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Aortic Dissection for USMLE Step 2 & COMLEX-USA Level 2

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Overview of Aortic Dissection
    • Definition: Aortic dissection is a medical emergency in which a tear occurs in the inner layer (intima) of the aorta, allowing blood to flow between the layers of the vessel wall, creating a false lumen.
    • Types:
  • Stanford Type A: Involves the ascending aorta and may extend into the descending aorta.
  • Stanford Type B: Involves only the descending aorta, starting distal to the left subclavian artery.
    • Pathogenesis: Blood entering the aortic wall creates a false lumen, which can compromise blood flow to major organs and lead to rupture, ischemia, or death.
    • Risk Factors:
  • Hypertension (most common risk factor)
  • Connective tissue diseases (e.g., Marfan syndrome, Ehlers-Danlos syndrome)
  • Bicuspid aortic valve
  • Atherosclerosis
  • Cocaine use
  • Trauma or prior aortic surgery
Clinical Presentation
    • Severe, sudden chest or back pain: Often described as "tearing" or "ripping"; Type A dissection typically causes anterior chest pain, while Type B causes back pain.
    • Hypertension: Common in Type B dissections; hypotension in Type A can indicate a rupture or cardiac tamponade.
    • Pulse deficits: Difference in blood pressure between arms or legs.
    • Neurological deficits: Syncope, stroke, or paraplegia due to disrupted blood flow to the brain or spinal cord.
    • Aortic regurgitation: A new diastolic murmur may develop in Type A dissections involving the aortic valve.
Diagnosis
    • Imaging:
  • CT angiography: Preferred diagnostic test in stable patients.
  • Transesophageal echocardiography (TEE): Often used in unstable patients or for bedside evaluation.
  • MRI: Useful for detailed imaging but less practical in acute settings.
    • Chest X-ray: May show widened mediastinum but is not definitive.
    • ECG: May be normal or show ischemia if the coronary arteries are involved.
Management
    • Initial stabilization:
  • Immediate blood pressure control: IV beta-blockers (e.g., labetalol, esmolol) to lower shear stress on the aortic wall.
  • Pain management: Morphine is commonly used.
    • Surgical intervention:
    • Type A dissections: Emergency surgery is required to prevent aortic rupture, cardiac tamponade, or other complications.
    • Type B dissections: Managed medically unless complications like organ malperfusion or rupture occur, in which case endovascular repair (TEVAR) may be considered.
Postoperative and Long-Term Care
    • Lifelong blood pressure control: Essential to prevent recurrence or further dissection.
    • Surveillance imaging: Regular follow-up with CT or MRI to monitor for progression or complications.
    • Genetic counseling: Important in patients with connective tissue disorders like Marfan syndrome.
Essential Points
    • Type A dissections require emergency surgery to prevent life-threatening complications.
    • Type B dissections are usually managed medically unless there are complications, which may require surgical intervention.
    • Hypertension control is critical to prevent the progression or recurrence of dissection.
    • CT angiography is the preferred imaging modality for stable patients, while TEE is often used for unstable patients.
    • Lifelong follow-up is necessary to monitor for further dissection or complications, especially in those with genetic predispositions.