Frequency content of the electrocardiogram. Spatial features and effects of myocardial infarction

The frequency content of electrocardiographic signals has been used to define amplifier characteristics and, more recently, to detect myocardial pathology. It was the purpose of this study to evaluate the differences in frequency content of ECG signals recorded from different volume conductor surface sites and to determine the effects of coronary ligation on these spatial features. To do so, 15 isolated perfused rabbit hearts, enclosed within a precisely machined sphere, were studied; ten were examined prior to and 15 minutes after ligation of the anterior descending coronary artery. ECG signals, recorded from 32 surface electrodes, were subjected to Fourier analysis. Prior to occlusion, the frequency content of the different electrode signals varied widely, with a greater variance between electrodes than between hearts (p less than 0.01). This variation was related to a reproducible spatial effect, with records over the basal left ventricle having higher frequency components than waves from other sites. After litigation, ECG records from electrodes over electrodes over ischemic areas showed augmented R-wave amplitude and ST-segment elevation. This was associated with a spatial shift of the control high frequency peak to a site overlying the ischemic lesion. Thus the frequency content of ECG is spatially variable and hence lead-dependent, and this spatial variability is directly affected by acute myocardial infarction.