Aortic dissection belongs to a group of aortic pathologies called Acute aortic syndromes (AAS).
These include aortic dissection, intramural haematoma (IMH), penetrating aortic ulcer (PAU), and aortic aneurysm rupture.
AAS share common features: 1. similar clinical presentation (‘‘aortic pain’’), 2. impaired integrity of the aortic wall, and 3. potential danger of aortic rupture requiring emergency attention.
Image 1 Aortic dissection risk factors
The DeBakey classification system (old system, not currently used):
Type I (50% of dissections): These dissections origine in the ascending aorta and extend at least to the aortic arch and sometimes even beyond.
Type II (35%): These dissections start in and are only limited to the ascending aorta (proximally to the brachiocephalic or innominate artery).
Type III (15%): These dissections start in the descending thoracic aorta beyond the origin of the left subclavian artery and extend distally or sometimes but not that often, proximally. Type IIIa dissections originate distal to the left subclavian artery and are only present in the thoracic aorta. Type IIIb dissections have their origin distally to the left subclavian artery and extend below the diaphragmatic part of the aorta.
The Stanford system (new, currently used system):
Type A: These dissections involve the ascending aorta.
Type B: These dissections are limited to the descending thoracic aorta (distal to the left subclavian artery).
Image 2 Types of Aortic dissection
Nasim, B., Mohammad, A., Zafar, S., Mathew, L., Sajjad, A., Shaikh, A., & Naroo, G. (2020). Aortic Dissection. Differential Diagnosis of Chest Pain. Published. https://doi.org/10.5772/intechopen.89210
Image 3 Clinical presentation of Aortic dissection
Echocardiography assessment diagnostic features
Assessment of the aorta (Image 4):
Evangelista, A., Flachskampf, F. A., Erbel, R., Antonini-Canterin, F., Vlachopoulos, C., Rocchi, G., Sicari, R., Nihoyannopoulos, P., Zamorano, J., Pepi, M., Breithardt, O. A., & Plonska-Gosciniak, E. (2010). Echocardiography in aortic diseases: EAE recommendations for clinical practice. European Journal of Echocardiography, 11(8), 645–658. https://doi.org/10.1093/ejechocard/jeq056
Aortic dissection echocardiography findings
Aortic dissection and its variants- intramural haematoma and penetrating aortic ulcer, included in the ESC classification of aortic dissection, can be correctly diagnosed by echocardiography (Image 5).
Camm, J. A., Lüscher, T. F., Maurer, G., & Serruys, P. W. (2018). The ESC Textbook of Cardiovascular Medicine (The European Society of Cardiology Series) Volume 1 & 2 (3rd ed.). Oxford University Press.
The diagnosis of classical aortic dissection is based on the demonstration of the presence of an intimal flap that divides the aorta into two, true and false, lumina.
In most cases, false lumen flow is detectable by colour Doppler but may be absent in totally thrombosed and retrograde dissections.
Intramural haematoma is characterized by circular or crescentic thickening of the aortic wall <5 mm.
Penetrating aortic ulcer (PAU) presents as an image of crater-like outpouching with jagged edges in the aortic wall, generally associated with extensive aortic atheromas.
Image 6 Important ECHO findings in Aortic dissection
1) TTE evaluation
TTE permits adequate assessment of several aortic segments- the aortic root, proximal ascending aorta, the aortic arch, proximal descending aorta and abdominal aorta.
Image 7 TTE, Dilatation of ascending aorta - visualize the ascending aorta at its widest diameter by adjusting the PLAX view and take a measurement. If the visibility is poor, try a higher parasternal window or ask the patient to remain in expiration. Here, the ascending aorta is dilated to 48 mm.
Image 8 TTE, PLAX window, Sinus of Valsalva (SoVAo) diameter - always look for dilatation of the aortic root and ascending aorta. Measure in end-diastole and take the maximum diameter of the sinus. SoVAo is 44mm.
Video 1 TTE, Pericardial effusion in an aortic dissection patient - Pericardial effusion is a frequent finding in aortic dissection patients, when the dissection propagates into the pericardial cavity. Below, you can see the separation along the heart’s apex.
2) TOE evaluation
TOE can image the entire thoracic aorta except for a small portion of the distal ascending aorta near the proximal arch.
It allows to evaluate: Intimal tear location, True lumen identification, Diagnosis of complications- pericardial effusion and periaortic bleeding, aortic regurgitation and arterial vessel involvement
- Intimal tear location
The intimal tear appears as a discontinuity of the intimal flap. TOE provides a direct image of the tear and permits its measurement.
Colour Doppler reveals presence of multiple small communications between the two lumina.
By pulsed Doppler imaging, flow velocities through the intimal tear reflect the pressure gradient between the two lumina.
It is important to differentiate these secondary communications from the main intimal tear.
The main intimal tear has a diameter over 5 mm and is frequently located in the proximal part of the ascending aorta in type A dissections and immediately below the origin of the left subclavian artery in type B dissections.
If 2D echocardiography does not permit visualization of the intimal tear. It is possible to use contrast echocardiography to show contrast flows in the false lumen from the more proximal part of the aortic arch dissection.
- True lumen identification
When the aortic arch is involved, the surgeon needs to know whether the supra-aortic vessels originate from the false lumen.
Similarly, when the descending aorta dissection affects visceral arteries and ischaemic complications arise, it may be important to identify the false lumen prior to surgery or endovascular treatment such as intima fenestration or stent-graft implantation.
Image 9 True and false lumen differentiation
Evangelista, A., Flachskampf, F. A., Erbel, R., Antonini-Canterin, F., Vlachopoulos, C., Rocchi, G., Sicari, R., Nihoyannopoulos, P., Zamorano, J., Pepi, M., Breithardt, O. A., & Plonska-Gosciniak, E. (2010c). Echocardiography in aortic diseases: EAE recommendations for clinical practice. European Journal of Echocardiography, 11(8), 645–658. https://doi.org/10.1093/ejechocard/jeq056
Diagnosis of complications
Appropriate diagnosis of dissection complications during the initial study may affect therapeutic decisions in the acute phase.
Pericardial effusion and periaortic bleeding - Echocardiography is the best diagnostic technique for estimating the presence and severity of tamponade.
Aortic regurgitation- The diagnosis and quantification of aortic regurgitation severity can be correctly made with Doppler echocardiography, both TTE and TOE. TOE provides information on possible mechanisms that influence aortic regurgitation, which may greatly aid the surgeon in deciding whether to replace the aortic valve.
Arterial vessel involvement- Diagnosis of involvement of the main arterial vessels of the aorta is important as it may explain some of the symptoms or visceral complications that accompany the dissection and permit selection of an appropriate therapeutic strategy.
Video 2 TOE, Acute aortic dissection - clearly visible undulation of the intimal flap inside the ascending aorta. Note the significant dilation of the aorta - Sinus Valsalva diameter - 50mm, AscAo - 51mm.
Video 3 TOE, cross section at the level of AV - Video Aortic dissection spreading to Ao valve
Video 4 Aortic dissection spreading to Ao valve and leading to severe Aortic regurgitation
Video 5 Aortic dissection documented above Aortic bioprosthesis
Video 6 Aortic dissection spreading to Aorta descendens
Video 7 TOE, Acute aortic dissection, Colour Doppler - the Colour Doppler may be of help when identifying the false and true lumen. As demonstrated below, you can see the flow only on the unobstructed side of the aortic valve.
Video 8 TOE, Aortic dissection - a clear visualization of the intimal flap in the ascending aorta.
Video 9 TOE, Chronic aortic dissection - Dilatation of proximal ascending aorta (58 mm) with the intimal flap visible on the anterior side of the aorta. False lumen diameter is 15mm and the flap shows minimal movement. The false lumen is filled with echogenic material.
Video 10 Intramural haematoma - Cross section of the ascending aorta with the echogenic intramural haematoma protruding into the lumen on the left side.
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