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CRT-D confers improved outcomes for nonspecific intraventricular conduction delay
Cardiac resynchronization therapy defibrillator implantation conferred improved outcomes vs. implantable cardioverter defibrillator implantation in patients without left bundle branch block, particularly in those with nonspecific intraventricular conduction delay who had a QRS duration of at least 150 milliseconds, according to a study published in the Journal of the American College of Cardiology.
“This means that if you have a patient with [right bundle branch block] who is still suffering from heart failure symptoms after medical therapy, there is not enough data to support using CRT blindly,” Hiro Kawata, MD, PhD, cardiologist at the Oregon Heart and Vascular Institute in Springfield, said in a press release. “But in [nonspecific intraventricular conduction delay] patients, we now know that those with a long QRS are likely to benefit from CRT.”
National Cardiovascular Data Registry
Researchers analyzed data from 11,505 patients from the National Cardiovascular Data Registry who were aged at least 65 years and did not have left bunch branch block. These patients underwent ICD implantation between April 2010 and December 2013. QRS duration and morphology including nonspecific intraventricular conduction delay and right bundle branch block were predictor variables of interest.
Two analyses were performed in this study:
- Outcomes in patients with non-left bundle branch block who were eligible for CRT and underwent CRT implantation compared with those only received ICD therapy.
- Outcomes were compared in patients who only received CRT-D with nonspecific intraventricular conduction delay vs. those with right bundle branch block.
Primary outcomes of interest for both analyses were all-cause mortality at 3 years after implantation, HF, and CV and all-cause readmission at 1 year. Secondary outcomes of interest for both analyses were complications during the index hospitalization, at 30 days and at 90 days.
During a median follow-up of 2.3 years, CRT-D implantation was not linked to improved outcomes vs. ICD alone in patients with right bundle branch block regardless of QRS duration.
Compared with ICD alone, patients with nonspecific intraventricular conduction delay and a QRS duration of at least 15 milliseconds had decreased mortality at 3 years (HR = 0.602; 95% CI, 0.416-0.871).
Of the 5,954 patients who underwent CRT-D implantation, those with nonspecific intraventricular conduction delay and had a QRS duration of at least 150 milliseconds had lower mortality at 3 years compared with those with right bundle branch block (HR = 0.757; 95% CI, 0.625-0.917).
“Future randomized studies may be necessary to fully understand whether patients with non-[left bundle branch block] conduction abnormality truly benefit from CRT,” Kawata and colleagues wrote. “A randomized controlled trial evaluating patients with in [nonspecific intraventricular conduction delay] is ongoing, and we expect their result to reveal characteristics of the patients who respond to CRT well.”
‘Important data’
“The results from this study provide important data indicating that not all non-[left bundle branch block] morphologies are the same,” Michael R. Gold, MD, PhD, professor and Michael E. Assey of Cardiology endowed chair at the Medical University of South Carolina College of Medicine in Charleston, and Scott M. Koerber, DO, electrophysiology cardiology fellow at the Medical University of South Carolina, wrote in a related editorial. “The authors should be commended for providing more detailed analysis of the electrocardiogram and not simply using what is now the conventional [left bundle branch block] vs. non-[left bundle branch block] morphologies. These findings will need to be confirmed with further studies, either from prospective trials or pooled data from previous randomized trials.” – by Darlene Dobkowski
Disclosures: Kawata and Koerber report no relevant financial disclosures. Gold reports he served as a consultant for Boston Scientific and Medtronic. Please see the study for all other authors’ relevant financial disclosures.