Analysis of the haemodynamics and biomechanics of endografts for complex aortic arch repair

The aorta originates from the left ventricle, directed upwards (ascending aorta), before it curves and begins to travel downwards (descending aorta), carrying blood to different parts of the body. This curved region of the aorta, referred to as the aortic arch, consists of branches that carry blood to the upper limbs and most importantly, the brain. Deformities in the arch can include tears in the vessel wall, i.e. aortic dissection, or more commonly when the walls weaken and expand, giving rise to an aneurysm. Aortic aneurysms can occur due to atherosclerotic changes in the vessel, irregularities in blood pressure, or as a result of conditions such as Marfan's Syndrome or Mega-Aorta Syndrome.

Aneurysms develop in size over time and require surgery when they rupture or have reached a certain size. Surgery in the aortic arch is a complex procedure and there have been several changes made and developments to the surgical procedure over the years, ever since it was first reportedly carried out back in 1964. Over the years, several variations to the procedure have presented with varying degrees of risk and reward. There has been much debate over the efficacy of open and/or hybrid surgical methods and what determines the suitability of patients for either repair method. Recent methods such as the Frozen Elephant Trunk Technique (involving the antegrade implantation of a stent graft) and TEVAR (Thoracic endovascular aortic repair) have proven successful in combining different previous surgical methods and treating complex arch abnormalities. These involve inserting an endograft in the arch, providing a means for blood to pass through without pushing on the weakened vessel lining.

Endografts used in the TEVAR could vary according to the method of deployment, and the region where they are placed. The effects of endografts on haemodynamic and biomechanical conditions of the aorta are of significant importance, as they are related to the long-term outcomes of the procedure. This study aims to investigate endografts and their impact on aortic flow and biomechanics using computational means. Computational Fluid Dynamics (CFD) is a common tool for investigating biological flows and is often used to simulate and study phenomena that cannot be measured in vivo. It allows one to obtain parameters such as fluid velocity, flow patterns, wall shear stress and displacement forces, all of which would be important in evaluating the performance of endografts. Computational means also allow one to carry out fluid-structure interaction (FSI) studies. This is useful in understanding how the blood flowing through grafted regions interact with the components of the endograft as well as the vessel lining. Computational studies have been previously carried out to investigate flow across stents and grafts in the aorta, primarily the thoracic and abdominal regions. The aortic arch however, is a region undergoing significant developments in terms of methods of repair, and thus provides a novel platform to carry out investigations. The study of flow patterns of blood through endografts of different designs and geometries would allow one to predict clinical outcomes of a procedure or specific grafts designs, thereby providing opportunities to optimise and improve upon endograft designs and characteristics.