Aortic Dissection for USMLE Step 3 & COMLEX-USA Level 3
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Overview of Aortic Dissection
- Definition: Aortic dissection occurs when a tear in the inner layer (intima) of the aorta allows blood to enter the aortic wall, creating a false lumen between the intimal and medial layers.
- Types:
- Stanford Type A: Involves the ascending aorta, with or without involvement of the descending aorta.
- Stanford Type B: Involves only the descending aorta, typically distal to the left subclavian artery.
- Pathogenesis: Blood enters the tear, creating a false lumen and separating the layers of the aortic wall, which can compromise blood flow to vital organs, including the heart, kidneys, and brain.
- Risk Factors:
- Hypertension (most common risk factor)
- Connective tissue disorders (Marfan syndrome, Ehlers-Danlos syndrome)
- Bicuspid aortic valve
- Atherosclerosis
- Cocaine use
- Trauma or previous cardiac surgery
- Pregnancy (rare)
Clinical Presentation
- Severe, sudden chest or back pain: Described as "tearing" or "ripping," with pain radiating to the back or abdomen.
- Hypertension: Common in Type B dissections; hypotension may indicate rupture or aortic involvement (Type A).
- Pulse deficits or unequal blood pressures: Between limbs due to compromised flow.
- Neurological signs: Stroke or paraplegia from compromised blood supply to the brain or spinal cord.
- Aortic regurgitation: New murmur may develop in Type A dissection involving the aortic valve.
Diagnosis
- Imaging:
- CT angiography: First-line imaging for stable patients.
- Transesophageal echocardiography (TEE): Preferred for unstable patients or bedside evaluation.
- MRI: Useful but not practical in emergencies.
- Chest X-ray: May show widened mediastinum but not definitive.
- ECG: May show normal results or ischemic changes if coronary arteries are involved.
Management
- Initial stabilization:
- Aggressive blood pressure control: IV beta-blockers (e.g., labetalol, esmolol) to reduce shear stress.
- Pain management: Morphine is commonly used to relieve pain.
- Surgical intervention:
- Type A dissections: Requires emergency surgery to prevent fatal complications like aortic rupture or tamponade.
- Type B dissections: Typically managed with blood pressure control unless complications arise, in which case endovascular repair (TEVAR) may be necessary.
Postoperative and Long-Term Care
- Blood pressure control: Lifelong strict blood pressure control is essential to prevent recurrence.
- Surveillance imaging: Regular follow-up with CT or MRI to monitor for progression.
- Genetic screening and counseling: Especially important in patients with connective tissue disorders such as Marfan syndrome.
Essential Points
- Type A dissections require immediate surgical intervention to prevent death.
- Type B dissections are managed medically unless complications such as malperfusion or rupture occur.
- Hypertension control is critical both acutely and chronically to prevent further aortic injury.
- CT angiography and TEE are essential diagnostic tools, with CT preferred in stable patients and TEE for bedside evaluation.
- Lifelong surveillance and follow-up are needed to monitor for progression or complications.