Introduction: Masquerading bundle branch block is a right bundle branch block with a left anterior hemiblock which appears similar to a left bundle branch block in the frontal plane leads.
Material and methods: We have followed 22 patients with such a pattern in the electrocardiogram for 3 years.
Results: Thirteen patients (59%) developed high degree atrioventricular block. During this period, there were 4 deaths, 3 from heart failure and 1 due to sepsis.
Conclusions: We conclude that progression to high degree atrioventricular block is quite common in the presence of this kind of branch block. It is frequently associated to advanced heart failure, so the prognosis is usually poor.