Editor's Choice – Activated Clotting Time Guided Heparinisation during Open Abdominal Aortic Aneurysm Repair (ACTION-1): A Randomised, Multicentre, Single Blind, Superiority Trial

Objective: The optimal dosage of intravenous unfractionated heparin and the role of monitoring its effect using activated clotting time (ACT) to prevent thromboembolic complications (TECs) during open abdominal aortic aneurysm (AAA) repair are uncertain. This trial aimed to compare ACT guided heparinisation with a single dose of 5 000 international units (IU) of heparin. Methods: This was a multicentre, randomised controlled, single blinded, superiority trial (NCT04061798). Patients undergoing elective open AAA repair were randomly assigned (1:1) to receive either ACT guided heparinisation with a dose of 100 IU/kg with a target duration of 200 seconds or a single heparin bolus of 5 000 IU as a control group. The primary efficacy outcome was the combined incidence of TECs and all cause death at 30 days. The safety outcome was the incidence of bleeding complications. ACT measurements were performed using the same device to limit variability. Results: The trial was ended prematurely due to futility after inclusion of 294 patients. After randomisation, 149 patients received ACT guided heparinisation and 145 patients were assigned to the control group. The primary outcome occurred in 34 patients (22.8%) in the ACT group vs. 37 patients (25.5%) in the control group (absolute difference –2.7%, 95% confidence interval [CI] –12.5 – 7.1%). Bleeding complications (absolute difference 9.2%, 95% CI –1.8 – 20.2%) and deaths (absolute difference 7.9%, 95% CI 2.3 – 13.6%) were higher in the ACT group. No difference was found in the incidence of TECs (absolute difference –5.4%, 95% CI –15.0 – 4.2%). Conclusion: In patients undergoing open AAA repair, heparinisation with 100 IU/kg and ACT monitoring at a target of 200 seconds did not reduce the primary efficacy outcome and increased the risk of peri-operative bleeding compared with a single bolus of 5 000 IU. Additionally, an increased mortality rate was observed.