Effects of exercise on signal-averaged electrocardiogram

Signal averaging can be used to assess changes in myocardial activation under a variety of physiological conditions including stress. This study prospectively evaluated patients who underwent rest and exercise recording of signal-averaged electrocardiograms. The 163 patients were divided into three groups based on thallium results: normal (group I), reperfusion (group II), and fixed defect (group III). Patients in group I showed shortening of the high frequency duration (P = 0.02) and the duration of the low amplitude signal (P = 0.024) after exercise. In these patients the terminal root mean square amplitude (RMSA) also increased significantly (P = 0.005). However, patients who were in either group II or group III showed little change in signal averaging measurements after exercise. The amplitude of the QRS in V5 and the RMSA of the total QRS also increased in all groups following exercise, with a lesser increase in the patients with reperfusion by thallium imaging (group II). There was no change among groups in the incidence of ventricular late potentials with exercise. This suggests that patients with ischemia or infarction may not have the same response to an increase in sympathetic tone with exercise as patients without abnormalities of cardiac perfusion. The clinical implications of these findings may include demonstration that an area of slow conduction exists in these latter two groups of patients.