Patients undergoing cardiac resynchronization therapy defibrillator (CRT-D) implantation in clinical practice with longer QRS duration and left bundle-branch block (LBBB) morphology have a lower risk of all-cause mortality and of all-cause cardiovascular and heart failure readmissions than patients without LBBB or shorter duration QRS, according to data published Aug. 13 in the Journal of the American Medical Association .

Researchers used data from the NCDR® ICD Registry™ to conduct a retrospective review of 24,169 patients 65 and older who had a CRT-D implantation between April 1, 2006, and December 31, 2009, in the U.S. After adjusting for demographic and clinical factors, patients with a QRS duration of 150 ms or longer and LBBB morphology had a lower risk of mortality at three years compared to those with a QRS duration of 120-149 ms and LBBB (HR=1.3, p<0.001), a QRS duration of 150 ms or longer and no LBBB (HR=1.34, p<0.001) or a QRS duration of 120-149 ms and no LBBB (HR=1.52, p<0.001). Results were similar for all-cause readmission, cardiovascular readmission and heart failure readmission one year post-implantation, with a QRS duration of 150 ms or longer and LBBB associated with the lowest risk (p<0.001 for all).

The authors note that clinicians have long recognized that between one-third and one-half of patients who receive CRT for heart failure do not improve. “Our real-world data add to the increasing body of evidence that patients with LBBB have better outcomes after CRT,” said lead author Pamela Peterson, MD, MSPH, FACC, Denver Health Medical Center, Denver. “Our findings in this large cohort of patients are concordant with guidelines, which provide stronger recommendations for patients with LBBB compared with those without and for patients with more prolonged QRS duration.”

Peterson notes that the observational study did not have a control group, and cautions that the results should not be used to assess the benefits of CRT in patients with a QRS duration of less than 150 ms or without LBBB morphology.

Keywords: Defibrillators, Demography, Heart Failure, Bundle-Branch Block, Cardiac Resynchronization Therapy