The minimum clinically important improvement in the incremental shuttle walk test following cardiac rehabilitation

BACKGROUND: The aim was to establish the minimum clinically important difference (MCID) in the incremental shuttle walk test (ISWT) following cardiac rehabilitation. DESIGN: This was a service evaluation, utilising anchor- and distribution-based methods. METHODS: Two hundred and twenty patients performed an ISWT following a six-week cardiac rehabilitation programme comprising supervised aerobic exercise, secondary prevention education and a home exercise programme. PRIMARY OUTCOME: Patient perception of change in ISWT distance following cardiac rehabilitation. After completing cardiac rehabilitation, subjects were asked to identify, from a five-point Likert scale, their perceived change in exercise performance (range: from 'better' to 'worse'). Two distribution-based methods were also employed (standard deviation (SD) and effect size). The agreement between all measures was observed. RESULTS: Mean (SD) age was 65.0 (10.5) years, body mass index 28.4 (5.1), 170 male. The baseline ISWT was 390.8 (173.1) metres (m), which increased to 456.0 (186.7) m (mean change 65.2 (95% confidence interval 55.4-74.9) m after cardiac rehabilitation (p < 0.001)). In those rating their exercise tolerance as 'slightly better', the mean improvement was 70.0 (95% confidence interval 51.5-88.5) m. The SD method yielded a minimum clinically important difference value of 36.65 m and the effect size for the change was 0.38. The agreement between the patients' perception of change and distribution-based methods was poor. CONCLUSIONS: The minimum clinically important difference for the ISWT following cardiac rehabilitation is 70 m. This patient-reported value is a more sensitive measure and has poor agreement with distribution-based estimates. This value may help clinicians interpret ISWT change in patients, help researchers estimate sample size and aid comparison between studies, when the ISWT is the primary outcome.