Left Bundle Branch Block and Mildly Reduced LV Function

Study Questions:

What is the prognosis for patients with left bundle branch block (LBBB) and a mildly to moderately reduced left ventricular ejection fraction (LVEF) between 36% and 50%?


Mayo Clinic medical records from 1994 to 2014 were queried for LBBB, and cases were selected if there was a baseline echocardiogram within 1 year and an LVEF between 36% and 50%. A control group without intraventricular conduction abnormality matched on age, sex, baseline LVEF, and date of echocardiogram was created. Outcomes were compared between the two groups.


There were 1,436 patients meeting inclusion criteria. Mean age was 67 years, and mean LVEF at baseline was 44%. There was no difference in baseline heart failure diagnosis between groups. LBBB was associated with significantly worse mortality (hazard ratio [HR], 1.17; 95% confidence interval [CI], 1.00-1.36), an LVEF drop to 35% or less (HR, 1.34; 95% CI, 1.09-1.63), and the need for an implantable cardioverter-defibrillator (HR, 1.50; 95% CI, 1.10-2.10). Mortality remained significantly higher in the LBBB group in multivariate analysis when controlled for heart failure, coronary artery disease, and aortic stenosis (p = 0.04).


Patients with a mildly to moderately reduced LVEF and LBBB have worse clinical outcomes than those without conduction system disease.


The fact that LBBB is associated with worse outcomes in patients with heart failure is well established. This study demonstrates that LBBB is associated with worse outcomes even in a cohort of patients with mild LV dysfunction, more than 90% of whom did not have a diagnosis of HF prior to the baseline echocardiogram. This has important implications, because cardiac resynchronization therapy could potentially prevent progression to overt heart failure and more severe LV dysfunction. This possibility should be explored in prospective randomized trials.

Clinical Topics: Arrhythmias and Clinical EP, Heart Failure and Cardiomyopathies, Noninvasive Imaging, Prevention, Valvular Heart Disease, Atherosclerotic Disease (CAD/PAD), Implantable Devices, EP Basic Science, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Acute Heart Failure, Echocardiography/Ultrasound

Keywords: Aortic Valve Stenosis, Arrhythmias, Cardiac, Bundle-Branch Block, Cardiac Resynchronization Therapy, Coronary Artery Disease, Defibrillators, Implantable, Echocardiography, Heart Conduction System, Heart Failure, Medical Records, Secondary Prevention, Stroke Volume, Ventricular Function, Left

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