CRT may be harmful in patients with RBBB, very wide QRS duration

ORLANDO, Fla. — Cardiac resynchronization therapy may be detrimental in patients with right bundle branch block and a very wide QRS duration, defined as 180 ms or more, according to findings presented at the American Heart Association Scientific Sessions.

Varun Sundaram, MD, and colleagues analyzed 14,902 patients (mean age, 73 years; 73% men) with left ventricular ejection fraction of 35% or less from the Medicare implantable cardioverter defibrillator registry who received a CRT defibrillator between January 2005 and April 2006. The goal was to determine whether patients with very wide QRS duration of at least 180 ms — who have been underrepresented in CRT trials — benefit from CRT-D in clinical practice.

“This group with a very wide QRS duration is unique because the mechanism of underlying QRS prolongation is different than those of moderately prolonged QRS duration of 150 ms to 179 ms,” Sundaram, from Harrington Heart and Vascular Institute, University Hospitals Case Medical Center, Case Western Reserve University, Cleveland, said during a presentation. “A wide QRS complex could be just due to a conduction block in the bundles or electrical uncoupling of the working myocardium or a combination of both. It has been shown from real-heart and close-to-human computer simulation models that with true left bundle branch block (LBBB), the QRS is around 140 ± 16 ms, and with true right bundle branch block (RBBB) it is even less. Any further widening of QRS duration beyond 156 ms is likely a combination of BBB and electrical uncoupling. With significant electrical uncoupling, the benefits of CRT may be negated by slow and dispersed conduction during pacing.”

Patients were stratified by QRS duration (120-149 ms; 150-179 ms; and ≥ 180 ms) and BBB morphology. They were followed for up to 6 years for outcomes including death and a composite of death and HF hospitalization.

Since the device registry lacked controls, patients with LBBB and QRS 150 ms to 179 ms, historically known as the optimal responders to CRT, were used as the reference group, Sundaram said. Compared with the reference group, patients with RBBB had increased risk for:

mortality at 1 year (QRS 120-149 ms, HR = 1.65; 95% CI, 1.34-2.03; QRS 150-179 ms, HR = 1.48; 95% CI, 1.2-1.82; QRS ≥ 180 ms, HR = 1.74; 95% CI, 1.28-2.38);
increased risk for mortality at 3 years (QRS 120-149 ms, HR = 1.54; 95% CI, 1.36-1.76; QRS 150-179 ms, HR = 1.37; 95% CI, 1.2-1.57; QRS ≥ 180 ms, HR = 1.72; 95% CI, 1.4-2.1);
death or HF hospitalization at 1 year (QRS 120-149 ms, HR = 1.43; 95% CI, 1.23-1.66; QRS 150-179 ms, HR = 1.4; 95% CI, 1.21-1.62; QRS ≥ 180 ms, HR = 1.68; 95% CI, 1.34-2.1); and
death or HF hospitalization at 3 years (QRS 120-149 ms, HR = 1.44; 95% CI, 1.29-1.61; QRS 150-179 ms, HR = 1.3; 95% CI, 1.17-1.45; QRS ≥ 180 ms, HR = 1.6; 95% CI, 1.35-1.9).

Considering all combinations of morphology and QRS duration, patients with RBBB and a very wide QRS duration > 180 ms had the highest adjusted mortality rates at 1, 3 and 6 years, he said.

Ischemic cardiomyopathy, elderly age and atrial fibrillation were associated with poor response to CRT, findings consistent with previous clinical trials, Sundaram said.

“In patients with RBBB, clinical outcomes with a very wide QRS duration were worse when compared to the other two [QRS duration of 120 ms to 149 ms and 150 ms to 179 ms] groups,” Sundaram said. “There appears to be a gradation effect with an incremental risk with biventricular pacing with widening QRS duration in patients with RBBB, but this was not noted in patients with LBBB, where with widening QRS duration, we continued to see HRs comparable to the reference group.”

He concluded that “very wide QRS duration prior to CRT implantation has complex and durable long-term effects on prognosis after resynchronization, with a strong dependency on BBB morphology. In patients with RBBB, very wide QRS duration is possibly a marker of advanced electrical remodeling and suggests that CRT may be ineffective in restoring synchronous contraction. In our analysis, with the inherent limitations of the registry, we observed that clinical outcomes were the worst for the narrower QRS duration group in LBBB and the very wide QRS duration group in RBBB.” – by Erik Swain

Reference:

Sundaram V, et al. CS.02: Cutting-Edge Technologies in EP. Presented at: American Heart Association Scientific Sessions; Nov. 7-11, 2015; Orlando, Fla.

Disclosure: Sundaram reports no relevant financial disclosures.