Effects of verapamil and lidocaine in a canine model of sudden coronary death.

The efficacy of verapamil and lidocaine for treating ischemia-induced arrhythmias was determined in a conscious canine model with a previous myocardial infarction remote from the ischemic area. Temporary (up to 5.5 minutes) occlusion of the circumflex coronary artery was made in eight conscious dogs that had sustained an anterior myocardial infarction 13 to 35 days previously. Each dog served as its own control. Ventricular arrhythmias were observed in 100% of control experiments but in only 25% of experiments after verapamil pretreatment at 0.4 mg/kg body weight. Repetitive ventricular complexes, defined as two or more consecutive ventricular complexes terminating spontaneously in sinus rhythm, were seen in 88% of control experiments and 13% of verapamil experiments, whereas ventricular fibrillation was seen in 6% of control experiments but in no verapamil experiment. Thus, verapamil abolished arrhythmias or reduced the grade of arrhythmias in all dogs. Six of the eight dogs were also tested with lidocaine pretreatment at one or two doses resulting in mean plasma levels of 3.8 +/- 2.0 micrograms/ml. Ventricular arrhythmias were seen in 92% of control experiments and 100% of lidocaine experiments. The incidence of ventricular fibrillation increased from 8% in control to 60% in lidocaine experiments. It is concluded that verapamil may prevent severe ischemia-induced arrhythmias after a recent myocardial infarction, whereas lidocaine may in some cases aggravate arrhythmias.