Explanatory Value of the Ability Index as Assessed by Cardiologists and Patients with Congenital Heart Disease.

Introduction. The Ability Index was developed to classify patients with congenital heart disease into four functional classes. Functional class is typically determined by the cardiologist, based on data from a clinical interview. The validity of the Ability Index as assessed by the patient has never been scrutinized. Objective. We tested the agreement between cardiologists and patients in assessing functional status using the Ability Index and compared the accuracy of the two assessments in explaining patient-reported outcomes (PRO). Methods. The Ability Index Scale was completed for 57 patients, independently by cardiologists and patients. Cohen's Kappa coefficient with quadratic weighting (K _w) was calculated. The area under the receiver operating characteristic (ROC) curve (AUC) (=C-index) was used to test the accuracy of the Ability Index in explaining PRO, as assessed by the cardiologist or the patient. Results. Agreement was observed in 61.4% of the patients. The K _w was 0.55, showing a moderate agreement; and the R ² was 0.29, displaying a limited shared variance. The AUC for cardiologists' assessments of the Ability Index in explaining PRO was consistently lower than the AUC for patients' assessments. The appraisal of the patients was more accurate. Discussion. When cardiologists and patients are assessing functional status using the Ability Index, two different constructs are measured. These assessments cannot be interchanged, but should be used complementarily. Because the assessment of the patients regarding the Ability Index is more precise in terms of explaining PRO, it could be valuable as a simple crude marker to identify patients at risk for poor functional and psychosocial outcomes.