The 6-minute walking test and all-cause mortality in patients undergoing a post-cardiac surgery rehabilitation program

Background: The 6-minute walking test (6mWT) is used to prescribe physical activity in cardiac surgery patients. The clinical value of a pre-discharge 6mWT and its association with outcome is not well defined. Design and methods: We retrospectively analyzed data from 313 patients (age 66 ± 11 years, 23% females, left ventricular ejection fraction (LVEF) 52 ± 11%, Hb 10.5 ± 1.3 g/dl, serum albumin 3.9 ± 0.4 mg/dl) who were admitted to our rehabilitation institute following cardiac surgery. A 6mWTwas performed at entry and at discharge and expressed as % of theoretical predicted values calculated on the basis of individual age, height, weight and sex. The endpoint was represented by all-cause mortality. The predictive value of 6mWT was tested in univariate and multivariate analysis. Results: A pre-discharge 6mWT was completed by 284 out of 313 patients. Two patients died in hospital. During a median of 23 months, mortality was 9% (26/284) and 44% (12/27) (p <0.0001) in patients who did or did not perform the pre-discharge 6mWT. The distance covered at the pre-discharge 6mWT as a continuous variable of % predicted values was a significant predictor of subsequent mortality (Hazard Ratio (HR) 0.97 (95% CI 0.96-0.99), p = 0.0019). After adjustment for all preselected covariates, the pre-discharge 6mWT (HR 0.97 (95% CI 0.95-0.99), p = 0.0038) and LVEF (HR 0.93 (95% CI 0.90-0.96), p <0.0001) remained significantly associated with the outcome. Conclusions: In recent cardiac surgery patients, the pre-discharge 6mWT is not only a valid measurement of the impact of cardiac rehabilitation but also provides outcome information offering the possibility to identify patients who may need more intensive follow-up.