Comparison of the arrhythmogenic effect of myocardial infarction in the cat and dog.

Myocardial infarction was produced in dogs and cats by occlusion of the left anterior descending coronary artery. Arrhythmia was present in dogs but not in cats 6 to 48 h after occlusion. The absence of arrhythmia in cats was not due to persistent myocardial depressant effects of anaesthesia administered during surgery. Studies in cats with surgically-induced heart block revealed multiple ventricular pacemakers but no change in average ventricular rate following coronary occlusion. These results suggest that sinus overdrive, although not elevated compared with the dog, is sufficient to suppress arrhythmia in the cat. Further, since small dogs developed significantly less arrhythmia than large dogs, heart size may be an additional factor in explaining the absence of arrhythmia in the cat.