Abstract
Masquerading bundle branch block (MBBB) is a rare presentation of bifascicular blocks. It is the result of a right bundle branch block associated with an advanced left anterior fascicular block due to extensive damage to the conduction system. We present the case of a 75-year-old male with late onset presentation anterior wall myocardial infarction (MI) with ongoing ischemia (which evolved into a ventricular septal defect [VSD]). Electrocardiographically, the MBBB is characterized by a prominent R in V1, left axis deviation and absence of small S waves in I and aVL. Its presence confers a poor prognosis and high risk of progressing to advanced atrioventricular block (AAVB). A mortality rate between 18% and 38.9% has been found and 41.4%-59% of the patients develop AAVB requiring pacemaker implantation. To our knowledge, this is the first reported MBBB case in the setting of an MI complicated with VSD, demonstrating its association with the presence of critical anteroseptal ischemia. The patient rejected any kind of intervention, palliative care was offered, and he died 2 months later.