Early Six-Minute Walk Test May Predict Midterm Outcomes Following Coronary Artery Bypass Grafting

ABSTRACT Objective: This study aims to investigate the ability of the six-minute walk distance (6MWD) as a prognostic marker for midterm clinical outcomes three months after coronary artery bypass grafting (CABG), to identify possible predictors of fall in 6MWD in the early postoperative period, and to establish the percentage fall in early postoperative 6MWD, considering the preoperative baseline as 100%. Methods: A prospective cohort of patients undergoing elective CABG were included. The percentage fall in 6MWD was assessed by the difference between preoperative and postoperative day (POD) five. Clinical outcomes were evaluated three months after hospital discharge. Results: There was a significant decrease in 6MWD on POD5 compared with preoperative baseline values (percentage fall of 32.5±16.5%, P<0.0001). Linear regression analysis showed an independent association of the percentage fall of 6MWD with cardiopulmonary bypass (CPB) and preoperative inspiratory muscle strength. Receiver operating characteristic curve analysis revealed that the best cutoff value of percentage fall in 6MWD to predict poorer clinical outcomes at three months was 34.6% (area under the curve = 0.82, sensitivity = 78.95%, specificity = 76.19%, P=0.0001). Conclusion: This study indicates that a cutoff value of 34.6% in percentage fall of 6MWD on POD5 was able to predict poorer clinical outcomes at three months of follow-up after CABG. Use of CPB and preoperative inspiratory muscle strength were independent predictors of percentage fall of 6MWD in the postoperative period. These findings further support the clinical application of 6MWD and propose an inpatient preventive strategy to guide clinical management over time.

摘要
目的：本研究旨在探讨六分钟步行距离（six-minute walk distance, 6MWD）作为冠状动脉旁路移植术（coronary artery bypass grafting, CABG）术后3个月中期临床结局的预后标志物的价值，识别术后早期六分钟步行距离下降的潜在预测因素，并以术前基线值为100%，确立术后早期六分钟步行距离的下降百分比。
方法：本研究纳入接受择期冠状动脉旁路移植术的患者组成前瞻性队列。通过术前与术后第5天（postoperative day, POD）的六分钟步行距离差值评估六分钟步行距离下降百分比。于患者出院后3个月评估其临床结局。
结果：与术前基线值相比，术后第5天的六分钟步行距离显著降低（下降百分比为32.5±16.5%，P<0.0001）。线性回归分析显示，六分钟步行距离下降百分比与体外循环（cardiopulmonary bypass, CPB）及术前吸气肌强度存在独立相关性。受试者工作特征曲线（receiver operating characteristic curve, ROC）分析显示，预测术后3个月不良临床结局的六分钟步行距离下降百分比最佳截断值为34.6%（曲线下面积=0.82，灵敏度=78.95%，特异度=76.19%，P=0.0001）。
结论：本研究表明，术后第5天六分钟步行距离下降百分比的34.6%截断值可有效预测冠状动脉旁路移植术后随访3个月时的不良临床结局。体外循环使用情况及术前吸气肌强度是术后六分钟步行距离下降百分比的独立预测因素。上述研究结果进一步支持了六分钟步行距离的临床应用价值，并提出了可指导长期临床管理的住院患者预防策略。