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 OSI¯ is calculated based on the wall shear stress (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 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 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 |∇_τp| 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 |∇_τp|. Therefore, the current study provides a two-step procedure for the hemodynamic diagnosis of TBIMH. First, by combining OSI¯ and T_d/T those patients with low risk of intimal tear can be excluded. Then, the location of elevated |∇_τp| can be adopted as the indicator for possible intimal tear locations.