Cardiac resynchronization therapy (CRT) in patients with heart failure (HF) without left bundle branch block (LBBB) may not help and might even harm, according to an international group of investigators.

As Dr. Yitschak Biton told Reuters Health by email, “Our findings suggest that patients without LBBB electrocardiogram (ECG) morphology are not likely to benefit from CRT implantation and a subgroup of patients with short QRS duration might even be at higher risk for mortality.”

In a paper in Circulation: Heart Failure, Dr. Biton, of the University of Rochester Medical Center, New York, and colleagues note that the efficacy of CRT is well established in patients with both mild and moderate to severe HF symptoms. However, data on non-LBBB patients “are more limited and conflicting.”

To investigate, the team examined data on 537 such patients with mild HF taking part in a larger study. At seven years, the cumulative probability of HF hospitalization or death was 45 percent in those randomized to an implantable cardioverter-defibrillator (ICD) and 56 percent in those given CRT with a defibrillator (CRT-D).

Multivariable-adjusted subgroup analysis by QRS duration showed that patients from the lower quartile (134 ms or less) had a 2.4-fold greater risk of HF hospitalization or death with CRT-D versus those with ICD-only therapy.

However, the effect of CRT-D in patients from the upper quartiles group (QRS greater than 134 ms) was neutral (hazard ratio 0.97).

In a further analysis based on PR interval, patients with prolonged QRS (more than 134 ms) and prolonged PR (at least 230 ms) were protected with CRT-D (HR 0.31). The association was neutral with prolonged QRS and shorter PR.

“Overall,” the researchers conclude, “patients with mild HF but without left bundle branch block morphology did not derive clinical benefit with CRT-D during long-term follow-up. Relatively shorter QRS was associated with a significantly increased risk with CRT-D relative to implantable cardioverter-defibrillator only.”

“This information should be taken into account when CRT therapy is considered in this subgroup of patients,” Dr. Biton told Reuters Health.

Boston Scientific Corporation funded the clinical trial this research is based on. Five coauthors reported disclosures.