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

A 21-year-old man with restrictive cardiomyopathy and diabetes insipidus presents 90 minutes after sudden, crushing substernal chest pain radiating to his right shoulder while lifting a heavy suitcase, accompanied by two syncopal episodes. Physical exam reveals jugular venous distention, a new holosystolic murmur, cool extremities, and hypoxemia. ECG shows ST segment changes, and echocardiography finds right ventricular dilation. What features should help you localize the culprit lesion and guide your next steps?

VIDEO INFO
Category: Cardiac Anatomy, Human Anatomy, USMLE Step 1
Difficulty: Hard - Advanced level - Challenges experienced practitioners
Question Type: Differential Comprehensive
Case Type: Critical Condition

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QUESTION
A 21-year-old man is brought to the emergency department 90 minutes after sudden, crushing substernal chest pain radiating to the right shoulder while lifting a heavy suitcase. He had two brief syncopal episodes without seizure activity during transport. He denies current cocaine use and drinks alcohol socially. He took tadalafil 20 mg last night for erectile dysfunction. He reports he ate spicy wings at the airport before boarding....

OPTIONS
A. Acute occlusion of the proximal right coronary artery before the right ventricular marginal and atrioventricular nodal branches, near the crux in a right-dominant heart, producing inferior STE with V4R STE and AV-nodal ischemia with RV failure signs.
B. Acute occlusion of the distal right coronary artery beyond the crux after the atrioventricular nodal branch, causing inferior STE but typically without V4R STE, prominent RV hypokinesis, or AV-nodal ischemia in a right-dominant pattern.
C. Acute occlusion of a dominant left circumflex artery in the atrioventricular groove near the crux supplying the AV node, yielding inferior STE but generally lacking right-sided precordial STE and the marked RV dilation seen on bedside echo.
D. Acute occlusion of the first septal perforator of the left anterior descending artery, leading to anteroseptal ischemia and possible conduction delay, but not the inferior STE with concomitant V4R STE and RV-predominant dysfunction described.

CORRECT ANSWER
A. Acute occlusion of the proximal right coronary artery before the right ventricular marginal and atrioventricular nodal branches, near the crux in a right-dominant heart, producing inferior STE with V4R STE and AV-nodal ischemia with RV failure signs.

EXPLANATION
This patient s ECG shows inferior ST-segment elevation in leads II, III, and aVF with reciprocal changes in I and aVL, plus right-sided precordial ST elevation maximal in V4R. Bedside echo demonstrates a dilated, hypokinetic right ventricle, functional tricuspid regurgitation, and a plethoric IVC without pulmonary edema. He also has a prolonged PR interval (220 ms) suggesting AV nodal ischemia. Taken together in a right-dominant coronary system (the most common pattern), the most parsimonious lesion is an acute occlusion of the proximal right coronary artery before the right ventricular marginal and atrioventricular nodal branches near the crux, which simultaneously produces inferior MI, right ventricular infarction, and AV nodal ischemia....


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