Breandan Yeats

BioE PhD Defense Presentation

Date: April 11, 2023

Time: 10 am

Zoom link: https://gatech.zoom.us/j/91933628382?pwd=OEtVY2Z5QkwvalR5N1d2ZnZNODlNZz09

Advisor: Lakshmi Prasad Dasi, PhD (Georgia Institute of Technology) 

Committee Members: 

Ajit P. Yoganathan, PhD (Georgia Institute of Technology) 

John Oshinski, PhD (Georgia Institute of Technology and Emory University) 

Rudolph Gleason, PhD (Georgia Institute of Technology)

Vinod H. Thourani, MD (Piedmont Heart Institute) 

Biomechanics of Transcatheter Aortic Valve Replacement for Bicuspid Aortic Valves

Bicuspid aortic valve (BAV) is the most common congenital heart defect and is associated with numerous pathologies including calcific aortic valve disease (CAVD) which requires replacement of the native valve. Replacements are delivered through either surgical or transcatheter aortic valve replacement (TAVR) approaches. The number of TAVR in BAV cases is expected to increase substantially due to the recent removal of the FDA precautionary label for TAVR use in BAV patients and deemed safe in low-surgical risk patients. Two of the main concerns when treating BAV patients with TAVR are paravalvular leak (PVL), a known associate of increased patient mortality, and long-term durability. Highly calcified BAV patients have shown increased incidence of PVL following TAVR. Additionally, stent asymmetry and undersizing are common in BAV patients both being indicators of reduced device durability however, very limited data exists on TAVR long-term durability in BAV patients. Determining the risk of these complications based on BAV anatomy is very difficult as current morphology classification systems do not encompass all aspects of the anatomy and there is limited data correlating anatomy to these outcomes beyond calcium scoring. The impact of device placement and balloon filling volume across varying BAV anatomies is also not fully understood. The studies contained within this thesis document aim to contribute to answering these clinical unknowns with the overarching goal of better understanding TAVR biomechanics in BAV patients.

The first aim details a study in which the aortic valve and aortic arch were parametrically quantified and a classification framework was developed for each. The aortic valve was classified based on the commissure orientation and characteristics of the fused region. The aortic valve was classified based on the severity of local area changes and high curvature in the ascending and descending aorta. In the second aim, simulation models of the stent deployment, bioprosthetic leaflet pressurization, and PVL were developed and used to assess the deformation and integral portions of the device functionality following simulated patient-specific device implantation. Analysis of patient cohorts of BAV and trileaflet patients revealed BAV patients to have worsened device deformation and leaflet functionality. BAV patients that had excessive calcification or abnormal anatomies lead to the worst outcomes. Several mechanisms for PVL were found which were caused by non-symmetric features of the BAV anatomy including local vessel enlargements and calcification. In the third aim, varying TAVR strategies were tested. Lower balloon filling volume led to worsened device deformation and leaflet functionality and increased PVL. No structural impact was found with varying deployment depth. PVL was reduced with a higher deployment depth. Finally, clinical translation of the developed models was demonstrated through model use to guide clinical planning of TAVR treatment for a BAV patient with an extremely large annulus. The outcomes of this thesis can help clinicians better analyse BAV anatomy, select BAV patients for TAVR, and choose optimal TAVR strategies when treating BAV patients.