Excerpt

Cardiac resynchronization therapy (CRT) improves left ventricular (LV) remodeling, quality of life, and survival among patients with heart failure and reduced ejection fraction (EF < 35%) and electrical dyssynchrony (wide QRS duration).1^–3 However, a significant proportion of patients do not derive the expected benefit from such expensive and invasive procedure.4 In 2011, Goldengerb et al. identified 7 factors from the Multicenter Automatic Defibrillator Implantation Trial With Cardiac Resynchronization Therapy (MADIT-CRT) trial that improved patient selection and predicted better CRT response;5 these included female gender, non-ischemic cardiomyopathy, left bundle branch block (LBBB), QRS ≥ 150 ms, prior hospitalization for heart failure, left ventricular end-diastolic volume index ≥ 125 ml/m², and left atrial volume index less than 40 ml/m². Shortly after, the 2012 guidelines for CRT implantation were updated and recommended CRT for patients with EF ≤ 35%, NYHA class ≥ II with LBBB, and QRS ≥ 150 ms (the only class I indication) as compared to a QRS threshold ≥ 120–130 ms with 2008 guidelines.6 …