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Page 6 of 24 Alberts et al. Vessel Plus 2023;7:34 https://dx.doi.org/10.20517/2574-1209.2023.37

branches, which show a low resistance type of flow pattern with prominent anterograde flow in both systole
[41]
and diastole. Veins, on the other hand, typically show a continuous blood flow in systole and diastole .
Left-sided pleural effusion, if present, can be seen in SAX as a dark, triangle-shaped collection next to the
aorta known as the tiger’s claw sign [42,43] .

Measurement of dimensions
When assessing the size of the aorta, it is essential to measure accurately and to use standardized techniques,
as these measurements guide the decision for surgery . By convention, aortic diameters should be obtained
[17]
from leading-to-leading edge as this method gives the best correlation with measurements done with inner-
to-inner edge measured by CT-scan or MRI . Moreover, it is the most used technique in guidelines and
[44]
reference articles [11,45] . For the best reproducibility, the aortic diameters should be measured in end diastole,
since the aortic diameter has a variable increase in systole depending on the cardiac output [11,17,18,44-46] .

Off-axis imaging should be avoided as it underestimates the size of the aorta in LAX views and, conversely,
overestimates the size of the aorta in SAX. We recommend using simultaneous bi-plane mode to image the
tubular part of the aorta from two perpendicular angles at the same time. This can help to prevent off-axis
[11]
imaging as the diameter is measured perpendicular to the LAX of the aorta .

It is noteworthy that on ultrasound, the aortic wall thickness is falsely increased by 2 mm due to reduced
[44]
axial resolution compared to CT or MRI, where the normal aortic wall thickness is typically 0.8-1.1 mm .

TEE DURING SURGERY OF THE AORTA
When assessing the thoracic aorta with TEE before and during surgery, it is important to use a systematic
approach. When visualizing the aortic root and ascending aorta, it makes sense to use the AV as a landmark
and retract the probe slightly. When the TEE probe is turned counterclockwise to posterior, the descending
aorta is usually well visualized. Retracting the probe slowly will reveal the aortic arch and its branches. A
summary of the standard views that can be used to visualize the aorta in SAX and LAX is shown in Figure 1.

Prior to surgery, but particularly before initiating cardiopulmonary bypass (CPB), it is essential to conduct a
comprehensive examination of the heart to detect or rule out any abnormalities. Several aortic pathologies
are associated with structural heart abnormalities, i.e., aortic dilatation, dissection, coarctation, and
endocarditis are linked to a bicuspid aortic valve . Furthermore, aortic pathologies, particularly if the
[47]
aortic root is involved, can lead to coronary dysfunction, regional wall motion abnormalities, pericardial
effusion, and aortic valve regurgitation.

After weaning from CPB, the result of the surgical repair and cardiac function have to be assessed carefully
and discussed with the surgeon. Surgical interventions and prolonged CPB may lead to cardiac
complications such as coronary occlusion and ventricular dysfunction.

Various surgical procedures potentially lead to distinct complications. During aortic root replacement,
coronary arteries are re-implanted. TEE with CFD can play a vital role by verifying blood flow in the
coronary arteries and excluding the presence of new regional wall motion abnormalities. If a valve-sparing
technique is used, close inspection of the aortic valve is essential. This inspection should include
measurements of the coaptation length, coaptation height, mean pressure gradient, and the presence of
residual regurgitation, along with the mechanism of regurgitation . After AV replacement, the mean
[48]
gradient over the prosthetic valve should be determined to rule out patient-prosthesis mismatch.