Syncope in Patients with Chronic Bifascicular Block

Syncope was prospectively evaluated in 186 patients with chronic bifascicular block. Syncope occurred in 21 of 124 patients with right bundle-branch block and left anterior hemiblock, 3 of 24 patients with right bundle-branch block and left posterior hemiblock, and 6 of 38 patients with left bundle-branch block. Each case was evaluated by using prolonged electrocardiographic monitoring, His bundle recordings, and other indicated studies. Probable and possible causes of syncope included intermittent heart block in five patients, sinus exit block in one patient, orthostatic hypotension in two patients, seizure disorders in three patients, ventricular arrhythmia in nine patients, and acute blood loss in one patient. No cause could be identified in nine patients. Comparison of patients with and without syncope did not show significant differences. Syncope was recurrent in only five patients (four with heart block and one with seizure disorder). The incidence of late sudden death in patients with and without syncope was identical. Syncope in patients with bifascicular block reflected various cardiac and noncardiac causes and tended not to recur. Permanent pacing seemed indicated in only those patients with documented serious bradyarrhythmia.