The risk of stanford type-A aortic dissection with different tear size and location: a numerical study

Abstract

Background: This study is to investigate the influence of hemodynamics on Stanford type-A aortic dissection with different tear size and location, to provide some support for the relationships between the risks (rupture, reverse tearing and further tearing) and tear size and location for clinical treatment.

Methods: Four numerical models of Stanford type-A aortic dissection were established, with different size and location of the tears. The ratio of the area between the entry and re-entry tears(RA) is various within the model; while, the size and the location of the re-entry in the distal descending aorta are fixed. In model A11 and A21, the entry tears are located near the ascending aorta. The RA in these models are 1 and 2, respectively; In the model B11 and B21, the entry tears are located near the proximal descending aorta and the RA in these models are again assigned to 1 and 2, respectively. Then hemodynamics in these models was solved with numerically and the flow patterns and loading distributions were investigated.

Results: The flow velocity of the true lumen in model A21, B21 is lower than that in A11, B11, respectively; the time-averaged wall shear stress (TAWSS) of the false lumen in model A21 and B21 is higher, and for ascending aorta false lumen, A11, A21 are higher than B11, B21, respectively. False lumen intimal wall pressure of A11, A21 are always higher than the true lumen ones.

Conclusion: The variation of the RA can significantly affect the dynamics of blood within the aortic dissection. When the entry tear size is larger than the re-entry tear ones, the false lumen, proximal descending aorta and the wall near re-entry tear are prone to cracking. Entry tear location can significantly alter the hemodynamics of aortic dissection as well. When entry tear location is closer to proximal ascending aorta, false lumen continues to expand and compress the true lumen resulting in the true lumen reduction. For proximal ascending aorta, high pressure in false lumen predicts a higher risk of reverse tear.

Keywords: Hemodynamic; Risk assessment; Stanford type-A aortic dissection.

Fig. 1

Four Stanford type-A aortic dissection digital models of different size and location of the tear (the size and location of the re-entry in the distal descending aorta are fixed). In model A11 and A21, the entry tears are located near the ascending aorta, and the RA are 1 and 2, respectively; In the model B11 and B21, the entry tears are located near proximal descending aorta and the RA are again assigned to 1 and 2, respectively

Fig. 2

a The figure shows the pulsatile waveform of the inlet pressure at the ascending aorta. b The figure shows the time-dependent pulsatile waveforms of flow at the descending aorta. c The whole aorta model with all boundary conditions shown

Fig. 3

Velocity and wall pressure analysis at systolic peak. a, b Flow velocity vector map consists of two parts: ascending aorta with aorta arch section (a); descending aorta section (b). Slices cut tears in half and can display true and false lumen intuitively. Trends in flow velocity distribution among all models are similar; however, flow patterns of ascending aorta with aorta arch section in false lumen are quite different. c Pressure distributions. The vessel wall pressure gradually decreases from the proximal to the distal end in all models

Fig. 4

Intima wall pressure contour plots at systolic peak. A view of two sides of intima shows pressure difference in true and false lumen. The first line and the second line in the figure are the pressure distributions of the true and false lumens sides, respectively

Fig. 5

A The selection of the key areas on both the true and false lumen sides of intima. The six areas are entry tear area near the proximal ascending aorta a, the middle of ascending aorta area b, entry tear area near the proximal descending aorta c, aorta ligament area d, the middle of descending aorta area e and re-entry tear area f. B The true and false lumen intima wall pressure difference of six key small circle areas in the whole cardiac cycle. (Horizontal coordinate: time/s; vertical coordinate: pressure difference/pa)

Fig. 6

Time-averaged wall shear stress (TAWSS) contour plots in the four models. High TAWSS is found at the entry tear site and the proximal descending aorta of the true lumen

Fig. 7

Relative residence time (RRT) contours plots of the four models. High RRT predicts larger possibility of false lumen thrombosis. RRT distribution trends and clinical phenomenon correlate well with areas of thrombus formation in the false lumen