The role of intraluminal thrombus formation for expansion of abdominal aortic aneurysms.

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Though the pathophysiology of initiation, formation, and expansion of abdominal aortic aneurysm (AAA) has been intensely researched, the distinct mechanisms driving these processes still remain unclear. In particular, human studies on predictors of AAA progression as a major determinant of rupture risk are scarce. All consecutive abdominal aortic ultrasound sonographic examinations performed at the duplex laboratory of the Division of Angiology of the Medical University of Vienna between 1999 and 2012 were reviewed. Patients with repeated measurements of the infrarenal aortic diameter, who had no prior AAA repair were included. Detailed informations on AAA, including length, anterior-posterior and transversal measurements of diameter, and intraluminal thrombus formation/size were obtained from ultrasound examination; patients' comorbidities, cardiovascular risk factors, and medications were obtained from outpatient charts. The expansion rate of AAA in relation to intraluminal thrombus size, gender, age, comorbidities, cardiovascular risk factors, and pharmacotherapy was evaluated. Independent predictors of AAA growth were identified through mixed effects models. In total, 166 patients (123 men and 43 women, mean age 68 ± 9 years) were included. Patients were followed over a mean period of 1.4 ± 1.2 years with a mean number of follow-up investigations of 4.4 ± 2.7. Overall, mean maximum AAA diameter at baseline was 37.4 ± 8.2 mm. The average expansion rate of AAA diameter throughout the follow-up period was 2.0 mm per year (95 % confidence interval: 1.6-2.4). At initial investigation, intraluminal thrombus formation was present in 56.6 % of all patients. AAA diameter at baseline, time of follow-up as well as presence and size of intraluminal thrombus formation were identified as independent predictors of AAA expansion rate. Importantly, gender and presence of cardiovascular risk factors were not associated with AAA progression rate. Intraluminal thrombus formation seems to be a key determinant for progression of AAA diameter. Further prospective longitudinal studies are warranted to confirm the potential impact of thrombus formation on AAA development and its implication on monitoring and treatment decisions in patients with AAA.