Patients with a Ruptured Abdominal Aortic Aneurysm Are Better Informed in Hospitals with an "EVAR-preferred" Strategy: An Instrumental Variable Analysis of the Dutch Surgical Aneurysm Audit

Eleonora G Karthaus*, Niki Lijftogt, Anco Vahl, Esmee M van der Willik, Sonia Amodio, Erik W van Zwet, Jaap F Hamming, Dutch Society for Vascular Surgery, Steering Committee of the Dutch Surgical Aneurysm Audit, Dutch Institute for Clinical Auditing, Joep Teijink

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review


BACKGROUND: While several observational studies suggested a lower postoperative mortality after minimal invasive endovascular aneurysm repair (EVAR) in patients with a ruptured abdominal aortic aneurysm (RAAA) compared to conventional open surgical repair (OSR), landmark randomized controlled trials have not been able to prove the superiority of EVAR over OSR. Randomized controlled trials contain a selected, homogeneous population, influencing external validity. Observational studies are biased and adjustment of confounders can be incomplete. Instrumental variable (IV) analysis (pseudorandomization) may help to answer the question if patients with an RAAA have lower postoperative mortality when undergoing EVAR compared to OSR.

METHODS: This is an observational study including all patients with an RAAA, registered in the Dutch Surgical Aneurysm Audit between 2013 and 2017. The risk difference (RD) in postoperative mortality (30 days/in-hospital) between patients undergoing EVAR and OSR was estimated, in which adjustment for confounding was performed in 3 ways: linear model adjusted for observed confounders, propensity score model (multivariable logistic regression analysis), and IV analysis (two-stage least square regression), adjusting for observed and unobserved confounders, with the variation in percentage of EVAR per hospital as the IV instrument.

RESULTS: 2419 patients with an RAAA (1489 OSR and 930 EVAR) were included. Unadjusted postoperative mortality was 34.9% after OSR and 22.6% after EVAR (RD 12.3%, 95% CI 8.5-16%). The RD adjusted for observed confounders using linear regression analysis and propensity score analysis was, respectively, 12.3% (95% CI 9.6-16.7%) and 13.2% (95%CI 9.3-17.1%) in favor of EVAR. Using IV analysis, adjusting for observed and unobserved confounders, RD was 8.9% (95% CI -1.1-18.9%) in favor of EVAR.

CONCLUSIONS: Adjusting for observed confounders, patients with an RAAA undergoing EVAR had a significant better survival than OSR in a consecutive large cohort. Adjustment for unobserved confounders resulted in a clinical relevant RD. An "EVAR preference strategy" in patients with an RAAA could result in lower postoperative mortality.

Original languageEnglish
Pages (from-to)332-344
Number of pages13
JournalAnnals of Vascular Surgery
Publication statusPublished - Nov 2020


  • Aged
  • Aged, 80 and over
  • Aortic Aneurysm, Abdominal/diagnostic imaging
  • Aortic Rupture/diagnostic imaging
  • Blood Vessel Prosthesis Implantation/adverse effects
  • Clinical Decision-Making
  • Endovascular Procedures/adverse effects
  • Female
  • Hospital Mortality
  • Humans
  • Male
  • Medical Audit
  • Netherlands
  • Postoperative Complications/mortality
  • Prospective Studies
  • Risk Assessment
  • Risk Factors
  • Time Factors
  • Treatment Outcome


Dive into the research topics of 'Patients with a Ruptured Abdominal Aortic Aneurysm Are Better Informed in Hospitals with an "EVAR-preferred" Strategy: An Instrumental Variable Analysis of the Dutch Surgical Aneurysm Audit'. Together they form a unique fingerprint.

Cite this