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BACKGROUND: Primary percutaneous coronary intervention (PCI) is the preferred reperfusion strategy for patients with ST-segment-elevation myocardial infarction (STEMI). We investigated the benefits and safety of pretreatment with unfractionated heparin (UFH) in patients with STEMI referred to primary PCI.

METHODS: In HEPARIN-STEMI (Pretreatment With Unfractionated Heparin for ST Elevation Myocardial Infarction)-a single-center, open-label, randomized controlled trial-patients with STEMI with =6 hours symptom duration were assigned to receive either a 70- to 100-IE/kg bolus of UFH at first prehospital medical contact plus a supplemental dose before PCI, adjusted to activated clothing time =250 seconds, or to a control group receiving standard UFH at the time of PCI. The primary efficacy end point was TIMI (Thrombolysis in Myocardial Infarction) flow grade 2-3 in the infarct-related artery at initial coronary angiography. The primary safety end point was BARC (Bleeding Academic Research Consortium) type 3-5 bleeding during the index hospital stay.

RESULTS: From March 2022 to February 2025, 298 patients were randomized to UFH pretreatment and 295 to the control group. The groups were comparable in age, sex, risk factors, previous cardiovascular events, and median delay from symptoms to coronary angiography (145 versus 150 minutes; P=0.814). The median time from UFH pretreatment to coronary angiography was 60 minutes (25th-75th interquartile range, 47-55 minutes). TIMI flow grade 2-3 in the infarct-related artery was documented in 43% of patients with UFH pretreatment and 27% of patients in the control group (relative risk, 1.59 [95% CI, 1.27-1.98]; P<0.001), with no significant difference in BARC type 3-5 bleeding (2.4% versus 2.0%; relative risk, 1.16 [95% CI, 0.39-3.45]; P=0.789).

CONCLUSIONS: In patients with STEMI undergoing primary PCI, in a mature STEMI network, pretreatment with UFH at first prehospital medical contact was associated with an absolute 16% increase in infarct-related artery patency without an increased risk of bleeding.

REGISTRATION: URL: https://www.clinicaltrials.gov; Unique identifier: NCT05247424.

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