Improving endovascular repair of aortic aneurysms using haemodynamic modelling

Project reference:  SIE_12_22
First supervisor:  Dr Jordi Alastruey
Second supervisor:  Prof. Kawal Rhode

Clinical champions:

Mr Said Abisi-Consultant Vascular and Endovascular Surgeon

Mr Hany Zayed-Consultant Vascular and Endovascular Surgeon

Start date: October 2022

Aim: .Endovascular aortic repair has become an established treatment for patients with aortic aneurysmal disease with relatively lower morbidity and mortality compared to open surgery. Thoracoabdominal, suprarenal, or juxta renal aneurysms require “complex” endografts to incorporate branches of the diseased or aneurysmal aortic segment. Patient specific, “custom-made” endografts with fenestrations, directional outer branches, or combination of both have been previously used. Design of complex endografts have recently evolved, but the different designs of complex endografts have not yet been studied in detail using haemodynamic modelling. This project will investigate the various designs using both bench and computational models of blood flow in the aorta and its main branches, which could potentially inform clinical decision on what is the best design for patients.

 

Objectives:

  1.  Development of a bench model of blood flow in the healthy and diseased aorta.

  2. Understand the haemodynamic effects of different designs of complex endografts on the local blood flow around the aneurysmal region.

  3. Investigate the effects of localised flow changes on the flow dynamics proximal and distal to different endograft designs, accounting for cardiac dynamics (proximally), collateral pathways (distally)

Project description:

The following tasks will be carried out to fulfil these objectives:

Task 1: Bench model development (12 months) – Blood flow in the aorta and its main branches will be simulated using an experimental model with arteries made of flexible tubes, blood modelled as a water–glycerol mixture to reproduce its rheological properties (i.e. blood density and viscosity), and a pulsatile pump connected to the aortic root to produce physiological blood flow waveforms. Anatomically-correct vascular geometries of healthy aortas will be produced using 3D printing from segmented computed tomography (CT) images. Existing equipment enables highly accurate measurements of flow waves using ultrasonic perivascular probes and pressure waves using Millar intravascular pressure-tip wires for a complete characterisation of flow dynamics along the healthy aorta.

Task 2: Addition of aortic aneurysmal disease (3 months) – The bench model will be modified by incorporating different aneurysm sizes obtained from segmented computed tomography (CT) images and produced by 3D printing.

Task 3: Endograft haemodynamic effects (9 months) – Pressure and flow measurements will provide a complete characterisation of flow dynamics across the aneurysm with several complex endografts, including fenestrated endovascular aortic aneurysm repair (FEVAR), branched endovascular aortic aneurysm repair (BEVAR), and a combination of both. These data will be used in the computational blood flow model to study proximal and distal haemodynamic effects.

Task 4: Computational model development (6 months) – Pulsatile blood flow will be simulated in the larger arteries of the systemic circulation by solving the one-dimensional (1-D) equations of blood flow in compliant vessels, using our in-house code. Several tests have shown the ability of the 1-D formulation to reproduce pressure and flow waveforms in systemic arteries under normal anatomical and physiological conditions and with the presence of stenoses and aneurysms (J Royal Soc Interface, 2021, Symmetry, 2021). The experimental data produced in Task 3 will be used to calibrate the computational model around the endograft, e.g. by providing the pressure drop across and the added vascular stiffness of different types of endografts.

Task 5: Proximal and distal haemodynamic effects (6 months) – The effects of different endograft designs on blood flow proximal and distal to the aneurysmal region will be studied using the computational model developed in Task 4. Changes in cardiac dynamics will be investigated by analysing simulated pressure-volume loops in the left ventricle. Alterations in blood flow downstream the endograft will be assessed under different anatomical variations of the collateral pathways in the abdominal and leg vasculatures.

Cryolife.jpg

Computed tomography images showing the aorta of a patient with an abdominal aortic aneurysm pre- (left) and post- (right) treatment using a “custom-made” endograft stent.