EFFECTS OF EXERCISE ON SIGNAL-AVERAGED ELECTROCARDIOGRAM

Signal averaging can be used to assess changes in myocardial activatio n un der 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 wer e divided into three groups based on thallium results: normal (group I ), reperfusion (group II), and fixed defect (group III). Patients in g roup 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 eit her group II or group III showed little change in signal averaging mea surements after exercise. The amplitude of the QRS in Vg 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 imagin g (group II). There was no change among groups in the incidence of ven tricular late potentials with exercise. This suggests that patients wi th ischemia or infarction may not have the same response to an increas e 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.