Abstract 261: Neutrophil Elastase Derived Fibrin Degradation Products are Increased in the Plasma of Patients with Abdominal Aortic Aneurysms and Correlate to the Intraluminal Thrombus Volume

Abstract

Introduction: Abdominal Aortic Aneurysms (AAA) often contain an intraluminal thrombus (ILT). AAA diameter and ILT volume are associated with growth of the aneurysm. Neutrophils, present in the ILT, contain elastase (NE). NE activity leads to production of fibrin degradation products (FDPs) with a specific epitope [[Unable to Display Character: –]] XDP. The present study evaluates NE-derived FDPs in aneurysm patients scheduled for elective aortic repair. The purpose of the study is to introduce an additional bio-marker for presence of AAA and possibly risk of rupture by measuring levels of NE derived FDPs in plasma of patients with AAA. Materials and Methods: 42 male patients, undergoing aortic repair for AAA were included. As controls, we collected blood samples from 42 men who attended an AAA screening program but had no AAAs on ultrasound. Computed Tomography (CT) images were available for 34 AAA patients and analyzed using A4 Clinics software (VASCOPS, Austria). Patient demographics, maximum diameter, aortic volume and ILT volume were recorded. Peak wall stress (PWS), peak wall rupture index (PWRI) and mean ILT stress were estimated by Finite Element Analysis using the A4 Clinics software. Plasma levels of elastase digests of cross-linked fibrin (E-XDP) were determined with a sandwich ELISA. Results: E-XDP levels were higher in AAA patients than in age-matched controls (8.5 vs 1.2 U/ml, p<0.0001). E-XDP levels correlated with ILT volume (r = 0.64, p<0.0001), aortic volume (r = 0.64, p<0.0001) and maximum diameter (r = 0.59, p=0.0003). AAA patients with other concomitant peripheral aneurysms had higher E-XDP levels than those with only an AAA (13.6 vs 6.8 U/ml, p=0.028). PWS, PWRI and bleeding signs in the thrombus did not significantly affect E-XDP levels. Interestingly, the mean ILT stress correlated significantly to E-XDP levels (r= 0.45, p=0.008). Conclusions: The study shows that it is feasible to measure E-XDP levels in plasma of patients with AAA and that E-XDP correlates with ILT volume and mean ILT stress. These results support the notion that the resident neutrophils in the ILT can actively lyse fibrin in the ILT, which may decrease ILT strength. E-XDP holds potential as a biomarker of the ILT in AAA patients and needs to be further investigated in AAA rupture risk assessment.