Blood Rheology Influence on False Lumen Thrombosis in Type B Aortic Dissection

Abstract

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 haemodynamic conditions in the FL significantly contribute to clotting of blood, so 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 haemodynamic conditions influence on platelet activation and aggregation, effectively boosting 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 haematocrit value (HCT), which affects the shear rate dependent viscosity and the yield stress observed in regions of low shear rate and stress, respectively, in the blood flow. In the current work, the influence of the haematocrit value on thrombosis in the FL is simulated. The simulations are done in idealized aortic dissection phantom models employing HCT-dependent non-Newtonian haemodynamics. The value for the HCT was 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, with increasing 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 haematocrit values have less chance of benefiting from complete thrombosis in the FL.