Wednesday, January 14, 2009

ST depression limited to Inferior leads is reciprocal to high lateral wall and represents STEMI

When there is inferior ST depression, one is tempted to diagnose "inferior ischemia". However (paradoxically and mysteriously) there is no correlation between location of subendocardial ischemia on the ECG and the location of the ischemia in the heart. When there is subendocardial ischemia, the ST depression tends to be diffuse.

So what does "inferior" ST depression represent? It is reciprocal to high ST elevation until proven otherwise.

Here is the EKG of a 50 year old man with epigastric discomfort:


Notice the very subtle ST depression in III and aVF. aVF (circled) has 0.5 mm of ST depression in the context of a 1 mm QRS (ST depression should be considered with proportionality in mind). Lead III also shows ST depression. These should be interpreted as reciprocal to aVL, the opposite lead. As in this case, the reciprocal ST depression is often much more evident than the ST elevation in aVL, which is only 0.5 mm in the context of a 5 mm R-wave. This inferior ST depression is most likely to be due to poor flow in the diagonal or circumflex arteries.

This was interpreted as normal, but it is not normal. This is very subtle and easily missed, but the prepared mind can see it.

The patient was sent home. He suffered a cardiac arrest and was resuscitated, underwent therapeutic hypothermia for coma, and had his occluded circumflex opened with PCI. He had a prolonged but nearly complete recovery and is able to go back to work part time.

11 comments:

  1. thank you! the concept of the size of the depressions relative to the qrs complex is new for me, but it seems a very important lesson. I will note it towards my practice and will share it with colleagues and trainees. Thank you, Demian

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  2. That is a tough one. I feel like I would miss that for sure unless the guy had an arrest and I was looking back for "subtle" changes.

    How would you propose catching things like this? Maybe use a straightedge to check for any depression in a CP patient?

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  3. But even if you didn't see these findings you wouldn't send the patient home. And if he had continued chest pain, you would do serial ECGs. And he would be on a monitor in case he arrested because he is a middle-aged man with chest pain. Maybe after seeing this, you WOULD recognize the abnormality in III, reciprocal to aVL. After seeing so many of these, they just jump out at me now.

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  4. Thank you Dr. Smith. I've come across quite a few articles that bring up the subtle depression/elevation that would normally be missed due to the low amplitude QRS.

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  5. Thank you Dr.Smith. A few important lessons for me on this case.
    1. ST depression on the ECG does not correlate the area of the heart that is affected.
    2. ST depression on the inferior leads is a lateral STEMI till proven otherwise.
    3. The ST depression must be interpreted relative to the size of the R wave.
    Jose.

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  6. What would you make of subtle ST depressions in a 50 year old female, complaining of chest pains, shortness of breath, fatigue, and edema?

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  7. It depends on many other factors, most important among them whether she had a previous history of heart disease, especially heart failure.

    Steve Smith

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  8. ST elevations in chest leads V1,V2 and V3 which suggest an anteroseptal MI without looking at the limb leads.This coupled with continuous chest pain, an echocardiogram could have been a better approach.

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    1. The ST elevation in precordial leads is normal ST elevation, completely proportional to the QRS. If there is any sign of ischemia in V2-V5, it is slight ST depression in V4 and an abnormally isoelectric ST segment in V3. Most people, males especially, have some ST elevation in V2-V4 at baseline.

      The best approach is to realize that these limb leads are diagnostic of ischemia, and that in the presence of continued chest pain (asssuming refractory to medical therapy such as aspirin, nitro, etc), are an indication for immediate angiography.

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  9. Sir, it reminds me, in one of your blog on Lateral ST MI, you mentioned that many a times reciprocal changes appear in Inferior leads before ST elevation in lateral leads as ECG records Lateral Leads poorly, QRS Vector Force is very so as ST.
    I think there is subtle ST elevation in aVL.
    Excellent case for revision. Thank you Sir

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