Abstract Number: Esoc2026a1024 Ultra-Early Intensive Blood-Pressure Reduction of Hyperacute Stroke in Different Emergency Medical Services Models: A Secondary Analysis of the Interact4 Trial

Abstract Background and aims The INTERACT4 trial showed that prehospital intensive blood pressure (BP) lowering improves outcomes in intracerebral hemorrhage (ICH). Participating sites used different emergency medical service (EMS) dispatch models: hospital-based and centralized-based systems. We investigated whether EMS model modified treatment efficacy and explored potential mechanisms. Methods Patients with suspected ICH in INTERACT4 were stratified by EMS dispatch model. The primary outcome was functional outcome at 90 days, analyzed using ordinal logistic regression. Treatment effects were assessed within subgroups, with interaction testing. Prehospital time intervals, antihypertensive dosing, and systolic BP trajectories were compared to explore mechanistic differences. Results Intensive BP lowering significantly improved functional outcome in the hospital-based subgroup (odds ratio OR, 0.72; 95% CI, 0.53–0.97; P=0.029), but not in the centralized-based subgroup (OR, 0.92; 95% CI, 0.57–1.49; P=0.74), with no significant interaction (P for interaction=0.384). Compared with the hospital-based subgroup, the centralized-based subgroup had shorter call-to-scene, onset-to-treatment, and transport times (Figure 1). Mean transport time was longer in the hospital-based subgroup (32.8 vs 26.6 minutes). Consistently, the total prehospital urapidil dose was higher in the hospital-based subgroup (31.84 vs 23.62 mg; P0.0001). Systolic BP during the prehospital period and within 6 hours before hospital arrival was lower in the hospital-based intervention group (Figure 2). Conclusions Prehospital intensive BP lowering was more effective within a hospital-based EMS model. Longer transport time, higher cumulative antihypertensive exposure, and potentially more streamlined handover processes may enable earlier and more sustained BP control, underscoring the importance of EMS system characteristics in optimizing prehospital ICH management. Conflict of interest All authors have nothing to disclose Figure 1 - belongs to Results Figure 2 - belongs to Results