Increased Cardiovascular Response to Epinephrine in Hypertrophic Cardiomyopathy

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To study the role of catecholamines in the pathogenesis of hypertrophic cardiomyopathy (HCM), hemodynamic responses to low and high dose infusions of epinephrine (0.037 and 0.074μg/Kg/min) were compared between 21 patients with nonobstructive HCM and 21 healthy controls, matched for age and sex. During low dose infusion, patients with HCM showed significantly greater responses (p<0.05) than controls in echocardiographic left ventricular (LV) end-systolic dimension (-8±1% vs -4±1%, mean±SEM), fractional shortening (12±2% vs 7±1%) and peak systolic velocity of the LV posterior wall (32±5% vs 15±4%), but the differences disappeared during high dose infusion. Thus, patients with HCM started to respond to epinephrine earlier than controls and seemed to have an increased sensitivity of β-adrenergic receptors in the cardiovascular system. As the augmented responses were more evident in younger patients (<35 years) who manifested frequent familial occurrences of HCM, the increased sensitivity to catecholamine was postulated to be genetically determined and to be related to the abnormal myocardial hypertrophy of HCM.