Nifedipine and Myocardial Performance in the Presence and Absence of Beta-blockade with Propranolol

The effects of intracoronary nifedipine on myocardial performance were studied in the absence and presence of beta-blockade with propranolol (0.5 mg X kg-1 i.v. bolus + infusion). In anaesthetized pigs nifedipine (0.025, 0.05 and 0.5 microgram X kg-1 X min-1) produced dose-dependent increases in coronary flow (up to 65% from base line, 39 +/- 4 ml X min-1) and decreases in myocardial O2-consumption (MO2-cons, up to 50%, base line 3.10 +/- 0.34 ml X min-1). The two lower doses caused a negligible depression of systemic haemodynamics (cardiac output, CO smaller than 8%, base line 2.70 +/- 0.14 l X min-1; mean arterial pressure, MAP smaller than 10%, base line 10.9 +/- 0.4 kPa), but after the highest dose MAP and CO decreased by 20%. Following pretreatment with propranolol, the effects of nifedipine on cardiac output and mean arterial pressure were additive for the two lower doses, but with 0.5 microgram X kg-1 X min-1 the superimposed effects were less pronounced. Nifedipine alone was able to increase cardiac efficiency, defined as (MAP X CO)/MO2-cons, by 10-20%, but failed to improve cardiac efficiency when this was previously reduced by administration of propranolol. Our data indicate that intracoronary infusion of nifedipine can be performed safely when beta-blockade is already instituted, but that nifedipine alone decreases MO2-consumption to the same level as the combination, with less depression of global myocardial function.