Cardiac resynchronization therapy for the treatment of mild heart failure: A review of the clinical data

Cardiac resynchronization therapy (CRT) was originally established as an effective treatment for patients with systolic heart failure (HF) with New York Heart Association Class III–IV symptoms, reduced left ventricular ejection fraction and prolonged QRS duration ≥120 ms. Subsequent studies expanded the role of CRT to the treatment of patients with mildly symptomatic HF as these patients experienced similar improvement in clinical symptoms and reverse remodeling of the left ventricle. These clinical trial results were incorporated into the 2013 guidelines on cardiac pacing and CRT from the European Society of Cardiology and the 2012 American College of Cardiology Foundation/American Heart Association/Heart Rhythm Society Focused Update on Device-based Therapy of Cardiac Rhythm Abnormalities. Additional data from careful post hoc and substudy analyses as well as long-term follow-up of the original study cohorts have been performed. These results attempt to identify subgroups more likely to benefit from CRT, to define the association between response and QRS morphology/duration and to demonstrate the sustained benefit of CRT in this population. More importantly, these results highlight that patients with mildly symptomatic HF who respond to CRT not only have improvement in clinical symptoms but also receive a therapy that may prevent or delay progression of HF. A review of the clinical trials in mildly symptomatic HF and the results of subsequent post hoc analysis are summarized herein.