Support for Broadening ECG Criteria for Using Resynchronization Therapy

Debra L. Beck

July 18, 2019

There are various criteria for identifying patients with heart failure (HF) most likely to respond to cardiac resynchronization therapy (CRT), with a presence of left-bundle-branch block (LBBB) being one of the most important. But some non-LBBB patients, especially those with prolonged electrocardiographic QRS durations, might also benefit, suggests a new analysis based on data from the NCDR-ICD Registry.

Such non-LBBB patients showing signs of response did not include those with right-bundle-branch block (RBBB), regardless of QRS duration. Rather, the non-LBBB sweet spot seemed to be patients with nonspecific intraventricular conduction delay (NICD) and a QRS duration of at least 150 ms.

In that group, CRT-D was associated with a significant 40% reduction in mortality at 3 years compared with patients who had received an implantable cardioverter-defibrillator (ICD) without CRT capability.

The adjusted hazard ratio (HR) was 0.602 (P = .0071), with similar reductions in the same subgroup observed for all-cause readmissions and cardiovascular (CV) readmissions, in the study published June 17 in the Journal of the American College of Cardiology with lead author Hiro Kawata, MD, PhD, University of California Irvine.

"This means that if you have a patient with RBBB who is still suffering from heart failure symptoms after medical therapy, there is not enough data to support using CRT blindly," Kawata stated in a press release issued by the publication.

"But in NICD patients, we now know that those with a long QRS are likely to benefit from CRT."

The NCDR-ICD cohort consisted of 11,505 fee-for-service Medicare patients who received CRT-D or ICD-only devices between April 2010 and December 2013. 

Many physicians restrict CRT referrals and implantation to patients with LBBB, likely based on a subanalysis of the MADIT-CRT trial that showed no benefit in patients with non-LBBB morphologies, observed Michael R. Gold, MD, PhD, and Scott M. Koerber, DO, both of the Medical University of South Carolina, Charleston, in an accompanying editorial.

But that may be an "oversimplification" of the ECG evaluation of candidates for CRT, they propose.

"These findings will need to be confirmed with further studies, either from prospective trials or pooled data from previous randomized trials. However, importantly, the results of the present study challenge our convention of lumping CRT candidates into two categories."

In a secondary analysis, the authors compared outcomes among 5954 CRT-D recipients with a QRS duration of ≥ 150 ms. After adjustment, those with NICD showed lower 3-year mortality (HR, 0.757; 95% CI, 0.625 - 0.917; P = .0044) and 1-year rate of HF readmission (HR, 0.755; 95% CI, 0.591 - 0.964; P = .0244) compared to those with RBBB.

"Future randomized studies may be necessary to fully understand whether patients with non-LBBB conduction abnormality truly benefit from CRT," write the authors.

"A randomized controlled trial evaluating patients with NICD is ongoing, and we expect their result to reveal characteristics of the patients who respond to CRT well."

Kawata had no disclosures; potential conflicts for the other authors are in the report. Gold discloses serving as a consultant to Medtronic and Boston Scientific. Koerber has reported no relevant financial relationships.

J Am Coll Cardiol. 2019;73:3082-3099. Abstract, Editorial

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