On the Impact of Intraluminal Thrombus Mechanical Behavior in AAA Passive Mechanics

Abstract

Intraluminal thrombus (ILT) is a pseudo-tissue that develops from coagulated blood, and is found in most abdominal aortic aneurysms (AAAs) of clinically relevant size. A number of studies have suggested that ILT mechanical characteristics may be related to AAA risk of rupture, even though there is still great controversy in this regard. ILT is isotropic and inhomogeneous and may appear as a soft (single-layered) or stiff (multilayered fibrotic) tissue. This paper aims to investigate how ILT constitution and topology influence the magnitude and location of peak wall stress (PWS). In total 21 patient-specific AAAs (diameter 4.2-5.4 cm) were reconstructed from computer tomography images and biomechanically analyzed using state-of-the-art modeling assumptions. Results indicated that PWS correlated stronger with ILT volume (ρ = 0.44, p = 0.05) and minimum thickness of ILT layer (ρ = 0.73, p = 0.001) than with maximum AAA diameter (ρ = 0.05, p = 0.82). On average PWS was 20% (SD 12%) higher for FE models that used soft instead of stiff ILT models (p < 0.001). PWS location strongly correlated with sites of minimum ILT thickness in the section of maximum AAA diameter and was independent from ILT stiffness. In addition, ILT heterogeneity, i.e., the spatial composition of soft and stiff thrombus tissue, can considerably influence stress in the AAA wall. The present study is limited to identification of influential biomechanical factors, and how its findings translate to an AAA rupture risk assessment remains to be explored by clinical studies.

Role of intraluminal thrombus in abdominal aortic aneurysm ruptures: A hemodynamic point of view

“…ECAP, which was generally considered as the thrombosis potential, could be a sign of rupture in AAAs without ILTs. (b) Thin‐layered ILTs provide stress shielding for the dilated AAA wall in the recirculation flow region with high ECAPs . However, the impact loading of the dominant flow on the wall leads to increased cyclic stretching, hastening wall fatigue, and rupture .…”

“…(b) Thin-layered ILTs provide stress shielding for the dilated AAA wall in the recirculation flow region with high ECAPs. 5,48 However, the impact loading of the dominant flow on the wall leads to increased cyclic stretching, hastening wall fatigue, and rupture. 49 (c) When thick-layered ILTs are present in AAAs, they serve as a barrier of oxygen flux to the aortic wall, which induces hypoxic conditions and wall degeneration.…”

Patient-specific numerical simulation of stent-graft deployment: Validation on three clinical cases

“…This assumption was validated by the good agreement between simulations and post-operative scans. Nevertheless, our simulations could benefit from more sophisticated modeling, including thrombus (Riveros et al, 2015;Toungara and Geindreau, 2013) and calcifications. This could enhance accuracy of SG position in the aneurysm sac.…”

Predictive Models with Patient Specific Material Properties for the Biomechanical Behavior of Ascending Thoracic Aneurysms

“…19,29,41 Obtaining the local thickness is still challenging, despite the importance of this parameter for AAAs and ATAAs. 37,44,49 The current study is focused on identifying, noninvasively and in vivo, the patient specific material properties of ATAAs, which represent essential biomechanical determinants for ATAA strength 2,11,26 and for ATAA growth. 31,32,49,60 Several inverse approaches have already been developed to estimate mechanical properties of soft tissues in the human body.…”