A 52 y/o male with history of hypertension, smoker, presents to the ED complaining of chest pain and SOB. His vital signs are normal. His EKG is below.
1. What does the EKG show?
2. How would you manage this patient?
The EKG shows a posterior wall MI
This patient should be treated like a STEMI. He should go emergently to the cath lab for PCI or receive tPA.
The EKG shows R waves with ST depressions in leads V1-V3 (as well as V4-V6, I and aVL). R waves with ST depressions in leads V1-V3 is consistent with a posterior wall MI.
Remember that the heart is a 3 dimensional structure. That means that it has an entire posterior side as well. Just as the anterior wall, the lateral wall, and the inferior wall can infarct, the posterior wall can infarct as well. Most of the time, the posterior wall does not infarct by itself. It usually occurs together with an inferior wall or infero-lateral MI. However, infarctions of the posterior wall alone can occur in up to 4% of MI’s. In these cases, the other walls of the heart will be normal. None of the standard 12 leads look directly at the posterior wall. So, how can we recognize a posterior wall MI on a 12 lead EKG? We have to infer the presence of a posterior wall MI based on reciprocal changes.
ST depressions can be a sign of primary ischemia, or they can be a reciprocal change of ST elevations in the opposite wall of the heart. Reciprocal ST depressions occur in the leads opposite the wall with the ST elevations. ST depressions in leads V1-V3 are a reciprocal change of ST elevations in the “opposite wall”. The opposite wall of the antero-septum is the posterior wall. ST depressions with R waves in leads V1-V3 are seen in a posterior wall MI.
Imagine a mirror situated between the posterior wall and the anterior wall. If an acute MI occurs in the posterior wall, it would cause ST elevations and Q waves. Since we can’t see the posterior wall on a standard 12 lead EKG, we can only see the “mirror image” of the posterior wall in the antero-septal leads. The mirror image of ST elevations and Q waves is ST depressions and R waves. So, when we see ST depressions and R waves in leads V1-V3, that indicates a posterior wall MI.
Some people will actually take this EKG and turn it upside down and backwards, and look at leads V1-V3 through the back of the page. If you do that, you will see ST elevations and Q waves.
To confirm a posterior wall MI, you can do posterior leads. Place leads V8 and V9 on the left back. They are placed at the same intercostal space as lead V6. Lead V8 is placed in the midscapular line. Lead V9 is placed at the left spinal border. Now run the EKG again and look for ST elevations in leads V8 and V9. If they are present, that is diagnostic of a posterior wall MI. The EKG below demonstrates posterior leads.