Hemodynamic criteria for intimal tear in Type-B intramural hematoma of aorta based on patient-specific geometry

Abstract

This study conducts hemodynamic simulations for a total of 20 patients with Type B aortic intramural hematoma (TBIMH) and aims to develop hemodynamic criteria for possible development of intimal tear and indicator for tearing location. The patients are divided into Group A without intimal tear and Group B with progression into tear. The mean oscillatory shear index $\overline{OSI}$ is calculated based on the wall shear stress ($\overline{WSS}$) distribution. The blood pressure drop along the main aortic vessel is calculated and the high pressure drop time fraction over one cardiac cycle $T_d/T$ is determined, with high pressure drop being defined as the pressure drop larger than half the maximal value. By combining $\overline{OSI}$ and $T_d/T$ at low heart rates 60bpm and 75bpm, we reveal statistically significant correlation between no progression to tear and both low $\overline{OSI}<0.121$ and low $T_d/T<0.067$, with a pvalue of $p=8.7e-5$. We also propose a new parameter, namely the magnitude of tangential pressure gradient at aortic wall $\left|{\nabla }_{\tau }p\right|$ at the time when the pressure drop is maximal during one cardiac cycle. Comparison with CT imaging reveals that nine out of ten patients in Group B develop intimal tear at the location with elevated $\left|{\nabla }_{\tau }p\right|$. Therefore, the current study provides a two-step procedure for the hemodynamic diagnosis of TBIMH. First, by combining $\overline{OSI}$ and $T_d/T$ those patients with low risk of intimal tear can be excluded. Then, the location of elevated $\left|{\nabla }_{\tau }p\right|$ can be adopted as the indicator for possible intimal tear locations.