Utility of 6-Minute Walk Test to Predict Response to Cardiac Resynchronization Therapy in Patients With Mild Heart Failure.

Clinical studies of heart failure (HF) generally utilize the 6-minute walk test (6MWT) for functional capacity (FC) assessment. However, data on the impact of cardiac resynchronization therapy (CRT) on 6MWT and its role to predict long-term outcomes in mild HF patients with CRT are lacking. We studied 1,381 subjects with mild HF enrolled in Multicenter Automatic Defibrillator Implantation Trial - Cardiac Resynchronization Therapy with 6MWT data at baseline and 1 year. We assessed the effects of CRT-D on percent change in 6MWT at 1 year by left bundle branch block (LBBB) status, identified independent predictors of 6MWT at 1 year, and evaluated the association between changes in 6MWT and risk for HF or death. Treatment with CRT-D versus implantable cardiac defibrillator (ICD) was not associated with a significant improvement in 6MWT at 1-year in LBBB subjects (2.2 % vs 0.0%, p = 0.428, but it was associated with a deterioration in 6MWT in non-LBBB subjects (4.1% vs 0.0%, p = 0.308). Multivariate analysis showed that each 5% reduction in 6MWT was independently associated with a corresponding 3% increase in the risk of subsequent HF or death (p = 0.014). In conclusion, our findings suggest that 6MWT has limited utility to identify CRT response in mild HF subjects with LBBB. However, 6MWT showed a signal toward deterioration in mild HF subjects with non-LBBB, and this was predictive of subsequent increased risk of HF or death.