Beat-to-beat spectral analysis of epicardial electrogram under acute ischemia in dogs

In order to study the dependence of the frequency content of the epicardial signal on local myocardial perfusion, beat-to-beat spectral analysis was applied to an epicardial electrocardiogram following coronary occlusion. Electrocardiograms were recorded from 13 anesthesized dogs prior to and following the ligation of the left anterior descending coronary artery, using a bipolar electrode placed on the epicardial surface of the left ventricle. The power spectrum of the first and every fifteenth subsequent electrographic waveform (up to 500) was evaluated using fast Fourier transform. The frequency domain was divided into three ranges: 2-40 Hz, 40-150 Hz, and 150-250 Hz. The power of the low-frequency range showed a gradual buildup to 140% of control after 50 heart beats. In the mid-frequency range, the power showed a monotonous decrease following the occlusion, reaching 16% of control at wave 500. In the high-frequency range, the power gradually decreased to 5% of the control value. These observations show that the high-frequency spectral components of the local epicardial potential are shifted by myocardial ischemia to lower frequencies