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Blood exits the aortic lumen via an intimal tear which separates the layers of the media (resulting in a false lumen)

Classification

Acute: presentation <14 days

Sub-acute: 14 days - 2 months

Chronic: >2 months

1. Stanford
   • Type A: ascending aorta (with or without descending)
   • Type B: descending aorta
2. BeBakey
   
   • Type I: ascending aorta + descending
   • Type II: confined to ascending aorta
   • Type III: confined to descening aorta, beyond origin of subclavian artery

Pathology

• Myxoid degeneration - loss of elastic fibres and replacement of musculo-elastic tissue with proteoglycan-rich matrix
• Cystic medial necrosis: may be associated with injury or occlusion of vasa vasorum
• Intimal tear - dissection propagates along plane that runs between inner 2/3 and outer 1/3 of media

Predisposing factors

1. Hypertension - leads to increased shearing forces across intima
2. Traumatic injury to aorta
3. Iatrogenic - cardiac catheterisation, aortic cannulation, AV replacement
4. High cardiac output states: Pregnancy
5. Inherited defects
   • Marfan's - 15q fibrillin defect
   • Ehlers-Danlos - procollagen formation
   • Pseudoxanthoma elasticum - fragmentation of elastic fibres in media
6. Age (up to 90% are >60 years old)
7. Competitive weightlifting

Effects of dissection

1. Propagation
   • Aortic ring - acute aortic regurgitation
   • Coronary arteries - Angina / MI
   • Carotid arteries - stroke
   • Abdominal aorta - gut ischaemia (if mesenteric vessels involved)
   • Renal artery - ARF
   • Intercostal / lumbar vessels - spinal cord ischaemia (loss of supply from arteria radicularis magna - great spinal artery of Adamkewicz)
2. Rupture
   • Pericardium - tamponade
   • Pleura - haemothorax
3. Compression
   
   • Trachea / oesophagus / SVC
4. Double-barrelled lumen (if re-enters lumen through another intimal tear)

Clinical features

• Shock
• New Murmur
• Tamponade
• Asymmetrical pulses
• Neurological signs - stroke, cord features

Investigations

Key aim is to distinguish between type A and B

• ECG: MI / exclude cardiac differentials
• CXR: 80% widened mediastinum
• Aortography: Gold standard - visualisation of ventricular valve function, permits assessment of coronary anatomy
• CT/MRI: 85-90% sensitivity + specificity
• TOE: >95%; can be used at bedside

Management

1. Resuscitate: fluids, maintain cardiac index (CO/BSA) and renal function
2. Bloods
3. Monitoring
   • Bilateral radial arterial lines + femoral line
   • Central venous lines
4. Pharmacological
   • Labetalol (250mg/250mls 5% dextrose) 2-8mg/min - control ejection fraction and arterial pressure
   • Sodium nitroprusside (can cause reflex tachycardia)
5. Transfer to cardiothoracic unit
   • Type A: Replacement of diseased segment of aorta with interpositional graft and re-implantation of coronary arteries if root involved +/- valve replacement
   • Type B: Conservative managment (surgery confers no additional benefit)