Temporal properties of high frequency Intra-QRS signals in myocardial infarction and healthy hearts

The prevalence of late potentials after myocardial infarction depends on th e site of the infarction. This may be caused by the different activation on sets of the anterior and inferior myocardial segments. Therefore, in anteri or infarcts the high frequency signals may be concealed within the QRS wher eas in the inferior infarcts they last beyond the end of the QRS. We compar ed the timing and the spatial patterns of high frequency intra-QRS signals (IQSs) in the different infarction sites. We investigated 14 patients with anterior infarcts, 17 patients with inferi or infarcts, and 10 healthy subjects. 31-lead magnetocardiograms were recor ded in left precordial position and averaged. The QRS signals were smoothed with a Savitzky-Golay filter. The smoothed QRS signals were subtracted fro m the measured ones. The difference of the signals (frequency band of about 60-200 Hz) representing the high frequency components was quantified. The percentage of the high frequency signals was calculated for the entire QRS, for the first and for the second half, respectively. We found that in patients with anterior infarcts the high frequency compone nts predominantly appeared in the first half of the QRS whereas in inferior infarcts these components predominantly appeared in the second half of the QRS. The different infarction sites were associated with different spatial patterns of the high frequency signals on the body surface. In healthy sub jects there was not such a preferential association of time intervals and h igh frequency signals. Late potentials are the special case of high frequency signals appearing in the terminal QRS. It is the general property of the myocardium to generate high frequency signals associated with the depolarization of infarcted tis sue. The timing of such signals and the spatial distribution patterns on th e body surface may help to identify the location of the sources.