Inpatient Six-minute Walking Test in Predicting Cardiovascular Mortality of Patients Following Cardiac Surgery

Background High mortality after cardiac surgery was related to poor functional capacity which can be evaluated by six-minute walking test (6MWT). Scanty literature was about the relationship between 6MWT distance and the mortality after heart surgery. Material and methods We conducted a retrospective cohort from National Taiwan University Hospital who received CABG and/or valve surgery in 2011 and 2012. We put 6MWT distance as the independent variable into Cox proportional hazards model for survival analysis. Outcome is cardiovascular mortality till 2013/12/31 via linking data to the Collaboration Center of Information Application (CCHIA). Results A total of 383 patients (mean age 60.5±11.3 years old, 28.5% female) undertook 6MWT (301.3±97.1m) during post-surgical hospitalization, and 14 died of cardiovascular causes during a follow-up of median 24 months (interquartile range, IQR=12 months). When 6MWT distance was put as continuous variable, the hazard radio (HR) was 0.27 (95% Confidence interval, CI: 0.10-0.69, p=0.007) with 100m increment. While compared with <200m group, HR of ≥200m and <300m group was 0.22 (95% CI: 0.05-0.91), and HR of ≥300m group was 0.09 (95% CI: 0.01-0.59). Subgroup analysis showed that 6MWT distance was a significant factor of predicting cardiovascular mortality in the lower LVEF group (<60%), but not in the higher LVEF group. Conclusion Our findings demonstrated the prognostic value of 6MWT in post cardiac surgery patients, implying to identify the vulnerable patients who may need more intensive follow-up and active participation in cardiac rehabilitation.