Monday, October 12, 2009

Comment on Posterior STEMI

I had a very good question regarding the post on posterior STEMI, and I wanted to be sure that the answer gets attention:

smallville said...

While your blog does an excellent job of highlighting posterior STEMIs that were mistaken, are there any solid criteria to help provide a DDx between anterior or subendocardial ischemia and posterior STEMI? Will posterior ST alteration always be limited to v2-v4?


This is a very good question, and not easily answered because there is very little solid research on this.

First, you should know that when there is precordial ST depression due to subendocardial ischemia, it is not necessarily due to anterior wall ischemia. Data from stress testing shows that subendocardial ischemia DOES NOT LOCALIZE on the ECG, and usually is in leads II, III, aVF and V4-V6. But, again, this does not tell you which artery is involved.

Second, ST depression in V1-V3, vs. V4-V6, is much more likely to be posterior than subendocardial ischemia.

Third, patients at higher risk of NSTEMI (older, more risk factors, h/o angiogram with multivessel disease) are much more likely to have subendocardial disease (vs., for instance, a younger smoker).

Fourth, patients with reasons to have demand ischemia (tachycardia, sepsis, GI Bleed, etc.) are much more likely to have subendocardial ischemia (like in a stress test); those with posterior MI are much more likely to present with onset of chest pain and with normal vital signs.

Fifth, look for tall R-waves in V1-V3 (the analog of Q-waves in other locations).

Sixth, an upright T-wave is much more likely to represent posterior MI, but probably signifies reperfusion of the artery rather than persistent occlusion. An inverted T-wave can be either subendocardial or posterior.

Seventh, placement of posterior leads is very helpful. Take leads V4-V6 and place them at the level of the tip of the scapula, with V4 placed at the posterior axillary line ("V7"), V6 at paraspinal area ("V9"), and V5 ("V8") between them. At lease 0.5 mm of ST elevation in 2 consecutive leads is very accurate for posterior MI.

References on posterior leads:

1) Matetzky S et al. Acute myocardial infarction with isolated ST-segment elevation in posterio chest leads V7-V9: "hidden" ST -segment elevation revealing acute posterior infarction. JACC 1999;34:748-53
2) Matetzky S et al. Significance of ST segment elevations in posterior chest leads (V7-V9) in patients with acute inferior myocardial infarction: application for thrombolytic therapy. JACC 1998;31 506-11.
3) Wung SF et al. New electrocardiographic criteria for posterior wall acute myocardial ischemia validated by a percutaneous transluminal coronary angioplasty model of acute myocardial infarction. Am J Cardiol 2001;87:970-4; A4.

3 comments:

  1. Great explanation as always.

    1. I won't expect upright R wave for posterior MI if there's a previous anterior MI with persistent Q wave (poor EF) or poor R wave progression

    2. I won't expect upright T wave for posterior MI and instead see inverted T wave if there's no reperfusion.

    Are these statements accurate?

    ReplyDelete
  2. 1. I doubt the accuracy of the first statement. If there is a previous MI with persistent Q wave, the T wave may be inverted or upright; if long after the MI, upright is most common. If you superimpose an acute posterior STEMI on this, the T wave may invert and then become upright with reperfusion. All of this is speculation; I don't have research or examples. Also, remember that the anterior leads are closeer to the anterior wall and will reflect the condition of the anterior wall better than that of the posterior. This is why there is less ST elevation in posterior leads with posterior STEMI. Also, all things being equal, non-reperfused acute posterior STEMI should have inverted T waves anterior and upright posterior, but, again, the anterior wall is closer to the leads and the condition of the anterior wall (whatever that may be) may overpower the posterior wall.

    2. The caveats above apply here as well.

    ReplyDelete
  3. I like this post friends, I would like get more information about this, thanks for sharing this information!

    ReplyDelete