EFFECT OF INTRALUMINAL THROMBUS ON ABDOMINAL AORTIC-ANEURYSM WALL STRESS

Purpose: Abdominal aortic aneurysms (AAAs) rupture when the wall stres s exceeds the strength of the vascular tissue. Intraluminal thrombus m ay absorb tension and reduce AAA wall stress. This study was performed to test the hypothesis that intraluminal thrombus can significantly r educe AAA wall stress. Methods: AAA wall stresses were determined by a xisymmetric finite element analysis. Model AAAs had external diameters ranging from 2.0 to 4.0 cm. Model parameters included: AAA length, 6 cm; wall thickness, 1.5 mm; Poisson's ratio, 0.49; Young's modulus, 1. 0 MPa; and luminal pressure, 1.6 x 10(5) dyne/cm(2). Stresses were cal culated for each model without thrombus, and then were recalculated wi th thrombus filling 10% of the AAA cavity. Calculations were repeated as thrombus size was increased in 10% increments and as thrombus elast ic modulus increased from 0.01 MPa to 1.0 MPa. Maximum wall stresses w ere compared between models that had intraluminal thrombus and the unm odified models. Stress reduction greater than 25% was considered signi ficant. Results: The maximum stress reduction of 51% occurred when thr ombus with elastic modulus of 1.0 MPa filled the entire AAA cavity. St resses were reduced by only 25% as modulus decreased to 0.2 MPa. Simil arly, decreasing thrombus size by 70% resulted in stress reduction of only 28%. Large AAAs experienced greater stress reduction than small A AAs (48% vs 11%). Conclusion: Intraluminal thrombus can significantly reduce AAA wall stress.