The Thrombus to Embolus Transition and its Contributing Factors

Abstract

Thromboembolic events are some of the major causes of death in the United States. They must be carefully monitored in persons who are susceptible to thrombus formation due to hypercoagulability problems which may arise as a result of surgery or diseases such as sickle cell anemia, thalassemia, leukemia and diabetes. Successful diagnosis and treatment of thrombosis pose a real challenge to the medical field and there exists an urgency to develop more sophisticated methods for countering this condition. When thrombi detaches from the vessel wall, patients are at great risk of stroke events and even death. In an effort to gain a better understanding with regard to the thrombus to embolus transition, we have performed simulations through CFD-ACE+ computational engine in which we vary thrombus height, shape, location along the vessel wall, blood pressure and blood viscosity. Results of this simulation model suggest a higher likelihood for the thrombus to embolus transition as the thrombus height increases. Results also show that a thrombus is more likely to become mobile in hypertensive patients but is less likely to become mobile in sickle cell, diabetic and leukemic patients. This we explain is due to higher blood viscosities in these patients which result in lowered wall shear stresses. In addition, we confirm the hypothesis that clot shape influences the occurrence of the thrombus to embolus transition as pressure on the clot is shown to be substantially greater in radially asymmetric thrombi. Pressure profiles also suggest that prolonged exposure to high pressure, as in hypertension, increases the probability of initiation of the transition as the clot becomes fatigued and weakens, resulting in the completion of the thrombus to embolus transition when the hemodynamic forces overcome the adhesive forces in the system. Finally, we propose a "peel-off " type mechanism as an explanation of the process of transitioning from a thrombus to an embolus.