Background: The improvement of cardiorespiratory fitness is one of the primary goals of Cardiac Rehabilitation (CR). In the UK, the Incremental Shuttle Walk Test (ISWT) is the most widely used field test to assess cardiorespiratory fitness in CR patients. Previous studies show that CR improves cardiorespiratory fitness, however, there is a lack of research into the difference in the change in fitness as a result of CR between males and females, particularly in post-CABG patients in the UK.
Purpose: The aim of the study was to evaluate the extent of change in the ISWT distance achieved by post-CABG males and females and to compare the likelihood of males and females achieving the minimum clinically important difference (MCID) of 70m.
Methods: A retrospective study used data from the National Audit Cardiac Rehabilitation (NACR) collected between April 2013 and December 2016 from 48 CR centres. The participants were included if they were ≥18 years and had completed their ISWT prior to and following their CR programme as a cardiorespiratory fitness assessment. Independent t-tests and Chi-square tests were used to compare the baseline results of the males and females as appropriate. Multiple linear regression was used to compare the change in ISWT distances between the two groups taking account of age and ISWT baseline measurement and other potential confounders namely BMI; height; weight; presence of hypertension or diabetes; smoking; and physical activity level based on 150 minutes per week of moderate activity. Binary logistic regression was used to investigate the likelihood of achieving the MCID controlling for the potential confounders and odds ratios (OR) were calculated as an affect size. Due to the nested nature of the data coming from 48 centres, the Huber-White sandwich estimator was used. A P-value of <0.05 is considered to be significant. The analyses were conducted using STATA V.13.1.
Results: A total of 1,899 CR outpatients (males 1621 and females 278) ranged in age from 24 to 99 years with a mean age of 66.2 (± 9.56) years for males and 67.6 (± 9.15) years for females. By adjusting for the other variables, the difference in the mean change in the distance walked between males and females was 33m (110m Vs 77m, p<0.001). Males were also twice as likely as females to achieve the MCID (70m) (OR 2, 95% CI 1.60– 2.67, p<0.001).
Conclusion: The MCID of 70m lacks relevance for female patients and so a gender specific MCID value is required.