Prehospital unfractionated heparin bolus improved TIMI flow in STEMI without increasing bleeding riskPretreatment with UFH improves artery flow for STEMI patients without extra bleeding risk

Circulation Published May 19, 2026 Study authors: Fister Misa, Noc Marko, Radsel Peter, Bunc Matjaz, Franco Danilo, Goslar Tomaz PubMed ↗ NCT05247424 ↗ DOI ↗ Editorial oversight: Dr. Amelia Tan, PhD · Internal Medicine & Chronic Disease

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Key Takeaway

Consider prehospital heparin bolus for STEMI to improve flow without increasing bleeding risk.

The study investigated the impact of administering unfractionated heparin at the first prehospital medical contact for patients with ST-segment-elevation myocardial infarction and symptom duration of six hours or less. Participants were randomized to receive a bolus dose followed by a supplemental dose before percutaneous coronary intervention, or to receive standard unfractionated heparin at the time of the procedure. The primary focus was on achieving improved blood flow in the infarct-related artery upon initial angiography.

The trial reported that pretreatment with unfractionated heparin was associated with a marked increase in the proportion of patients achieving TIMI flow grade two or three compared with the control group. This improvement in vessel patency occurred without a statistically significant difference in the incidence of major bleeding events during the hospital stay. The authors observed that the safety profile remained comparable between the two groups despite the more aggressive anticoagulation strategy in the intervention arm.

The authors noted that this association was observed within a mature network setting, though the study was conducted at a single center. No specific limitations were explicitly detailed in the provided data, but the findings are presented as an association rather than definitive causality. The clinical relevance lies in the potential to enhance reperfusion success without compromising patient safety regarding bleeding complications.

A single-center trial looked at patients with ST-segment-elevation myocardial infarction who had symptoms for six hours or less. Researchers randomized 298 patients to receive unfractionated heparin at the first prehospital medical contact plus a supplemental dose before the procedure. Another group of 295 patients received standard heparin only at the time of the procedure.

The main result showed that pretreatment with unfractionated heparin was associated with a higher rate of good blood flow in the blocked artery. Specifically, 43 percent of patients in the pretreatment group had improved flow compared to 27 percent in the control group. This represents an absolute increase of 16 percent in artery patency.

Safety was also monitored during the hospital stay. The rate of serious bleeding was 2.4 percent in the pretreatment group versus 2.0 percent in the control group. This difference was not statistically significant. The study found no increased risk of bleeding and no serious adverse events were reported. Readers should note that this was a single-center trial, so results may vary in other settings.

What this means for you:

Early unfractionated heparin improved artery flow in heart attack patients without increasing bleeding risk during the hospital stay.

Study Details

Study typeRct

Sample sizen = 298

EvidenceLevel 2

PublishedMay 2026

PMID41910504

TrialNCT05247424

View Original Abstract ↓

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; =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]; <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]; =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.

Prehospital unfractionated heparin bolus improved TIMI flow in STEMI without increasing bleeding riskPretreatment with UFH improves artery flow for STEMI patients without extra bleeding risk

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