Role of six-minute walk test as a risk stratification tool in patients undergoing surgery for secondary ischemic mitral regurgitation

Abstract

Secondary ischemic mitral regurgitation (SIMR) remains associated with an unfavourable prognosis. Mitral valve replacement (MVR) or restrictive mitral annuloplasty (RMA) combined with coronary artery bypass grafting represent the most common surgical techniques. Nevertheless, 5-year mortality rates remain high and up to half of patients may experience hospitalization for heart failure (HF) within a few years following surgery(1). The Six-Minute Walk Test (6-MWT) is a well-validated measure of functional capacity widely used in patients with HF: it’s sensitive to strongly predicts mortality, morbidity and quality of life(2). A 6-MWT distance ≤300m is a strong independent predictor of adverse outcome(3).

The primary composite endpoint was all-cause mortality or HF–related readmission at 5 years in patients undergoing surgery for SIMR. The secondary endpoint was to assess the role of the 6-MWT in monitoring early and mid-term postoperative functional capacity.

On-hundreds and thirty-seven consecutive patients with SIMR undergoing RMA or MVR plus CABG were analysed. A 6-MWT was performed at baseline, at 30 days, and at 1 year. ROC analysis was used to identify the optimal pre-operative 6-MWT cut-off for prediction of the primary endpoint. Predictors of adverse outcomes were assessed using Cox regression analysis.

Mean age was 66.9±8.6 years, 24.6% were female, median LVEF was 35.8±8.4%, complete revascularization was achieved in all, RMA and MVR were performed in 63 (46%) and 74 (54%) patients, respectively. The ROC analysis identified 217m as the optimal threshold for predicting the primary endpoint (AUC 0.64; sensitivity 77%; specificity 49%). Patients were stratified into impaired (<217m, n=82) and preserved (≥217m, n=55) functional capacity. Patients with preserved functional capacity demonstrated significantly higher event-free survival at 2 years (90.9±7.6% vs 70.7±9.8%, p=0.0238) and at 5 years (81.8±10.2% vs 58.5±10.3%; log-rank p=0.0036) (Figure 1). Age was strongly associated with adverse outcome while MVR was independently associated with a lower risk of events compared with RMA. At 30 days, both groups (impaired and preserved) showed slight or stable improvement. At 1 year, patients with pre-operative preserved 6-MWT showed a dichotomous response pattern, with approximately 50% showing significant improvement whereas the remaining 50% showed a significant decline. By contrast, patients with impaired pre-operative 6-MWT showed a more evenly distributed functional trajectory (Figure 2).

These preliminary findings further corroborate the 6-MWT as sensitive and robust tool for long-term functional capacity assessment in patients with SIMR. In this context, our findings suggest a systematic inclusion of the 6-MWT into pre-operative algorithms in order to identify high-risk patients, to improve the decision-making process and to monitor the efficacy of therapy.FIGURE 1FIGURE 2