Cardiac Anatomy, Human Anatomy, USMLE Step 1 - Full Vignette with Extended Explanations

Описание: A 31-year-old woman with well-controlled HIV, hypertension, and obstructive lung disease presents with sudden, severe, tearing chest pain radiating between the scapulae, high blood pressure in both arms, a diastolic murmur, and signs of heart dysfunction. ECG shows inferior ST elevation and PR prolongation. How do these findings relate to her clinical presentation, and what underlying anatomical process could explain this combination of symptoms?

VIDEO INFO
Category: Cardiac Anatomy, Human Anatomy, USMLE Step 1
Difficulty: Hard - Advanced level - Challenges experienced practitioners
Question Type: Diagnostic Failure
Case Type: ED Case

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QUESTION
A 31-year-old woman (graduate student) with HIV infection well controlled on antiretroviral therapy and a history of moderate obstructive lung disease presents to the emergency department 35 minutes after abrupt, severe, tearing chest pain radiating between the scapulae that began while walking to class. She reports the pain is maximal at onset, constant, and associated with diaphoresis and a brief sense of doom. She denies cocaine or amphetamine use....

OPTIONS
A. Proximal right coronary artery at or just distal to its ostium from the right coronary sinus, proximal to the acute marginal branches and before the typical AV nodal artery origin near the crux in right-dominant hearts, producing inferior ischemia with AV nodal block.
B. Distal right coronary artery near or beyond the acute marginal branches and past the crux, a location that often spares the AV nodal branch in right-dominant circulation and is less likely to cause AV block with inferior ST elevation.
C. Left circumflex artery in the atrioventricular groove near the crux, the AV nodal artery source in a minority (about 10-20%) of hearts, making AV block with isolated inferior changes unlikely in a right-dominant circulation.
D. Proximal left anterior descending artery in the anterior interventricular sulcus, which typically produces anterior wall changes and does not usually result in inferior ST elevation or AV nodal ischemia.

CORRECT ANSWER
A. Proximal right coronary artery at or just distal to its ostium from the right coronary sinus, proximal to the acute marginal branches and before the typical AV nodal artery origin near the crux in right-dominant hearts, producing inferior ischemia with AV nodal block.

EXPLANATION
This presentation of abrupt, tearing chest pain, pulse/BP differentials between arms, a widened mediastinum, an intimal flap on echocardiography, and severe acute aortic regurgitation indicates an acute ascending aortic dissection with coronary malperfusion. The persistent inferior ST-segment elevation with PR prolongation points to ischemia of the inferior wall and AV node. In a right-dominant coronary system, the AV nodal artery most often originates from the right coronary artery near the crux; therefore, dynamic compromise at or just distal to the right coronary ostium will jeopardize flow to the entire proximal RCA tree, producing inferior ischemia and AV nodal conduction delay. Per the 2022 ACC/AHA aortic disease guideline, anticoagulation and thrombolysis should be avoided in suspected type A dissection; the anatomic reasoning clarifies why the ECG can mimic an inferior STEMI while the true problem is ostial RCA malperfusion from the dissection flap.

The alternatives fail on anatomic-physiologic grounds....


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