Different β-adrenergic regulation of myocardial contraction and relaxation between apical and nonobstructive hypertrophic cardiomyopathy

Background: The impaired adrenergic control of both inotropic and lusitropic reserves has been evaluated in patients with hypertrophic cardiomyopathy (HCM) but not in those with apical HCM (APH). Objectives We examined the influence of increases in heart rate and adrenergic stimulation on inotropic and lusitropic reserves in HCM and APH with normal resting left ventricular (LV) systolic function. Methods: We evaluated LV isovolumic contraction and relaxation during atrial pacing and during supine leg exercise in 7 patients with APH and in 8 patients with HCM. Results: Heart rate was significantly correlated with LV isovolumic contraction and relaxation during pacing and exercise in all patients. In all patients with APH, the increase in LV isovolumic contraction was greater during exercise (101%) than pacing alone (27%) for similar increase in heart rate. In 5 patients with HCM, the increase in LV isovolumic contraction was greater during exercise (83%) than pacing alone (24%), whereas in 3 patients with HCM the increase in LV isovolumic contraction was similar between during exercise (25%) and during pacing alone (22%). In all patients with APH, relaxation was shorter during exercise (39%) than pacing alone (16%). Conversely, in patients with HCM relaxation was similarly shortened between during pacing alone (20%) and during exercise (19%). Conclusions: The force-frequency and the relaxation-frequency relations were well-preserved in all patients. In patients with HCM, the adrenergic enhancement of force-frequency relation and/or relaxation-frequency relation was impaired. In patients with APH, however, adrenergic control of both force-frequency and relaxation-frequency relations was well-preserved, which may indicate a preserved β-adrenergic signaling pathway.