Effects of thrombolysis and atenolol or metoprolol on the signal-averaged electrocardiogram after acute myocardial infarction

Abstract

Late potentials (LPs) detected on the signal-averaged (SA) electrocardiogram (ECG) predict arrhythmic events after acute myocardial infarction (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 β blockers on the SAECG have not been studied. Six hundred eighteen patients with AMI were studied; thrombolysis was given to 228 (37%). In comparison with patients treated conventionally, those receiving thrombolysis were significantly younger and more frequently male, had higher peak values of creatine kinase, a lower prevalence of non-Q-wave AMI, and a higher incidence of ventricular fibrillation in the acute phase, and more frequently received β 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 β blockers were administered to 110 patients (18%); those receiving β 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 treated with β blockers (15 vs 27%; p = 0.007); however, this effect was found only in those with an ejection fraction ≥40%. Independent predictors of LPs by multivariate analysis were an ejection fraction <40% (p = 0.007), ventricular fibrillation in the acute phase (p = 0.02), and absence of β-blocking therapy (p = 0.03). During a mean follow-up of 12 ± 7 months, there were 39 cardiac deaths (6%), 13 of which were sudden (2%), and 9 sustained ventricular tachycardias. Thrombolysis significantly reduced cardiac mortality but not the occurrence of arrhythmic events (3.9 vs 7.7%), whereas β blockers reduced cardiac mortality (1.8 vs 7.3%, p = 0.03) and reduced the incidence of arrhythmic events by 50% (p = NS). In conclusion, thrombolytic therapy does not reduce the incidence of LPs after AMI and its beneficial effects on prognosis are not related to a reduction of arrhythmic events. Conversely, β blockers administered in the acute phase of the infarction, followed by chronic oral therapy, significantly reduce the incidence of LPs; this effect may explain, at least in part, the reduced incidence of arrhythmic events during follow-up.