Cardiac resynchronization therapy in patients with mildly impaired left ventricular function.

AIMS: We sought to determine the unknown effects of cardiac resynchronization therapy (CRT) in patients with a left ventricular ejection fraction (LVEF) >35%. Because of its technical limitations, echocardiography (Echo) may underestimate LVEF, compared with cardiovascular magnetic resonance (CMR). METHODS: Of 157 patients undergoing CRT (New York Heart Association [NYHA] functional class III or IV, QRS > or = 120 ms), all of whom had a preimplant Echo-LVEF <or =35%, 130 had a CMR-LVEF <or =35% (Group A, 19.7 +/- 7.0%[mean +/- standard deviation]) and 27 had a CMR-LVEF >35% (Group B, 43.6 +/- 7.7%). All patients underwent a CMR scan at baseline and a clinical evaluation, including a 6-minute walk test and a quality of life questionnaire, at baseline and after CRT. RESULTS: Both groups derived similar improvements in NYHA functional class (A =-1.3, B =-1.2, [mean]), quality of life scores (A =-21.6, B =-33.0; all P <0.0001 for changes from baseline), and 6-minute walking distance (A = 64.5, B = 70.1 m; P <0.001 and P <0.0001, respectively). Symptomatic response rates (increase by > or =1 NYHA classes or 25% 6-minute walking distance) were 79% in group A and 92% in group B. Over a maximum follow-up period of 5.9 years for events, patients in group A were at a higher risk of death from any cause, hospitalization for major cardiovascular events (P = 0.0232), or cardiovascular death (P = 0.0411). There were borderline differences in the risk of death from any cause (P = 0.0664) and cardiovascular death or hospitalization for heart failure (P = 0.0526). CONCLUSIONS: This observational study suggests that the benefits of CRT extend to patients with a LVEF > 35%.