Aortic dissection

‍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

Classification

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

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‍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

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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

1. 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.

2. 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

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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. 

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‍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.

‍References

[1] MSD Manuals. (2020, November 1). Aortic Dissection. MSD Manual Professional Edition. https://www.msdmanuals.com/professional/cardiovascular-disorders/diseases-of-the-aorta-and-its-branches/aortic-dissection

[2] Camm, J. A., Lüscher, T. F., & Serruys, P. (2006). The ESC Textbook of Cardiovascular Medicine (1st ed.). Wiley-Blackwell.

[3] Evangelista A, Flachskampf FA, Erbel R, Antonini-Canterin F, Vlachopoulos C, Rocchi G, Sicari R, Nihoyannopoulos P, Zamorano J; European Association of Echocardiography; Document Reviewers:, Pepi M, Breithardt OA, Plonska-Gosciniak E. Echocardiography in aortic diseases: EAE recommendations for clinical practice. Eur J Echocardiogr. 2010 Sep;11(8):645-58. doi: 10.1093/ejechocard/jeq056. Erratum in: Eur J Echocardiogr. 2011 Aug;12(8):642. PMID: 20823280.

[4] Goldstein SA, Evangelista A, Abbara S, Arai A, Asch FM, Badano LP, Bolen MA, Connolly HM, Cuéllar-Calàbria H, Czerny M, Devereux RB, Erbel RA, Fattori R, Isselbacher EM, Lindsay JM, McCulloch M, Michelena HI, Nienaber CA, Oh JK, Pepi M, Taylor AJ, Weinsaft JW, Zamorano JL, Dietz H, Eagle K, Elefteriades J, Jondeau G, Rousseau H, Schepens M. Multimodality imaging of diseases of the thoracic aorta in adults: from the American Society of Echocardiography and the European Association of Cardiovascular Imaging: endorsed by the Society of Cardiovascular Computed Tomography and Society for Cardiovascular Magnetic Resonance. J Am Soc Echocardiogr. 2015 Feb;28(2):119-82. doi: 10.1016/j.echo.2014.11.015. PMID: 25623219.

[5] Mayo Clinic staff. (2021, August 6). Aortic dissection - Symptoms and causes. Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/aortic-dissection/symptoms-causes/syc-20369496

[6] Zhao L, Chai Y, Li Z. Clinical features and prognosis of patients with acute aortic dissection in China. J Int Med Res. 2017 Apr;45(2):823-829. doi: 10.1177/0300060517699319. Epub 2017 Mar 27. PMID: 28345421; PMCID: PMC5536687.

[7] NASIM, Bina, Anas MOHAMMAD a Sardar ZAFAR. Aortic Dissection [online]. December 13th 2019 [cit. 2021-8-6]. Dostupné z: doi:10.5772/intechopen.89210

[8] Szalay, D., Frołow, M., & Leśniak, W. (2018, November 29). Aortic Dissection. Acute Aortic Syndrome - Aortic Diseases - Vascular Diseases, Peripheral - Cardiovascular Diseases - Diseases - McMaster Textbook of Internal Medicine. https://empendium.com/mcmtextbook/chapter/B31.II.2.23

[9] Nickson, C. (2020, November 3). Aortic Dissection Echocardiography. Life in the Fast Lane • LITFL. https://litfl.com/aortic-dissection-echocardiography/

[10] Evangelista A, Maldonado G, Gruosso D, Gutiérrez L, Granato C, Villalva N, Galian L, González-Alujas T, Teixido G, Rodríguez-Palomares J. The current role of echocardiography in acute aortic syndrome. Echo Res Pract. 2019 Jun 1;6(2):R53-R63. doi: 10.1530/ERP-18-0058. PMID: 30921764; PMCID: PMC6454227.