Computational Biomechanics in Thoracic Aortic Dissection: Today’s Approaches and Tomorrow’s Opportunities

Abstract

Dissection of an artery is characterised by the separation of the layers of the arterial wall causing blood to flow within the wall. The incidence rates of thoracic aortic dissection (AoD) are increasing, despite falls in virtually all other manifestations of cardiovascular disease, including abdominal aortic aneurysm (AAA). Dissections involving the ascending aorta (Type A) are a medical emergency and require urgent surgical repair. However, dissections of the descending aorta (Type B) are less lethal and require different clinical management whereby the patient may not be offered surgery unless complicating factors are present. But how do we tell if a patient will develop a complication later on? Currently, there is no consensus and the evidence base is limited. There is an opportunity for computational biomechanics to help clinicians decide as to which cases to repair and which to manage with blood pressure control. In this review article, we look at AoD from both the clinical and biomechanical perspective and discuss some of the recent computational studies of both Type A and B AoD. We then focus more on Type B where the real opportunity for patient-specific modelling exists. Finally, we look ahead at some of the promising areas of research that may help clinicians improve the decision-making process surrounding Type B AoD.

A simplified method to account for wall motion in patient-specific blood flow simulations of aortic dissection: Comparison with fluid-structure interaction

“…Pressure differences between TL and FL might provide important diagnostic and prognostic information [28], but cannot be easily assessed in the clinic. For instance, higher pressure in the FL can lead to further expansion, or even rupture of the FL, whilst causing a narrowing of the TL [5,7]. The transmural pressure, TMP, obtained with the FSI and MBM Figure 2: Comparison between pressure and flow-rate waves obtained at the inlet and outlets of the AD model by the FSI (solid line), MBM (dashed line) and Rigid (dotted line) approaches.…”

“…Other useful markers that can be extracted from CFD simulations are the Wall Shear Stress (WWS)based indices, such as the TAWSS and the OSI [29]. WSS is thought to affect the growth and enlargement of the FL [30][31][32]; for instance, it has been recently reported by Doyle and Norman [5] that areas of low TAWSS may be correlated to regions of rapid local expansion in Type-B AD. The TAWSS distributions obtained with the FSI, MBM and rigid wall models are shown in Fig.…”

“…Surgical intervention is the preferred choice in the presence of complications, whereas 'uncomplicated' ADs (referring to ADs without complications, such as organ malperfusion, rupture, refractory pain or hypertension, at presentation) [3] are usually managed by controlling the blood pressure [4]. Long-term prognosis of medically treated ADs remains poor, with aortic dilation and late-term complications reported in 25-50% of the cases within 5 years [5].…”

Computational tools for clinical support: a multi-scale compliant model for haemodynamic simulations in an aortic dissection based on multi-modal imaging data

“…Pressure differences between the TL and the FL can provide insight into the actual state and probable progression of the dissection but cannot usually be assessed in the clinic. For instance, high pressure in the FL can lead to further expansion, or even rupture of the FL, while causing a narrowing of the TL [ 4 ]. Simulated pressure distributions at peak systole ( figure 7 a ) show higher pressure in the TL than in the FL.…”

“…AD involving only the descending aorta) have lower initial mortality than type A (i.e. AD of the ascending aorta), they carry a poor long-term prognosis, with late-term complications reported in 20–50% of cases within 5 years [ 4 ].…”