Comparative cardiovascular effects of verapamil, nifedipine, and diltiazem during halothane anesthesia in swine

The cardiovascular effects of the calcium channel blockers verapamil (V), nifedipine (N) and diltiazem (D) were compared in halothane-anesthetized swine. Equipotent hypotensive doses of the three calcium channel blocking drugs were administered randomly by continuous infusion to three groups of six animals each to produce a uniform 25-30% reduction in mean systemic arterial blood pressure (BP). An additional group of six animals received sodium nitroprusside (S) to demonstrate the effects of lowering blood pressure with a pure vasodilator on this experimental preparation. Hemodynamic indices monitored before and after drug administration included ECG, mean systemic and pulmonary artery blood pressure, mean central venous and pulmonary capillary wedge pressure, thermodilution cardiac output, left ventricular pressure, and left ventricular dP/dt. All four study drug infusions reduced BP an average of 28%. V and D reduced BP by decreasing cardiac output (41% and 42%, respectively) without affecting systemic vascular resistance. N and S produced hypotension by decreasing systemic vascular resistance (36% and 21%, respectively) without affecting cardiac output. D reduced heart rate (18%) and both D and V increased the PR interval (60% and 40%, respectively). Calcium chloride (20 mg X kg-1 intravenous bolus) improved indices of myocardial contractility but did not affect drug-induced changes in cardiac electrophysiology. These data demonstrate that in this halothane-anesthetized swine model the administration of equihypotensive doses of verapamil or diltiazem has a more pronounced affect on cardiac conduction and myocardial contractility than does nifedipine, which predominantly reduces systemic vascular resistance with minimal effects on cardiac function.