Spectral analysis of canine epicardial electrogram. Short-term variations in the frequency content induced by myocardial ischemia.

Abstract

Power spectra of epicardial electrograms were studied in 13 anesthetized dogs subjected to occlusion of the left anterior descending coronary artery. Electrograms were obtained from a bipolar electrode placed on the epicardial surface of the left ventricle and recorded before and after coronary occlusion. After digitization, power spectra of the first and every 50th subsequent waveform were evaluated and compared with the power spectrum of the average waveform obtained from the baseline recording. In particular, we examined variations in relative power content in three frequency ranges: 150-250 Hz, previously shown to be directly affected by myocardial ischemia; 40-150 Hz, presumably corresponding to the fine notches and slurs on the body surface QRS; and 2-40 Hz, the low-frequency range. Apart from a mild initial rise during the first 50 heart beats, the power in the high-frequency range gradually decreased, reaching 5% of the control value at wave 500. The power in the mid-frequency range showed a monotonous decrease after the occlusion and reached 16% of the control. The power in the low-frequency range showed a gradual buildup to 140% of the control after 500 heart beats. Therefore, ischemia causes a shift of the high-frequency spectral components of the local electrographic waveform to lower frequencies. Our findings and the fact that body surface ECG is produced by spatial summation of local electric potentials over the different regions of the myocardial tissue may explain two previously described effects of acute myocardial ischemia on the body surface ECG complex. First, local loss of spectral components in the range 150-250 Hz may produce a zone of reduced amplitude within a QRS complex band-pass filtered in this range. Second, displacement of power in the frequency domain may suggest an explanation to the increased incidence of visible notches and slurs on the surface QRS complex, characteristic to various myocardial pathologies.

High‐frequency QRS electrocardiogram

“…Other animal studies have shown similar results (Abboud, 1987; Abboud et al. , 1989, 1990; Mor‐Avi & Akselrod, 1990b).…”

Characterisation of acute myocardial ischaemia in a canine model based on principal component analysis of unipolar endocardial electrograms

“…Although most of the ST elevation observed on an ischaemic body surface ECG (BRAUNWALD and SOBEL, 1992;NABEL et al, 1998;SCLAROVSKY, 1999) can be explained by ST elevation in the epicardial electrograms (MoR-AvI et al, 1990), our study shows that this is true, although to a lesser extent, for endocardial electrograms as well. This is apparent on inspection of the classification vector in the time domain for the immediate stage, which interestingly relates to the suggestion made by GARCIA et al (1998; 1999) that PCA-based indices better express the transformations undergone by the electrograms as a result of short-term ischaemia.…”

Some aspects of the wideband recording of the electrocardiogram

“…On the contrary, such a power shift toward the lower frequency range can be expected, considering the reduced conduction velocity caused by myocardial ischemia. 34 …”

“…34 epicardial surface, caused variations in the high frequency waveforms similar to those produced by myocardial ischemia . 44 A cross correlation beat-to-beat analysis was applied to the high frequency waveforms and to the conventional electrocardiographic signals obtained during percutaneous transluminal coronary a n g i~p l a s t y .~~ Based on the results of this study, the morphology of the high frequency QRS complex is unequivocally more sensitive to transient myocardial ischemia than the conventional ECG.…”