Risk-based selection for carotid revascularisation using the IMPROVE score versus standard care in symptomatic carotid artery disease: a model-based cost-effectiveness analysis using pooled-data

Background: A clinical prediction model (IMPROVE) for ipsilateral ischaemic stroke risk in symptomatic patients with carotid disease was recently developed with good performance. We aim to evaluate the model-based cost-effectiveness of IMPROVE-based triage versus triage in care-as-usual (CAU) for optimal medical treatment (OMT) alone or carotid endarterectomy plus OMT. Methods: A dataset of 678 patients with carotid disease and a recent ipsilateral ischaemic stroke, transient ischaemic attack or amaurosis fugax from four cohort studies informed a decision-analytic model. Stratification of patients for carotid endarterectomy was based on ≥50% carotid stenosis (CAU arm) or a range of 3-year ipsilateral ischaemic stroke risk thresholds (IMPROVE arm). The threshold resulting in the lowest number of ipsilateral strokes and perioperative strokes and deaths was selected as the optimal threshold. Patients with <50% stenosis (CAU) or an IMPROVE risk score below the threshold (IMPROVE) were modelled to receive OMT only. Parameter uncertainty was incorporated in probabilistic analyses using Monte Carlo simulations for a 3-year and lifetime horizon. Subgroup analyses for <50%, 50–69% and 70–99% carotid stenosis were performed. Results: IMPROVE-based triage reduced ipsilateral ischaemic strokes and perioperative strokes and deaths by 34.5% (CAU: 4.3%, IMPROVE: 2.8%) over 3 years. Revascularisations decreased by 20% with IMPROVE, while Quality-Adjusted Life Years slightly increased. Procedural stroke occurred in 1.8% of patients in CAU versus 1.4% of patients for IMPROVE. Societal costs decreased on average by €1441/patient for IMPROVE versus CAU for a 3-year time horizon (lifetime cost reduction: €6101/patient). Subgroup analyses identified IMPROVE as the superior strategy for 50–69% and 70–99% stenosis (3-year and lifetime horizon) and <50% stenosis (lifetime horizon). Conclusions: In this modelling analysis, triage of symptomatic patients with carotid disease with the IMPROVE model can lead to the prevention of one-third of ipsilateral ischaemic strokes and perioperative strokes and deaths, while also reducing societal costs. These findings should be validated in a clinical trial.