A Study on Thrombus Formation in Case of Type B Aortic Dissection and Its Hematocrit Dependence

Aortic dissection is a disease caused by the occurrence of a rupture in the innermost layer of the aortic wall. Due to the pulsation of the heart, blood penetrates through the tear between the layers of the aortic wall, which causes a new, so-called false lumen (FL). The local Hemodynamic conditions in the FL significantly contribute to the formation of a thrombus. The level of thrombosis in the FL affects patients’ prognosis and chances of survival, in which a complete thrombosis is usually beneficial. In recent studies on platelet deposition in the FL, it is demonstrated that the change in hemodynamic conditions in the FL effectively boosts platelet activation and aggregation in regions of recirculation. Blood coagulation has the highest chance of occurrence in these recirculation regions within the FL. Considering the dominant influence of shear rate in FL thrombosis, the non-Newtonian rheological properties and behaviour of blood play a crucial role. The most important rheological factor is the volume fraction of red blood cells in the blood, i.e., the hematocrit value (HCT), which affects the shear rate dependent viscosity and the yield stress observed in low shear rate flow of blood. In the current work, the influence of the hematocrit value on thrombosis in the FL is investigated. The simulations are done in idealized aortic dissection phantom models employing HCT-dependent non-Newtonian hemodynamics. The values for the HCT were varied within a physiological range. On the one hand, an increase in the total volume of thrombus in time was found for all HCT values. On the other hand, by increasing the HCT values, less thrombus is formed in the FL. This suggests that high HCT values impede thrombus formation due to rheological effects and that patients with higher hematocrit values have less chance of benefiting from complete thrombosis in the FL. Keywords: Aortic Dissection, Thrombus Formation, Hematocrit, Carreau Model