Saturday, March 10, 2018

ECG Blog #148 (Ventricular Fibrillation - VFib - Artifact )

Is the patient whose 6 limb leads are shown in Figure-1 in VFib (Ventricular Fibrillation)?
  • Can you tell from these 6 leads, even before you see the rest of his 12-lead ECG?
Figure-1: Is this patient in VFib? NOTE — Enlarge by clicking on the Figure.
If one simply looked at these 6 leads — it would be easy to think this patient had just gone into VFib. However, there is enough information on this limited tracing to tell that this is not the case.
  • The presence of artifact is extremely common. Potential sources of artifact include tremor, shivering, brief seizure activity or other body movement; loose or faulty lead connection; external devices that may produce various types of interference; and application of a monitoring lead in close contact with a pulsating artery, among others. Extreme clinical conditions with acutely ill patients may at times lead to unavoidable artifact. That said, most of the time interpretation of the ECG will still be possible despite a less-than-perfect recording. However, when artifact becomes as pronounced as it is in leads III, aVL and aVF of Figure-1 — interpretation of the ECG may become extremely challenging.
  • The best way to prove artifact — is to recognize persistence of an underlying spontaneous rhythm that is unaffected by any erratic or suspicious deflections that are seen. Therefore, despite close resemblance to VFib in leads III, aVL and aVF of this ECG — an underlying regular supraventricular (that is, narrow QRS) rhythm at a rate just under 100/minute can still be seen in other leads.
Figure-2 shows the remaining 6 leads for this 12-lead tracing. Do the 6 chest leads that are now seen support your answer?
Figure-2: Complete 12-lead ECG for the patient whose 6 limb leads were shown in Figure-1.
Answer: The baseline “noise” and artifact deflections continue in the chest leads. However, it is now much easier to appreciate that a regular underlying supraventricular rhythm continues throughout the entire tracing.
  • Proof that the high-amplitude chaotic deflections seen in leads III, aVL and aVF constitute artifact is forthcoming from inspection of simultaneously-obtained leads (Figure-3).
Figure-3: We have dropped vertical lines (in red) from definite QRS complexes seen in leads I, II and aVR (See text). NOTE: The baseline ECG is a photograph, and was unfortunately somewhat tilted. This is why the red lines may appear with slight angulation — but they are parallel with the ECG grid lines, and therefore do correspond to simultaneously-recorded QRS complexes.
PEARL: Awareness that almost all modern ECG machines produce simultaneous recordings of at least 3 leads at a time may prove invaluable in arrhythmia interpretation.
  • It allows accurate determination of QRS duration. This is especially important when part of the QRS complex lies on the baseline and appears narrow in some leads, when in fact other leads clearly demonstrate QRS prolongation.
  • It tells us if atrial activity is arising from a single site or multiple atrial sites (ie, P waves from different atrial sites may look similar in some but not all leads).
  • It facilitates detection of artifact — which often appears much more marked in some (but not all) leads.
Analysis of Figure-3 should remove any doubt that the chaotic deflections seen in Figure-2 are the result of artifact. Vertical RED lines should make it evident that you can clearly “walk out” a regular supraventricular rhythm at a rate just under 100/minute in virtually all leads on this tracing.
  • Note that while we suspect the mechanism of the underlying narrow rhythm in this ECG is sinus (upright P waves are suggested in lead II ) — the amount of artifact prevents clear distinction between a sinus vs junctional rhythm. But we can say with certainty that a regular supraventricular rhythm is present.
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Acknowledgment: — My thanks to MG for his permission allowing me to use this tracing and clinical case.
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NOTE: For additional examples of Artifact — See ECG Blog #44 — Blog #132 — and Blog #139

6 comments:

  1. Though I think it is fairly obvious that those bizarre deflections are trivial artifacts involving patient's arms and legs, the current case is a very instructive lesson.
    In a recent post of an ECG group on internet, wandering baseline was maskerading an important sign for the diagnosis: close scrutinization of all leads AND beats allowed to reach the right diagnosis.
    The lesson here is that it is of paramount importance to distinguish what is real and what is not.
    Ken, thanks for presenting!

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  3. Well written and informative! Thank you for taking the time to do this.

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