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Publication Detail
On the relation between different Left Atrial Appendage morphologies and thrombosis risk: a Computational Fluid Dynamic analysis
  • Publication Type:
    Conference presentation
  • Authors:
    Bosi GM, Cook A, Rai R, MENEZES L, Torii R, Burriesci G
  • Date:
    10/07/2018
  • Name of Conference:
    8th World Congress of Biomechanics
  • Conference place:
    Dublin
  • Conference start date:
    08/07/2018
  • Conference finish date:
    12/07/2018
  • Notes:
    P2043
Abstract
During Atrial Fibrillation (AF) more than 90% of the left atrial thrombi responsible for thromboembolic events – e.g. stroke and vascular ischemia – originate in the left atrial appendage (LAA), a small chamber protruding from the left atrium (LA) [1]. Currently available treatments to prevent thromboembolic events are based on oral anticoagulation, surgical LAA exclusion or percutaneous LAA occlusion. However, the mechanism behind thrombus formation in the LAA is poorly understood. The LAA morphology can vary substantially from patient to patient and is typically classified into four shape groups: “Chicken wing”, “Cactus”, “Windsock” and “Cauliflower” [2]. The aim of this work is to analyse the hemodynamic behaviour in these four typical LAA morphologies, to identify potential relationships between the different shapes and the risk of thrombotic events. Computerised tomography (CT) images from four subjects, each falling in one of the four LAA shape groups, were segmented to derive the 3D anatomical model of LA, including LAA, pulmonary veins and the mitral valve orifice. Transient Computational Fluid Dynamic (CFD) analyses based on the patient-specific anatomies were carried out using Ansys CFX (ANSYS, Inc.), imposing both healthy and AF flow conditions for 4 consecutive cardiac cycles. Velocity and shear strain rate (SSR) were analysed for all cases. Residence time in the different LAA morphologies was estimated with a virtual contrast agent washing out. CFD results indicate that both velocity and SSR decrease along the LAA, from the access ostium to the distal tip, at each instant in the cardiac cycle. This suggests that the LAA tip is more prone to fluid stagnation, and therefore to higher risk of thrombus formation. Velocity and SSR also decreased from normal to AF conditions; this reduction was different depending of the LAA shape, being the largest for the Cactus morphology and the smallest for the Chicken wing (Figure 1). After 4 cardiac cycles, the lowest washout of contrast agent was observed for the Cauliflower (3.27% of residual contrast in AF), and the highest for the Windsock (0.56% of residual contrast in AF), thus suggesting that the former is expected to be associated with a higher risk of thrombosis. This finding confirms the observations from clinical reports in the literature [3]. The presented computational approach could result in a powerful tool to quantitatively analyse parameters otherwise impossible to measure in clinics and to study the geometrical factors influencing thrombus formation. Lastly, this methodology could support clinical stratification of AF patients under higher risk of thrombus formation, complementing the standard clinical assessment and enhancing patient safety. References [1] Holmes et al, J. Am. Coll. Cardiol. 63, 291–298, 2014. [2] Beigel et al., JACC Cardiovasc. Imaging 7, 1251–1265, 2014. [3] Di Biase et al., JAC 60, 531–538, 2012.
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