Ivabradine in Patients With an Unsatisfactory Percentage of Cardiac Resynchronization Therapy

The purpose of this study is to determine the role of ivabradine in cardiac resynchronization recipients with an unsatisfactory percentage biventricular pacing. The study protocol 60 patients with heart failure NYHA (New York Heart Association) II-IV treated with optimal medical therapy as clinically indicated who received CRT-D device more than 3 months ago. Patients with biventricular pacing \50% of heart rate in device memory \>70 will receive ivabradine. The minimal follow-up of patients in the study will be at least six months.