Cardiology MCQ 51

Q. A 50 year old man presents with severe crushing chest pain radiating to left arm. His ECG showed dominant R waves in V1 and V2 leads. The T waves were upright and tall along with ST segment depressions. Which artery is most likely to be occluded?

A. Right coronary artery
B. Septal branch of left anterior descending artery
C. Circumflex artery
D. Left main coronary artery

Answer: C. Circumflex artery

Explanation:

The ECG changes are suggestive of posterior wall MI. Posterior myocardial infarction usually results from occlusion of the left circumflex coronary artery but the anatomy can vary a little.

Occlusion of the right coronary artery may also result in a posterior MI.

The changes of posterior myocardial infarction are seen indirectly in the anterior precordial leads. Leads V1 to V3 face the endocardial surface of the posterior wall of the left ventricle. As these leads record from the opposite side of the heart instead of directly over the infarct, the changes of posterior infarction are reversed in these leads. The R waves increase in size, becoming broader and dominant, and are associated with ST depression and upright T waves

  

Posterior MI is suggested by the following changes in V1-3 (Figure 1):

•Horizontal ST depression

•Tall, broad R waves

•Upright T waves

•Dominant R wave (R/S ratio > 1) in V2

Figure 1. Posterior wall MI: ECG changes in anterior leads

In patients presenting with ischaemic symptoms, horizontal ST depression in the anteroseptal leads (V1-3) should raise the suspicion of posterior MI.

Posterior infarction is confirmed by the presence of ST elevation and Q waves in the posterior leads (V7-9) (Figure 2).

The degree of ST elevation seen in V7-9 is typically modest – note that only 0.5 mm of ST elevation is required to make the diagnosis of posterior MI.

Figure 2. Posterior leads in same patient showing ST elevation.