Effect of frequent ventricular ectopy on myocardial infarct size in dogs

Tachycardia is known to increase the size of an evolving myocardial infarction, but the effect of frequent ventricular extrasystoles on infarct size is unknown. To determine the effect dogs were allocated to a control group (n = 15) or to groups of dogs with electrically induced ventricular bigeminy. Ventricular extrasystoles with short coupling intervals (mean 251 ms) were used to simulate interpolated premature complexes in 10 dogs, and extrasystoles with long coupling intervals (mean 606 ms) resulting in compensatory pauses were applied in 10 additional dogs. All dogs underwent single stage left anterior descending coronary artery ligation followed by a 6 h monitoring period. Premature stimulation was begun at the time of coronary artery occlusion and continued throughout the observation period. The ratio of myocardial infarct size to the region at risk of infarction was substantially larger in dogs with electrically induced, closely coupled extrasystoles (0.58(0.07); p less than 0.01) than in control dogs (0.24(0.06)) or dogs with widely coupled induced extrasystoles (0.32(0.07)). It is concluded that frequent closely coupled ventricular extrasystoles can increase the size of an evolving acute myocardial infarction.