Original article
Adult cardiac
Wall Stress Distribution in Bicuspid Aortic Valve–Associated Ascending Thoracic Aortic Aneurysms

Presented at the Fifty-fifth Annual Meeting of The Society of Thoracic Surgeons, San Diego, CA, Jan 26-29, 2019.
https://doi.org/10.1016/j.athoracsur.2019.12.035Get rights and content

Background

Bicuspid aortic valve–associated ascending thoracic aortic aneurysms (BAV-aTAAs) carry a risk of acute type A dissection. Biomechanically, dissection may occur when wall stress exceeds wall strength. Our aim was to develop patient-specific computational models of BAV-aTAAs to determine magnitudes of wall stress by anatomic regions.

Methods

Patients with BAV-aTAA diameter greater than 4.5 cm (n = 41) underwent electrocardiogram-gated computed tomography angiography. Three-dimensional aneurysm geometries were reconstructed after accounting for prestress and loaded to systemic pressure. Finite element analyses were performed with fiber-embedded hyperelastic material model using LS-DYNA software (LSTC Inc, Livermore, CA) to obtain wall stress distributions. The 99th percentile longitudinal and circumferential stresses were determined at systole.

Results

The 99th percentile longitudinal wall stresses for BAV-aTAAs at sinuses of Valsalva, sinotubular junction (STJ), and ascending aorta were 361 ± 59.8 kPa, 295 ± 67.2 kPa, and 224 ± 37.6 kPa, respectively, with significant differences in ascending aorta vs sinuses (P < 1 × 10-13) and STJ (P < 1 × 10-6). The 99th percentile circumferential wall stresses were 474 ± 88.2 kPa, 634 ± 181.9 kPa, and 381 ± 54.0 kPa for sinuses, the STJ, and the ascending aorta, respectively, with significant differences in the ascending aorta vs sinuses (P = .002) and STJ (P < 1 × 10-13).

Conclusions

Wall stresses, both circumferential and longitudinal, were greater in the aortic root, sinuses, and STJ than in the ascending aorta on BAV-aTAAs. These results fill a fundamental knowledge gap regarding biomechanical stress distribution in BAV-aTAA patients, which when related to wall strength may provide prognostication of aTAA dissection risk by patient-specific modeling.

Section snippets

Material and Methods

Patients with electrocardiogram-gated computed tomography angiography (CTA) undergoing routine aneurysm surveillance were evaluated for BAV-aTAA with diameter greater than 4.5 cm. Patients with motion artifact or poor image quality resolution were excluded. Patients were required to have neither a history of aortic valve surgery nor isolated aortic root dilatation. BAVs were not differentiated by subtype. This study was approved by the Committee on Human Research at the University of California

Clinical Profiles

There were 41 male BAV-aTAA patients, with mean age of 66 ± 9 years. Mean aTAA diameter was 5.05 ± 0.46 cm. Patient characteristics are summarized in Table 1.

BAV-aTAA Wall Stresses

There was a significant effect of region on peak circumferential wall stresses for the sinuses (474 ± 88.2 kPa), STJ (634 ± 181.9 kPa), and AscAo (381 ± 54.0 kPa) at systolic pressure (F = 46, P < 1 × 10-12), which were significantly lower at the AscAo than in the sinuses (P = .002) and STJ (P < 1 × 10-13), and higher in the STJ than in

Comment

Current American College of Cardiology/American Heart Association aTAA surgical repair guidelines base their recommendations primarily on diameter, along with growth rate, connective tissue disorder, and family history of dissection.6 We, among others, demonstrated that aTAA diameter is not a good predictor for aneurysm dissection or rupture.7, 8, 9,16,19 Biomechanical studies suggest higher wall strength of BAV than TAV-aTAAs,12, 13, 14 highlighting the importance of patient-specific wall

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