisted of 7 patients in whom the HR-dP/dt(max) relation showed simi lar enhancement during exercise (28+/-7%) and atrial pacing (28+/-11%) . There was no difference in the HR-tau (derivative method [TD] and pr essure half-time method [T-1/2]) relation between pacing and exercise in groups A and B. Both the mean maximal wall thickness and the hypert rophy 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 pre ssure, or the plasma level of catecholamines at baseline, at 50 W of e xercise, 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-tau relation in the control group was enhanced during exercise (TD, 35+/-9%; T-1/2 34+/-8%) compared with during pacing (TD, 12+/-7%; T-1/2 14+/-7%). Con clusions Exercise-induced enhancement of the relaxation-frequency rela tion 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 pati ents with the enhancement, indicating that the adrenergic control of t he force-frequency relation may, at least in part, depend on the sever ity of LV hypertrophy or the stage of HCM.