ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

dissection occurs when blood intrudes into the wall layers of the thoracic aorta, creating
an artificial channel known as the false lumen. The original channel for blood flow is
termed as the true lumen. The incidence rate of aorta dissection is approximately ranged
from 2.9 to 3.5 cases per 100,000 persons in the population [2]. Although the formation
mechanism of TAD is not exactly known, the hemodynamic and biomechanical factors
are believed to play a significant role, in particular for the thoracic aorta under high
blood pressure. Without appropriate medical diagnosis and treatment, the weakened
aortic walls may continue to expand and cause the rupture of the false lumen, resulting
in high mortality rate due to massive bleeding.
In accordance with the Stanford classification scheme [3], TAD can be divided into two
different groups, i.e. Type A / B. This clinical nomenclature is used to identify the
anatomical location of a dissection occurring in the ascending or descending thoracic
aorta. In this work, we focus on the investigation of Type B TAD which occurs in the
descending aorta and originates below the subclavian artery. In clinical practice, the
conventional management of Type B TAD is open surgical repair [4]. With modern
technological advances, a less invasive medical treatment of Type B TAD is
endovascular repair, where a stent graft is placed inside the thoracic aorta to prevent
blood flowing into the false lumen [5]. Nevertheless, both procedures may carry a
certain degree of risk, depending on the physical conditions of the patients. In general,
uncomplicated Type B TAD can be treated with antihypertensive medication to prevent
further dissection [6]. For more complicated scenarios, e.g. imminent expansion and
rupture, surgical repairs must be performed [7]. In terms of mortality and associated
complications, endovascular treatment provides better short-term outcomes than those
using open surgery for acute Type B dissection [5, 8].
The false lumen is likely to be the most dangerous location since the blood vessel walls
have been weakened. Basically, the status of the false lumen can be classified as patent,
partial thrombosis, and complete thrombosis. The formation of complete thrombosis is
capable of reducing the risk of growth and rupture of aortic dissection, i.e. dissection
healing. Before receiving medical treatment, the case of complete thrombosis in the
false lumen seldom occurs in patients. On the other hand, the risk of death for the
patients with partial thrombosis of the false lumen is relatively high for those patients
with a fully patent false lumen [9]. In order to prevent the occurrence of partial
thrombosis in the false lumen, the endovascular stent grafting technique can be
employed. The coverage of the entry tear can induce stagnant blood flow inside the
false lumen, leading to a high level of thrombus formation. However, the effect of
endovascular treatment for Type B TAD and the timing for medical intervention are still
under study [10, 11]. To gain new insights into Type B TAD, the objectives of this
paper will include
creating an idealized three-dimensional (3D) aortic dissection model for
computational fluid dynamics (CFD) analysis; and
investigating the effects of the dissecting aneurysm size and the corresponding force
in the false lumen with partial thrombosis.
3. METHODOLOGY
3.1 Software and model