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Aortic Dissection for the American Board of Internal Medicine (ABIM) Exam

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Overview of Aortic Dissection
    • Definition: Aortic dissection is a life-threatening condition where a tear in the intimal layer of the aorta allows blood to flow between the layers of the aortic wall, creating a false lumen.
    • Types:
  • Stanford Type A: Involves the ascending aorta, with or without extension into the descending aorta.
  • Stanford Type B: Confined to the descending aorta, distal to the left subclavian artery.
    • Pathogenesis: Blood enters through a tear in the intima, propagating a false lumen, leading to compromised blood flow to various organs, including the heart, kidneys, and brain.
    • Risk Factors:
  • Hypertension (most common risk factor)
  • Connective tissue disorders (e.g., Marfan syndrome, Ehlers-Danlos syndrome)
  • Atherosclerosis
  • Prior cardiac surgery (e.g., aortic valve replacement)
  • Bicuspid aortic valve
  • Cocaine use
  • Pregnancy (rare but important risk factor)
Clinical Presentation
    • Sudden onset of severe chest or back pain: Often described as "tearing" or "ripping"; pain location can indicate the site of dissection (anterior chest for Type A, back for Type B).
    • Hypertension: Common in Type B dissections, while hypotension or shock may indicate rupture or involvement of the aortic root (Type A).
    • Pulse deficits or blood pressure discrepancies: Between limbs, suggesting impaired blood flow.
    • Neurological symptoms: Syncope, stroke, or paraplegia due to compromised blood flow to the brain or spinal cord.
    • Aortic regurgitation: New murmur, especially in Type A dissection involving the aortic valve.
Diagnosis
    • Imaging:
  • CT angiography: The gold standard for rapid diagnosis, especially in hemodynamically stable patients.
  • Transesophageal echocardiography (TEE): Useful in unstable patients for bedside evaluation.
  • MRI: An alternative, but typically not used in emergencies due to longer acquisition times.
  • D-dimer testing: Useful for ruling out aortic dissection when levels are below 500 ng/mL, particularly in low-risk patients.
    • Chest X-ray: May show a widened mediastinum, though not definitive.
    • ECG: Typically normal but may show signs of ischemia if the dissection involves the coronary arteries.
Management
    • Initial stabilization:
  • Anti-impulse therapy: Aims to decrease the force of left ventricular contraction and reduce heart rate, targeting a heart rate of 60 beats per minute and systolic blood pressure of 100-120 mmHg to minimize stress on the aortic wall and prevent further dissection.
  • Control blood pressure aggressively: IV beta-blockers (e.g., labetalol, esmolol) are the first-line agents.
  • Pain management: Morphine is commonly used.
    • Surgical intervention:
    • Type A dissections: Emergency surgery to prevent aortic rupture, pericardial tamponade, or malperfusion.
    • Type B dissections: Managed medically unless there is evidence of complications (e.g., organ malperfusion, rupture), in which case surgery or endovascular repair (TEVAR) may be indicated.
Postoperative and Long-Term Care
    • Lifelong blood pressure control: Critical to prevent recurrence or progression of dissection.
    • Surveillance imaging: Regular follow-up with CT or MRI to monitor for dissection progression or complications.
    • Genetic counseling: For patients with connective tissue disorders like Marfan syndrome.
Essential Points
    • A clinical triad of abrupt, tearing pain, pulse or blood pressure variation between arms, and mediastinal or aortic widening on chest X-ray is often used to identify acute aortic dissection.
    • CT angiography and TEE are key diagnostic tools, with CT preferred for stable patients and TEE for unstable patients.
    • Type A dissection is a surgical emergency and requires prompt intervention to prevent death.
    • Type B dissection is often managed medically, but complications may require surgery or endovascular repair.
    • Hypertension control is paramount in both acute and long-term management to prevent further aortic injury.
    • Regular follow-up and lifelong surveillance are necessary to monitor for progression, especially in patients with genetic predispositions like Marfan syndrome.