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In order to determine the electrophysiological changes that occur during coronary occlusion and following reperfusion, 19 mongrel dogs were studied. Refractory periods were determined by the extrastimulus method in nonischemic and ischemic zones prior to and after variable periods of left anterior descending artery occlusion and reperfusion. After 15-30 minutes of occlusion, refractory periods in the nonischemic zones remained unchanged while in the ischemic zone they shortened by 17%, resulting in a dispersion of refractoriness. Within three minutes of reperfusion, arrhythmias appeared together with a marked directional change of refractory periods to a prolongation by 34% (P less than 0.001) in the ischemic zone and by 3% (P less than 0.02) in the nonischemic zone. Refractory periods returned to baseline values after 60 minutes of reperfusion. After 60-90 minutes of occlusion, refractory periods in the nonischemic zones were unchanged whereas in the ischemic zone they demonstrated a decrease by 28% (P less than 0.01), again resulting in a dispersion of refractoriness. Within five minutes of reperfusion, refractory periods in the ischemic zone prolonged by 44% (P less than 0.001). Similar but smaller directional changes were also seen in nonischemic zones. Concomitant with the observed prolongation in refractory periods frequent ventricular ectopic activity was again documented. In addition, refractory periods did not return to control values after periods of observation up to 120 minutes in this group. In seven dogs, complete heart block was induced to ascertain the rate of idioventricular pacemaker and the effect of ventricular overdrive on the escape interval. Control ventricular rates (53.3 +/- 5.7 beats/min) remained unchanged (52.3 +/- 5.6) following coronary occlusion, but decreased to 48.0 +/- 4.4 (P less than 0.05) during reperfusion. Mean control escape intervals (1.8 +/- 0.2 sec) did not change after occlusion (1.7 +/- 0.2 sec) but prolonged to 2.1 +/- 0.2 sec (P less than 0.05) following reperfusion.

Electrophysiologic effects of coronary occlusion and reperfusion. Observations of dispersion of refractoriness and ventricular automaticity.