The following are key points to remember from a viewpoint on heparin use in acute coronary syndromes (ACS) and cardiovascular interventions:

1. Unfractionated heparin (UFH) exerts its clinical antihemostatic effects predominantly by antithrombin-mediated inactivation of factors IIa and Xa, thus inhibiting thrombin generation and activity.
2. Although multiple trials have been conducted to assess the application of UFH in cardiology practice, current contemporary use remains largely supported by anecdotal practice rather than robust trial data.
3. UFH administration during primary percutaneous coronary intervention (PCI) was associated with reduced acute stent thrombosis when compared with bivalirudin in the HORIZONS-AMI trial, and reduced catheter-related thrombosis when compared with fondaparinux in the OASIS-6 trial. These trials have indirectly highlighted the necessity of anticoagulation during primary PCI to prevent catheter and acute stent thrombosis due to the thrombogenic nature of coronary catheters and the prothrombotic milieu associated with ST-segment elevation myocardial infarction (STEMI).
4. Although there are no placebo-controlled trials evaluating the need for anticoagulation during PCI for non–ST-segment elevation acute coronary syndrome (NSTE-ACS), subgroup analysis of the OASIS-5 trial demonstrated that patients who received a bolus of UFH in addition to fondaparinux had lower rates of catheter-related thrombosis compared with fondaparinux alone despite similar ischemic endpoints between groups. This has supported the convention that parenteral anticoagulation is required during PCI for NSTE-ACS similar to primary PCI.
5. The CIAO study remains the only randomized controlled trial assessing the efficacy of UFH against placebo during elective PCI for stable coronary artery disease. In this study, there was no difference in ischemic outcomes between both groups, but numerically more bleeding events in the UFH group.
6. UFH is routinely administered both during balloon aortic valvuloplasty (BAV) and transcatheter aortic valve replacement (TAVR) to prevent catheter thrombosis and systemic thromboembolism.
7. This practice was adopted from initial BAV procedures in 1986, similar to other percutaneous interventions at the time. Current guidelines continue to recommend the administration of UFH during contemporary BAV and TAVR despite a lack of trials evaluating the utility of anticoagulation in these procedures.
8. Although untested by randomized trials, it is routine for intraprocedural UFH to be administered during left-sided electrophysiological studies or ablation procedures to reduce the risk of systemic thromboembolism following transseptal puncture.
9. The BRUISE CONTROL study was a randomized trial demonstrating that UFH bridging during device implantation was associated with significantly increased risk of device-pocket hematoma when compared with uninterrupted vitamin K antagonist therapy. Current guidelines recommend the cessation of oral anticoagulants without UFH or low molecular weight heparin bridging prior to device surgery where feasible, but continuation of vitamin K antagonist or direct oral anticoagulant in situations where cessation is not possible.
10. Since certain applications of UFH remain guided by historical experience rather than robust clinical trials, there is an opportunity for further investigative studies to evaluate the indication, optimal dosing, and monitoring required for UFH use, as well as other alternative agents to UFH, in routine cardiovascular procedures.

Clinical Topics: Acute Coronary Syndromes, Anticoagulation Management, Arrhythmias and Clinical EP, Cardiac Surgery, Cardiovascular Care Team, Dyslipidemia, Invasive Cardiovascular Angiography and Intervention, Prevention, Stable Ischemic Heart Disease, Valvular Heart Disease, Anticoagulation Management and ACS, Implantable Devices, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Aortic Surgery, Cardiac Surgery and Arrhythmias, Cardiac Surgery and SIHD, Cardiac Surgery and VHD, Lipid Metabolism, Novel Agents, Interventions and ACS, Interventions and Structural Heart Disease, Interventions and Vascular Medicine, Chronic Angina

Keywords: Acute Coronary Syndrome, Anticoagulants, Antithrombins, Arrhythmias, Cardiac, Cardiology Interventions, Catheters, Catheter Ablation, Electrophysiology, Factor Xa Inhibitors, Heart Valve Diseases, Hematoma, Heparin, Heparin, Low-Molecular-Weight, Myocardial Ischemia, Percutaneous Coronary Intervention, Secondary Prevention, ST Elevation Myocardial Infarction, Non-ST Elevated Myocardial Infarction, Stents, Thrombin, Thromboembolism, Thrombosis, Transcatheter Aortic Valve Replacement, Vitamin K

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