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Loose electrode artifact

Artifact

Sat, 03/05/2016 - 15:25 -- Dawn

This ECG is being offered as a teaching aid, to show how artifact can affect our ability to interpret an ECG, and to encourage our students to be meticulous in obtaining a good-quality tracing whenever possible.  If there are insurmountable obstacles preventing a technically good tracing, the circumstances should be written on the ECG.  Such obstacles could be:  seizures, tremors, vigorous resuscitation efforts underway, or patient not cooperating. 

When an ECG has obvious signs of artifact, the causes of the artifact should be corrected and the ECG repeated.  Teach your students to strive for perfection. Even though we cannot obtain “perfection”, if we settle for sloppiness, it will breed more sloppiness. 

This ECG has some intriguing abnormal signs, but we should wait for a better tracing before attempting a firm interpretation.  We do see abnormal ST segments and T waves in the high lateral leads I and aVL. These, along with the high voltage in aVL, suggest left ventricular hypertrophy with strain.  We would expect to see similar signs in the lateral chest leads, V5 and V6, also.  The second beat on the ECG appears different from the others, and has a P wave.  Even though it is not premature, it could be presumed to have been conducted aberrantly.  The precordial leads show poor R wave progression.  They should all have an RS pattern, with V1 having a small r wave and a large S wave.  The R waves should get more prominent as we move across the chest toward V6, while the s waves become less prominent.  So, V1 should be mostly negatively deflected, and V6 should be nearly all positive, with a gradual transition across the chest leads.  Poor R wave progression can have many causes.  The most preventable one is poor lead placement. 

This ECG offers a chance to illustrate to your students why they should understand how each lead is derived.  Knowing which limb electrodes are used for each limb lead will lead you, in this case, to the faulty electrode, which may simply be loose.  We can see that Lead I is unaffected by the baseline artifact.  Lead I is derived from the left and right arm electrodes.  Lead II is derived from the left leg and the right arm, and Lead III is derived from the left leg and the left arm.  Since Leads II and III are obviously affected by the artifact, which makes the left leg the culprit electrode. 

 

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