Inotropic responsiveness of the heart in catecholamine cardiomyopathy

Abstract

Inotropic responsiveness to norepinephrine (NE) or Ca 2+ was studied in 15 rabbits with catecholamine cardiomyopathy (CM) and the results were compared with 11 controls. The former group was prepared by infusing NE (2 μg/min/kg) for 90 minutes, 2 to 3 days prior to study, and injury was confirmed and quantified histologically. Comparison of NE dose-response curves relating percent increase of left ventricular (LV) dP dt max to NE dose in six controls and 10 CM hearts revealed significant depression of CM contractility. Responses to graded infusions of Ca 2+ were also determined in five controls and in five CM animals. With the increases in serum Ca 2+ identical in the two groups, the percent increases in dP dt max were less in CM hearts. Further, NE dose-response curves obtained during continuous CaCl 2 infusion were sharply attenuated in CM hearts and initial LV end-diastolic pressure (LVEDP) in the CM hearts was considerably higher than in the controls. It is concluded that inotropic sensitivity to NE is reduced in CM hearts. This cannot be ascribed to altered β-receptors alone, because responsiveness to Ca 2+ was also reduced. Myocardial damage was indicated by histology and elevated LVEDP. Moreover, the normalized percent data suggest that the remaining viable fibers in the CM hearts were functioning subnormally and thus reduced performance was not due solely to the decreased number of contracting units.