USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

Which artery is likely affected in a patient presenting with ST Elevation in leads II, III, and aVF?

1. Left anterior descending artery

2. Right coronary artery

3. Left circumflex artery

4. Internal thoracic artery

The correct answer is: Right coronary artery

In a patient presenting with ST elevation in leads II, III, and aVF, the likely affected artery is the right coronary artery. This pattern of ST elevation indicates that there is an inferior wall myocardial infarction, which typically occurs due to occlusion of the right coronary artery in a right-dominant coronary system. The right coronary artery supplies the right atrium, right ventricle, inferior part of the left ventricle, and often the inferior wall of the left ventricle through its branches. In a right-dominant system, it also supplies the inferior wall which corresponds to the leads that show ST elevation in this scenario. Other arteries listed do not typically correlate with the inferior leads. The left anterior descending artery generally affects the anterior wall of the heart and would lead to ST elevations in leads V2-V4. The left circumflex artery is associated with lateral wall ischemia involving leads I and aVL. The internal thoracic artery is primarily involved in anterior chest wall interventions and does not directly supply the myocardium in a way that would cause ST elevation in the inferior leads. Thus, the right coronary artery is the vessel most likely implicated in this presentation.