[The effects of a left bundle-branch block on ventricular repolarization dispersion]

L Calò, M Levato, L Sciarra, M S Nazzaro, F Benvissuto, M Borzi, D De Nardo, D Cannata
Cardiologia: Bollettino Della Società Italiana di Cardiologia 1996, 41 (11): 1073-7
Patients with left bundle-branch block (LBBB) often present electrocardiographic abnormalities and, therefore, are excluded from studies concerning electrocardiographic evaluation of ventricular repolarization. The aim of the study was to assess whether LBBB could influence dispersion of ventricular repolarization. Surface electrocardiograms of 16 patients (9 males and 7 females, mean age 58 +/- 14 years) with episodes of intermittent LBBB were analyzed. Six patients were affected by coronary artery disease, 6 by hypertensive cardiomyopathy and 4 by dilated cardiomyopathy. Maximal QT and JT corrected intervals, QT and JT dispersion, and QT and JT dispersion corrected for heart rate, were obtained before and after LBBB. We observed a significant prolongation of maximal QT (412 +/- 29 vs 433 +/- 25 ms; p < 0.05), and of maximal corrected QT (457 +/- 37 vs 497 +/- 56 ms; p < 0.05) after LBBB. Maximal JT interval, also corrected for heart rate, did not show any significant modification after LBBB. Moreover, we did not observe any significant difference in electrocardiographic parameters of dispersion of repolarization. Our results seem to indicate that LBBB did not alter significantly dispersion of ventricular repolarization. QT dispersion is considered an important marker of risk for incidence of ventricular arrhythmias. If our results will be confirmed in larger groups of patients, analysis of QT dispersion could be extended even to patients with LBBB.

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