Cost-effectiveness of CT perfusion for the detection of large vessel occlusion acute ischemic stroke followed by endovascular treatment: a model-based health economic evaluation study

Abstract

Objectives: CT perfusion (CTP) has been suggested to increase the rate of large vessel occlusion (LVO) detection in patients suspected of acute ischemic stroke (AIS) if used in addition to a standard diagnostic imaging regime of CT angiography (CTA) and non-contrast CT (NCCT). The aim of this study was to estimate the costs and health effects of additional CTP for endovascular treatment (EVT)-eligible occlusion detection using model-based analyses.

Methods: In this Dutch, nationwide retrospective cohort study with model-based health economic evaluation, data from 701 EVT-treated patients with available CTP results were included (January 2018-March 2022; trialregister.nl:NL7974). We compared a cohort undergoing NCCT, CTA, and CTP (NCCT + CTA + CTP) with a generated counterfactual where NCCT and CTA (NCCT + CTA) was used for LVO detection. The NCCT + CTA strategy was simulated using diagnostic accuracy values and EVT effects from the literature. A Markov model was used to simulate 10-year follow-up. We adopted a healthcare payer perspective for costs in euros and health gains in quality-adjusted life years (QALYs). The primary outcome was the net monetary benefit (NMB) at a willingness to pay of €80,000; secondary outcomes were the difference between LVO detection strategies in QALYs (ΔQALY) and costs (ΔCosts) per LVO patient.

Results: We included 701 patients (median age: 72, IQR: [62-81]) years). Per LVO patient, CTP-based occlusion detection resulted in cost savings (ΔCosts median: € - 2671, IQR: [€ - 4721; € - 731]), a health gain (ΔQALY median: 0.073, IQR: [0.044; 0.104]), and a positive NMB (median: €8436, IQR: [5565; 11,876]) per LVO patient.

Conclusion: CTP-based screening of suspected stroke patients for an endovascular treatment eligible large vessel occlusion was cost-effective.

Clinical relevance statement: Although CTP-based patient selection for endovascular treatment has been recently suggested to result in worse patient outcomes after ischemic stroke, an alternative CTP-based screening for endovascular treatable occlusions is cost-effective.

Key points: • Using CT perfusion to detect an endovascular treatment-eligible occlusions resulted in a health gain and cost savings during 10 years of follow-up. • Depending on the screening costs related to the number of patients needed to image with CT perfusion, cost savings could be considerable (median: € - 3857, IQR: [€ - 5907; € - 1916] per patient). • As the gain in quality adjusted life years was most affected by the sensitivity of CT perfusion-based occlusion detection, additional studies for the diagnostic accuracy of CT perfusion for occlusion detection are required.

Keywords: Diagnosis; Four-dimensional computed tomography; Health Care Economics and Organizations; Ischemic stroke; Thrombectomy.

Fig. 1

Markov model structure. A Patients presenting within 6 h after stroke symptom onset at an endovascular treatment (EVT)–capable stroke center are subject to one of the following diagnostic imaging protocols for EVT-eligible occlusion detection: (1) non-contrast CT (NCCT), CT angiography (CTA), and CT perfusion (CTP), or (2) NCCT and CTA. No EVT*: In the NCCT + CTA + CTP arm, the number of patients without an EVT-eligible occlusion (no EVT) was computed using the number needed to image (NNI) calculations. Costs of CTP-based screening of non-EVT-eligible occlusions were multiplied with the NNI and added to the overall costs of this simulated arm, in the models’ CTP—no EVT group did not suffer any health consequences and was not further simulated. In the NCCT + CTA arm, the no EVT compromised all patients from the NCCT + CTA + CTP arm in addition to all patients that were missed due to less optimal EVT-eligible occlusion screening. The long-term modified Rankin Scale (mRS) of the missed EVT-eligible occlusion group was further simulated. ** The sensitivity gain due to CTP-based EVT-eligible occlusion detection was used to compute the size of the group of missed EVT-eligible occlusions if a diagnostic imaging protocol consisting of NCCT + CTA was used. B The 90-day mRS was modeled after EVT or no EVT. C Yearly mRS transitions were modeled based on death and recurrent stroke rates beyond 90 days after stroke. EVT, endovascular treatment; NCCT, non-contrast enhanced CT; CTA, CT angiography; mRS, modified Rankin scale

Fig. 2

Flowchart of patient selection. ^*CTP source data without time information or CTP source data not available due to local storage in the primary stroke center. ^†Reasons for inaccurate CTP results include severe patient motion, severe curve truncation, no timely contrast arrival or incorrect timing CTP, or severe artifacts in CTP source data. CTP, CT perfusion; ICA, internal carotid artery

Fig. 3

Tornado diagram of the one-way sensitivity analyses. Changes in average NMB compared to the baseline (€3447) are depicted for a 10% increase (black) and decrease (gray) of the ten most influential model input variables. A 5-year horizon was used with an NNI of 8.3 and a baseline sensitivity gain. Variations in NNI, sensitivity gain, and EVT effect were not considered for this analysis. EVT, endovascular treatment; QALY, quality-adjusted life-years; mRS, modified Rankin Scale; CTP, CT perfusion; NMB, net monetary benefit

Fig. 4

Incremental cost-effectiveness ratio (ICER) plot per occlusion location. Incremental cost-effectiveness ratio plots are presented for (A) ICA, (B) M1, (C) M2, and (D) all simulated patients together. Simulations considered the baseline sensitivity gain per occlusion location, and a 5-year follow-up period. Panels A–C do not include the CTP screening costs; panel D does include the CTP screening costs using the NNI multiplier (NNI = 8.3). Positive values represent more costs or QALYs when CTP is included in an imaging protocol consisting of NCCT and CTA for occlusion detection. The dashed diagonal line represents the willingness to pay of €80,000 per QALY

Fig. 5

Net monetary benefit for dedicated probabilistic sensitivity analyses. Each panel shows the NMB at a willingness to pay of €80,000 per quality-adjusted life years (QALY) on the y-axis. A positive net monetary benefit implies that the additional costs of CTP-based screening, EVT, and long-term care costs are lower than the health gain. On the x-axis, the percentage point in sensitivity difference relative to the baseline values of additional CTP (NCCT + CTA + CTP) compared to NCCT + CTA is depicted. The baseline sensitivity difference was 6% for ICA occlusions and 16% for M1 and M2 occlusions. The colors represent the median OR for the treatment effect used for simulations. Panels A–D depict varying NNI and years of follow-up. (A) NNI of 4.3 considering 5-year follow-up. (B) NNI of 8.3 considering 5-year follow-up. (C) NNI of 4.3 considering 10-year follow-up. (D) NNI of 8.3 considering 10-year follow-up. NNI, number of patients needed to image; OR, odds ratio; WTP, willingness to pay; QALY, quality-adjusted life years; NMB, net monetary benefit