Cardiac resynchronization therapy with a defibrillator (CRT-D) in patients with mild heart failure symptoms, left ventricular dysfunction and a left bundle branch block may improve survival, researchers found. They presented their late-breaking clinical trial data March 30 at the American College of Cardiology (ACC) scientific session in Washington, D.C. Investigators conducted a follow-up of the Multicenter Automatic Defibrillator Implantation Trial with Cardiac Resynchronization Therapy (MADIT-CRT), a study that evaluated the safety and effectiveness of CRT-D in patients with asymptomatic or mildly symptomatic heart failure, a reduced ejection fraction of 30 percent or less and a prolonged QRS wave duration. For the follow-up, they assessed the effect of CRT-D on long-term survival among MADIT-CRT participants who survived after the original study. They assessed survival in 1,691 patients over an average of 5.6 years and again among 854 participants who enrolled in post-trial registries. Analyses were conducted on an intention-to-treat basis. Seven years after the initial enrollment, the cumulative all-cause mortality rate among patients with a left bundle branch block randomly assigned to CRT-D was 18 percent compared with those assigned to defibrillator therapy alone (29 percent). The survival benefit was independent of sex, cause of cardiomyopathy or QRS duration. However, there was no association between CRT-D and long-term clinical outcomes in patients without left bundle branch block. After adjusting for multiple variables, the data suggested an increased risk of death associated with CRT-D in patients without left bundle branch block. But the researchers cautioned that this finding should be interpreted with caution since it was obtained only after multivariate adjustment. The findings were published simultaneously in the New England Journal of Medicine. Boston Scientific provided the funding for this research.