UCSF

Background

Elective repair of bicuspid aortic valve (BAV)-associated ascending thoracic aortic aneurysm (aTAA) is recommended at lower size limits than tricuspid aortic valve (TAV)-associated aTAA. Rupture/dissection can occur when wall stress exceeds wall strength. Previously, a validated computational method was developed for determining aTAA wall stress, but to date this method has not applied to a patient-specific BAV aTAA. The study aim was to develop a patient-specific BAV aTAA computational model to determine regional wall stress, using the required zero-pressure geometry, wall thickness, material properties, and residual stress.

Methods

A BAV aTAA specimen was excised intact during elective repair, and zero-pressure geometry generated using micro-computed tomography. Residual stress was determined from the aTAA opening angle. aTAA material properties determined using biaxial stretch testing were incorporated into an Ogden hyperelastic model. Finite element analyses (FEAs) were performed in LS-DYNA to determine wall stress distribution and magnitudes at systemic pressure.

Results

The left aTAA region had the highest stiffness, followed by the right, and then anterior/posterior walls, suggesting regional variability in mechanical properties. During systole, the mean principal wall stresses were 108.8 kPa (circumferential) and 59.9 kPa (longitudinal), while peak wall stresses were 789.4 kPa (circumferential) and 618.8 kPa (longitudinal). Elevated wall stress pockets were seen in anatomic left aTAA regions.

Conclusions

To the present authors' knowledge, this was the first patient-specific BAV aTAA model based on surgical specimens to be developed. Surgical specimens serve as the 'gold standard' for determining wall stress to validate models based on in-vivo imaging data alone. Regions of maximal wall stress may indicate sites most prone to rupture, and are crucial for evaluating rupture risk based on the wall stress/strength relationship.