Efficacy of Cardiac Resynchronization for Nonspecific Intraventricular Conduction Delay

Implantable Defibrillator in surgeon's hands
Implantable Defibrillator in surgeon’s hands
Patients with nonspecific intraventricular conduction delay and QRS duration <150 ms or right bundle branch block may not benefit from cardiac resynchronization therapy with defibrillator, compared with implantable cardioverter-defibrillator therapy alone.

Cardiac resynchronization therapy (CRT) with defibrillator (CRT-D) conferred better survival outcomes compared with implantable cardioverter-defibrillator (ICD) alone in patients with nonspecific intraventricular conduction delay (NICD) and a QRS duration of ≥150 ms, according to a study published in the Journal of the American College of Cardiology.

The National Cardiovascular Data Registry ICD registry was used to enroll patients eligible for CRT who received CRT-D implantation as well as CRT-eligible patients who received ICD only between 2010 and 2013 (age, ≥65 years). Survival outcomes were compared between groups, and comparisons were also performed between patients with NICD and right bundle branch block (RBBB). Another analysis was conducted in only recipients of CRT-D, with a focus on those with NICD vs RBBB.

The adjusted analysis found that CRT-D was associated with a higher risk for heart failure (HF) readmission compared with ICD only in patients with NICD and a QRS duration of 120 to 149 ms vs patients with RBBB (HR, 1.330; 95% CI, 1.098-1.612; P =.0036). Patients with NICD who received CRT-D also had higher 3-year mortality (HR, 1.167; 95% CI, 1.014-1.347; P =.0311).

In CRT-D recipients, patients with NICD also had a higher 1-year rate of HF readmission compared with patients with RBBB conduction abnormality (HR, 1.221; 95% CI, 1.009-1.478; P =.0401).

According to the multivariable-adjusted analysis, CRT-D was associated with a lower risk for mortality at 3 years compared with ICD in patients with NICD and a QRS of ≥150 ms (hazard ratio [HR], 0.602; 95% CI, 0.416-0.871; P =.0071), cardiovascular readmission at 1 year (HR, 0.626; 95% CI, 0.437-0.896; P =.0104), and all-cause readmission at 1 year (HR, 0.587; 95% CI, 0.436-0.790; P =.0004).

In CRT-D recipients, there was a lower 3-year mortality rate in patients with NICD and a QRS duration of ≥150 ms vs patients with RBBB (HR, 0.757; 95% CI, 0.625-0.917; P =.0044) as well as a lower 1-year rate of heart failure readmission (HR, 0.755; 95% CI, 0.591-0.964; P =.0244).

Limitations of the study included its retrospective nature, lack of randomization, and lack of a control group (ie, sham intervention).

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“The observations seen in our study would explain a lack of benefit of CRT-D among patients with NICD and a shorter QRS duration of 120 to 149 ms,” the researchers wrote, “and call into question the use of CRT-D in this subgroup of HF patients.”

Disclosures: Multiple authors disclosed affiliations with pharmaceutical companies. See the reference for complete disclosure information.


Kawata H, Bao H, Curtis JP, et al. Cardiac resynchronization defibrillator therapy for nonspecific intraventricular conduction delay versus right bundle branch block. J Am Coll Cardiol. 2019;73(24):3082-3099.