Impact of left bundle branch block on heart rate and its relationship to treatment with ivabradine in chronic heart failure

Left bundle branch block (LBBB) increases morbidity and mortality in heart failure (HF). Heart rate reduction with ivabradine improves outcomes in patients with systolic HF. Therefore, we aimed to analyse the impact of LBBB on outcomes in patients with systolic HF as a function of heart rate, and the relationship between LBBB and the effect of treatment with ivabradine. Patients from the SHIFT (n 6505) were divided into groups with (n 912) or without (n 5593) LBBB at baseline, and according to tertiles of heart rate (7073, 7480, and 81 b.p.m.). The effect of LBBB, heart rate, and ivabradine on the primary endpoint (cardiovascular death or HF hospitalization) and other endpoints was analysed. LBBB was associated with increases in the primary endpoint by 65, cardiovascular mortality by 49, HF hospitalization by 86, and all-cause mortality by 49 (all P 0.001). No interaction appeared between the impact of heart rate on outcomes and presence of LBBB (P 0.83 for the primary endpoint); thus LBBB increases risk for all heart rates. No interaction was apparent in the effect of ivabradine with LBBB or without LBBB. Ivabradine did not increase the prevalence of bradycardia in patients with LBBB. LBBB increases risk in HF patients with heart rates 70 b.p.m. in sinus rhythm, unmodulated by heart rate. Ivabradine was safe in LBBB. Its effect was directionally similar to that in patients without LBBB, but did not reach statistical significance, possibly due to lack of power to test this effect because of the small number of LBBB patients.