Acute Aortic Syndrome

Introduction

Acute aortic syndromes encompass a group of life-threatening thoracic aortopathy comprising aortic dissection, intramural hematoma (IMH), and penetrating atherosclerotic ulcer. These conditions arise from pathology in one of the layers of the aortic wall and present with the common symptom of acute chest pain.

Acute Aortic Dissection

Definition

Disruption of the medial layer of the aorta, with bleeding within and along the wall of the aorta.

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Risk Factors

Genetic Disorders

• Marfan’s syndrome (fibrillin gene (FBN1) mutation)
• Ehlers-Danlos syndrome (type IV collagen defect)
• Turner syndrome
• Annulo-aortic ectasia
• Familial aortic dissection
• Bicuspid aortic valve
• Loeys Dietz Syndrome

Aortic Wall Stress

• Hypertension 72%
  • Crack-Cocaine – Catecholamine-induced hypertension
• CV risk factors: smoker, hyperlipidaemia
• Previous cardiovascular surgery
• structural abnormalities (e.g. bicuspid or unicommisural aortic valve, aortic coarctation)
• Iatrogenic (e.g. recent cardiac catheterisation)
• Infection (syphilis)
• Arteritis such as Takayasu’s or giant cell
• Aortic dilatation/aneurysm
• Wall thinning

Reduced resistance

• Increasing age
• Pregnancy (debatable)

Clinical Presentation

• Severe chest pain
  • Classically sharp “tearing” nature, sudden onset, maximal severity at time of onset (vs crescendo as seen in acute myocardial infarction).
  • Retrosternal chest pain suggests with ascending aortic involvement
  • Intrascapular pain suggests descending aorta
  • May be absent altogther
• Hypotension, shock, congestive heart failure

Pathogenesis

• The initial insult to the aorta is a tear in the aortic intima. This may be due to:
  • Atherosclerotic ulcer leading to intimal tear
  • Disruption of vasa vasorum causing intramural haematoma
  • De novo intimal tear
• Intraluminal pulsatile blood enters the medial layer through the initimal tear and progressively cleaves the diseased medial layer, separating the initima and media from the the aortic wall from the site of initial tear
• Propagation of the dissection cna proceed in anterograde or retrograde directions
• Distension and systolic pressure within the false lumen may lead to dynamic compression of the true lumen, resulting in distal malperfusion
• It may also involve side branches, leading to malperfusion syndromes, tamponade or aortic valve insufficiency

Classification

Stanford (most commonly used)

• Type A
  • Involves the ascending aorta (from the valve to the origin of the brachiocephalic trunk).
  • Can extend distally ad infinitum.
  • Emergent surgical repair usually indicated.
• Type B
  • Involves aorta beyond left subclavian artery only
  • Often managed medically with BP control.

DeBakey

The De Bakey classes are distinguished by the site of the initial intimal tear.

• Type I
  • Originates in the ascending aorta and propagates into the aortic arch at least
• Type II
  • Originates in the ascending aorta without arch involvement beyond the innominate artery origin
• Type III
  • Originates in the descending aorta

Svensson (defines type of acute aortic syndrome)

1. classic dissection with true and false lumen
2. intramural haematoma or haemorrhage
3. subtle dissection without haematoma
4. atherosclerotic penetrating ulcer
5. iatrogenic or traumatic dissection

Complications

• aortic rupture
• aortic regurgitation
• acute myocardial infarction
• cardiac tamponade
• end-organ ischaemia (brain, limbs, spine, renal, gut, liver)
• death

Imaging

• CXR
  • Widened mediastinum (56-63%), abnormal aortic contour (48%), aortic knuckle double calcium sign >5mm (14%), pleural effusion (L>R), tracheal shift, left apical cap, deviated NGT.
  • Normal (11-16%)
• Echocardiography
  • Transthoracic
    • 75% diagnostic Type A (ascending), 40% descending (Type B)
    • can identify complications (e.g. aortic regurgitation, regional wall abnormalities in cardiac ischaemia, cardiac tamponade)
  • Transoesophageal (TOE)
    • Much higher sensitivity/specificity, though operator-dependent, need sedation, and is less available
    • Useful in ICU / perioperative
    • Upper ascending aorta and arch not well visualised
• Helical CT
  • Useful screen for widened mediastinum. Newer multiplane/slice scanners may now negate additional need for TOE or aortography to plan operative management.
• Aortography – Was the traditional gold standard, delineating aortic incompetence and associated branch vessel involvement as well.
• MRI / MRA – Excellent sensitivity and specificity limited by availability.

Intramural Haematoma

Definition

Intramural haematoma is defined as crescentic thickening of the aorta in the absence of an intimal flap or entry tear, resulting from a haemorrhage within the aortic wall (typically the descending aorta).

Incidence

• Mean age 70 years

Pathogenesis

• It is thought that rupture of the vasa vasorum is the mechanism for haematoma formation

Imaging

Non-contrast images are useful for identification of IMH

No flow communication is seen.

Penetrating Atherosclerotic Ulcer

Definition

Penetrating atherosclerotic ulcer is defined as an atherosclerotic lesion with ulceration that penetrates the internal elastic lamina and allows haematoma formation with the media of the aortic wall. Mostly seen in the descending thoracic aorta.

Incidence

Patients > than 65 years

Complications

Progression to aneurysm formation 28% and rupture 4%