Development and validation of a multidimensional tool for baseline functional phenotyping in cardiac rehabilitation

Functional recovery after cardiac events is heterogeneous, with up to 40% of patients showing limited improvement despite standardized rehabilitation. Current assessment tools demonstrate modest accuracy (~ 61%) and rarely capture the multidimensional aspects of functional status. This study aimed to develop and internally validate a pragmatic bedside functional stratification tool for patients entering cardiac rehabilitation. We conducted a cross-sectional study of 80 patients (mean age 72.7 ± 5.2 years, 65% male) at rehabilitation intake. Four routinely available parameters were assessed: age, six-minute walk test (6MWT), Timed Up and Go (TUG), and the Edmonton Frail Scale (EFS). Each was categorized into four levels (0–3 points), yielding a composite score of 0–12. Patients were stratified as Low (0–3), Moderate (4–6), High (7–9), or Very High (10–12) functional impairment. Internal validation employed bootstrap resampling (n = 1000). Functional capacity declined progressively across categories: 6MWT decreased from 364.3 ± 75.7 m (Low Impairment) to 185.2 ± 32.9 m (Very High Impairment), and TUG increased from 6.9 ± 1.0 s to 14.2 ± 2.8 s (all p < 0.001). The composite score correlated strongly with functional performance (r = − 0.75, p < 0.001) and demonstrated excellent discrimination (AUC 0.93, 95% CI 0.87–0.97), outperforming individual measures. Bootstrap validation confirmed stability. We propose a simple, multidomain bedside score requiring ~ 25 min and no specialized equipment. This tool enables functional stratification at rehabilitation intake, supports personalized care, and facilitates matching rehabilitation pathways to baseline functional status. External validation is warranted.