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 ≥ 120 ms), all of whom had a preimplant Echo‐LVEF ≤35%, 130 had a CMR‐LVEF ≤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 ≥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%.