Prevalence, risk factors and clinical impact of intraprosthetic thrombus deposits after EVAR

The aim was to define the prevalence, the evolution and the clinical relevance of the intraprosthetic thrombus deposit (IPT) after endovascular abdominal aortic repair (EVAR).

Patients treated with EVAR from 2009 to 2017 for abdominal aortic aneurysm were retrospectively considered. Patients with at least one postoperative computed tomography angiography (CTA) performed after a 3-month follow-up were included. Postoperative medical therapy (antiplatelet and/or oral anticoagulant) were recorded. Aorto-iliac anatomical characteristics were measured on pre-operative CTA, while structural and dimensional endograft features were extracted from instructions for use. IPT was defined as intra-endograft thrombus with minimum thickness of 2mm and longitudinally extended for minimum 4 mm, and was assessed in all postoperative CTA. Primary endpoints were freedom from IPT occurrence, risk factors for IPT and evolution of IPT. Secondary endpoints were the prevalence of overall and IPT-related tromboembolic events (TEE: main-body or limb occlusion, distal embolization) during follow-up and its correlation with IPT.

Two-hundred twenty-one patients (mean age 76±7 years; male 94%) were included. Deployed endografts were: aorto-biiliac 96%, aorto-uniiliac 3%, aortic tube 1%; dacron 90%, ePTFE 10%. Mean follow-up was 30±25 months. Overall IPT prevalence was 36% (80/221). At 6, 12, 24 and 48 months, overall estimated freedom from IPT occurrence was 86%, 80%, 60% and 52%, respectively (Kaplan-Meier analysis). At Cox uni-variate analysis, postoperative medical therapy has no influence on IPT; aorto-iliac anatomical risk factors for IPT were larger neck diameter (P<0.001), severe neck thrombus (P=0.043), higher percentage of sac thrombus (P<0.001), hypogastric occlusion/coverage (P=0.040); endograft risk factors were proximal diameter ≥30mm (P<0.001), longer main body (P=0.002), dacron fabric (P=0.025), higher ratio between main body area/gate areas and main body area/distal iliac areas (P<0.001 and P<0.001, respectively). At Cox multi-variate analysis, independent risk factors for IPT were larger neck diameter (P=0.003), higher percentage of sac thrombus (P=0.005) and longer main body (P=0.028). During follow-up, IPT disappeared in 14 cases (18%). Overall TEE prevalence was 4% (8/221) and overall estimated freedom from TEE occurrence at 6, 12, 24 and 48 months was 99%, 99%, 95.3%, 94.1%, respectively (Kaplan-Meier analysis). TEE was IPT-related in 5/8 cases (63%). No statistical correlation were found between IPT and TEE.

The development of intraprosthetic graft thrombus (IPT) is a frequent event after EVAR. The risk of IPT is closely correlated with the proximal aortic neck size, the presence of intra-aneurysmal sac thrombus, and the length of the endograft main body. However, there was no statistical correlation between the presence of IPT and TEE.