• Pamela N Peterson, Melissa A Greiner, Laura G Qualls, Sana M Al-Khatib, Jeptha P Curtis, Gregg C Fonarow, Stephen C Hammill, Paul A Heidenreich, Bradley G Hammill, Jonathan P Piccini, Adrian F Hernandez, Lesley H Curtis, and Frederick A Masoudi.
• Division of Cardiology, Department of Medicine, Denver Health Medical Center, Denver, CO 80204, USA. pamela.peterson@ucdenver.edu
• JAMA. 2013 Aug 14;310(6):617-26.

ImportanceThe benefits of cardiac resynchronization therapy (CRT) in clinical trials were greater among patients with left bundle-branch block (LBBB) or longer QRS duration.ObjectiveTo measure associations between QRS duration and morphology and outcomes among patients receiving a CRT defibrillator (CRT-D) in clinical practice.Design, Setting, And ParticipantsRetrospective cohort study of Medicare beneficiaries in the National Cardiovascular Data Registry's ICD Registry between 2006 and 2009 who underwent CRT-D implantation. Patients were stratified according to whether they were admitted for CRT-D implantation or for another reason, then categorized as having either LBBB or no LBBB and QRS duration of either 150 ms or greater or 120 to 149 ms.Main Outcomes And MeasuresAll-cause mortality; all-cause, cardiovascular, and heart failure readmission; and complications. Patients underwent follow-up for up to 3 years, with follow-up through December 2011.ResultsAmong 24 169 patients admitted for CRT-D implantation, 1-year and 3-year mortality rates were 9.2% and 25.9%, respectively. All-cause readmission rates were 10.2% at 30 days and 43.3% at 1 year. Both the unadjusted rate and adjusted risk of 3-year mortality were lowest among patients with LBBB and QRS duration of 150 ms or greater (20.9%), compared with LBBB and QRS duration of 120 to 149 ms (26.5%; adjusted hazard ratio [HR], 1.30 [99% CI, 1.18-1.42]), no LBBB and QRS duration of 150 ms or greater (30.7%; HR, 1.34 [99% CI, 1.20-1.49]), and no LBBB and QRS duration of 120 to 149 ms (32.3%; HR, 1.52 [99% CI, 1.38-1.67]). The unadjusted rate and adjusted risk of 1-year all-cause readmission were also lowest among patients with LBBB and QRS duration of 150 ms or greater (38.6%), compared with LBBB and QRS duration of 120 to 149 ms (44.8%; adjusted HR, 1.18 [99% CI, 1.10-1.26]), no LBBB and QRS duration of 150 ms or greater (45.7%; HR, 1.16 [99% CI, 1.08-1.26]), and no LBBB and QRS duration of 120 to 149 ms (49.6%; HR, 1.31 [99% CI, 1.23-1.40]). There were no observed associations with complications.Conclusions And RelevanceAmong fee-for-service Medicare beneficiaries undergoing CRT-D implantation in clinical practice, LBBB and QRS duration of 150 ms or greater, compared with LBBB and QRS duration less than 150 ms or no LBBB regardless of QRS duration, was associated with lower risk of all-cause mortality and of all-cause, cardiovascular, and heart failure readmissions.

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