Masquerading bundle branch block as a marker of poor prognosis

Abstract

Masquerading bundle branch block is a rare and unique finding on a 12-lead electrocardiogram, consisting of the pattern of right bundle branch block in the precordial leads and left bundle branch block in the limb leads. We experienced a 77-year-old woman with masquerading bundle branch block. She had been well, but died suddenly 9 months after the diagnosis of masquerading bundle branch block. The presence of masquerading bundle branch block indicates severe degeneration of the conduction system, leading to a poor outcome. <Learning objective: Masquerading bundle branch block is a rare and unique finding on a 12-lead electrocardiogram, consisting of the pattern of right bundle branch block in the precordial leads and left bundle branch block in the limb leads. The presence of masquerading bundle branch block indicates severe degeneration of the conduction system, leading to a poor outcome. Close follow-up is mandatory in patients with masquerading bundle branch block even if they do not have any symptoms.>.

Keywords: Bundle branch block; Electrocardiography; Masquerading; Prognosis.

Fig. 1

An electrocardiogram shows left axis deviation (−64°), prolonged PR interval (233 ms), and prolonged QRS duration (159 ms), suggesting trifascicular block. The chest leads show an rSR’ in V1 and wide and deep S waves in V5 and V6, features consistent with right bundle branch block. In contrast, an absence of S waves in leads I and aVL and an absence of septal Q waves in leads V5 and V6 resemble a left bundle branch block pattern.

Fig. 2

An electrocardiogram obtained 8 years before admission shows prolonged QRS duration (138 ms) with an rsR’ wave in V1 and wide S waves in leads I, aVL, and V5 and V6, suggesting right bundle branch block.