Background and Aims: Functional capacity assessment in Cardiac Rehabilitation (CR) is traditionally performed using graded exercise stress testing on a treadmill and measurement of maximal ventilatory oxygen uptake (VO2max). Coronary artery disease (CAD) mortality has declined over the years due to improved medical management and cardiology interventions, resulting in an increased number of the elderly patients in CR. The elderly patients often have a low fitness level and many have several age related chronic diseases, limiting the ability to perform VO2max testing on a treadmill. These patients typically participate in the on-site low intensity (LI) CR programs. The needs of the LI patients are to restore physical function to maintain activities of daily living (ADL). ADL activities are mostly performed at sub maximal levels of intensity. The 6MWT assesses sub maximal level of physical function and is thus more suitable for functional capacity assessment than VO2max testing. While the 6MWT has been used in COPD and CHF population, its use as an alternative functional capacity assessment in the CR setting is not common. Our purpose was: to evaluate the effectiveness of the 6MWT as an outcome measure in the LI CR patients; to assess the suitability of the 6MWT in exercise prescription; and to evaluate the measured variables.
Methods and Materials: The investigation is a retrospective analysis of 106 walk tests performed pre and post LI CR 12 week intervention consisting of 2x weekly exercise training in on-site CR program in the period of 2007-2008. The distance walked in 6 minutes is converted into metabolic equivalent (MET) using the American College of Sports Medicine (ACSM) walking equation. This MET level is used for initial exercise intensity. Predicted walking distance is determined using reference equations for healthy adults developed by P. Enright. The pre and post measures were compared with a signed rank test using SAS(R) version 9.1.3.
Results: The mean improvement in the walking distance in meters was 67 +/- 91, (P <= .001). Mean increase in MET 0.3 +/- 0.4, (P <= .001). The mean increase in the % predicted walking distance was 14 +/- (P <= .001). The mean difference in the peak attained heart rate was 3.7 (P <= .009). Females showed shorter initial (P <= .025) and final (P <= .097) walking distances, as expected. The % increase in the distance walked was greater for males, but this was not statistically different. Multiple regression analysis showed that gender predicted walking distance, but age, height and weight did not in this cohort.
Conclusions: The 6MWT is easily administered, effectively measures functional capacity, and can be used for exercise prescription. The current prediction equations for walk distances may not be of use in this patient population and need further investigation.