Effects of myocardial ischemia and localized epicardial hypothermia on the high frequency content of ECG in dogs

The high-frequency (HF) content (150-250 Hz) of an epicardial electrogram was studied in 19 anesthetized dogs undergoing left arterial descending occlusion. Signals were obtained from epicardial bipolar electrodes placed in the ischemic left ventricular (LV) region and the noninjured right ventricular (RV) surface, and from body surface ECG. All recordings were taken simultaneously before, during, and following the occlusion, and subjected to the same analysis. The waveform obtained from the LV showed a considerable decrease in the HF content, while that obtained from the RV remained unchanged. The results correlated with the appearance of a zone of reduced amplitude in the body surface HF QRS complex. Therefore, this variation in the morphology of the waveform obtained noninvasively from the body surface is explained by local reduction of the HF activity in the ischemic myocardial tissue. It was also shown that local reduction in HF activity, produced by two different interventions affecting local electrical characteristics of the myocardial tissue, is reflected by overall reduction of the HF power or sometimes by a zone of reduced amplitude of limited duration.