Aortic Dissection

Aortic dissection refers to when a break or tear forms in the inner layer of the aorta, allowing blood to flow between the layers of the wall of the aorta. 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. Intramural refers to within the walls of the blood vessel.

 

Classification

Aortic dissection most commonly affects the ascending aorta and aortic arch but can affect any part 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. There are two classification systems.

 

The Stanford system:

  • Type A – affects the ascending aorta, before the brachiocephalic artery
  • Type B – affects the descending aorta, after the left subclavian artery

 

The DeBakey system:

  • Type I – begins in the ascending aorta and involves at least the aortic arch, if not the whole aorta
  • Type II – isolated to the ascending aorta
  • Type IIIa – begins in the descending aorta and involves only the section above the diaphragm
  • Type IIIb – begins in the descending aorta and involves the aorta below the diaphragm

 

Risk Factors

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

 

TOM TIP: For your exams, a man aged around 60 with a background of hypertension, presenting with a sudden onset tearing chest pain, has aortic dissection. Marfan’s and Ehlers-Danlos syndrome are worth remembering as risk factors, as these may be options on an MCQ exam.

 

Presentation

Aortic dissection can be difficult to spot. The diagnosis is often missed.

The typical presentation is a sudden onset, severe, “ripping” or “tearing” chest pain. The pain may be in the anterior chest when the ascending aorta is affected, or the back if the descending aorta is affected. The pain may change location (migrate) over time. Some patients with aortic dissection do not have chest pain.

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

 

Diagnosis

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. Myocardial infarction can occur in combination with aortic dissection, and treatment of the myocardial infarction (e.g., thrombolysis) can cause fatal progression of the aortic dissection.

CT angiogram is usually the initial investigation to confirm the diagnosis and can generally be performed very quickly. 

MRI angiogram provides greater detail and can help plan management but often takes longer to get.

 

Management

Aortic dissection is a surgical emergency and needs immediate involvement of experienced seniors, vascular surgeons, anaesthetists and intensive care teams. There is a very high mortality.

Analgesia (e.g., morphine) is required to manage the pain.

Blood pressure and heart rate need to be well controlled to reduce the stress on the aortic walls. This usually involves beta-blockers.

Surgical intervention from the vascular team will depend on the type of aortic dissection.

Type A may be treated with open surgery (midline sternotomy) to remove the section of the aorta with the defect in the wall and replace it with a synthetic graft. The aortic valve may need to be replaced during the procedure.

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

There is a long list of complications. Some of the key ones to remember are:

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

 

Last updated May 2021
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