Tuesday, September 3, 2013

ECG Interpretation Review #74 (Computerized ECG Interpretation – Peaked T Waves – QS complexes - Computer)


     The 12-lead ECG shown below in Figure-1 was obtained from a 78-year old woman who presented with atypical chest pain. The computer interpretation was: Sinus rhythm; left axis (-10 degrees) — but otherwise “normal” ECG.
  • Do you agree with the computerized interpretation?
  • Do you usually or “never” agree with the computerized interpretation? Do you use the computer at all?
Figure-1: 12-lead ECG obtained from a 78-year old woman with atypical chest pain. Do you agree with the computer interpretation? (Figure reproduced from ECG-2014-ePub). NOTE — Enlarge by clicking on Figures — Right-Click to open in a separate window (See text).
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INTERPRETATION of Figure 1:
     This example highlights the importance of overreading the computerized interpretation. This is not a “normal” ECG:
  • There is normal sinus rhythm at a rate of ~85/minute. Intervals (PR/QRS/QT intervals) are normal.
  • There is LAD (Left Axis Deviation) with an estimated axis of -10 degrees — but the axis is not leftward enough to satisfy criteria for LAHB (Left Anterior HemiBlock), since the QRS is positive in lead II (ie, the axis is not more negative than -30 degrees).
  • No chamber enlargement.
  • QRST Changes: There are QS complexes in leads V1,V2. A small but definite r wave is seen in lead V3. Transition is slightly delayed (the R becomes taller than the S is deep between V4-to-V5). There is shallow T inversion in lead III. Perhaps the most remarkable finding is the presence of abnormally peaked T waves in leads V1-thru-V4. The T wave in V2 is quite tall.
IMPRESSION: Clinical correlation is needed to determine the significance of these findings:
  • The QS complex in leads V1,V2 could indicate septal infarction of uncertain age. Notching on the downslope of the QS complex in lead V2 supports this supposition – but the presence of a definite r wave by lead V3 means that we cannot be certain if this pattern represents prior septal infarction — lead placement error — or anatomic variant.
  • Note was made of the shallow, symmetric T inversion in lead III. Although this could be ischemic — isolated T wave inversion in either lead III and/or lead aVF may at times be a normal finding. This is especially true when the QRS complex with the T inversion is predominantly negative (as seen here) and T inversion is absent in the other inferior leads (leads II, aVF).
  • The tall, peaked T waves with narrow base in a number of precordial leads clearly suggests hyperkalemia. That said — serum potassium in this patient was normal! Another cause of abnormally peaked T waves is ischemia (IF we perform a mirror test by inverting the tracing, the reciprocal of tall, peaked anterior T waves — is deep symmetric T inversion in what corresponds to the posterior lead distribution).
  • BOTTOM LINE: It turned out that this ECG was absolutely unchanged from prior tracings done on this patient. Given that serum potassium was normal — our interpretation was: “Sinus rhythm; possible old septal infarction; peaked precordial T waves suggestive of ischemia — but no acute change compared to prior tracings.” That said — the computerized interpretation clearly failed to recognize several abnormal findings ...
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Computerized ECG Interpretations: Friend or Foe
     A frequent question that arises is, “How best to use (or not use) the computerized ECG interpretation?” Opinions vary. We feel the answer depends on the goals and experience level of the interpreter.
  • Computerized ECG analysis systems are not infallible. They are far from perfect at ECG interpretation. Our task is to appreciate what computer systems do well — and what they do not do well.
     At the current time — virtually all modern ECG machines automatically provide a computerized interpretation. This has benefits and drawbacks. Consider the following:
  • Computerized systems excel at computing values. That’s what computers do. As a result — computerized systems are extremely accurate in calculating: i) Rate; ii) Intervals (PR/QRS/QT ); and iii) Axis.
  • They are usually reliable in recognizing sinus rhythm mechanisms and normal tracings.
  • For the Expert Interpreter — the most advantageous feature of computerized systems is saving time! There is no longer need to calculate rate, intervals or axis — since the computer instantly provides legible and accurate printout of these values. IF the computer says, “Normal ECG” — it may literally take no more than 2-3 seconds for an experienced interpreter to overread and sign the report (provided they agree with the interpretation).
  • For the Non-Expert Interpreter — the major benefit of computerized systems is the backup opinion the system provides. The computer may suggest findings not initially thought of by a less experienced interpreter. This encourages more careful, targeted review of the tracing. It may also be educational by the suggestions it makes. Finally — confidence may be boosted when computer analysis agrees with the clinician’s interpretation.
  • NOTE: The computer backup opinion may help the expert-in-a-hurry from overlooking any ECG findings.
CAVEATS: Computerized systems do not do as well in evaluation of abnormal tracings as they do with normal or relatively normal tracings (especially when complex abnormalities are present ).
  • They are far less accurate interpreting rhythms that do not have a sinus mechanism.
  • They may miss subtle infarctions ...
  • They tend to overinterpret the J-point ST elevation that is commonly seen with early repolarization patterns (at times mislabeling these normal variants as “acute MI” ).
  • They may miss pacemaker spikes / WPW / tall R in V1.
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Suggested Approach: How to Use the Computer
     Expertise of the interpreter dictates the approach:
  • For the Non-Expert Interpreter — Do not initially read the computer report (because you do not want to bias your interpretation by what the computer says). Instead — WRITE OUT (or at least think out) your interpretation before you look at the computer readout. Check findings you note with each computer statement. Then delete, modify and/or add to the computer interpretation as needed. Admittedly — it will take a little longer to interpret ECGs in this manner — but given the limited number of tracings most non-expert interpreters must assess, time-saving is far less important than optimizing accuracy. Checking your interpretation with what the computer says may suggest findings not initially thought of — as well as forcing you to relook at any questionable findings. This increases accuracy.
  • For the Expert Interpreter — Review the computer report either before or after evaluation of the ECG itself. Minimize time devoted to determination of heart rate, intervals and axis (since the computer is very accurate for these parameters). Consider more careful evaluation IF the rhythm is not sinus — or IF the ECG is interpreted by the computer as abnormal. Overread each computer statement. Place a check mark next to those that are accurate. Delete, modify or add to incorrect statements. Optimal speed is attained by quick overview of the tracing in conjunction with review of the computer report. Normal ECGs should literally take the expert no more than 2-3 seconds to complete. Awareness of computer strengths and weaknesses in interpretation allows the expert to quickly determine when the computer report should be partially or completely ignored.
  • For any Interpreter — If you disagree with one or more computer statements — cross these out! The computer reading is part of the medical record — so incorrect statements should not stand unmarked.
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Editorial Comment by the Author:  Prior to researching this topic (references of my work below) — I thought computerized interpretations were a waste of time. However, once I learned to appreciate their benefits and drawbacks — I learned to love computerized interpretations. They literally tripled my speed of interpretation — especially when sinus rhythm and minimal abnormalities are present. On the other hand — I ignore what the computer says when the rhythm is anything other than sinus. I’m fully aware of the need to carefully overread early repolarization patterns and tracings on patients with chest pain. Finally — I’ve observed that when less experienced interpreters truly make an honest attempt to interpret the ECG first before they look at what the computer says — that accuracy is increased.
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- For more information  GO TO:
  • See this pdf on Computerized ECG Interpretations excerpted from Section 13.0 (in ECG-2014-ePub).
Our Publications on Computerized ECG Interpretation include the following:
  • Grauer K: Chapter 21  Does the Computer Know Better? – from Grauer K: Practical Guide to ECG Interpretation (2nd Edition) – Mosby, St. Louis, 1998, pp 374-379.
  • Grauer K, Kravitz L, Ariet M, Curry RW, Nelson WP, Marriott HJL: Potential Benefits of a Computer ECG Interpretation System for Primary Care Physicians in a Community Hospital. J Am Bd Fam Prac 1:17-24, 1989.
  • Grauer K, Kravitz L, Curry RW, Ariet M: Computerized Electrocardiogram Interpretations: Are They Useful for the Family Physician? J Fam Prac 24:39-43, 1987.
  • Grauer K, Curry RW: Chapter 11: Use of Computerized ECG Interpretation Programs. - from Clinical Electrocardiography (Grauer & Curry Blackwell Scientific Publications, Boston, 1992, pp 418-425.
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2 comments:

  1. Hello doctor....
    What about Lead 2.... T wave looks hyperacute plus the lead 3 and aVF findings you have mentioned... are they significant??? esp hyperacute looking T wave in lead 2????

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    1. The answer to your question is under the IMPRESSION. The overly peaked T waves in V2,V3 (and to a lesser extent in other leads) is clearly abnormal. Serum K+ was normal. At the least, this looks ischemic. IF the patient had new chest pain — this could be DeWinter-like T waves — but as I state in the Impression, given LACK of any change from prior tracings — this turned out not to be an acute finding. But it clearly is abnormal — and this was not picked up by the computerized interpretation — :)

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