Introduction:
Ascending thoracic aortic aneurysms (aTAAs) carry a risk of dissection. Elective repair guidelines are designed around size thresholds, but the one-dimensional parameter is insufficient to predict acute events in small aneurysms. Biomechanically, aortic events can occur when wall stress exceeds wall strength. Patient-specific aTAA wall stresses may be a better predictor of complications. Our aim was to compare wall stresses in aTAAs associated with a tricuspid aortic valve (TAV) based on diameter.
Methods:
Patients with TAV-aTAA and diameter >4.0cm (n=448) were divided into groups by 0.5 cm diameter increments. Pre-stress three-dimensional aneurysm geometries were reconstructed from ECG-gated computer tomography images. A fiber-embedded hyperelastic material model was applied to obtain longitudinal and circumferential wall stress distributions under systolic pressure. Medians with interquartile ranges are reported. The Kruskal-Wallis test is used for comparisons between size groups.
Results:
Peak longitudinal wall stresses for TAV-aTAA were 308[282-338] kPa for size 4.0-4.4cm vs 341[309-362] kPa for 4.5-4.9cm vs 339[289-370] kPa for 5.0-5.4cm vs 319[297-355] kPa for 5.5-5.9cm vs 373[364-449] for 6.0cm (p=0.003). Peak circumferential wall stresses were 487[448-579] kPa for size 4.0-4.4cm vs 516[473-619] kPa for 4.5-4.9cm vs 506[422-580] kPa for 5.0-5.4cm vs 540[468-591] kPa for 5.5-5.9cm vs 565[506-634] for >6.0cm (p=0.19) (figure). 95th-percentile longitudinal peak stress for TAV-aTAA <5.5cm vs ≥5.5cm is 408 vs 465 kPa.
Conclusions:
Longitudinal wall stresses are higher as diameter increases. The 95% percentile longitudinal peak stress for diameter ≥5.5cm is ~450 kPa, which correlates with established ~5% dissection risk for size ≥5.5cm. Wall stress thresholds may be a better predictor of patient-specific risk of dissection than diameter and require testing in clinical trials.
Raman microspectroscopy as a useful new tool in understanding thoracic aortic aneurysms
