Effect of Exercise On Arrhythmias Following Experimental Acute Myocardial Infarction

The effects of treadmill exercise on cardiac mechanism were studied in 34 dogs, two to eight days following ligation of the anterior descending coronary artery. Physical exercise abolished all ventricular arrhythmias which were present at rest. Some of the animals displayed return of ventricular rhythm disorders towards the end of exercise when studied as early as 48 hours after the coronary occlusion. In experiments carried out on the second and third days, a transient intensification of ventricular arrhythmias during recovery was observed. Physical exertion beyond the third day after infarction did not provoke ventricular arrhythmias during or after the exercise. However, isoproterenol and epinephrine infusions resulted in reappearance of ventricular arrhythmias up to four days after coronary ligation. The effects of exercise on cardiac mechanism are probably a result of diverse factors; the faster rate during exercise tends to abolish ventricular arrhythmias whereas other unidentified factors, perhaps related to myocardial oxygen requirement, catecholamines or the appearance of left heart failure, tend to provoke ventricular arrhythmias especially after the exercise as the sinus rate slows. These results may have implications in the interpretation of exercise tests and in assessing the role of physical activity in patients with ischemic heart disease.