Abstract
The purpose of this study was to examine whether short (5 minute) serial left anterior descending coronary artery occlusions produced consistent changes in ST segment elevation, bipolar electrogram variables, myocardial blood flow and incidence of arrhythmia when separated by short (3 minute) or long (> 40 minute) periods of reperfusion. In eight adult control dogs, neurally decentralized and paced at 150 beats/min, occlusions separated by greater than 40 minutes resulted in consistent changes in endocardial and epicardial electrogram activity, ST segment elevation and incidence of arrhythmia. In the same dogs, left anterior descending coronary artery occlusions following a short period of reperfusion demonstrated significantly less (p < 0.01) ST segment elevation and arrhythmia (p < 0.001) with no change in bipolar electrogram variables. On the other hand, myocardial blood flow was not altered within the ischemic zone at the electrode sites during any occlusion protocol, demonstrating that improved electrophysiologic variables and decreased incidence of arrhythmia were not due to enhanced myocardial blood flow to the ischemic zone. Similar experiments in an additional eight neurally decentralized dogs receiving 3 cycles/s left efferent sympathetic nerve stimulation (sympathetic stimulation group) showed greater incidence of arrhythmia (p < 0.01), larger electrogram changes (p < 0.01) and increased ST segment elevation (p < 0.01) during all occlusions when compared with the nonstimulated animals. Time interval between occlusions also significantly affected the results in these animals. These data suggest that the time interval between repeated left anterior descending coronary artery occlusions must be carefully controlled to eliminate artifactual changes in electrophysiologic variables being measured. In addition, improvement in the electrophysiologic variables seen after short reperfusion could not be attributed to increased myocardial blood flow to the ischemic zone or electrode site, suggesting that other mechanisms must be involved.
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