Monday, January 3, 2011

ECG Interpretation Review #12 (Computerized ECG Interpretation, Normal Variant vs ST Elevation)

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QUESTION: The ECG below was one of many in "the pile to be read".  It was from a middle-aged adult.  No history was given. No prior tracing was available for comparison. The computerized interpretation of this tracing was the following: "Sinus rhythm. Normal ECG."
  • How would you interpret his ECG?  - Do you agree with the computer?
  • Clinically - How would you proceed?
Figure 1 - This ECG was read by the computer as "within normal limits". Do you agree?
(ECG reproduced from our files)
Note - Enlarge by clicking on Figures -
INTERPRETATION:  The rhythm is sinus at a regular rate of 80/minute. All intervals (PR, QRS, QT) are normal.  The mean QRS axis is normal (at +70 degrees). There is no chamber enlargement.
  •  Q-R-S-T Changes:  - There are small and narrow q waves in infero-lateral leads (II,III,aVF; and V5,V6). Transition occurs early (between leads V1-to-V2). Subtle but real ST segment elevation is seen in multiple leads (II,III,aVF,V1-thru-V6). There is symmetric T wave inversion in lead aVL and to a lesser extent in lead V1.
CLINICAL IMPRESSION:  Despite the computerized interpretation - this is not a "normal tracing". The findings of small, inferolateral q waves, early transition, and fairly shallow T wave inversion in leads aVL and V1 by themselves all could be normal variants. However - one cannot discount the small amplitude but real ST elevation seen in multiple leads. The differential diagnosis includes:
  1. Acute MI (less likely given the diffuse nature of the changes; acute MI is most often localized to a given lead area).
  2. Acute Pericarditis (a definite possibility given diffuse ST segment elevation).
  3. Early Repolarization as a Normal Variant (a diagnosis of exclusion to be made only after #1 and #2 considerations above are ruled out).
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COMMENT:  - It is sometimes difficult to recognize subtle ST segment elevation (as seen in leads V4,V5,V6 in Figure 1). To assist in this task - it is well to remember that it is the PR segment baseline (Figure 2) that serves as the landmark for judging ST segment deviations (elevation or depression). With this in mind - we can clearly identify the takeoff of the ST segment as being elevated with respect to the preceding PR segment for each of the leads mentioned above.
Figure 2 - Use of the preceding PR Segment as a baseline to judge ST elevation or depression. 
(Figure reproduced from our ECG Web Brain - pg 46)
Note - Enlarge by clicking on Figures -
We make several additional points:
  1. Computerized ECG Interpretations are not always correct (and this case is a glaring example of how they can go wrong). That said - computerized ECG interpretations can have utility IF used correctly (Click HERE for a link to download our pdf Review on "Optimal Use of Computerized ECG Interpretations").
  2. This case also illustrates the tremendous importance of knowing the history. We are literally lost without it - as we have no idea if the patient in question was having new-onset crushing chest pain, having pleuritic-type chest pain with pericardial friction rub on exam - or was entirely asymptomatic. Our clinical interpretation would vary dramatically based on answers to these questions. Having a prior ECG for comparison would also be invaluable for determining if the ST elevation seen here is new or old.
  3. As we note above, without a history of new-onset cardiac-sounding chest pain - the diffuse nature of the ST changes makes us less suspicious of acute infarction. That said - each of the inferior leads show q waves with ST elevation, and the symmetric T wave inversion in lead aVL could be a reciprocal change. The onus remains on us to rule out acute MI as a possibility.
  4. We would be very suspicious of acute pericarditis - IF the history was fitting (especially if a pericardial friction rub was heard). In addition to diffuse ST elevation - PR segment depression can be a helpful clue suggestive of acute pericarditis - and this appears to be present (albeit subtly) in the inferior leads.
  5. Finally - the findings in Figure 1 could reflect a normal repolarization variant. In favor of this is the upward concavity (ie, "smiley") shape to the elevated ST segments (See ECG Blog Review #2 for review of Early Repolarization). In addition - J-point notching is seen in leads V2, V6, and intermittently in other leads.
BOTTOM Line:  We ignore the computerized ECG interpretation in this case. Small q waves and diffuse ST elevation is noted. History (and ideally a prior ECG for comparison) is needed to know how to interpret this tracing in context.
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  - See also ECG Blog Review #16
NOTE - For a Review on Use of Computerized ECG Interpretations - Click HERE.
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4 comments:

  1. There is also pr segment elevation in aVR which along with st elevation in multiple segments probably corresponds more with pericadial injury pattern rather than myocardial injury, good one, thanks.

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  2. Good pick up! THANK YOU for your comment - Ken Grauer, MD (ekgpress@mac.com)

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  3. My understanding is that the TP segment seems to be a more constant baseline to use in measuring ST changes especially if there is PR segment elevation or depression present. Most of what I have read or heard has been talking about measuring against the TP segment. I would be interested if you can comment on that and have some references that you can point me to review this. Thanks.
    Yen Chow

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  4. Thank you Yen Chow for your Comment! I have made up a web page that reviews my perspective on use of both the TP vs PR segment as a baseline - Please GO TO: https://www.kg-ekgpress.com/ecg_-_what_is_the_st_baseline/ - I don't think this is something you can find "definitive studies" on in the literature, since there is really no "Gold Standard" and other factors (ie, baseline wander. baseline PR and ST-T associated abnormalities) may alter whether PR or TP is more effective in any given case. Hopefully I express the correct overview approach in my web page. My preference in most cases is to look first at the PR baseline first - but I often use both PR and TP depending on the case at hand. I do agree that when there is PR depression (as there seems to be in this case) - that I use both the TP and PR baselines in assessing to determine whether the ST segment is elevated, and if so by how much.

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