Rate Dependent Ventricular Ectopia Following Acute Coronary Occlusion

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Abstract
Recent reports have indicated that tachycardia as well as bradycardia may be arrhythmogenic in acute myocardial infarction. The present experimental study was designed to systematically evaluate the arrhythmogenic and antiarrhythmic effect of heart rate over a wide spectrum using sinus node crush and atrial pacing. Serial recordings of the surface electrocardiograms and local electrograms for a maximum period of three hours were taken at rates of 60-200 beats/min before and after ligation of the left anterior descending coronary artery in 24 open chested dogs. Immediately following coronary occlusion, the incidence of ventricular ectopic complexes was 7.6 ± 1.6/min at a rate of 60, and gradually decreased to 2.5 ± 0.4/min at a rate of 90 ( P < 0.01). At rates of 110-150 ⪕ 1 ventricular ectopic complex/min was noted. However, at rates of 180 and above, the incidence of ventricular ectopic complexes dramatically increased with frank ventricular tachycardia and/or fibrillation being provoked on seventeen occasions. Similarly, at rates of 60-90, ventricular tachycardia and/or fibrillation was exhibited on sixteen occasions, but never at rates between 110-150. Local electrograms exhibited marked ST segment elevation with higher heart rates compatible with increased local ischemia. It is concluded that ventricular ectopia is more common at rapid as well as slow heart rates after acute coronary occlusion. There appears to be an optimal intermediate rate for maximal antiarrhythmic effect.