Aortic Dissection for USMLE Step 1 & COMLEX-USA Level 1
Overview of Aortic Dissection
- Definition: Aortic dissection occurs when a tear in the inner layer (intima) 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 involvement of the descending aorta.
- Stanford Type B: Involves only the descending aorta, distal to the left subclavian artery.
- Pathogenesis: Blood enters through a tear in the intima, splitting the layers of the aorta and forming a false lumen, which can compromise blood flow to major organs or cause rupture.
- Risk Factors:
- Hypertension (most common)
- Connective tissue disorders (e.g., Marfan syndrome, Ehlers-Danlos syndrome)
- Bicuspid aortic valve
- Atherosclerosis
- Cocaine use
- Trauma or prior cardiac surgery
Clinical Presentation
- Severe, sudden chest or back pain: Described as "tearing" or "ripping"; pain can radiate to the back, neck, or abdomen depending on the location of the dissection.
- Hypertension: Common in Type B dissections; hypotension may indicate aortic rupture or involvement of the aortic root in Type A.
- Pulse deficits or blood pressure discrepancies: Between arms or legs, due to impaired blood flow.
- Aortic regurgitation: A new diastolic murmur may develop in Type A dissections involving the aortic valve.
Diagnosis
- Imaging:
- CT angiography: Preferred diagnostic tool for confirming the dissection and determining its extent.
- Transesophageal echocardiography (TEE): Useful in unstable patients or as a bedside tool.
- MRI: Can be used for detailed imaging but is less practical in acute emergencies.
- Chest X-ray: May show widened mediastinum but is not diagnostic.
- ECG: Often normal, but may show signs of ischemia if coronary arteries are affected.
Management
- Initial stabilization:
- Blood pressure control: IV beta-blockers (e.g., labetalol, esmolol) to reduce shear stress on the aortic wall.
- Pain management: Morphine is commonly used.
- Surgical intervention:
- Type A dissections: Require emergency surgery to prevent complications such as aortic rupture, tamponade, or death.
- Type B dissections: Typically managed medically with blood pressure control unless complications (e.g., organ malperfusion or rupture) arise, in which case surgery or endovascular repair (TEVAR) may be needed.
Postoperative and Long-Term Care
- Lifelong blood pressure management: Critical to prevent recurrence or further dissection.
- Surveillance imaging: Regular follow-up with CT or MRI to monitor for complications.
- Genetic screening: Recommended for patients with connective tissue disorders (e.g., Marfan syndrome).
Essential Points
- Type A dissections are surgical emergencies and must be addressed immediately to prevent life-threatening complications.
- Type B dissections are usually treated medically, but surgical intervention may be necessary if complications occur.
- Blood pressure control is the cornerstone of both acute and long-term management to prevent further aortic damage.
- CT angiography is the preferred imaging modality for diagnosis, while TEE is used in unstable patients.
- Lifelong monitoring is required to prevent progression and monitor for recurrence, particularly in patients with genetic predispositions.