Effect of Myocardial Infarction

a microprocessor system capable of averaging 256 QRS complexes to reduce noise. The QRS was digitally filtered and the root-mean-square (RMS) voltage of the residual (80-300 Hz) signal computed. High-frequency RMS values were significantly (p < 0.01) greater in leads II, III and aV7 in normal subjects (n = 12) than in patients with inferior infarction (n = 12). Similarly, high-frequency RMS values were higher (p < 0.01) in leads Vs and V, in normal subjects (n = 14) than in patients with prior anterior MI (n = 14). A reduction in high-frequency RMS values with inferior infarction was independently confirmed using Fourier analysis of the QRS in lead II. QRS notching in these subjects was also quantified by computing the number of baseline crossings of the first derivative (dV/dt). As predicted, notching was significantly greater (p < 0.05) both with inferior MI (lead II) and anterior MI (lead V&). However, contrary to clasic theory, the number of notches correlated negatively with direct measurements of high-frequency RMS voltage in lead II (r = -0.63) and lead V8 (r = -0.49). Positive correlations were obtained between high-frequency potentials and two new indexes that measure the amplitude of QRS dV/dt peak-to-peak amplitude of dV/dt and RMS dV/dt. Using these indexes, absolute separation of inferior MI patients and normal subjects was obtained. We conclude that MI increases low-amplitude QRS notching but diminishes total high-frequency voltage, probably because of an overall decrease in electromotive potentials and slowing of ventricular conduction.