ABSTRACT NUMBER: ESOC2026A1218 IMPACT OF FOLLOW-UP CT VERSUS MRI ON ANTIPLATELET INITIATION DECISIONS AFTER ACUTE ISCHAEMIC STROKE

Abstract Background and aims Antiplatelet therapy (APT) is a cornerstone of secondary prevention after acute ischaemic stroke (AIS). Haemorrhagic transformation (HT) directly influences antiplatelet initiation timing. While noncontrast CT is commonly used for HT detection, MRI (particularly SWI) can identify subtle haemorrhagic lesions. The impact of follow-up imaging modality on antiplatelet initiation decisions remains poorly studied. We aimed to compare antiplatelet initiation decisions based on follow-up MRI versus CT and assess inter-rater agreement. Methods We retrospectively analysed AIS patients admitted within 24 hours of last known well from a prospective single-center registry (2015–2023) who underwent both follow-up CT and MRI within 24 hours of initial imaging and within 24 hours of each other. Four blinded raters independently reviewed anonymised CT and MRI scans and recorded a binary decision regarding APT initiation. MRI vs CT-based decisions were compared using paired chi-square test; inter-rater agreement was assessed with Fleiss’ kappa (95% CI). Results Among 115 patients (median age 66 years; median NIHSS 12, median interval between follow-up CT and MRI: 6 hours), decisions to withhold APT were more frequent with MRI than with CT (26.9% vs 17.4%; p<0.001). MRI led to non-resumption of APT in 31 cases, including 12 patients in whom APT would have been resumed based on CT alone, whereas only one CT-based decision was not confirmed by MRI. Inter-rater agreement was higher for MRI than for CT (kappa 0.81 vs 0.54). Conclusions MRI-based decisions lead to more frequent withholding of APT and show higher inter-rater agreement, indicating that MRI-detected haemorrhagic lesions require careful interpretation. Conflict of interest All authors: nothing to disclose