Spontaneous heart rate, ventricular tachycardia, and the response to procainamide during acute ischemia

Abstract

Summary Acute pacing-induced tachycardia in early ischemia allegedly promotes ventricular arrhythmias which appear unresponsive to antiarrhythmic agents, rasing question as to the efficacy of drug intervention clinically. To determine whether spontaneous sinus rate has the same relationship to arrhythmia incidence and responsiveness in the intact anesthetized dog, 82 animals were continuously monitored during a high-risk arrhythmic period, the inital 15 minutes of ischemia. Proximal occlusion of the anterior descending artery was induced by inflating a balloon tipped catheter. There was a modest increase in the incidence of VPB's at heart rates of 106 to 140 per minute compared to 70 to 105 beats, which was not seen at higher heart rates. However, ventricular tachycardia was not correlated with the sinus rate over a range of 70 to 210 beats per minute. To assess the relation of heart rate and responsiveness to antiarrhythmic agents, a group of 17 dogs received procainamide, 10 mg./Kg. intravenously at the onset of ventricular tachycardia. These were compared with an untreated group having similar heart rate levels and equivalent injury in terms of the number and sum of precordial leads with ST segment elevation. Nine of the 18 untreated animals with VPB's progressed to fibrillation; the incidence of fibrillation was reduced to one of 17 after procainamide (P