A computational investigation to predict vessel and plaque injury risk due to catheter delivery in transcatheter aortic valve replacement surgery

This thesis aims to enhance the understanding of catheter tracking in transcatheter aortic valve replacement (TAVR) surgery. Stroke occurrence post-TAVR is a significant concern for TAVR patients. Injury to the arterial vessel or plaque tissue can result in embolus formation, which can lead to downstream complications such as stroke. However, it is unclear whether the cause of embolism formation during TAVR is due to the replacement valve or the catheter delivery system. Therefore, there is a need to quantify the stresses that arise during catheter delivery to understand the risks that catheter delivery systems may pose for emboli formation. In this thesis, computational methodologies are developed to investigate catheter tracking within idealised and patient-specific aorta arch anatomies. These finite element simulations are performed to analyse and predict the stresses experienced in arterial and plaque tissue during catheter delivery. Chapter 3 developed computational models to simulate catheter tracking within an idealised aorta arch and predict the influence of catheter design on tracking forces and contact pressures. Frictional coefficients markedly impacted reaction forces during catheter tracking, highlighting the importance of hydrophobic-treated catheters during intervention with materials such as Teflon. Catheter tip stiffness did not affect reaction forces during tracking, but increased tip stiffness correlated with increased applied contact pressures. The models predicted corresponding increases in reaction forces when the arch lumen diameter and arch centreline curvature were narrowed. This chapter has emphasised the importance of many catheter design inputs and patient geometrical factors that can impact patient injury risk during catheter delivery. Chapter 4 utilised the model developed in Chapter 3 to examine plaque tissue stresses during catheter delivery in TAVR. Finite element (FE) analysis was implemented to investigate further design inputs. Catheter tip length was positively correlated with reduced peak contact pressures. Next, the idealised aorta anatomy was further developed to include idealised plaque inclusions in the arch region and applied to investigate catheter tracking in an idealised calcified aorta anatomy. It was predicted that there was a risk of rupture for highly stiff calcified plaques during catheter tracking, regardless of location, compared to published plaque rupture stress thresholds. Plaques with reduced stiffness (less mature calcification) were shown to be susceptible to rupture if located at the aorta arch apex during catheter tracking. The results of this chapter could be applied to pre-TAVR planning by identifying highly calcified plaques and their location with respect to the arch apex to determine injury risk. Chapter 5 developed two patient-specific aorta and plaque anatomies for catheter tracking analysis. The patient anatomies were developed from pre-TAVR computed tomography (CT) scans of two patients with moderate and mild plaque burdens. Mimics (Materialise) imaging software was utilised to create 3D part meshes for analysis within the FE solver. Catheter tracking was simulated, applying the approach from the previous chapters within both anatomies with various plaque burdens and stiffnesses. The predicted stresses were compared to plaque rupture stress thresholds. It is reported that catheter tracking during TAVR produces a risk of plaque rupture in the intermediate stiffness plaques at a high burden only in Patient 1 but predicts no risk in Patient 2. Catheter tracking with highly stiff calcified nodules produces high peak stresses in the plaque tissue during catheter delivery. The results of this thesis provide evidence that there is a risk of plaque rupture due to catheter tracking in TAVR in high plaque burdens. These findings could inform physicians on treatment planning regarding the use of cerebral embolic protection devices during TAVR delivery.

Publisher

University of Galway

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Attribution-NonCommercial-NoDerivatives 4.0 International

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University of Galway Theses (PhD Theses)