A standardized conventional evaluation of the mechanism of syncope in patients with bundle branch block.

BACKGROUND The finding of bundle branch block in patients with syncope suggests that paroxysmal AV block may be the cause of syncope, even though its prevalence is unknown. METHODS We evaluated 55 consecutive patients with syncope and bundle branch block (mean age 75 +/- 8 years; median of two syncopal episodes per patient) referred to three Syncope Units. The hierarchy and appropriateness of diagnostic tests and the definitions of the final diagnoses followed standardized predefined criteria. RESULTS Cardiac syncope was diagnosed in 25 patients (45%): AV block in 20, sick sinus syndrome in 2, sustained ventricular tachycardia in 1, aortic stenosis in 2. Neurally mediated syncope was diagnosed in 22 (40%): carotid sinus syndrome in 5, tilt-induced syncope in 15, adenosine-sensitive syncope in 2. Syncope remained unexplained in 8 (15%). CONCLUSIONS Less than half of the patients with bundle branch block have a final diagnosis of cardiac syncope; in these patients, paroxysmal AV block is the most frequent but not the only mechanism supposed.