A 62-year-old man comes to the emergency department with chest discomfort and shortness of breath that began 1 hour ago while climbing stairs. He describes the discomfort as a pressure-like sensation in the center of his chest, radiating to his left arm. He denies fever, cough, or palpitations. Past medical history includes hypertension and hyperlipidemia. He takes lisinopril and atorvastatin. He has a 20-pack-year smoking history and drinks alcohol socially. His father died of a myocardial infarction at age 58. Vital signs show the following: temperature 37.1°C (98.8°F), blood pressure 142/86 mmHg, heart rate 96 beats/min, respirations 20/min, and SpO2 97% on room air. Physical examination reveals normal S1 and S2 with no murmurs, rubs, or gallops. There is no jugular venous distention. Lungs are clear. There is no peripheral edema. An electrocardiogram shows ST-segment elevations in leads II, III, and aVF.
D) Right coronary artery
This patient is having an acute inferior wall myocardial infarction (MI), as evidenced by ST elevations in leads II, III, and aVF. The most common cause of an inferior MI is occlusion of the right coronary artery (RCA).
Answer choice A: Left anterior descending artery, is incorrect. The left anterior descending (LAD) artery supplies the anterior wall and septum. Occlusion results in ST elevations in leads V1–V4, not the inferior leads.
Answer choice B: Left circumflex artery, is incorrect. The left circumflex artery supplies the lateral wall. Occlusion would cause ST elevations in leads I, aVL, V5, and V6.
Answer choice C: Posterior descending artery, is incorrect. The posterior descending artery may be a branch of either the RCA (right-dominant circulation) or left circumflex (left-dominant circulation). It supplies the posterior wall. Posterior MI typically causes ST depressions in the anterior leads (V1–V3). Leads V7, V8, and V9 can be placed on the back to help identify a posterior MI. Leads V7-V9 are mirror images of leads V1-V3 and will demonstrate ST elevations.
Answer choice E: Second diagonal branch, is incorrect. The second diagonal branch is a branch of the LAD that supplies part of the anterior and lateral walls. Occlusion would affect leads V4–V6, not the inferior leads.
Key Learning Point
Acute inferior myocardial infarction is most commonly due to right coronary artery occlusion and present with ST elevations in leads II, III, and aVF on electrocardiogram.
