Cardiac Resynchronization Therapy

Abstract

More than 2 decades of research has established the role of cardiac resynchronization therapy (CRT) in medically refractory, mild to severe systolic heart failure (HF) with abnormal QRS duration and morphology. CRT confers a mortality benefit, reduces HF hospitalizations, and improves functional outcome in this population, but not all patients consistently demonstrate a positive CRT response. The reported nonresponder rate ranges between 20% and 40%, depending on the response criteria used.1 Efforts to improve response to CRT have focused on methods to optimize the correction of electrical and mechanical dyssynchrony (the primary target of CRT) and on improving patient selection and optimizing postimplant care. The present article reviews the state-of-the-art of CRT and discusses developments on potential promises and areas of controversy. Although CRT became common clinical practice >10 years ago, the last 2–3 years have shown a series of large clinical trials that clearly outlined the categories of patients that benefit of CRT. First of all, 3 landmark studies—REsynchronization reVErses Remodeling in Systolic left vEntricular dysfunction (REVERSE),2 Multicenter Automatic Defibrillator Implantation Trial-Cardiac Resynchronization Therapy (MADIT-CRT)3 and Resynchronization for Ambulatory Heart Failure Trial (RAFT)4—have been performed to investigate the effectiveness of CRT in HF patients with a wide QRS complex and mild symptoms (New York Heart Association [NYHA] class I–II), in which patients have been randomized to CRT-ON and CRT-OFF. The main findings were that REVERSE showed significant reverse remodeling, MADIT-CRT showed less hospitalization, and RAFT also showed significant reduction in mortality in the CRT arm. The CRT benefit shown in these studies is consistent with those from older studies performed in patients with more severe HF symptoms. Figure 1 displays that the increase in left ventricular (LV) ejection fraction (EF) by CRT is independent of baseline EF. Figure 1. Change in left ventricular ejection fraction after …