[Analysis of initial potential of signal-averaged QRS complex in patients with acute myocardial infarction].

Non-invasive recording of the late potential (LP) by signal-averaging technique is useful in predicting ventricular tachycardia (VT), especially in patients with myocardial infarction (MI). However, the rate of positive LP is LOW in anterior or anteroseptal MI, since the LP is masked by QRS complex. The purpose of the present study is first, to detect local conduction delay in initial portion of QRS complex and secondly, to evaluate the clinical significance of the initial delay in patients with MI. Eighty patients with MI were analyzed; AS: anteroseptal, n = 18, including 6 VT, A: anterior, n = 22, 7 VT, I: inferior, n = 28, 9 VT, and P: posterior, n = 12, no VT. Twenty non-MI patients were used as normal controls (N). A signal processor (NEC 7 T 18) was used to record signal-averaged electrocardiograms and each 10 msec integral value of filtered QRS complex from the initial upstroke to the 60 msec point was automatically measured. The integral values of groups AS and A were lower than those of groups I, P, and N. AS with VT showed a lower integral value than AS without VT, but no differences were observed between A with VT and A without VT. We conclude that there is a much lower upstroke of signal-averaged initial QRS complex in patients with anteroseptal MI with VT, suggesting that the local conduction delay at the ventricular septum plays an important role in the mechanism of VT in these patients.