Model-based cost-effectiveness of the IMPROVE score versus care as usual for risk-based selection of symptomatic patients for carotid revascularization

Background. A clinical prediction model (IMPROVE) for ipsilateral ischemic stroke risk in symptomatic patients with carotid artery disease was recently developed and internally validated with good performance. In this decision-analytic study, we evaluated the model-based cost-effectiveness of IMPROVE-based triage versus triage in care-as-usual (CAU) for optimal medical treatment (OMT) alone or carotid revascularization plus OMT. Methods. A dataset of 678 patients with a recent ipsilateral ischemic stroke, TIA or amaurosis fugax pooled from 4 cohort studies, informed a decision-analytic model. Stratification of patients for carotid revascularization was either based on ≥50% carotid stenosis (CAU arm), or based on a range of 3-year ipsilateral ischemic stroke risk thresholds (IMPROVE arm). The threshold resulting in the lowest number of strokes was selected as the optimal threshold. Patients with <50% stenosis (CAU arm) or an IMPROVE risk score below the threshold were modeled to receive OMT only. Parameter uncertainty was incorporated in probabilistic analyses using 10,000 Monte Carlo simulations for a 3-year and lifetime horizon. Subgroup analyses for mild (<50%), moderate (50-69%), and severe (70-99%) carotid stenosis were performed. Results. IMPROVE-based triage, as compared to triage in CAU, reduced ipsilateral ischemic strokes and perioperative stroke/death by 34.5% (CAU: 4.3% vs. IMPROVE: 2.8%) over 3 years. Perioperative stroke occurred in 1.8% of the patients in CAU versus 1.4% for IMPROVE. Revascularizations decreased by 20% with IMPROVE, while QALYs slightly increased. Societal costs decreased on average by €1,441/patient for IMPROVE versus CAU for a 3-years time horizon (lifetime cost reduction: €6,101/patient). Subgroup analyses identified IMPROVE as the superior strategy for moderate/ severe stenosis (3-year and lifetime horizon) and mild stenosis (lifetime horizon). Conclusions. Triage of symptomatic patients with carotid artery disease with the IMPROVE model versus CAU can lead to the prevention of one-third of ipsilateral ischemic strokes, while also reducing societal costs.