Masquerading bundle branch block (MBBB) is associated with more severe myocardial and conduction system impairment compared to standard bifascicular bundle branch block (SBBB), supporting its role as a marker of worse prognosis.
Patients with MBBB had significantly longer HV intervals compared to patients with standard bifascicular block.
Pacemaker implantation was required in nearly half of MBBB patients and in none of the SBBB patients.
Persistent atrial fibrillation was more frequent in MBBB patients than in SBBB patients.
MBBB patients had worse functional status, larger ventricular diameters, and lower ejection fraction compared to SBBB patients.
MBBB is a rare variant of bifascicular bundle branch block associated with poor prognosis and higher need for pacemaker implantation, with most prior data limited to case reports and reviews.
This research compared two types of electrical conduction problems in the heart: masquerading bundle branch block (MBBB) and standard bifascicular bundle branch block (SBBB). Both conditions affect how electrical signals travel through the heart's lower chambers, but MBBB has a distinctive and somewhat deceptive appearance on an electrocardiogram. The study followed 27 patients with MBBB and 18 with SBBB, putting all of them through heart ultrasound, 24-hour heart rhythm monitoring, and an invasive electrical testing procedure called an electrophysiological study. The study found that patients with MBBB were significantly worse off in several measurable ways. Their hearts showed weaker pumping function, larger chamber sizes, and more severe symptoms of heart failure. A specific electrical measurement called the HV interval — which reflects how efficiently signals travel through the heart's wiring system — was notably longer in MBBB patients, indicating more impaired conduction. Nearly half of MBBB patients (48%) needed a pacemaker implanted to keep their heart beating properly, compared to none of the SBBB patients. MBBB patients also had higher rates of persistent atrial fibrillation, an irregular heart rhythm that can increase stroke risk and worsen heart function. This research suggests that MBBB is not just a variant appearance on a heart tracing but a clinically meaningful signal of more serious underlying heart disease. Because most prior knowledge about MBBB came from isolated case reports, this study — though still relatively small — provides some of the first structured comparative data. The findings indicate that patients identified with MBBB may warrant closer monitoring and earlier consideration of interventions like pacemaker implantation.
Tavares de Albuquerque A, Coutinho Vaz de Lira C, de Carvalho Neto J, Rufino Pereira Silva R, Salviano de Macedo Neto I, Filho D. (2026). Maskerading Bundle Branch Block Versus Standard Bifascicular Block: A Prognostic Analysis Results Through Electrophysiological Study.. Annals of noninvasive electrocardiology : the official journal of the International Society for Holter and Noninvasive Electrocardiology, Inc. https://doi.org/10.1111/anec.70235