Significance of abnormal root mean square voltages in signal averaged electrocardiogram as a reliable predictor of sustained ventricular tachycardia

The late potential is useful to predict patients with sustained ventricular tachycardia (VT). However, because positive predictive value for sustained VT is low, the validity of late potential for screening the patients to be studied by electrophysiological tests was not high. We examined 923 cases, including 63 cases of sustained VT. When we separated patients showing abnormal values of the root mean square voltage of the QRS end part 40 milliseconds (RMS40) into four groups, there was a tendency of a higher incidence of sustained VT with lower value of RMS40. When we conducted electrophysiological tests on 121 cases without sustained VT, it turned out a high induction rate of sustained VT in patients with low RMS40 values (RMS40 < 10 μV, 67%; < 20 μV, 30%; 20 μV, <- 5%). We conclude abnormally low value (less than 10 μV) of RMS40 can be useful for screening the late potential-positive cases who are high risk for inducible sustained VT.