The Impact of Intra-Operative Heparin on Thromboembolism and Death in a Matched Cohort of Patients with a Ruptured Abdominal Aortic Aneurysm

Objective: Portuguese nationwide estimates indicate that 20% of abdominal aortic aneurysms (AAAs) are treated when ruptured. In these cases, intra-operative unfractionated heparin (UFH) usage rates vary widely. Evidence on this topic is scarce and focused on patients treated by open repair (OSR). The aim was to determine the influence of UFH on peri-operative thromboembolic events (TEs) and death in a cohort of ruptured AAA (rAAA). Methods: Retrospective, single-centre, comparative study. From 2011 to April 2023, all consecutive rAAAs (endovascular repair [EVAR] and OSR) were considered. Primary outcomes were 30-day TE free survival and TE rates. The secondary outcome was 30-day death. Safety endpoints were procedural blood loss, blood product requirements, and secondary interventions due to haemorrhage. Using propensity score matching (PSM) each UFH patient was matched with one no UFH patient in a 1:1 ratio. Results: The study included 250 patients. After PSM, 190 patients were analysed (EVAR: 60.0% no-UFH vs. 64.4% UFH). TE free survival estimates favoured the UFH group (67.3% vs. 47.2%, p = .009; UFH adjusted odds ratio [aOR] 2.01, 95% confidence interval [CI] 1.04–4.17). TEs were more frequent in the no UFH group (20.0% vs. 44.2% patients, p < .001; UFH aOR 0.31, 95% CI 0.15–0.65 for any TE), driven by an increase in bowel ischaemia (17.9% no UFH vs. 3.2% UFH, p = .001). Most events occurred in the first 72 hours. EVAR was associated with reduced TE and improved TE free survival (aOR 0.20, 95% CI 0.09–0.45 and aOR 5.54, 95% CI 2.34–13.08, respectively). No significant differences in 30-day survival were noted (75% no-UFH vs. 83% UFH, p = .26; aOR 1.08, 95% CI 0.48–2.43) nor in blood loss, peri-operative red blood cell and fresh frozen plasma requirements, or secondary interventions due to haemorrhage (p = .10; p = .11; p = .13 and p = .18 respectively). Conclusion: In this cohort, intra-operative UFH was safe and associated with improved TE free survival, driven by a reduction in bowel ischaemia. Conversely, mortality remained unaffected. Randomised controlled trials are required to confirm these findings.