Abstract Body (Do not enter title and authors here): Background: There are currently no specific guidelines regarding pre-hospital antiplatelet therapy in patients with out-of-hospital cardiac arrest (OHCA) suspected of acute coronary syndrome (ACS).

Purpose: To evaluate efficacy and safety of pre-hospital administration of antiplatelet therapy in patients with OHCA directed to a cardiac catheterization laboratory (cath lab).

Method: Using the cath lab database of a tertiary cardiovascular center, we included consecutive patients referred for coronary angiography within 24 hours of OHCA for suspected ACS from January 2012 to January 2024. Pre-hospital antiplatelet treatment was defined as prescribing any antiplatelet therapy before cath lab admission (aspirin alone or combined with a P2Y12 inhibitor). The outcomes of interest were: 1) all-cause death at 30 days, 2) intra-hospital major adverse cardiovascular events (MACE), defined by the composite of all-cause death, myocardial infarction, or stroke, and 3) intra-hospital major bleedings (BARC ≥ 3). To help account for the non-randomized pre-hospital antiplatelet administration, an Inverse Probability Weighting (IPW) approach was used to compare outcomes between the two groups.

Result: Between January 2012 and January 2024, n = 411 patients with OHCA were referred to the cath lab, of whom 217 (52.8%) received a pre-treatment. Pre-hospital antiplatelet administration did not show a reduced risk of death from any cause at 30 days (56.7% [50.0%;63.1%] vs 59.8% [52.8%;66.4%], p=0.21) (Figure 1). The rates of intra-hospital MACE (57.1% [50.5%;63.5%] vs (61.3% [54.3%;67.9%]), p=0.38) and major bleedings (18.9% [14.2%;24.6%] vs (18.6% [13.7%;24.6%], p=0.51) did not differ significantly in pre-treated patients compared to non-pre-treated ones.

Conclusion: In our cohort of patients with OHCA suspected of ACS, we did not observe an association between pre-hospital administration of an antiplatelet loading dose and outcomes.