Importance of dynamic aortic evaluation in planning TEVAR

Abstract

Dynamic aortic evaluation in planning thoracic endovascular aortic repair (TEVAR) is important to provide optimal stent graft sizing. Static imaging protocols do not consider normal aortic dynamics and may lead to stent graft to aorta mismatch, causing stent graft related complications, such as type I endoleak and stent graft migration. Dynamic imaging can assist in accurate stent graft selection and sizing preoperatively, and evaluate stent graft performance during follow-up. To create new imaging technologies, integration of knowledge between diverse scientific fields is essential (i.e., engineering, informatics and medicine). Different dynamic imaging modalities, such as electrocardiographic-gated computed tomography angiography (ECG-gated CTA) and four-dimensional phase-contrast MRI (4D PC-MRI), are progressively investigated and implemented into clinical practice as important instruments in preoperative planning for TEVAR. In time, further application of dynamic imaging tools for preoperative screening and follow-up after TEVAR might lead to better outcomes for patients. The advances in dynamic imaging for evaluation of the thoracic aorta using new imaging modalities and their future perspectives are addressed in this manuscript.

Keywords: Dynamic imaging; computational fluid dynamics (CFD); thoracic aortic disease; thoracic endovascular aortic repair (TEVAR); type B aortic dissection.

Figure 1

(A) Diagram showing the 3 measured aortic levels with the central lumen line. Level a: 5 mm distal to the coronary arteries, b: 5 mm proximal to the innominate artery, and c: halfway up the ascending aorta; (B) The mean percentage of maximum diameter change is shown at each of the 3 measured levels. Maximum diameter change at all levels is significant (*P<0.001). Level a differs significantly from b and c (†P=0.02). Adapted from van Prehn et al. with permission of the Journal of Endovascular Therapy (6).

Figure 2

(A) Diagram showing the four measured thoracic aortic levels. These levels included 1 cm proximal to the left subclavian artery, 1 cm distal to the left subclavian artery, 3 cm distal to the left subclavian artery, and 3 cm proximal to the celiac artery; (B) The maximum percentage diameter change is shown at each of the four measured levels. Mean maximum diameter pulsatility is approximately 10% at all four levels (P<0.05). There is no difference in pulsatility between any of the measured levels. Adapted from Muhs et al. with permission of Elsevier (5).

Figure 3

Visualization of entry tears. Communications between the true and false lumen (entry tears) were identified using path line analysis. These images can be viewed in 3D over time in any chosen orientation. A single plane has been selected for illustration and flow shown at five time points in the cardiac cycle. (A) One entry tear is seen at the origin of the left subclavian artery. In systole (158 and 215 ms), the velocity in the true and false lumen is approximately equal; (B) Blood flows from the true to the false lumen through an entry tear in the proximal descending thoracic aorta. An area of high velocity is seen just distal to the entry tear as the false lumen expands (due to the additional flow) and true lumen narrows. Flow is seen in the celiac and superior mesenteric arteries (SMA) distally. Figure adapted from Clough et al. with permission of Elsevier (16).

Figure 4

Thoracic endovascular aortic repair (TEVAR) of a type B aortic dissection extending from the aortic arch to the abdominal aorta. (A) Pre- and (B,C) post-implantation angiograms showing two stent grafts placed from the arch, covering the left subclavian artery, to the distal descending aorta in order to treat different entry tears and the true lumen compression; (D) MRA and (E) velocity computational fluid dynamics (CFD) study at 1 year from the implantation: the true lumen is well expanded at the proximal and mid descending aorta, while a smaller diameter is observed at the distal part of the vessel. Acceleration of blood flow is highlighted by red streamlines corresponding to >1.20 m/s velocity profiles, as indicated by the color-coded scale (speed in meters per second); (F) Patterns of turbulent flow are depicted during different phases of the cardiac cycle just above the stenotic segment. Figure adapted from Midulla et al. with permission of Springer (28).