NEW YORK (Reuters Health) – The benefits of cardiac resynchronization therapy (CRT) are less pronounced for typical “real-world” patients — particularly those with right bundle-branch block — than previously recognized, report investigators at the University of Virginia Health System, Charlottesville.

Writing in the November 16th issue of Circulation, Dr. Kenneth C. Bilchick and colleagues note that patient recruitment was selective in the clinical trials establishing that CRT either without an implantable cardioverter-defibrillator (ICD) or with (CRT-D) improved survival in heart failure.

To look into factors influencing outcomes in typical older patients, the researchers analyzed data from the Medicare ICD Registry. In particular, the study focused on the effect on survival of bundle-branch block morphology — left bundle-branch block (LBBB), right bundle-branch block (RBBB), and intraventricular conduction delay (IVCD).

“Among 14,946 patients who received CRT-D and met standard QRS and LVEF criteria for CRT implantation, 10,356 (69%) had an LBBB, 1638 (11%) had an RBBB, and 2952 (20%) had a nonspecific IVCD,” the team reports.

During a median follow-up of 40 months, 45.8% of patients with RBBB died compared with 35.0% of those with LBBB. Corresponding rates of the composite endpoint of death or hospitalization for heart failure were 60.2% and 50.0%.

After age >80 years and advanced heart failure class, the next strongest predictors of mortality were RBBB and ischemic cardiomyopathy, according to the report. Specifically, hazard ratios for mortality at 1 year and 3 years were 1.44 and 1.37 with RBBB, and 1.39 and 1.44 for ischemic cardiomyopathy.

In fact, the combination of RBBB and ischemic cardiomyopathy doubled the risk for death (HR, 1.99) compared to LBBB and nonischemic cardiomyopathy, the researchers found.

“These data offer a realistic picture of HF as a progressive disease and show that outcomes vary significantly on the basis of BBB morphology and other covariates,” Dr. Bilchick and colleagues conclude.

Furthermore, they advise, “In light of the increased complexity, procedure time, and follow-up requirements associated with CRT-D relative to standard ICD implantation, these factors influencing real-world outcomes after CRT-D should be considered when referring patients for CRT-D in clinical practice.”

Should we make changes in our practice on the basis of these results? ask two editorialists.

After discussing the findings in some detail, Dr. Karoly Kaszala and Dr. Kenneth A. Ellenbogen of the Virginia Commonwealth University School of Medicine and Hunter Holmes McGuire Veterans Affair Medical Center, Richmond, Virginia, conclude: “For now, decisions about CRT implantation in patients with RBBB should continue to rely on the American Heart Association/American College of Cardiology guidelines until prospective studies demonstrate a lack of benefit.”

Reference:

Bundle-Branch Block Morphology and Other Predictors of Outcome After Cardiac Resynchronization Therapy in Medicare Patients

Circulation 2010;122:2022-2030.