Influence of Thrombolysis on Signal-Averaged Electrocardiogram and Late Arrhythmic Events After Acute Myocardial Infarction Roberto Pedretti, MD, Antonio Laporta, MD, Mario D. Etro, MD, Adelia Gementi, MD, Roberto Bonelli, MD, Claudio Anza, MD, Enrica Colombo, MD, Franc0 Maslowsky, MD, Francesco Santoro, MD, and Bruno Car& MD The influence of intravenous thrombolysis on both prevalence of ventricular late potentials and inci- dence of late arrhythmic events was evaluated in 174 consecutive patients surviving a first acute myocardial infarction; 106 patients (61%) re- ceived thrombolysis (group A) and 66 (34%) had conventional therapy (group B). In group A, 18 pa- tients (17%) had late potentials compared with 23 (34%) in group B (p <O.OS); mean left ventricular ejection fraction was not different (0.50 f 0.09 vs 0.50 f 0.10; p = not significant [NS]). Of 63 pa- tients who underwent coronary arteriography be- cause of postinfarction ischemia, 28 (44%) had a closed infarct-related artery; of these, 11 (39%) had late potentials compared with 3 of 35 (9%) with a patent artery (p <O.Ol). Mean left ventricu- lar ejection fraction was not significantly different between the 2 groups (0.49 f 0.09 vs 0.53 f 0.09; p = NS). At a mean follow-up of 14 f 8 months, 8 of 161 patients (5%) had a late arrhyth- mic event; 6 of 8 (75%) with and 28 of 153 (18%) without events had late potentials (p <O.OOl). In group A, 4 of 99 patients (4%) had events com- pared with 4 of 62 (6%) in group B (p = NS, rela- tive risk 1.6). Of 24 patients with anterior wall AMI and left ventricular dyskinesia, 6 events oc- curred. In this group of patients, a higher rate of events was observed (25%); 3 of 16 (19%) treated with thrombolysis had an event compared with 3 of 8 (37%) treated conventionally (p = NS, relative risk 2.6). Thrombolysis and patency of the infarct- related artery significantly reduce the rate of late potentials independently of global left ventricular function. Although no significant difference was found in the follow-up results, the reduced rate of late potentials suggests an improved ventricular electrical stability both in patients treated with thrombolysis and in those with a patent vessel. (Am J Cardiol 1992;69:866-672) From the Fondazione Clinica de1Lavoro, Istituto di Ricovero e Cura a Carattere Scientifico, Divisione di Cardiologia, Centro Medico di Tra- date, Italy. Manuscript received August 15, 1991; revised manuscript received and accepted December 3,199 1. Address for reprints: Roberto Pedretti, MD, Fondazione Clinica del Lavoro, Istituto di Ricovero e Cura a Carattere Scientifico, Divi- sione di Cardiologia, Centro Medico di Tradate, Via Roncaccio 16/ 18, 21049, Tradate (VA), Italy. T he early fibrinolytic treatment of acute myocar- dial infarction (AMI) improvessurvival by reduc- ing infarct size and left ventricular dysfunction.’ However, thrombolytic therapy decreases mortality also in the absence of demonstrablemyocardial salvage, and patency of the infarct-related coronary artery appears to be an important independent predictor of survival.’ Therefore, the reduction of left ventricular impairment is not the only mechanismresponsible for improved sur- vival in patients treated with thrombolysis; both limita- tion of remodeling of the left ventricle and increased electrical heart stability could have an important role.’ The signal-averaged electrocardiogram (SAECG) al- lows the noninvasive detection of late potentials at the end of or after the QRS complex.2Late potentials rep- resent low-amplitude fractionated electrical activity, are markers for an “arrhythmogenic substrate” that may become the site for re-entry,3 and provide important prognostic information in identifying patients at risk of arrhythmic eventsafter AMI.4-8 Controversial data are available concerning the influence of fibrinolytic treat- ment on the prevalence of ventricular late potentials,g-15 and the effect of both thrombolysis and coronary reper- fusion on late arrhythmic eventsafter AM1 is unknown. Furthermore, no data are available concerning a possi- ble influence of thrombolysis on the predictive ability of the SAECG for post-AM1 arrhythmic events.16 We performed a prospective study of unselected patients surviving a first AM1 to assess: (1) the influence of in- travenous thrombolysis on both the rate of late poten- tials and ventricular ectopic activity, (2) the influence of patency of the infarct-related coronary artery on the SAECG, (3) the possible influence of intravenous thrombolysis on late potentials as markers of future ma- lignant ventricular tachyarrhythmias, (4) and the possi- ble influence of fibrinolysis on the occurrence of late arrhythmic events after AMI. METHODS Patient population: From May 1989 to December 1990, 174 consecutive patients surviving a first AMI, and admitted to our institute for functional evaluation and cardiac rehabilitation were enrolled in the present study. Of patients included in the study, 106 (61%) re- ceived intravenous thrombolytic therapy within 6 hours of the onset of symptoms, and 68 (39%) were treated conventionally because of late hospitalization or contra- indications to fibrinolytic treatment. In the group treat- ed with thrombolysis, 58 patients (55%) receivedstrep- tokinase (1.5 million U over 30 to 60 minutes), 17 666 THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 69 APRIL 1, 1992