EFFECTS OF THROMBOLYSIS AND ATENOLOL OR METOPROLOL ON THE SIGNAL-AVERAGED ELECTROCARDIOGRAM AFTER ACUTE MYOCARDIAL-INFARCTION

Late potentials (LPs) detected on the signal-averaged (SA) electrocard iogram (ECG) predict arrhythmic event after acute myocardial infarctio n (AMI). The effect of thrombolysis on the incidence of LPs after AMI is controversial and its impact on subsequent arrhythmic events is not known. Moreover, the effects of beta blockers on the SAECG have not b een studied. Six hundred eighteen patients with AMI were studied; thro mbolysis was given to 228 (37%). In comparison with patients treated c onventionally, those receiving thrombolysis were significantly younger and more frequently male, had higher peak values of creatine kinase, a lower prevalance of non-Q-wave AMI, and a higher incidence of ventri cular fibrillation in the acute phase, and more frequently received be ta blockers. An SAECG obtained 6 to 8 days after AMI showed LPs in 24% of patients receiving and in 25% not receiving thrombolysis (p = NS). On admission, intravenous beta blockers were administered to 110 pati ents (18%); those receiving beta blockers were younger, had lower peak values of creatine kinase and more frequently received thrombolysis. LPs were less frequently found in patients treated than in those not t reated with beta blockers (15 vs 27%; p = 0.007); however, this effect was found only in those with an ejection fraction greater-than-or-equ al-to 40%. Independent predictors of LPs by multivariarte analysis wer e an ejection fraction < 40% (p = 0.007), ventricular fibrillation in the acute phase (p = 0.02), and absence of beta-blocking therapy (p = 0.03). During a mean follow-up of 12 +/- 7 months, there were 39 cardi ac deaths (6%), 13 of which were sudden (2%), and 9 sustained ventricu lar tachycardias. Thrombolysis significantly reduced cardiac mortality but not the occurrence of arrhythmic events (3.9 vs 7.7%), whereas be ta blockers reduced cardiac mortality (1.8 vs 7.3%, p = 0.03) and redu ced the incidence of arrhythmic events by 50% (p = NS). In conclusion, thrombolytic therapy does not reduce the incidence of LPs after AMI a nd its beneficial effects on prognosis are not related to a reduction of arrhythmic events. Conversely, beta blockers administered in the ac ute phase of the infarction, followed by chronic oral therapy, signifi cantly reduce the incidence of LPs; this effect may explain, at least in part, the reduced incidence of arrhythmic events during follow-up.