A spectral analysis of the high frequency QRS potentials observed during acute myocardial ischemia in dogs.

Electrocardiographic manifestations of transient myocardial ischemia were studied in 10 dogs undergoing occlusion of the left anterior descending coronary artery, using frequency domain analysis of the high frequency QRS potentials. Ischemia was induced via a balloon occluding cuff placed around the coronary artery. Electrocardiographic waveforms recorded before and during the ischemic state were averaged together and then filtered between 150 and 250 Hz to obtain the high frequency QRS complex. The spectral curve in the power spectrum of the high frequency QRS components was calculated using an algorithm for fast Fourier transformation. Balloon inflation was accompanied by morphological changes in the spectral curve in 7 of 10 experiments. Morphological changes, seen as zones of reduced amplitude in the time domain, appear as two separate peaks in the frequency domain. These changes were seen early in ischemia and were not accompanied by significant changes in the QRS complex or ST segment of the conventional surface electrocardiogram. The power spectrum of the high-frequency QRS potentials appears to detect evidence of transient ischemia and may provide useful information regarding the presence of myocardial ischemia.