Effect of Fixed-Bolus (5,000 Units) Unfractionated Heparin Before Primary Percutaneous Coronary Intervention on Activated Clotting Time, Time Flow, and All-Cause Mortality

The American College of Cardiology Foundation /American Heart Association guidelines recommend a weight-based dose of unfractionated heparin (UFH) for primary percutaneous coronary intervention (PCI). However, it is convention to administer a fixed-bolus dose of 5,000 units of UFH. It is unclear if 5,000 units are sufficient to achieve a therapeutic first activated clotting time (ACT). We conducted a retrospective cohort study to determine the proportion of therapeutic first ACT in patients who received 5,000 units of UFH before primary PCI. We examined the association of therapeutic first ACT with clinical outcomes, including post-PCI Thombolysis in Myocardial Infarction (TIMI) grade flow, myocardial infarction, bleeding, and mortality. Among the 269 included patients, 74.7% were men, and 61.4% were overweight or obese. The mean first ACT was 243.4 (SD = 61.5) seconds. Most patients (56.1%) had an infratherapeutic first ACT, 21.9% had a therapeutic first ACT, and 21.9% had a supratherapeutic first ACT. Furthermore, 44.6% of patients who achieved the American College of Cardiology Foundation/American Heart Association target weight-based dosing had an infratherapeutic ACT. The proportion of patients with post-PCI TIMI grade flow 0 to 2 was 14.6% among those with a first ACT that was infratherapeutic versus 6.8% among those with a first ACT that was not infratherapeutic (relative risk 2.15, 95% CI 0.99 to 4.65). In conclusion, over half of patients with ST-elevation myocardial infarction administered 5,000 units of UFH have an infratherapeutic first ACT and the high rate of poor TIMI grade flow in patients with an infratherapeutic ACT is concerning.