Reliability of two questionnaires on physical function in patients with stable coronary artery disease

Exercise-based cardiac rehabilitation is highly recommended for patients with coronary artery disease, as it improves physical fitness and reduces mortality and morbidity. Physical fitness per se does not always correlate with the patient's physical function. For this reason, additional measurements of physical function could be included in cardiac rehabilitation programmes to further tailor interventions to suit the individual patient. As a result, reliable measurements to assess physical function are required for patients with coronary artery disease.

The aim of this study was to evaluate the reliability of the Patient-Specific Functional Scale (PSFS) and the Disability Rating Index (DRI) in patients with stable coronary artery disease.

Fifty-one patients (11 women), age 63.9 (SD 7.6) years, with stable coronary artery disease and coronary-angiographic changes indicating an elective percutaneous coronary intervention, were recruited at the Cardiology Department at Sahlgrenska University Hospital, Gothenburg.

The reliability tests included stability over time, evaluated with a test-retest procedure using the intraclass correlation coefficient (ICC), and internal consistency, measured with Cronbach's alpha and item-total correlation coefficients.

Both questionnaires were stable over time (DRI, ICC=0.74, and PSFS, ICC=0.72). The internal consistency for the DRI was good, with a Cronbach's alpha value of > 0.85 for all items. The item-total correlation coefficients presented acceptable values of > 0.40, apart from two items.

We have provided introductory support for the reliability of the DRI and PSFS questionnaires in patients with stable CAD. These questionnaires can be used to assess physical function and to evaluate the effect of interventions in addition to measuring physical fitness.