6MWT May Be Inadequate for Evaluating Response to Cardiac Resynchronization Therapy in Mild Heart Failure With LBBB

The 6-minute walk test (6MWT) was found to have limited value for the identification of response to cardiac resynchronization therapy (CRT) in patients with mild heart failure and left bundle branch block (LBBB), according to a study published in the American Journal of Cardiology.

The data of 1381 patients with mild heart failure who were enrolled in the Multicenter Automatic Defibrillator Implantation Trial—Cardiac Resynchronization Therapy with 6MWT data available at baseline and 1 year were examined. Participants were randomly assigned to receive CRT-defibrillator (CRT-D) or implantable cardioverter-defibrillator (ICD) therapy at a 3:2 ratio. The primary outcome measure was long-term heart failure events or death during the median follow-up of 5.6 years.

Treatment with CRT-D compared with ICD was not associated with a significant improvement in 6MWT at 1 year in patients with LBBB (2.2% vs 0.0%, respectively; P =.428), but was associated with a deterioration in 6MWT in patients without LBBB (4.1% vs 0.0%, respectively; P = .308).

Each 5% reduction in 6MWT was independently associated with a corresponding 3% increase in the risk for subsequent heart failure or death (P = .014) in a multivariate analysis. The 6MWT showed “a signal towards deterioration in [patients with] mild HF with non-LBBB, and this was predictive of subsequent increased risk [for] HF or death,” noted the study authors. This deterioration in 6MWT was predicted by older age, higher body mass index, higher creatinine level, prior myocardial infarction, and female sex.

Study limitations include the fact that it was a post-hoc analysis of a randomized clinical trial, and that the evaluation of performance on the 6MWT was not part of the pre-specified primary and secondary end points. Furthermore, a number of patients had missing 6MWT at either baseline or 1 year, potentially introducing bias.

“These results suggest that 6MWT, one of the most common tests of functional capacity in heart failure trials, does not predict CRT response in clinical trials enrolling [patients with] mild heart failure and it may have a limited utility as a tool for measuring clinical improvement,” the researchers commented. “However, it may have potential utility in detecting harm, especially in [patients with] non-LBBB, with a greater sensitivity than deterioration in clinical end points such as heart failure or death.”

Disclosures

One study author declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of disclosures.

Reference

Rosero SZ, Hernandez N, Goldenberg I, et al. Utility of 6-minute walk test to predict response to cardiac resynchronization therapy in patients with mild heart failure [published online July 13, 2020]. Am J Cardiol. doi:https://doi.org/10.1016/j.amjcard.2020.07.019