Does administration of heparin (unfractionated heparin) in the ambulance improve outcomes for patients with ST-Elevation Myocardial Infarction (STEMI)?

From the Guidelines

Administration of heparin in the ambulance for STEMI patients may not be necessary for all EMS systems, and the decision to administer heparin should be based on current practice and system capabilities. According to the 2015 American Heart Association guidelines update for cardiopulmonary resuscitation and emergency cardiovascular care 1, EMS systems that do not currently administer heparin to suspected STEMI patients do not need to add this treatment, whereas those that do administer it may continue their current practice (Class IIb, LOE B-NR).

Key Considerations

• The guidelines suggest that administration of unfractionated heparin can occur either in the prehospital or in-hospital setting for suspected STEMI patients with a planned primary percutaneous coronary intervention (PCI) reperfusion strategy (Class IIb, LOE B-NR) 1.
• The usefulness of supplementary oxygen therapy has not been established in normoxic patients, and withholding supplementary oxygen therapy in normoxic patients with suspected or confirmed acute coronary syndrome may be considered (Class IIb, LOE C-LD) 1.
• In systems where unfractionated heparin is currently administered in the prehospital setting for patients with suspected STEMI who are being transferred for PCI, it is reasonable to consider prehospital administration of enoxaparin as an alternative to unfractionated heparin (Class IIa, LOE B-R) 1.

Recommendations

• EMS systems should not add heparin administration to their protocol if they do not currently use it, but can continue their current practice if they do administer heparin 1.
• Prehospital administration of heparin or enoxaparin should be considered as part of a comprehensive approach that includes aspirin, P2Y12 inhibitors, and rapid transport to a PCI-capable facility.
• The decision to administer heparin in the prehospital setting should be based on system capabilities, current practice, and the potential benefits and risks of heparin administration in the prehospital setting.

Rationale

The guidelines emphasize the importance of early restoration of blood flow to ischemic myocardium in acute STEMI, and the choice between fibrinolysis and PCI should be based on clinical circumstances, system capabilities, and timing 1. While heparin administration in the ambulance may not be necessary for all EMS systems, it is essential to consider the potential benefits and risks of heparin administration in the prehospital setting and to make decisions based on current practice and system capabilities.

From the Research

Administration of Heparin in Ambulances for STEMI Patients

• The administration of heparin (unfractionated heparin) in ambulances for patients with ST-Elevation Myocardial Infarction (STEMI) has been studied in several research papers 2, 3, 4, 5, 6.
• A study published in 2011 found that pre-hospital treatment with a fixed bolus dose of unfractionated heparin (UFH) was not within the therapeutic activated clotting time (ACT) range in most patients with STEMI 2.
• Another study from 2007 investigated the use of prehospital fibrinolysis with dual antiplatelet therapy in STEMI patients and found that the addition of clopidogrel to medical reperfusion with fibrinolysis, heparin, and aspirin before reaching the hospital was feasible and tended to show better early coronary patency compared to placebo 3.
• A 2013 study examined the prognostic value of post-procedural activated partial thromboplastin time (aPTT) in patients with STEMI treated with primary percutaneous coronary intervention (PCI) and found that low aPTTs in the first 24 hours after PCI were not associated with an increase in ischemic events, whereas high aPTT values were associated with more frequent bleeding complications 4.
• The 2010 European Society of Cardiology (ESC) guidelines for the management of STEMI recommend the use of unfractionated heparin (UFH) as an anticoagulant, with bivalirudin as an upcoming alternative 5.
• A 2021 study investigated the effect of early upstream antithrombotic therapy administration (ATTA) with aspirin, ticagrelor, and UFH in STEMI patients with prolonged transport times to primary PCI and found that early upstream ATTA was associated with greater pre-PCI TIMI flow and less definite acute stent thrombosis, without increased bleeding risk 6.

Key Findings

• The use of heparin in ambulances for STEMI patients may improve outcomes, but the optimal dosing and timing of administration are still being studied 2, 6.
• The addition of other antiplatelet and anticoagulant therapies, such as clopidogrel and ticagrelor, may also be beneficial in improving outcomes for STEMI patients 3, 6.
• The monitoring of aPTT and ACT values is important in patients with STEMI treated with heparin to minimize the risk of bleeding complications 2, 4.