A 59-year-old African American male presents to the emergency room with crushing chest pain, sweating, and lightheadedness. His blood pressure is 90/60 mm Hg and his heart rate is 48 beats per minute. Electrocardiogram (ECG) shows sinus bradycardia and ST segment elevation in leads II, III, and aVF. Occlusion of which of the following coronary arteries is most likely responsible for this patient's symptoms?

Question

A 59-year-old African American male presents to the emergency room with crushing chest pain, sweating, and lightheadedness.  His blood pressure is 90/60 mm Hg and his heart rate is 48 beats per minute.  Electrocardiogram (ECG) shows sinus bradycardia and ST segment elevation in leads II, III, and aVF.  Occlusion of which of the following coronary arteries is most likely responsible for this patient's symptoms?

Quizplus · Accepted Answer

11ec160b_38c9_239b_9249_1b7ebdca3d5d_MD0001_00 Click here for posterior view. This patient presents with symptoms and ECG findings consistent with transmural ischemic injury to the inferior wall of the heart. In 90% of individuals, the posteroinferior wall of the left ventricle is supplied by the posterior descending branch of the right coronary artery (RCA). The patient's bradycardia and resultant hypotension suggests that there may have been ischemic injury to the sinus node as well. (The sinus node normally receives its arterial blood supply from the RCA.) (Choices A, B, and C) The left main coronary artery gives rise to the left anterior descending (LAD) and the left circumflex (LCX) coronary arteries. The LAD supplies the interventricular septum and the anterior wall of the left ventricle. Transmural ischemia of the septum would produce ST elevation mainly in leads V1 and V2. Infranodal (Mobitz type II) second-degree or third-degree heart block is a possible result as well; but sinus bradycardia would not occur with this type of injury. Transmural ischemia of the anterior left ventricular wall would produce ST elevations mainly in leads V3 and V4. An occlusion of the proximal LAD would cause anteroseptal transmural ischemia, with ST elevations in leads V1-V4. The LCX supplies the lateral wall of the left ventricle. Transmural ischemia secondary to LCX occlusion would produce ST elevations mainly in leads V5 and V6, and possibly also in leads I and aVL. An occlusion of the left main coronary artery would therefore be expected to produce widespread transmural ischemia of the interventricular septum and left ventricle, with ST elevations in all of the chest (V) leads, and possibly also in leads I and aVL. (Choice E) Intramural arteries in the substance of the myocardium are unlikely sites of occlusion because, unlike the epicardial coronary arteries, they are rarely affected by atherosclerosis. Moreover, if occlusion of intramural arteries did occur, subendocardial ischemia (with associated ST depression) would be more likely than transmural ischemia (with ST elevation). Educational Objective: In 90% of individuals, occlusion of the right coronary artery can result in transmural ischemia of the inferior wall of the left ventricle, producing ST elevation in leads II, III, and aVF as well as possible sinus node dysfunction. Occlusion of the proximal LAD would be expected to result in anteroseptal transmural ischemia, with ST elevations in leads V1-V4. Occlusion of the LCX would produce transmural ischemia of the lateral wall of the left ventricle, with ST elevations mainly in V5 and V6, and possibly also in I and aVL.

A 59-Year-Old African American Male Presents to the Emergency Room