Clinical significance of the pattern of incomplete left bundle branch block with bifascicular block.

A comparative analysis was carried out of 126 patients (group I) with chronic right bundle branch block (RBBB) and left anterior (LAFB) or left posterior fascicle block (LPFB), and of 44 patients (group II) with the same bifascicular block associated with an ECG pattern of incomplete left bundle branch block (ILBBB). The two groups were found to be clinically different. In group II, heart failure, arrhythmia and first-degree atrioventricular block occurred significantly more frequently. During a mean follow-up period of 1581 +/- 118 days (85-6260 days), complete heart block (CHB) developed in 3.2% of patients in group I and in 22.7% in group II (p less than 0.01). In the same period, sudden cardiac death (SCD) occurred in 3.9% in group I and in 15.9 in group II (p less than 0.01). These results were analysed assuming a quadrifascicular character of the intraventricular conduction system. This made it possible to isolate on the basis of standard ECG findings patients with trifascicular block (group II--RBBB and LAFB or LPFB and septal LBBB) in whom prophylactic pacemaker implantation should be considered in view of high risk of CHB and SCD.