Incidence and Natural History of Left Bundle Branch Block Induced Cardiomyopathy.

September 2019 1 Left bundle branch block (LBBB) is associated with left ventricular dysfunction, heart failure, and increased mortality in patients with/without cardiac diseases.1–3 In our previous study of 1436 patients with mild to moderately reduced left ventricular ejection fraction (LVEF) and LBBB, the clinical outcomes were significantly worse than those of patients without conduction disease.3 Current data on incidence of LBBB-induced cardiomyopathy remain sparse. We further studied adult patients with LBBB and baseline normal LVEF of >50% from 1994 to 2014. Institutional Review Board approval was obtained for this study. Informed consents were waived given the retrospective aspect of the study and the minimal risks involved. Categorical variables were compared with the χ2 test and continuous variables with the ANOVA test. All statistical analysis was performed using JMP software (SAS Institute, Cary, NC). Only 549 patients who had baseline and follow-up echocardiograms were included out of a total 2235 patient with LBBB and baseline LVEF >50%. Patients who had a significant drop in LVEF (>10%) to less than 50% were reviewed to determine the cause of cardiomyopathy. The study cohort consisted of 549 patients (age 66.7±11.0 years; 55% females) with a LBBB, normal LVEF (>50%) at baseline, and a follow-up echocardiogram. Of these, 134 (24.4%) had a significant drop in LVEF. The baseline characteristics were comparable between patients with and without drop in the LVEF except for sex and hyperlipidemia (Table). Patients who had a drop in LVEF were more likely to be males (P=0.02) and more likely to be hyperlipidemic (P=0.04). The majority of patients who developed LV dysfunction had clearly identifiable causes of worsening LVEF (Figure). It is important to note that patients with other potential causes of cardiomyopathy may, in fact, have developed LV dysfunction due the LBBB. Nevertheless, to limit potential confounders, we did not consider the LBBB as the cause unless there were no other causes. Ischemic heart disease was the most common condition associated with LVEF drop (10%). The cause of cardiomyopathy in the remaining 29 patients (5.3%) was potentially related to the LBBB itself. All patients with suspected LBBB-induced cardiomyopathy had been evaluated with advanced imaging (cardiac MRI and cardiac positron emission tomography /computed tomography) to rule out other etiologies. Patients with possible LBBB-induced cardiomyopathy were more likely to be younger (average of 59.8 versus 66.6 years, P=0.02). Mean baseline LVEF was 56% and dropped to a low EF of 31% at an average of 4.6 years. Of this group, 83% developed new onset of heart failure; 30% died at an average of 7.2 years from the drop in EF. The EF was ≤35% in 24 (83%) patients, with cardiac resynchronization therapy instituted in only 7 (24%). In these patients, there was a significantly greater improvement in EF in those receiving cardiac resynchronization therapy compared with those who did not (mean absolute LVEF increase of 16% versus 4%, P=0.001). The most recent LVEF for patients receiving cardiac resynchronization therapy was a mean of 41%. RESEARCH LETTER