Scenario: This 12-lead electrocardiogram (ECG) was obtained during stent placement in the distal portion of a codominant left circumflex (LCx) artery in a 56-year-old male who came to the cardiac catheterization laboratory for suspected acute coronary syndrome. Coronary angiography showed a 90% occlusion in the distal LCx. The patient had arrived at the hospital 24 hours earlier with crescendo angina. He had no prior history of coronary artery disease.

Sinus rhythm at 75/min with acute myocardial injury of the posterior myocardium manifested as down-sloping ST-segment depression in leads V1 to V5

The posterior descending artery (PDA) supplies the inferior wall of the left ventricle and inferior part of the septum. The coronary artery that supplies the PDA determines coronary “dominance.” In approximately 70% of the population, the PDA originates from the right coronary artery; it is codominant in 20%, meaning both the right coronary artery and LCx feed...

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