10th March 2024

Aortic Dissection

Background

Aortic syndromes refer to life-threatening conditions, including aortic dissection, intramural haematoma and penetrating atherosclerotic ulcer. Aortic dissection is defined as the separation of the aortic wall layers due to an intimal tear. The incidence of aortic dissection is 5 to 30 cases per 1 million people per year and carries a mortality of 1 to 2% per hour after the onset of symptoms in untreated patients, with an overall in-hospital mortality rate of 27%. Aortic dissection can be spontaneous, iatrogenic, or traumatic. 

Risk factors for aortic dissection include: 

• Hypertension
• Trauma
• Connective tissue disorders (Marfan’s and Ehlers-Danlos syndrome
• Aortic aneurysm
• Previous aortic dissection
• Bicuspid aortic valve (Turner’s syndrome)
• Pregnancy
• Aortic instrumentation or surgery
• Coarctation of the aorta
• Inflammatory disease (vasculitis, rheumatoid arthritis, giant cell arteritis, Takayasu’s arteritis
• Fluoroquinolone use

Classification 

Aortic dissection can be classified according to the anatomical location of the lesion, location of the initial tear and onset of presentation. The Stanford (most used) and DeBakey classifications describe aortic dissection according to the location of the lesion (See Table 1). This section will use the Stanford classification to understand clinical presentation and management. According to time, aortic dissection can be classified as:

• Hyperacute: <24 hours
• Acute: 1 to 14 days
• Subacute: >14 to 90 days 
• Chronic: >90 days

Table 1. Aortic dissection classification systems. Image source: https://en.wikipedia.org/wiki/Aortic_dissection

Clinical presentation

Aortic dissection commonly presents with acute severe chest or back pain. Most patients will describe the pain as sharp, stabbing or tearing. Pulse deficit (e.g., weak or absent carotid, brachial, or femoral pulse), unequal blood pressure in both arms, aortic regurgitation murmur, hypotension, syncope, or neurological symptoms can often present in type A dissection. In contrast, abdominal pain and hypertension are more common in type B dissection. It is worth noting that depending on the type of dissection, and hypotension can represent a rupture of the abdominal aorta (type B) or secondary severe aortic regurgitation (resulting in a new diastolic murmur) and/or extravasation into the pericardial space leading to cardiac tamponade (type A). Additionally, type A dissection can cause acute myocardial ischemia due to coronary occlusion, haemothorax or hemoperitoneum and compression of the surrounding structure, causing focal neurological deficit (e.g. stroke or altered consciousness, Horner syndrome, hoarseness, acute paraplegia, etc.). Due to the clinical presentation, other conditions should be considered when assessing patients with suspected aortic dissection (e.g., myocardial infarction or pulmonary embolism). 

Diagnosis

Initial investigations include chest x-ray, which may reveal mediastinal widening of the aortic silhouette (60-90% of cases). ECG can differentiate between aortic dissection and acute coronary syndromes but is less valuable when coronary occlusion is secondary to aortic dissection. A D-dimer can rule out aortic dissection with levels below 500 ng/mL, indicating that a patient does not have acute aortic dissection. 

Aortic dissection should be considered in patients presenting with any high-risk features (see Table 2). Diagnosis is confirmed with a CT Aortogram. This modality has similar accuracy to transoesophageal echo and magnetic resonance aortogram.

Table 2. High-risk features associated with aortic dissection 

Management 

Patients should ideally be managed in an intensive care unit for anti-impulse therapy aimed at reducing the velocity of left ventricular contraction and reducing the shear stress and progression of the lesion. Anti-impulse therapy is accomplished using IV beta-blockers (Labetalol or Esmolol) to reduce heart rate below 60 bpm and blood pressure range between 100 and 120 mmHg. It should be noted that blood pressure should be lower, preserving mental state and urine output. Where beta-blockers are not tolerated, diltiazem or verapamil may be used as an alternative. IV morphine and anxiolytics are used to control pain and anxiety. 

Initial management in aortic dissection type A focuses on aggressive blood pressure control and cardiac surgical consultation. For type B dissections, management is aimed at blood pressure control and only requires surgery if there is a rupture or worsening pain. Chronic aortic dissection is usually managed medically.

Surgical management of aortic dissection type A may involve replacing the ascending aorta, resectioning intimal tears and aneurysmal aorta, and aortic valve repair or replacement. Surgical intervention should be considered in type B aortic dissection where there is persistent severe hypertension or pain, lesion progression, aneurysmal expansion, poor perfusion leading to end-organ ischemia, or rupture.