Predictors of Advanced His-Purkinje Conduction Disturbances in Patients With Unexplained Syncope and Bundle Branch Block

Background: For patients presenting with syncope and bundle branch block (BBB), results during electrophysiological studies (EPS) might depend on the electrocardiographic pattern of conduction disturbances. We sought to identify predictors of advanced His-Purkinje conduction disturbances (HPCDs) in these patients. Methods: In this retrospective multicentre study, patients were included who: (1) presented with unexplained syncope; (2) had BBB (QRS duration >= 120 ms); and (3) were investigated with EPS. HPCD was diagnosed if the baseline His-ventricular interval was >= 70 ms or if second- or third-degree His-Purkinje block was observed during atrial pacing or pharmacological challenge. Results: Of the 171 patients studied (72 +/- 13 years, 64% male sex, mean left ventricular ejection fraction 57 +/- 9%), advanced HPCD was found in 73 patients (43%). The following electrocardiographic features were associated with HPCD (P = 0.01): isolated right BBB (34.4%), right BBB with left anterior fascicular block (36.4%), left BBB (46.2%), and right BBB with left posterior fascicular block (LPFB, 78.6%). Multivariate analysis identified first-degree atrioventricular block (odds ratio, 2.4; 95% confidence interval, 1.2-4.7; P = 0.01) and LPFB (odds ratio, 4.8; 95% confidence interval, 1.3-18.5; P = 0.02) as the only 2 independent predictors of advanced HPCD. Conclusions: For patients presenting with syncope and BBB, first-degree atrioventricular block and LPFB increased the likelihood of finding HPCDs during EPS. However, no single electrocardiographic feature could consistently predict the outcome of EPS, so this investigation is still necessary in assessing the need for pacemaker implantation, irrespective of the precise appearance of abnormalities on ECG.