Signal-averaged ECG prognostic significance in patients with myocardial infarction and bundle branch block

The late potential analysis has been reported to identify ventricular arrhy thmias and adverse prognosis in patients with myocardial infarction. The purpose of this study was to investigate whether the presence of a comp lete bundle branch block (BBB) affects prognostic information of signal-ave raged ECG (SA EGG). We prospectively obtained SAECG in 119 patients with my ocardial infarction and BBB. 76 of them had a right (R)BBB (group I) and 43 st left (L)BBB. According to the clinical history of spontaneous ventricul ar tachycardia (VT) and/or syncopes and to the results of programmed ventri cular stimulation, the patients were divided into 4 groups : 1) group IA wi th RBBB and VT (n=52); 2) group IB with RBBB but without VT (n=24); 3) grou p IIA with LBBB and VT (n=33);4) group IIB with LBBB but without VT (n=10). Individual and combined criteria were evaluated to obtain the best diagnos tic value of SA ECG for the detection of patients with BBB and VT. In those with RBBB, the combination of 2 of the 3 available criteria, QRS duration >155 ms, LAS duration >30 ms and RMS 40 < 17 mu V leaded up to the best ove rall statistical result with a sensitivity and specificity of respectively 50 and 57%. The diagnostic value was higher for the LBBB : the combination of 2 of the 3 criteria QRS duration > 165 ms, LAS duration > 40 ms and RMS 40 < 17 mu V had the best value with a sensitivity and specificity of respe ctively 73 and 55,5%. The risk of cardiac mortality was not predicted by SA ECG and was found higher in patients with LBBB, who had a lower ejection f raction, than those with a RBBB, independently of the SAECG abnormalities a nd VT. In conclusion, the low diagnostic value of SA ECG in patients with RBBB for the detection of VT should lead to exclude these patients from the SA ECG analysis. The diagnostic value of SA ECG was better in patients with LBBB f or the prediction of VT, but SAECG should be interpreted in the light of cl inical history and results of other investigations. Moreover, the high inci dence of inducible sustained VT in symptomatic patients with BBB should lea d directly to invasive studies and the bad prognosis found in patients with a BBB and VT was not predicted by SAECG.