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CRT-D for Nonspecific Intraventricular Conduction Delay vs. RBBB
Study Questions:
What are the clinical outcomes among Medicare-aged patients with nonspecific intraventricular conduction delay (NICD) versus right bundle branch block (RBBB) in patients eligible for implantation with a cardiac resynchronization therapy (CRT) with defibrillator (CRT-D)?
Methods:
Using the National Cardiovascular Data Registry implantable cardioverter-defibrillator (ICD) registry data between 2010 and 2013, the authors compared outcomes in CRT-eligible patients implanted with CRT-D versus ICD-only therapy among patients with NICD and RBBB. Also, among all CRT-D–implanted patients, the authors compared outcomes in those with NICD versus RBBB. Survival curves and multivariable adjusted hazard ratios (HRs) were used to assess outcomes including hospitalization and death.
Results:
In 11,505 non–left BBB (non-LBBB) CRT-eligible patients, after multivariable adjustment, among patients with RBBB, CRT-D was not associated with better outcomes, compared with ICD alone, regardless of QRS duration. Among patients with NICD and a QRS ≥150 ms, CRT-D was associated with decreased mortality at 3 years compared with ICD alone (HR, 0.602; 95% confidence interval [CI], 0.416-0.871; p = 0.0071). Among 5,954 CRT-D–implanted patients, after multivariable adjustment, NICD compared with RBBB was associated with lower mortality at 3 years in those with a QRS duration of ≥150 ms (HR, 0.757; 95% CI, 0.625-0.917; p = 0.0044).
Conclusions:
Among non-LBBB CRT-D–eligible patients, CRT-D implantation was associated with better outcomes compared with ICD alone specifically in NICD patients with a QRS duration of ≥150 ms. Careful patient selection should be considered for CRT-D implantation in patients with non-LBBB conduction.
Perspective:
Patients with non-LBBB respond less well to CRT, compared with patients with LBBB, and they have been a minority of subjects in clinical trials of CRT. Some patients with NICD do have conduction delay in the left bundle, as opposed to a complete block. Those patients respond to CRT better than those with overt RBBB. In this study, in patients with NICD and a QRS duration of >150 ms, an improvement in both overall survival, all-cause readmission, and cardiovascular readmission was seen with implantation of a CRT-D versus ICD only. In patients with NICD and a QRS duration of 120-149 ms, CRT-D compared with ICD only implantation was associated with increased mortality and HF readmission. Future randomized studies may be necessary to fully understand whether patients with non-LBBB conduction abnormality truly benefit from CRT.
Clinical Topics: Arrhythmias and Clinical EP, Geriatric Cardiology, Heart Failure and Cardiomyopathies, Implantable Devices, EP Basic Science, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Acute Heart Failure
Keywords: Arrhythmias, Cardiac, Bundle-Branch Block, Cardiac Resynchronization Therapy, Defibrillators, Implantable, ICD Registry, Geriatrics, Heart Failure, ICD Registry, Myocardial Ischemia, Patient Readmission, Patient Selection, National Cardiovascular Data Registries, ICD Registry
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