Level 2: Mid-level evidence

Current guidelines from the American College of Cardiology and the American Heart Association recommend cardiac resynchronization therapy (CRT) for patients with NYHA class III or IV heart failure symptoms who have an ejection fraction <35% and a QRS interval >120 milliseconds, and are in sinus rhythm (ACC/AHA Class I, Level A recommendation, (Circulation. 2009;119:1977-2016).

Systematic reviews have found that CRT may reduce mortality and hospitalization in patients with QRS prolongation, in patients with class III-IV symptoms (Health Technol Assess. 2007;11:iii-iv, Ann Intern Med. 2004;141:381-390) and patients with class I-II symptoms (Ann Intern Med. 2011;154:401-412).

A new systematic review examined data from randomized trials that provided subgroup analyses of patients stratified by severity of QRS prolongation (Arch Intern Med. 2011;171:1454-1462). QRS intervals 120-149 milliseconds were classified as moderately prolonged and intervals >150 milliseconds as severely prolonged. Analyses included 1,738 patients with class III-IV symptoms (from two trials; 64% with severe prolongation) and 4,228 patients with class I-II symptoms (from three trials; 60% with severe prolongation).

The primary outcome in all trials was a composite of adverse clinical events including mortality and hospitalization. CRT was associated with reduced risk of adverse clinical events in patients with severely prolonged QRS intervals in the overall analysis (risk ratio [RR]=0.6, 95% CI 0.53-0.67) and in analyses of patients with class III-IV symptoms (RR 0.67, 95% CI 0.57-0.8) and patients with class I-II symptoms (RR 0.47, 95% CI 0.37-0.6). In patients with only moderately prolonged QRS intervals, there were no significant differences in risk overall or in either symptom subgroup.

Alan Ehrlich, MD, is a deputy editor for DynaMed, Ipswich, Mass., and assistant clinical professor in Family Medicine, University of Massachusetts Medical School in Worcester. DynaMed is a database that provides evidence-based information on more than 3,000 clinical topics and is updated daily through systematic surveillance covering more than 500 journals. The most important evidence identified is summarized here.