Myocardial infarction diminishes both low and high frequency QRS potentials: power spectrum analysis of lead II.

Previous studies based primarily on counts of QRS notches and slurs have suggested that myocardial infarction (MI) increases high frequency QRS components. However, this technique does not quantitatively measure total high frequency voltage. To further study this problem, a microprocessor ECG system was employed capable of averaging multiple QRS complexes to reduce noise. Power spectrum analysis of the QRS using a Fast Fourier Transform was then performed in lead II in ten normal subjects and ten patients with prior inferior MI. The infarct group showed a decrease in QRS potentials over a broad frequency range (7.81-304.7 Hz). Therefore, contrary to previous estimates, MI may attenuate high as well as low frequency QRS potentials as part of a general decrease in electromotive force.