Thoracic Endovascular Aneurysm Repair Simulations

Aneurysm refers to irreversible dilation of the artery, which, if left untreated, can be fatal. Although aneurysms can occur in any artery in the human cardiovascular system, most of them are found in the cerebral arteries, the thoracic and abdominal aorta. Once identified, they are typically treated through minimally invasive endovascular aneurysm repair (EVAR) surgeries, where a stent-graft is deployed at the aneurysm site using a catheter. Once deployed, this stent-graft relieves the weakened arterial wall from the hemodynamic loads and thus prevents the future of the aneurysmal artery. Some of the most common post-surgical complications associated with EVAR are stent-graft related, including thrombosis due to non-physiologic flow conditions, device migration, endoleaks and, in extreme cases, complete device failure. Computational fluid dynamics (CFD) and fluid-structure interaction (FSI) simulations offer a very lucrative pathway to quantitatively assess during the surgical planning phase if such complications can arise for a given patient or not, as elaborated below.

Thoracic Endovascular Aneurysm Repair simulations

As the name suggests, aneurysms located in the thoracic part of the human aorta are called thoracic aneurysms. These aneurysms have very complex anatomies due to brachiocephalic, left common carotid, and left subclavian arterial branches. Hence, stent-grafts that are used to treat thoracic aneurysms must have branches to ensure that the blood flow to these critical arteries is not interrupted after the surgery. As the blood flow in thoracic aortic aneurysms is highly irregular, with flow recirculation zones and vortices, insertion of a branched stent-graft may further increase the complexity of the flow lead to future complications such as thrombosis. Such post-surgical scenarios can be simulated effectively using FSI simulations to gain an insight into the most likely outcome of an operation. Furthermore, within the FSI model, Navier-Stokes equations that govern the blood flow can easily be coupled with the advection-diffusion equations, which can be used to model the blood coagulation cascade, leading to thrombosis. Not only that, once the flow and the pressure field has been quantified through FSI simulations, the displacement forces acting on the stent-graft, which are responsible for the device migration, can be calculated using the technique proposed by Kandail et al. (2014). The magnitude and direction of such displacement forces can give physicians accurate insight if the device will migrate under the hemodynamic loads or not.

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