The restoration of anterograde flow in the infarct-related artery(IRA) may improve electrophysiological consequences and survival. Patients with occluded IRA are more likely than those with patent IRA to have late potentials on signal-averaged electrocardiogram(SAEKG).

The natural history of late potentials in the acute phase after AMI was reported to vary in recent studies and requires further investigation. Therefore, we investigated 1) whether parameters of SAEKG and incidence of late potentials are changed in 2 weeks after AMI, and 2) whether the status of IRA, ejection fraction, ventricular premature beats(VPB) on Holter and the use of thrombolytic agent can influence the developement of late potentials.

SAEKGs were performed in 40 patients with acute myocardial infarction(AMI, mean age : 56.6yr) and 20 normal controls(mean age : 53.0yr). SAEKGs were recorded first in 48 hours and then 2 weeks after AMI. Late potential were considered to be positive if two of the three following criteria were identified : 1) duration of filtered QRS complex>118ms, 2) duration of HFLA signal>40 ms, and 3) RMS voltage<20µV.

1) The duration of filtered QRS complex and HFLA signal in patients with AMI in 48 hours and 2 weeks were longer than in the controls(p<0.01, p<0.05. respectively), and the RMS voltage in only 2 weeks was lower than in the controls(p<0.05). 2) There was no significant difference in the 3 parameters of SAEKG between 48 hours and 2 weeks after AMI, but the incidence of late potentials increased from 35%(14/40) to 42.5%(17/40). Of the 26 patients with a normal initial SAEKG, 3(11.5%) had late potentials in 2 weeks, whereas none of the patients with positive late potentials on initial SAEKG was normalized in 2 weeks. 3) The ejection fraction, the degree of VPB on the Holter EKG and the history of thrombolyic therapy in patients whose late potentials were positive were not different from those in patients with normal SAEKG. 4) In the 3 parameters of SAEKG, RMS voltage in patients with occluded IRA was significantly lower than in those with open IRA(p<0.05), and the incidence of late potentials were higher in the patients with occluded IRA(75%) than in those with open IRA(28.6%)(p<0.05).

The incidence of late potentials on SAEKG after AMI was modestly increased in 2 weeks, but the development of late potentials was not influenced by the degree of frequently in patients with occluded IRA. These findings may indicate that the development of late potential after AMI tends to increase even in 2 weeks, and that the occlusion in IRA may unfavorably alter the electrophysiological state identified by SAEKG.