Monday, October 4, 2010

Inferior STEMI: can we predict the infarct related artery?

Inferior STEMI may be due to RCA or circumflex occlusion (and occasionally due to a "Type III" or "wraparound" LAD, with concomitant anterior MI). If inferior STEMI is due to RCA occlusion, then the right ventricle may be involved, and a right sided ECG is indicated. If due to circumflex, then one need not worry about RV MI. In addition, the interventionalists like to know which artery is involved before the angiogram, if possible.

Here is the ECG of a previously healthy 35 year old male with one hour of chest pain:


There is obviously an inferior STEMI.

Notice:

1. There is no reciprocal ST depression in lead I
2. There is ST elevation in leads V5 and V6.
3. ST elevation in lead II is at least as high as that in lead III

These are 3 criteria which are highly correlated with circumflex occlusion.

Kontos MC et al. Am J Cardiol 1997;79:182
Chia BL et al. Am J Cardiol 2000;86:341
Bairey CN et al. Am J Cardiol 1987;60:456

DeVerna et al. (including Kurz MC and Smith SW) has more recently developed a decision rule (see diagram), presented at ACEP Research Forum in 2008 [DeVerna CJ et al. Ann Emerg Med2008;52(4 Suppl):S117.]. We are in the process of validating this tool. A score greater than or equal to 5 diagnosed circumflex occlusion with very high specificity.
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8 comments:

  1. Teel ya the truth. I was thinking that 3 was higher then 2, which would make it a RCA. I am interested in your scoring system. Have you done post cath procedural studies on its accuracy?

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  2. We derived this in a group of 139 angiographically proven occlusions, 29 of them circumflex and 110 RCA. We are in the process of validating this.

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  3. could you tell a bit more about how to use this tool???

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  4. Just answer each of the 4 questions. If the answer is "yes", assign the indicated number of points. Add the result for the 4 questions. If the total is greater than or equal to 5, then it is probably a circumflex lesion (15 of 17 with such a score were circumflex). If less than 5, then probably RCA (14 vs. 105 had RCA).

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  5. Hi Dr Smith.

    A great post as usual.
    In this ECG, there's no reciprocal depression of ST segment in lead I, but there's depression in aVL. Does this make a difference ?
    Thank you.

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  6. That was the first observation I made above, and it is important. As a single criterion, absence of ST depression in lead I indicates that a circumflex occlusion is more likely than it otherwise would be.

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  7. Any role of St depression in aVr?

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    Replies
    1. ST depression in aVR implies ST elevation in -aVR, which could happen in lateral MI but mostly happens in pericarditis. ST depression in aVR with PR elevation in aVR is classic pericarditis.

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