Effects of nicardipine and urapidil on length-dependent regulation of myocardial function in coronary artery surgery patients

Objective: To assess effects of a decrease in left ventricular (LV) afterlo ad (pharmacologically induced by nicardipine and urapidil) on myocardial co ntraction and relaxation, with emphasis on the effects on load dependence o f myocardial function. Design: Prospective, blinded study. Setting: University hospital. Participants: Coronary artery surgery patients. Interventions: Alterations of systolic load were effected by leg elevation in control conditions and after administration of either nicardipine or ura pidil before and after cardiopulmonary bypass. Measurements and Main Results: High-fidelity LV pressure tracings were obta ined at end-expiration while hearts were paced at a fixed rate of 90 beats/ min. Hemodynamic effects of leg elevation were compared before and after ni cardipine, 7 mu g/kg (n = 15), and before and after urapidil, 0.4 mg/kg (n = 15). The effects of leg elevation on parameters of contraction and relaxa tion were coupled. Both nicardipine and urapidil similarly decreased systol ic pressures and peripheral resistance. Nicardipine decreased rate of press ure development (dP/dt(max)) and slowed LV pressure fall, whereas load depe ndence of LV relaxation was not altered. Urapidil did not alter dP/dt(max), rate of LV pressure fall, or load dependence of relaxation. Similar result s were observed after cardiopulmonary bypass. Conclusions: The results of the present study indicate that a pharmacologic ally induced moderate reduction in LV afterload with nicardipine or urapidi l did not alter the length-dependent regulation of myocardial function. Cop yright (C) 1999 by W.B. Saunders Company.