Protective effect of tiapamil against ventricular fibrillation during coronary artery occlusion

Calcium channel antagonists differ in their effects on myocardial excitable properties. This study examines whether tiapamil (100 micrograms/kg/min intravenously) is capable of reducing the susceptibility to ventricular fibrillation (VF) during acute occlusion and reperfusion of the left anterior descending coronary artery. During occlusion, tiapamil elevated the VF threshold to 17.5 +/- 8.2 mA compared to a control of 8.6 +/- 5.9 mA (2p less than 0.01). However, no significant effect was noted upon reperfusion of the vessel. Adrenergic stimulation with norepinephrine, 0.5 microgram/kg/min, lowered the VF threshold by 32% (2p less than 0.02), and by 6% (N.S.) when tiapamil was infused concurrently. Thus, tiapamil protects the heart against VF during coronary occlusion, but not during reperfusion. This appears to be mediated in part by an antiadrenergic action of the drug.