EKG artifacts

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Editor-in-Chief: Santosh Patel M.D., FRCA [1]; Associate Editor-In-Chief: Kashish Goel, M.D.; Cafer Zorkun, M.D., Ph.D. [2]

Overview

Electrocardiograph (EKG) artifacts are defined as EKG abnormalities, which are a measurement of cardiac potentials on the body surface and are not related to electrical activity of the heart. As a result of artifacts, normal components of the EKG can be distorted. It is very important to recognize these artifacts, otherwise they can lead to unnecessary testing and therapeutic interventions. In this chapter, we will present the common causes and ways to characterize EKG artifacts.

Causes

EKG artifacts can be generated by internal and external causes.

Internal

These are physiological causes that could be due to:

• Patient's motion: Does not allow electronic filtration (large swings, usually by epidermal stretching).
  • Tremors and shivering cause motion artifacts.
  • Simple movements such as brushing and combing the hair can produce EKG disturbances during ambulatory EKG monitoring.

• Muscular activity: Allows electronic filtration (small spikes).

External

These are non-physiological causes associated with other electrical devices attached to or implanted (e.g. deep brain stimulator) in the body and includes the following:

• Electromagnetic interference:
  • Power line electrical disturbances/ Light fixtures
  • Electrocautery
  • Electrical devices in the room
  • Radiofrequency based commercial (e.g. mobile phones) products

• Cable and electrode malfunction:
  • Insufficient electrode gel
  • Misplaced leads
  • Inappropriate filter settings
  • Broken wires
  • Loose connections
  • Accumulation of static energy

• Medical equipments: In operation theatres and intensive care unit various equipments can affect EKG monitoring system (e.g. electrodes, leads, amplifier, filters).

Medical equipment related EKG artifacts

Type of equipment	Artifact
IVAC intravenous infusion controller	Atrial or ventricular extrasystoles, pseudowaves (QRS)
Cardiopulmonary bypass pump	Uninterpretable tracing, non-specific
Pressure-controlled irrigation pump	Atrial flutter
COBE Prisma System for continuous venovenous hemofiltration	Atrial flutter
Flexible bronchoscope	Atrial fibrillation
Deep brain stimulator	Uninterpretable tracing
Straight shot microdebrider (nasal endoscopy)	Ventricular tachycardia
Intra-aortic balloon pump	Pseudowaves (P), premature atrial contraction
Somatosensory evoked potential monitoring units	Supraventricular tachycardia
High-frequency oscillatory ventilation	Atrial flutter, atrial fibrillation, ventricular tachycardia
Intraoperative high-field MRI	Ventricular tachycardia, ventricular fibrillation, non-specific
Transcutaneous electrical nerve stimulator	Spikes, runaway pacemaker, ventricular fibrillation, non-specific
Peripheral nerve stimulator	Spikes, loss of pacemaker spikes

The table includes data from references

Identification

Artifacts can distort individual or all components (P, QRS, T waves and PR and ST segments) on the EKG. Most of the time, they are easily identifiable and neglected as they do not resemble any specific pattern. It is important to differentiate these artifactual changes from genuine changes to prevent misdiagnosis. If ST segments are affected by artifacts, either ST segment depression or elevation can occur on the EKG. These changes can be misinterpreted as myocardial ischemia or infarction.

Differentiating an Artifact from Ventricular tachycardia

On occasions, changes may mimic specific arrhythmia like ventricular tachycardia and atrial flutter or fibrillation. It is important to differentiate these, as misdiagnosis can lead to inadvertent use of medications and procedures in such a patient.

• Characteristics that can help in differentiate an artifact from ventricular tachycardia include:
  • Absence of hemodynamic deterioration during the event.
  • Normal QRS complexes within the artifact.
  • An unstable baseline on the EKG before the event, after the event, or both.
  • Association with bodily movement.

• Huang et al also described 3 signs that may help in differentiating a tremor-induced pseudo-ventricular tachycardia from true ventricular tachycardia. Presence of any of these signs is suggestive of pseudo-ventricular tachycardia:
  • "Sinus" sign: One of the frontal leads (I, II and III) may present with sinus rhythm showing normal P, QRS, and T waves. The reason is that one of the upper limbs may be free off tremor.
  • "Spike" sign: Presence of regular or irregular tiny spikes among wide-QRS complexes.
  • "Notch" sign: Notches superimposed in the wide-QRS-like complex artifact, coinciding with the cycle length when sinus rhythm was recorded.

Electrode misplacement

Electrode misplacements are a common artifact that can mimic life-threatening arrhythmias. Early identification and replacement of electrodes can help in avoiding unnecessary therapies. An algorithm has been described previously, which may help in recognizing these artifacts.

Table: REVERSE mnemonic: Approach to EKG artifacts

	EKG findings	Explanation
R	R wave is positive in lead aVR (P wave also positive)	Reversal of left arm and right arm electrodes
E	Extreme axis deviation: QRS axis between -9- and +180	Reversal of left arm and right arm electrodes
V	Very low (<0.1 mV) voltage in an isolated limb lead (isolated "flat" line)	Reversal of right leg and left arm or right arm electrodes
E	Exchanges amplitude of the P waves (P wave in lead I > lead II)	Reversal of left arm and left leg electrodes
R	R wave abnormal progression in precordial lead (pre-dominal R in V1; pre-dominant S in V6)	Reversal of precordial electrodes (V1 through V6)
S	Suspect dextrocardia (negative P waves in lead I)	Reversal of left arm and right arm electrodes
E	Eliminate noise and interference (artifact mimicking tachycardias or ST-T changes

Consequences

Apart from the poor quality of EKG, artifacts can cause serious consequences particularly when they mimic like genuine changes. If EKG artifacts are not recognized by physician, anesthesiologist or intensivist unneccasry diagnostic and therapeutic measures could be taken. Such actions may subject patients to invasive investigations or they may receive unnecessary medications like antiarrythmics.

Correction

Attention to basic principles such as proper electrodes placement and lead connections is required during EKG measurement. Well designed and maintained EKG measurement devices can withstand routine internal or external electrical and motion-related disturbances. However, it is not always possible to eliminate artifacts completely. It is essential that physicians keep high vigilance and interpret EKG keeping EKG artifacts in differential diagnosis list.

Examples of Artifacts

The gallery of images below shows a variety of EKG artifacts that are due to tremor, movement, movement disorders and electrical interference. These artifacts should not be confused with an abnormality in the patient's electrocardiogram. Atrial fibrillation can be confused with these artifacts.

• 

  Movement artifacts

• 

  Increasing movement artifacts in a Parkinson patient.

• 

  Baseline drift. The amplifier in the ECG machine has to re-find the 'mean'. This often occurs right after lead connection and after electric cardioversion.

• 

  Cardioversion from atrial fibrillation to sinus rhythm, with clear baseline drift.

• 

  Electrical interference from a nearby electrical appliance. A typical example is a 100 Hz background distortion from fluorescent lights. Not to be confused with atrial fibrillation.

• 

  Another example of an artifact caused by an electrical appliance. The patients rhythm is regular. This strip shows 10 QRS complexes.

Video explaining ECG artifacts

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References

1. Einthoven W. Le telecardiogramme. Arch Int de Physiol 1906;4:132-164
2. Marquez PMID 12177632
3. Hurst PMID 9799216
4. Kligfield PMID 17322457
5. Patel S, Souter M: PMID 18156892
6. Patel S: PMID 19344913
7. Patel S: PMID 16632773
8. Patel S: PMID 19563573
9. Patel S, Souter M: PMID 18648245
10. Patel S: http://www.springerlink.com/content/w054881370x61802/

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