EXERCISE PRODUCING ALTERATIONS IN THE SIGNAL-AVERAGED ELECTROCARDIOGRAM IN PATIENTS AFTER MYOCARDIAL-INFARCTION

Late potentials are considered to be a marker for regional slow conduc tion which might predispose to reentrant ventricular arrlythmias. Sinc e these arrhythmias may be induced by ischaemia it may be speculated t hat exercise-induced myocardial ischaemia may trigger late potentials. Exercise testing was performed in 53 patients early after myocardial infarction and in 20 healthy controls. Typical 12 lead ECG and signal averaged ECG (SA-ECG) from 12 leads were recorded before and after exe rcise testing. Changes in filtered QRS (QRS) and low amplitude signal durations, and in the root mean square voltage of the last 40 ms of th e QRS complex (RMS40) were analysed. Thirty patients developed ST chan ges, consistent with transient ischaemia, that persisted during the SA -ECG recording before exercise. There were significant differences bet ween baseline SA-ECG and SA-ECG after exercise in patients with positi ve exercise tests (QRS, 102 +/- 15ms vs 114 +/- 15 ms (P<0.01), LAS, 3 6+/-12 ms vs 42+/11 ms (P<0.05), and RMS40, 29+/-14 mu V vs 20+/-13 mu V (P<0.01)). No differences were observed in SA-ECG parameters in eit her patients with negative exercise tests or in controls. During follo w-up, four patients died sulddenly, all four had positive exercise tes ts and in thr ee of them late potentials were induced by exercise. We conclude, that in post-infarction patients with positive exercise test s SA-ECG parameters deteriorate after exercise. This suggests that exe rcise-induced ischaemia triggers development of late potentials.