Characterization of super-response to cardiac resynchronization therapy

Background: In patients with chronic systolic heart failure who undergo cardiac resynchronization therapy (CRT), improvements in left ventricular ejection fraction (LVEF) and reductions in left ventricular volume are generally modest. A minority of patients experience a dramatic response to CRT (super-responders), but the attributes associated with these patients have not been fully characterized. Objective: The purpose of this study was to identify baseline clinical attributes of super-responders and to assess the survival benefit associated with this response. Methods: We reviewed clinical, echocardiographic, and ECG data from a cohort of 233 patients undergoing new implantation of a CRT device between December 2001 and November 2006. All patients had a baseline LVEF ≤40% and New York Heart Association class II to IV symptoms on standard medical therapy. Patients whose absolute LVEF improved by ≥20% were termed super-responders. A multivariate model was constructed to determine factors predictive of super-response, and an assessment of mortality was made. Results: In this cohort of 233 patients, 32 (13.7%) met criteria for super-response. In univariate analysis, super-responders were more likely to be female and have a native left bundle branch block, lower preimplant brain natriuretic peptide and red cell distribution width levels, and smaller baseline left ventricular volumes with trends toward having more nonischemic cardiomyopathy and midventricular lead positions. In multivariate analysis, only left bundle branch block remained significantly associated with super-response. Super-responders had a considerably lower incidence of mortality compared to non-super-responders (9.4% vs 43.2%, P = .006) at mean follow-up of 5.5 ± 1.2 years. Conclusion: Baseline left bundle branch block is strongly associated with super-response to CRT. Super-responders derive better long-term outcomes with CRT than do non-super-responders.