Nifedipine Reduces Arrhythmias But Does Not Alter Prostanoid Release During Coronary Artery Occlusion and Reperfusion in Anaesthetised Greyhounds

We examined the effects of nifedipine, a calcium slow-channel blocking drug, on haemodynamics, blood gases, cardiac arrhythmias, and prostanoid release in anaesthetised greyhounds before, during, and after a 40-min occlusion of the left anterior descending coronary artery. Fifteen minutes after commencing treatment with nifedipine (5 micrograms/kg + 0.67 micrograms kg-1 min-1), there were significant reductions in arterial blood pressure, left ventricular end-diastolic pressure, and vascular resistance, with increases in cardiac output and stroke volume. Although coronary artery blood flow was unchanged, oxygen extraction was decreased, indicating that nifedipine reduced oxygen consumption. Nifedipine prevented the haemodynamic changes that occur in control dogs during acute myocardial ischaemia and markedly reduced the number of arrhythmias during coronary artery occlusion. The incidence of ventricular fibrillation induced by release of the occlusion was significantly reduced from 88% in the control group to 22% in the group receiving nifedipine. The release of thromboxane B2 and 6-keto PGF1 alpha (stable breakdown products of thromboxane A2 and prostacyclin, respectively) from the acutely ischaemic myocardium was not altered by nifedipine. It is concluded that this low dose of nifedipine had marked antiarrhythmic activity during both coronary artery occlusion and reperfusion. The relationship to dosage and possible mechanisms for this effect are discussed.