TRANSIENT ISCHEMIA INDUCED BY RAPID CARDIAC PACING RESULTS IN MYOCARDIAL PRECONDITIONING

Study objective - The aim was to determine whether rapid ventricular pacing can protect against the ventricular arrhythmias occurring during a subsequent coronary artery occlusion. Design - The effect was examined of two 2 min periods of pacing (300 beats.min-1) in chloraloseurethane anaesthetised dogs on a subsequent 25 min coronary artery occlusion. Ventricular arrhythmias, ST segment elevation, and inhomogeneity of conduction were analysed. Experimental material - 25 anaesthetised mongrel dogs in a restricted body weight range were used. Measurements and main results - Preocclusion pacing reduced the severity of occlusion induced ST segment elevation, degree of inhomogeneity, and arrhythmias: ventricular premature beats were reduced from 528(SEM 40) to 136(45), and there were lower incidences of ventricular fibrillation (0% v 47%) and ventricular tachycardia (30% v 80%). Conclusions - Rapid ventricular pacing "preconditions" the myocardium in a manner similar to that following short coronary artery occlusions. Short periods of ischaemia no matter how induced protect the heart against the arrhythmogenic effect of a prolonged coronary artery occlusion.