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

Epicardial mapping of polymorphous ventricular tachycardias induced in the canine heart with procainamide

To elucidate the mechanisms of the arrhythmogenic and antifibrillatory action of procainamide, 24 episodes of polymorphous ventricular tachycardia were analyzed. They were induced electrically in 12 canine hearts before and after the administration of 40 mg/kg of procainamide. The isochronal maps of the epicardial activation sequence were successfully constructed by 40 simultaneously recorded bipolar electrograms in 14 of 17 episodes after procainamide. The isochronal maps showed a possible macroreentrant circuit in 12 episodes, and in four of them the functional block was noticed to have disappeared before the termination of tachycardia. This study suggests that procainamide predisposes the ventricle to reentrant tachyarrhythmias and that the dimension of the reentrant circuit induced is too large to be fragmented into multiple reentries, which results in the prevention of the development of ventricular fibrillation.

Ventricular tachyarrhythmias in regional myocardial hyperkalemia: efficacy of three antiarrhythmic agents

Potassium chloride infusion into the left anterior descending coronary artery induces a sequence of events analogous to those occurring during acute transmural ischemia. These include ST elevation, intramural conduction delay, ventricular techyarrhythmias and fibrillation. The influence of antiarrhythmic agents in an intact anesthetized canine model have not previously been tested. We have evaluated the efficacy of lidocaine, procaine amide and practolol in animals during regional hyperkalemia. In the untreated, only 9% survided a 20 minute observation period. All three treatment groups exhibited a reduced incidence of tachycardia and 74% survived the test period. In each treatment group this was associated with a further prolongation of intramural conduction time in the affected wall. This antiarrhythmic efficacy, thought possibly to be due to transformation of unidirectional to bidirectional block, supports the view that modulation of transcellular potassium activity contributes to the control of ischemic arrhythmias.