Abstract 14845: Masquerading Bundle Branch Block: An Electrocardiographic Marker of Poor Prognosis

Abstract

Introduction: Masquerading bundle branch block (MBBB) is a rare cardiac conduction anomaly characterized in the Electrocardiogram (EKG) by Right Bundle Branch Block in the precordial leads and Left Bundle Branch Block in frontal leads. The available evidence indicates that it carries poor prognosis and that it is often underdiagnosed. We studied epidemiological peculiarities, electrocardiographic features and prognosis of this rare kind of ventricular conduction delay. Methods: In a review of over 600,000 EKGs from the database of Tele-Electrocardiography department of Dante Pazzanese Institute of Cardiology during the last seven years, we found twenty-five cases of MBBB. Diagnostic criteria were presence of QRS ≥ 0.12 s, dominant positive waves in V1, left axis deviation and absent or minimal S wave in DI and aVL. Epidemiological data was collected for each EKG and the follow-up of patient′s health status was assessed by telephone contact. Kaplan-Meier survival curves were based on the following endpoints: mortality, pacemaker implantation and the composite of both. Results: We identified twenty-five cases (21 males and 4 females) of MBBB. The average age was 69 (±14) years. Sinus rhythm was present in 17 patients (68%), atrial fibrillation in 7 (28%) and atrial flutter in one (4%). Average heart rate, PR interval, QRS length, QTc and QRS axis were, respectively: 70 (±17) bpm, 205 (±50) ms, 159 (±24) ms, 463 (±37) ms and -76° (±6) degrees. Follow-up data was successfully obtained from 15 patients: 4 (26.6%) had a pacemaker implanted, 7 (46.6%) died and 9 had combined endpoints (60%). According to the Kaplan-Meier survival curve, at 48 months, the estimated ratios of death, pacemaker implantation or combined endpoints were 41.4%, 38.9% and 80.2%, respectively. Conclusions: MBBB represents a high-risk condition and, although rare, this EKG pattern should be taken into consideration due to the poor prognosis associated with its presence.