Evaluation of: Curtis AB, Worley SJ, Adamson PB, et al; Biventricular versus Right Ventricular Pacing in Heart Failure Patients with Atrioventricular Block (BLOCK HF) Trial Investigators. Biventricular pacing for atrioventricular block and systolic dysfunction. N. Engl. J. Med. 368(17), 1585–1593 (2013).
Recent trials have shown the benefit of cardiac resynchronization (CRT) in mild or moderate heart failure with a left bundle branch block or intraventricular conduction delay. Randomized trials (including the BLOCK-HF study) have now shown that irrespective of baseline QRS duration, long-term left ventricular (LV) remodeling, dysfunction and heart failure are more common in patients with long-term conventional right ventricular (RV) than those with biventricular (BiV) pacing. The detrimental effects of long-term RV pacing may occur in patients with normal and abnormal LV ejection fractions (LVEF). LV dysfunction induced by RV pacing can be improved by upgrading to a BiV system. Possible new indications for CRT (currently under investigation), include heart failure due to diastolic dysfunction (normal LVEF) with left bundle branch block or intraventricular conduction delay in the absence of bradycardia, and conditions not necessarily associated with a wide QRS complex or bradycardia, such as hypertrophic cardiomyopathy and LV non-compaction. The widespread use of CRT will be limited by the greater complications of LV pacing, unfamiliarity with implantation techniques and cost. At first, CRT will be favored in young patients and those with a low LVEF where ventricular pacing is required >40% of the time.