[Effect of complete bundle-branch block on the averaged signal of high amplification electrocardiogram].

Intraventricular conduction defects delay ventricular activation and change the appearances of the signal averaged electrocardiogram. The aim of this study was to determine criteria capable of identifying patients with bundle branch block at high risk of ventricular tachycardia (VT). Two hundred and twenty four patients were studied by Simson's method. One hundred and twenty eight patients (Group I control) had narrow QRS complexes and sequellae of previous myocardial infarction. Eighty four patients had no clinical or inducible VT; 44 had clinical and/or inducible VT with programmed stimulation. Forty six patients (Group II) had complete right bundle branch block (RBBB); 30 had no VT and 16 had VT. Twenty seven patients (Group III) had complete left bundle branch block of whom 18 had no VT and 9 had VT. Twenty three patients (Group IV) had RBBB with operated tetralogy of Fallot; 16 had no VT and 7 had VT. In the control group, the results of signal averaged ECG were the same as those reported in the literature: prolongation of the duration of the averaged QRS (136 +/- 35 ms vs 104 +/- 14 ms), decrease in amplitude of the last 40 ms (11 +/- 15 microV vs 43 +/- 28 microV) and an increase in the duration of less than 40 microV terminal activity (53 +/- 30 ms vs 28 +/- 11 ms) in those subjects with VT compared to those without VT. In Groups II, III and IV no significant difference was found in the amplitude of the last 40 ms or duration of less than 40 microV activity between patients with and without VT.(ABSTRACT TRUNCATED AT 250 WORDS)