Aortic Dissection: A High-Yield USMLE Review

Aortic dissection is a life-threatening vascular emergency in which an intimal tear allows blood to enter the media and create a false lumen. It is a cannot-miss diagnosis in any patient with acute chest pain and is a critical mimic of ACS on the exam. Recognizing it—and distinguishing Stanford Type A from Type B—determines both workup and whether the patient goes to surgery or medical management.

Presentation

• Sudden, severe tearing or ripping chest pain classically radiating to the back (interscapular region)
• Blood pressure asymmetry between arms (>20 mmHg differential) and possible pulse deficit
• New diastolic murmur of aortic regurgitation when the dissection extends to the aortic root (acute AR)
• Syncope
• Widened mediastinum on chest imaging in a hypertensive patient
• Signs of downstream branch involvement—e.g., inferior ST elevation (II, III, aVF) from extension into the right coronary ostium causing true myocardial ischemia

Diagnosis

• CT angiography is the confirmatory test when any dissection feature is present—and must be obtained before any anticoagulation
• Clinical examination: check for BP differential in both arms, pulse deficit, and a new diastolic (aortic regurgitation) murmur
• Chest imaging may show a widened mediastinum in a hypertensive patient with tearing chest pain
• ECG may show ischemic changes (e.g., inferior ST elevation) if the dissection extends into a coronary ostium

Management

• Immediate heart rate and blood pressure control for all patients
• Stanford Type A (involves the ascending aorta): surgical emergency
• Stanford Type B (does not involve the ascending aorta, starting at or beyond the left subclavian): usually managed medically
• Always look for complications, since dissection can affect any aortic branch

High-yield

• Buzzword: sudden "tearing" or "ripping" chest pain radiating to the back
• BP asymmetry >20 mmHg between arms suggests aortic dissection
• Widened mediastinum in a hypertensive patient with tearing chest pain is aortic dissection until proven otherwise
• Stanford Type A = ascending aorta = surgery; Type B = does not involve ascending aorta = usually medical
• DeBakey: Type I (ascending + descending), Type II (ascending only), Type III (descending only)
• Aortic dissection is a classic cause of acute aortic regurgitation (an emergency)
• Associated with connective tissue disorders—Marfan, Loeys-Dietz, vascular Ehlers-Danlos—and aortic root dilation/hypertension

Pitfalls

• Never give thrombolytics for a suspected STEMI if aortic dissection is possible—it doesn't treat the dissection, promotes bleeding into the false lumen, and can cause rupture. Suspected dissection is a contraindication to fibrinolytics.
• Don't anchor on ACS: dissection into the coronary ostium causes true ischemia with real ECG changes and troponin elevation, mimicking inferior MI. Always ask whether dissection features are present before anticoagulating.
• Don't overlook the inter-arm BP differential, pulse deficit, or new diastolic murmur—these bedside findings point away from simple ACS toward dissection.