Outcomes With Left Bundle Branch Block and Mildly to Moderately Reduced Left Ventricular Function.

OBJECTIVES: This study aimed to define the prognosis for patients with left bundle branch block (LBBB) and a mildly to moderately reduced left ventricular ejection fraction (LVEF) (36% to 50%) as well as to clarify whether LBBB remained a negative prognostic marker in this group.

BACKGROUND: LBBB is associated with worse outcomes in patients with heart failure in the setting of severely reduced LVEF. The level of morbidity and mortality associated with LBBB in the setting of a mildly to moderately reduced LVEF (36% to 50%) has not been clearly characterized. This knowledge is important to clarify the potential benefit of cardiac resynchronization therapy in this group.

METHODS: All patients identified as having an LBBB from 1994 to 2014 were included in the study if they had 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 2 groups.

RESULTS: Of 1,436 patients meeting inclusion criteria, 54% were male. Mean age was 67 ± 13 years, and mean LVEF at baseline was 44 ± 4%. There was no difference in baseline heart failure diagnosis between groups. There were significantly higher rates of baseline coronary artery disease in the control group and higher rates of aortic stenosis in the LBBB group. LBBB was associated with significantly worse mortality (hazard ratio [HR]: 1.17; 95% confidence interval [CI]: 1.00 to 1.36), an LVEF drop to 35% or less (HR: 1.34; 95% CI: 1.09 to 1.63), and the need for an implantable cardioverter-defibrillator (HR: 1.50; 95% CI: 1.10 to 2.10). Mortality remained significantly higher in the LBBB group when controlled for heart failure, coronary artery disease, and aortic stenosis (p = 0.04).

CONCLUSIONS: Patients with a mildly to moderately reduced LVEF and LBBB have poor clinical outcomes that are significantly worse than those for patients without conduction system disease. This group may obtain benefit from cardiac resynchronization therapy and deserves to be studied in prospective trials.