Electrophysiologic properties of the myocardial infarction border zone: effects of transient aortic occlusion.

This study used transmural multipolar electrodes, ventricular pressure monitoring, and cardiac electrical stimulation techniques to examine the effects of transient aortic occlusion on ventricular refractoriness in a canine model of recent myocardial infarction. Six previously instrumented resting awake dogs were atrially paced, followed by timed premature extrastimuli inserted at epicardial pacing sites adjacent to an apical left ventricular (LV) myocardial infarction or in an LV control zone remote from the myocardial infarction. Electrophysiologic and pressure recordings were obtained before and during periods of transient aortic occlusion. Aortic occlusion was applied before the last beat of an eight-beat atrial pacing sequence and resulted in increased peak LV pressure (92.8 +/- 27.7 mm Hg, p = 0.003). Aortic occlusion shortened LV effective refractory period (ERP) recorded from the myocardial infarction border zone in both the subepicardial (-17.0 +/- 11.8 msec, p = 0.019) and subendocardial (-17.7 +/- 10.9 msec, p = 0.011) regions, whereas LVERP of the control zone was unchanged. Conduction latency of premature beats at equivalent coupling intervals and maximum latency observed were unchanged by aortic occlusion. atrioventricular conduction interval shortened in association with aortic occlusion. Thus transient aortic occlusion reduced ventricular refractoriness in the border zone adjacent to the myocardial infarction while control zone refractoriness was minimally or not changed. Heterogeneity of ventricular myocardial refractoriness may result from mechanical dysfunction, potentially increasing susceptibility to arrhythmias.