Aortic Dissection

Pathophysiology

  1. Aortic lining intima tear (usually <3cms distal to AoV or left SC artery) haemorrhage into false lumen double lumen aorta.
  2. Dissection can result in
    1. Occlusion of aortic branches organ → ischaemia
    2. False lumen rupture back into aorta or into mediastinum, pericardium, GIT or IVC

Epidemiology

  1. Commonest emergency affecting the aorta. 4:100,000 per year. 25% Post Mortem diagnosis
  2. 2M:1Ft im
  3. Usual age range: 50–70y & rare <40y unless inherited, congenital, iatrogenic conditions.

Risk Factors

  1. HT in up to 75%
  2. Atherosclerosis & so smoking and cholesterol.
  3. Genetic: Marfan’s, Turner’s, Ehlers-Danlos type IV, familial thoracic aortic aneurysm types 1 & 2
  4. Cong bicuspid AoV & coarctation of aorta.
  5. Cocaine use
  6. Arteritis (Takayasu, Giant Cell), syphilis
  7. Pregnancy
  8. Iatrogenic dissection (Cx of cardiac catheterisation, cardiopulmonary bypass or balloon valvotomy).
  9. Trauma

Starting Site

  1. Asc aorta: 50%
  2. Arch: 30%
  3. Distal aorta: 20%

Classifications

Stanford classification

  1. Type A involves ascending aorta (DeBakey types I & II) 60–70%
  2. Type B does not involve the ascending aorta (DeBakey type III).

DeBakey classification

  1. Type I: ascending aorta, aortic arch, and descending aorta.
  2. Type II: ascending aorta only
  3. Type III: descending aorta distal to left SCA, IIIa stops before & IIIb after diaphragm

Assessment

  1. Can be quite variable.
  2. History: >90% have pain – sudden severe, worst-ever pain of short duration. 75% chest (A>B), 50% back (B>A) and 30% abdo pain. Sharp (65%) or tearing (50%). Radiates in 30% to back, arms, chest, abdo. Neurological features (15–40%) – syncope, TIA, focal neurological deficits (this plus CP = very likely dissection).
  3. Examination: ~50% have BP (B>A), unequal pulses (<40%), BP diff>20mmHg significant, may have diastolic murmur of AR (A>B), S3 or Austin Flint murmur. Evidence of tamponade (25% in A). Also may have signs of CVA/TIA, limb ischaemia, visceral ischaemia, paraplegia or Horner’s.

Investigations

Bloods

  1. FBC, UEC, Trop/CK, coags, XM, D-Dimer, [smooth muscle myosin heavy chain not useful]

ECG

  1. 70% abnormal (non-specific ST-T wave changes, LVH or ischaemic changes – <5% have pattern indication for thrombolysis – which would be disastrous if given)

Imaging

  1. CXR – cannot conclusively diagnose or exclude dissection, but 90% abnormal including:
    1. Wide mediastinum in 60% (AP supine>8cm; PA erect>6cm or >25% chest width)
    2. Obscured aortic knob; abnormal aortic contour
    3. Ring sign – separation of aortic knuckle calcification > 5–10mm
    4. Apical cap (i.e. pleural blood)
    5. Left pleural effusion
    6. Deviation of nasogastric tube rightward
    7. Deviation of trachea rightward and/or left main stem bronchus downward
    8. Left paraspinal stripe
    9. Disparity in ascending/descending aorta size or double density of aorta
    10. Loss of aorto-pulmonary window
    11. Loss of paratracheal stripe
  2. Multidetector CT angiography:
    1. 100% sens/98% spec. Can’t assess AV. SE: contrast, Xrad
  3. TTE:
    1. 80% sens, 90 spec for asc dissections & assessing AV. Not good for desc ones.
  4. TOE:
    1. 98% sens, 95% spec. Less sensitive for distal asc & desc aorta. Op-dependent.
  5. Aortic angiography (aortogram):
    1. ~90% sensitive, ~95% specific. Requires contrast. But can assess involvement of branches. Possibility of cannulating false lumen.
  6. MRI:
    1. 98–100% sensitive & specific but not usually stable enough and not readily available.

Management

Supportive

  1. ABC, O2, analgesia, monitoring, arterial line, CVL, good access (2 x large bore IVC).

Medical

  1. Aim BPsys 100–110mmHg with nitroprusside titrate 0.25–10µg/kg/min IV or labetalol IV
  2. Intravenous beta blockers (or CCB if COPD) to keep HR 60–80 & as negative inotrope,e.g. propranolol 0.5–1mg IV q5min or esmolol.

Surgical: (cardiology & cardiothoracic consultations)

  1. If type A (type I and II) to prevent aortic rupture, tamponade, and relieve AR.
  2. If type B (distal dissection) often medical Mx unless significant AR, tamponade, leaking aneurysm, major vessel involved (& so limb/visceral ischaemia), or continued dissection.
  3. Rel CI: Poor outcome for type III dissections due to compromise of spinal blood flow.
  4. Acute dissections with ischaemia are treated usually endovascularly by stenting, graft or aortic fenestrations.
  5. Chronic dissections continue to be managed by open surgical techniques, usually grafts.
  6. If the aortic valve is involved it may need resuspension or replacement.

Prognosis

  1. Up to 20–50% die before reaching hospital, 30% in hospital.
  2. Operative mortality ~25%.
  3. Aortic rupture has 80% mortality.
  4. If undiagnosed: 50% mortality @ 48hrs rising by 1%/hr.
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