Artifacts

Question 1

muscle artifact

Answer 1

• Frequencies from 1 to 35Hz, amplitude 0.03 to 5mV
• Muscle tremors/shiver: irregular artifact from rapid stretching of the skin
  o Fine, irregular oscillations of isoelectric line
  o ↑ w inspiration, ↓ w expiration
  o Periodic pattern
• Movement of somatic muscles/twitch: f = 1-15Hz, amp = 0.1-0.5mV
  o Sporadic character → distort isoelectric line
  o Can mimic P waves → pseudo atrial dissociation
  o From somatic muscle mvt, loss of contact of electrodes, diaphragm
   If due to respiratory artifact: P’ follow respiratory rate
   Rapid superficial respiratory mvt: fluctuations of isoelectric line can look like Afib/flutter
• Motion form large group of muscle: high amplitude deflections, can mimic bizarre QRS
  o Tail wagging: can mimic Vtach
• Synchronous diaphragmatic flutter (thumbs)
  o Hiccup like contraction of Eq diaphragm
   Dehydration, electrolyte depletion (Ca2+) in Eq performing endurance races
   Cantharidin ingestion: blister beetles and insects harvested I alfalfa hy
• Eliminate by activation of low pass filters, reposition electrodes, avoid standing, calm animal, extend limbs

Question 2

Breathing/purring artifacts

Answer 2

• Low frequency artifacts
  o Wandering baseline → rhythmic fluctuations of isoelectric line
• Eliminate by activating high pass filter with cutoff of 0.5Hz

Question 3

Electrical artifacts

Answer 3

• Electrical interference: alternating current poser source
  o Regular sinusoidal waveze at f = 60Hz (USA) or 50Hz (Europe)
  o From electromagnetic field in the room, poor contact of electrodes/skin, excessive alcohol (bridge limbs/table)
  o Rapid, regular, low voltage undulations
• Eliminate by activating notch filter, grounding of electrical system, good electrode-skin contact, gloves for holding the animal
  o Setting diagnostic mode to 0.05-40Hz

Question 4

Errors in electrode placement

Answer 4

• Change in polarity of ECG waves
• P waves with reversed polarity in leads I and aVL suggest correct placement or dextrocardia
• Loose lead artifact

Question 5

Pacemaker artifact: unipolar pacing

Answer 5

o cathode at the tip (negative pole) and anode

Unipolar: 1 electrode in contact with heart → anode is the generator

larger pacing artifact sine current has to travel large area from lead to generator
o More susceptible to oversensing and inhibition by skeletal muscle potential
o Can stimulate local skeletal muscle where generator is implanted
 Pectoralis muscle
o Insulated side of generator in contact with tissue for pacing

Question 6

Pacemaker artifact: bipolar pacing

Answer 6

Stimulus can be difficult to see on ECG → small distance btw 2 poles

Question 7

Transcutaneous pacing

Answer 7

o Pseudo QRS complexes after pacing spike → false capture
o Pacing spike = current about to pass btw pacing pads → followed by short blanking period and stimulus
 If ECG catches the pacing current → pseudo QRS

Question 8

Fetal ECG

Answer 8

• Fetal ECG can be recorded with
  o Fetal scalp electrode (invasive)
  o Electrodes on abdomen (non invasive)
   Smaller fetal beats with broadband noise
   Larger amplitude artifacts (transient oscillations) → mother’s heart