Aortic dissection


Longitudinal intimal tear forming a false lumen.


Classification

Stanford classification:

Classifies dissections into two types based on whether ascending or descending part of the aorta involved.
  • Type A: Dissection involves ascending aorta
  • Type B: Dissection does not involve ascending aorta

DeBakey classification:

Based on site of origin of dissection.
  • Type 1: Originates in the ascending aorta and to at least the aortic arch
  • Type 2: Originates in and is limited to the ascending aorta.
  • Type 3: Begins in the descending aorta and extends distally above the diaphragm (type 3a) or below the diaphragm (type 3b).
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The most common classification systems of thoracic aortic dissection: Stanford and DeBakey. | Nienaber, C. A. and Eagle, K. A. (2003) ‘Aortic Dissection: New Frontiers in Diagnosis and Management’, Circulation, 108(5), p. 628 LP-635. Available at: http://circ.ahajournals.org/content/108/5/628.abstract.

Etiology

Risk factors:

  • Hypertension (70% cases with distal Stanford type B AAD)
  • Family history
  • Aortic instrumentation or surgery (coronary artery bypass, aortic or mitral valve replacement, and percutaneous stenting or catheter insertion)

Associated conditions:

  • Marfan syndrome (cystic medial necrosis seen in tissues)
  • Ehlers-Danlos syndrome
  • Turner syndrome
  • Bicuspid aortic valve
  • Coarctation of the aorta
  • Pre-existing aortic aneurysm
  • Atherosclerosis
  • Pregnancy (third trimester) and delivery
  • Inflammatory/infectious diseases causing vasculitis (syphilis, cocaine use)

Pathophysiology

Common sites for AAD:

  • 2-2.5 cm above aortic root (M/C site)
  • Distal to origin of left subclavian artery
  • In the aortic arch
aortic-dissection
The Calgary Guide | http://calgaryguide.ucalgary.ca/

Presentation

Presentation of AAD is subject to the extent of the dissection, with complaints corresponding to those affected cardiovascular structures.

  • Abrupt onset of severe ‘tearing’ chest pain radiating to the back (CLASSICAL FINDING)
  • Neurological deficits (1/5th cases)
  • Syncope (d/t hypovolemia, arrhythmias, MI, or an increased vagal tone)
  • Horner’s syndrome (compression of superior cervical ganglion)
  • Hoarseness of voice (compression of recurrent laryngeal nerve)

Physical examination:

  • Discrepancy of blood pressures in upper extremities
  • Pulse deficit
  • Diastolic murmur
  • Chest pain + any neurological finding/abdominal pain/limb weakness/paresthesia

Complications:

  • Aortic valve regurgitation
  • Cardiac ischemia
  • Hemopericardium
  • Cardiac tamponade
  • Cardiogenic shock
  • Malperfusion syndromes
  • Rupture of aorta
    • Hemorrhage → Hemothorax → Hypovolemic shock → Death
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Type A dissection with pericardial effusion as a result. | James Heilman, MD – CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=71424103

Diagnosis

X-ray:

  • Mediastinal widening (60% cases)
  • Left apical cap
  • Pleural effusion
  • Deviation of the esophagus/trachea (to the right)
  • Depression of the left mainstem bronchus
  • Loss of the paratracheal stripe
625px-aodiss_chestxray
Chest x-ray of aortic dissection type Stanford A. Note is made of a wide aortic knob. | J. Heuser JHeuser – CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=604868

CT-scan:

  • Intimal dissection flap
  • Double lumen
  • Aortic dilation and hematoma
  • Regions of malperfusion
  • Contrast leak indicates aortic rupture
Axial and coronal CT of the chest with IV contrast demonstrating a descending (Type B Stanford) traumatic aortic dissection. | Jason Robert Young, MD – CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=38278027

Transesophageal echocardiography (TEE):

  • Dissection flap with differential Doppler flow
  • True and false lumen in the ascending aorta
  • Thrombosis in the false lumen
  • Central displacement of intimal calcification
  • Pericardial effusion

Differential diagnosis:

  • Intramural hematoma
  • Penetrating aortic ulcer
jrv160016f1
Nienaber, C. A. and Eagle, K. A. (2003) ‘Aortic Dissection: New Frontiers in Diagnosis and Management’, Circulation, 108(5), p. 628 LP-635. Available at: http://circ.ahajournals.org/content/108/5/628.abstract.

Management

Medical management:

Reductions in HR and BP reduces aortic wall tension and limit the extent of dissection
  • Analgesia (morphine)
  • Short-acting IV β-blockers
  • Non-dihydropyridine CCBs (if β-blockade contraindicated)
  • Nitroprusside (refractory hypertension)

Surgical management:

  • Type A AAD: Excision of the intimal tear, obliteration of entry into the false lumen proximally, and reconstitution of the aorta with interposition of a synthetic vascular graft
  • Type B AAD: Endovascular stent-grafting (TEVAR) primarily performed for complicated type B dissections
599px-typebdisectionlumonclosed
Closure of the lumen of a Type B aortic dissection following medical management | James Heilman, MD – CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=16263234

Prognosis

Risk of death in untreated aortic dissection:

25%in first 24 hours
50%in first 48 hours
75%in first week
90%in first month

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