Monday, December 9, 2013

How to measure ST Elevation at 60 milliseconds after the J-point in lead V3, relative to the PR Segment

The formula for differentiating early repol and anterior STEMI requires one measurement which many have found difficult to understand.

Here is the paper we published on the topic.

Here is a diagram to demonstrate the measurement:

Lower black line: PR segment.        Red line: tangent to the tracing, where the angle on either side of the tangent is equal; this is the J-point (end of the QRS and beginning of the ST segment).      Blue arrow: points to the J-point.    Green line is 1.5 little boxes, or 60 milliseconds, after the J-point.   Upper black line intersects the tracing where the green line demonstrates 60 ms after the J-point.                     Measure voltage difference (black arrows) (1 mm = 0.1 mV, but we measure in mm) between black lines.        So the STE at 60 ms after the J-point in lead V3 = 3.75 mm here.  It is usually not possible to be more accurate than 0.5 mm, but here it is so enlarged that one can do it.   FYI: ST elevation at the J-point in this diagram is about 2.5 mm.

8 comments:

  1. Replies
    1. Thanks. I knew that sounded wrong!

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    2. Thanks for posting this great diagram to help measure ST segment elevation. My question is in regards to the reference point. I was always taught to measure the ST segment in reference to the TP segment either before or after the ST segment you are measuring. It is known that certain conditions such as pericarditis and atrial infaction can depress PR segments. In your example the PR segment is depressed by approximately 0.5mm. What are your thoughts about this?

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    3. Michelle,

      You are exactly right about PR depression. The teachings on measurement of ST elevation are very variable throughout the decades. In the thrombolytic trials of the 1980s, the physicians did not have any instructions on how to measure STE. The ACC now says to measure at the J-point, relative to the PQ jct. (end of PR segment). PR depression lasts long enough that this should not distort the STE measurement.

      The measurement I have illustrated here is only for use in my BER LAD formula: we measured STE at J-point, and at 60 ms after the J-point, both relative to the PQ jct. (PR segment), and found that the best prediction came from this measurement at 60 ms after the J-point. If you're really interested, read this paper: http://download.journals.elsevierhealth.com/pdfs/journals/0196-0644/PIIS0196064412001606.pdf

      Steve Smith

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    4. Thanks for your reply and the link to your article.

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  2. Dr. Smith,

    I'm still confused on how to measure ST elevation.
    I get how to measure it in the setting of the BER LAD formula.
    What is the criteria otherwise.
    I've heard the following reference points:
    1) baseline: a) TP segment or b) PQ junction.
    2) ST segment: a) at the J-point or b) 40 ms after the J-point.

    Thanks for any help. Lawrence

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    1. The guidelines say to measure at the J-point relative to the PQ jct. MacFarlane's article, on which the guidelines are based, (2004) (http://www.jecgonline.com/article/S0022-0736%2804%2900102-5/abstract?cc=y) used this (it is not in the methods, I had to write the author!). Sens. for MI was 46%, spec. 48% using their mm criteria. Outcomes were biomarker based, not angiographic. Measurements are very crude and unreliable estimates. Thrombolytic trials used various definitions but did not specify in the methods how to measure, so this was useless. The bottom line is, I believe, that the efficicay of reperfusion therapy was based more on a subjective ECG diagnosis of STEMI than on any critieria. And this is as it should be.
      Steve Smith

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    2. Thanks. I've spent quite a bit of time looking.

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