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Artifact on an ECG Showing Inferior, Posterior, Lateral M.I.

Sat, 07/05/2014 - 00:01 -- Dawn

If you are an ECG instructor, it is important that you address the subject of artifact on the ECG.  Artifact has many causes, and it is important eliminate it whenever possible.  We should strive for the "cleanest" ECG possible.  As you can see in this example, the presence of artifact has caused the machine's computer rhythm interpretation to be incorrect.  The noisy baseline has caused the computer to call this rhythm "atrial fibrillation", but we clearly see P waves in all leads, especially in Lead II.  We recognize these P waves as authentic because they are regular, they  all look alike, and they have the same relationship to the QRS complexes each cycle (PR interval is the same).  

The patient is suffering a very large M.I., showing as ST segment elevation in Leads II, III, aVF, with slight elevation in V5 and V6.  In addition, Leads V1 through V3 have definite  ST depression, indicating extension of the inferior wall injury up the posterior wall of the heart.  There has been quite a bit of discussion lately in the literature about whether to call this a "posterior" M.I, or "high lateral", or just "inferior".  Semantics aside, the involvement of so many leads tells us that this  is a large M.I.  The patient was in the Emergency Dept. complaining of chest pain.

It is fortunate that the artifact did not affect our ability to see the ST elevation, but it could have.  And, of course, we would not want to treat this patient's "atrial fib" based on the machine interpretation.  But, it is always prudent to try to get rid of artifact.  In this example, Lead III has no artifact, so it could be assumed that the right arm electrode is the culprit, as Lead III does not utilize the RA electrode, and the other leads do.  

Troubleshoot for the cause of the artifact, and then retake the ECG.  Some common causes of baseline  artifact of this nature include:  patient movement, loose electrode, dried electrode, something touching the electrode, faulty or broken lead wire, and poor skin contact due to substances on the skin.  The electrodes should be fresh from the package, and applied to skin that is clean and dry.  The patient should be encouraged to relax and hold still (not so easy for a patient in distress).  Others at the bedside should avoid touching or manipulating the limbs of the patient during acquisition of the ECG data.  This only takes about 10 seconds.  I have seen artifact many times when a patient's blood was being drawn during the ECG, and the patient was squeezing his fist for the phlebotomist.

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Comments's picture

     Excellent case by Dawn for several reasons. First  it is a good example of an acute infero-postero STEMI most probably from acute RCA occlusion (note ST elevation in lead III is clearly greater than in lead II with marked reciprocal ST depression in lead aVL). ST elevation also appears to be present in leads V5,V6 with a hyperacute T wave in lead V6. This may occasionally be seen with RCA occlusion in which large posterolateral branches may sometimes originate from the RCA. When the cause of infero-postero MI is due to left circumflex occlusion  one usually sees ST elevation more in lead II than in lead III, and the ST elevation in V6 tends to be more than it is in lead III.

  • As per Dawn  determining the rhythm is essential in this patient with an obvious large acute STEMI. This is no easy task given all of the artifact that we see! Dawn astutely surmised the RIGHT ARM as the probable "culprit"  given that lead III looks unaffected (by Einthoven's Triangle  lead III is determined by the electrical difference between the left leg and left arm electrode).
  • The BEST way to determine that artifact is operative  is to see if you can find the underlying rhythm despite the extra "noise" on the tracing. Fortunately we have a long lead II rhythm strip in this case. Definite sinus P waves can be seen preceding beats #3,4; 6,7 and 10. If we now look at beat #3 in the long lead II rhythm strip  and imagine a vertical line above it that passes through simultaneously recorded leads I,II,III  you can see a definite P wave in each of these leads.
  • In contrast  the large deflection that is seen midway between beats #1 and #2 in leads I and II is NOT seen at all in lead III. This tells us that this large deflection is NOT a PVC  but rather artifact. Knowing the rhythm is sinus is important in this patient with a large acute infero-postero STEMI.
  • Clinically  the BEST way to problem-solve when you suspect artifact is to LOOK AT THE PATIENT. You'll be amazed at what you see. While health care providers at the telemetry station may be ready to bring paddles  a look at the patient may reveal innocent activity such as scratching, shaking, brushing teeth  or physiologic activity such as tremor. Much of the time  the cause of the unusual ECG deflections will become obvious on seeing the patient while this is occurring.
  • For an example of one of the most common artifacts ( = Parkinsonian Tremor) — Check out my ECG Blog #44. 
  • Finally  this brief write-up from the NEJM on ECG ARTIFACT illustrates identifying the underlying rhythm as the way to make the diagnose of artifact.  

NOTE: For those wanting more on determining that the "culprit artery" with acute STEMI is likely to be the RCA (Right Coronary Artery Please check out my ECG Blog #80.




Dave Richley's picture

I agree with everything Dawn and Ken say and would just add that the reaction of many people to ECG artefact is simply to activate one or more filters on the ECG machine and repeat the recording. This may reduce the artefact but also distort the ECG waveforms; it’s much better to address the cause of the artefact directly.

Dave R

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