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Case Presentation
Apatient in their 70s presented to the emergency department with a history of syncope that occurred 7 days before admission without preceding signs or symptoms. Since then, the patient had been experiencing fatigue, mainly from exertion. The patient had a history of hypertension, heart failure, and aortic valve replacement surgery in 2020, complicated on follow-up by prosthetic valve thrombosis. The patient had been taking warfarin, furosemide, metoprolol succinate, and spironolactone. Initial evaluation revealed a heart rate of 61 beats/min, blood pressure of 114/74 mm Hg, oxygen saturation of 96%, and temperature of 36.6 °C. The physical examination was unremarkable, and a 12-lead electrocardiogram (ECG) was obtained (Figure).
The ECG demonstrated features that are suggestive of right bundle-branch block in the precordial leads with left bundle-branch block and left axis deviation in the frontal plane leads.
Questions: What are the notable findings of the patient’s initial ECG? What are the prognostic implications of these findings?
Interpretation
The ECG at presentation demonstrated regular sinus rhythm, heart rate of 75 beats/min, prolonged PR interval (240 milliseconds), and prolonged QRS duration (170 milliseconds). Morris index was presented in lead V1. In the precordial lead, a notched and monophasic R-wave was observed in V1, an electrocardiographic sign of right bundle-branch block (RBBB). However, S wave was absent in leads I and aVL, and a pattern of left bundle-branch block (LBBB) with left axis deviation (−81°) was present in the frontal plane leads. These ECG abnormalities were compatible with the diagnosis of masquerading bundle-branch block (MBBB), a rare form of bifascicular block associated with diffuse disease in the conduction system, poor prognosis, and a higher incidence of progression to advanced atrioventricular block.
