Elongation of the proximal descending thoracic aorta and associated hemodynamics increase the risk of acute type B aortic dissection

Abstract

BACKGROUND:

Acute type B aortic dissection (ATBAD) is a life-threatening aortic disease. However, little information is available on predicting and understanding of ATBAD.

OBJECTIVE:

The study sought to explore the underlying mechanism of ATBAD by analyzing the morphological and hemodynamic characteristics related to aortic length.

METHODS:

The length and tortuosity of the segment and the whole aorta in the ATBAD group ( $n=$ 163) and control group ( $n=$ 120) were measured. A fixed anatomic landmark from the distal of left subclavian artery (LSA) to the superior border of sixth thoracic vertebra was proposed as the proximal descending thoracic aorta (PDTA), and the dimensionless parameter, length ratio, was introduced to eliminate the individual differences. The significant morphological parameters were filtrated and the associations between parameters were investigated using statistical approaches. Furthermore, how aortic morphology influenced ATBAD was explored based on idealized aortic models and hemodynamic-related metrics.

RESULTS:

The PDTA length was significantly increased in the ATBAD group compared with the control group and had a strong positive correlation with the whole aortic length ( $r=$ 0.89). The length ratio (LR₂) and tortuosity (T₂) of PDTA in the ATBAD group were significantly increased (0.15 $\pm$ 0.02 vs 0.12 $\pm$ 0.02 and 1.73 $\pm$ 0.48 vs 1.50 $\pm$ 0.36; $P<$ 0.001), and LR₂ was positive correlation with T₂ ( $r=$ 0.73). In receiver-operating curve analysis, the area under the curve was 0.835 for LR₂ and 0.641 for T₂. Low and oscillatory shear (LOS) was positive correlation with LR₂, and the elevated LOS occurred in the distal of LSA.

CONCLUSION:

Elongation of PDTA is associated with ATBAD, and the length ratio is a novel predictor. Elongated PDTA induced more aggressive hemodynamic forces, and high LOS regions may correspond to the entry tear location. The synergy of the morphological variation and aggressive hemodynamics creates contributory conditions for ATBAD.