Subtherapeutic activated clotting time after pre-hospital unfractionated heparin in ST-elevation myocardial infarction

Background Primary percutaneous coronary intervention (PPCI) is the preferred reperfusion strategy for ST-elevation myocardial infarction (STEMI). Pre-hospital administration of unfractionated heparin (UFH) is standard practice to ensure effective anticoagulation before arrival in the catheterization lab, yet evidence on the effect of pre-hospital UFH on Activated Clotting Time (ACT) upon catheterization lab arrival is limited. Purpose To assess ACT at catheterization lab arrival following a standardised pre-hospital bolus of 5000 IU UFH, and to evaluate associations with key time intervals, efficacy, procedural outcomes, and short-term clinical events. Methods This prospective, multicentre, observational pilot study included 100 STEMI patients transported by ambulance and treated with PPCI between April 2021 and June 2022. All patients received 5000 IU UFH pre-hospital, followed by an optional additional UFH dose at the catheterization lab. ACT was measured immediately upon arrival at the catheterization lab. Time intervals (symptom onset to administration of UFH (SO-UFH), administration of UFH to ACT measurement (UFH-ACT), SO-PPCI) were recorded and TIMI flow scale was used to assess patency in the infarct-related artery. Clinical, procedural, and 30-day outcomes were obtained retrospectively from electronic health records. Results The 100 STEMI patients had a mean age of 65 ± 13 years and 70% were male. Median ACT at arrival was 175 s (158-196), with 97% of patients below the therapeutic ACT target of 250 s. Median SO-UFH, UFH-ACT, and SO-PPCI intervals were 76 min, 45 min, and 121 min, respectively. Intervals were not significantly correlated with ACT values. No associations were observed between ACT levels and pre-procedural TIMI flow, peri-procedural complications, post-procedural complications, or 30-day MACE. However, SO-UFH was significantly associated with pre-procedural TIMI flow (OR = 0.994, p = 0.04). Conclusions A pre-hospital bolus of 5000 IU UFH resulted in subtherapeutic ACT levels in nearly all STEMI patients upon catheterization lab arrival. No associations were found between ACT and pre-procedural TIMI flow or short-term clinical outcomes. In contrast, the SO-UFH interval showed a significant association with pre-TIMI flow, suggesting that earlier pre-hospital anticoagulation may influence initial coronary patency. Larger, randomised studies with serial ACT monitoring are needed to define optimal pre-hospital anticoagulation strategies in STEMI.abstract visual