Aortic dissection

• There are three layers to the aorta, the intima, media and adventitia. 
• With aortic dissection, blood enters between the intima and media layers of the aorta. A false lumen full of blood is formed within the wall of the aorta. 
• The right lateral area of the ascending aorta is the most common site of a tear of the intima layer, as this is under the most stress from blood exiting the heart
• The Stanford system:

  • Type A – affects the ascending aorta, before the brachiocephalic artery
  • Type B – affects the descending aorta, after the left subclavian artery
• Aortic dissection shares the same risk factors as peripheral arterial disease, such as age, male sex, smoking, hypertension, poor diet, reduced physical activity and raised cholesterol. 
• Hypertension is a big risk factor. Dissection can be triggered by events that temporarily cause a dramatic increase in blood pressure, such as heavy weightlifting or the use of cocaine.
• Conditions or procedures that affect the aorta increase the risk of a dissection, such as:

  • Bicuspid aortic valve
  • Coarctation of the aorta
  • Aortic valve replacement
  • Coronary artery bypass graft (CABG)
• Conditions that affect the connective tissues can also increase the risk of a dissection, notably:

  • Ehlers-Danlos Syndrome
  • Marfan’s Syndrome
• Typical presentation:

  • Severe ripping or tearing chest pain
  • Pain may be in the chest when the ascending aorta is affected
  • Pain may be in the back if the descending aorta is affected
  • Pain may migrate over time
• Other features that may suggest aortic dissection are:

  • Hypertension
  • Differences in blood pressure between the arms (more than a 20mmHg difference is significant)
  • Radial pulse deficit (the radial pulse in one arm is decreased or absent and does not match the apex beat)
  • Diastolic murmur
  • Focal neurological deficit (e.g., limb weakness or paraesthesia)
  • Chest and abdominal pain
  • Collapse (syncope)
  • Hypotension as the dissection progresses
• An ECG and chest x-ray are often used to exclude other causes (such as myocardial infarction), although they may be normal and falsely reassuring. 
• Relevant laboratory investigations include:

  • FBC, U&Es, LFTs, and coagulation screen
  • Arterial blood gas (including lactate): elevated lactate might indicate potential tissue ischaemia
  • Group and save and crossmatch (if concerns over bleeding)
  • Troponin: may be elevated if dissection causes myocardial ischaemia
  • D-dimer: a negative D-dimer indicates that dissection is very unlikely (however it is not sufficient to exclude aortic dissection).
• most patients will undergo an urgent CT angiogram (CTA) of the whole aorta
• Chest X-ray findings of AAD include:

  • Widened mediastinum (>8cm): classic finding, but only present in approximately 60% of cases
  • Double or irregular aortic contour: occurs in 50% of cases
  • Inward displacement of atherosclerotic calcification
  • Pleural effusion or haemothorax: indicative of dissection rupture
• initial management:

  • ABCDE
  • IV opiate analgesia
  • BP and HR control - IV beta blocker (labetalol)
  • Aim systolic BP 100-120
  • Aim HR 60-80
• Subsequent surgical management depends upon the classification of AAD:

  • Type A dissections require open surgery to prevent aortic rupture and generally carry a worse prognosis than Type B dissections.
  • Type B dissections (TBAD) are usually managed medically, with endovascular intervention indicated for complicated dissections
• Type B may be treated with thoracic endovascular aortic repair (TEVAR), with a catheter inserted via the femoral artery inserting a stent graft into the affected section of the descending aorta. Complicated cases may require open surgery.
• Complications:

  • Myocardial infarction
  • Stroke
  • Paraplegia (motor or sensory impairment in the legs)
  • Cardiac tamponade 
  • Aortic valve regurgitation
  • Death