Instrumentation & Measurement Magazine 24-2 - 39

Table 1 - A list of ECG contaminants,
organized by contaminant type
Type

Contaminant

Measurement

Motion artifact
Skin stretch reflex
Baseline wandering
Poor electrode contact

Instrumentation

Amplifier saturation
ADC over-ranging
Quantization noise

Interference

Power line
Electromagnetic
Undesired physiological signals

Power line interference, caused by the coupling of the
power lines with the instrumentation, electrodes, or the human body, introduces 50 or 60 Hz frequency components
and its harmonics in the ECG. Electromagnetic interference is
generally high-frequency noise injected into ECG signal due
to radiofrequency transmitters (e.g., handheld two-way radios) and nearby devices with rapidly switched electrical and
magnetic gradients (e.g., electrocautery devices, MRI). Physiological signal interference is caused by biosignals other than
the desired ECG. For example, when recording the ECG with
chest electrodes, EMG signals from respiratory muscles would
also be recorded.

Impact of Contaminants on Applications of ECG
Contaminants can be detrimental to the analysis of biosignals,
leading to misinformation, including misdiagnoses and false
alarms. Incorrect disease diagnoses can result in additional
medical tests or unnecessary medical interventions, increasing healthcare costs and patient risks needlessly. False alarms
can result in alarm fatigue and desensitization of healthcare
workers and have been identified as one of the top health technology hazards [13].
A study conducted at The Ottawa Hospital demonstrated
that remote, continuous postoperative ECG monitoring could
enable the real-time detection of myocardial ischemia, providing the opportunity for early intervention to avoid myocardial
infarctions and save patient lives [14]. However, with ambulatory monitoring, motion artifact contaminated the ECG
resulting in many false alarms (>140 false alarms in two days
for one patient) [1], [15]. A study conducted in our lab showed
that the detection of atrial fibrillation (AF) in ECG could be
impeded by the presence of motion artifacts [2]. An ECG segment that was contaminated with motion artifact at an SNR of
15 dB had AF detection precision and recall of over 85%. As the
SNR was decreased to -20 dB, the precision and recall fell below 30%. In another study on ECG based biometric systems,
we found that the ECG collected during ambulation resulted
in false identification nearly half of the time [16]. In [17], the
authors reported that of the 4050 cardiac arrhythmia alarms
found for the Multiparameter Intelligent Monitoring in Intensive Care (MIMIC II) database [18], 1840 were false alarms.

Fig. 3. Examples of ECG contaminants. (a) No contaminants; (b) Baseline wandering; (c) Quantization noise; (d) Motion artifact; (e) Power line interference; (f)
Amplifier saturation; (g) Poor electrode contact; and (h) EMG interference.
April 2021	

IEEE Instrumentation & Measurement Magazine	39



Instrumentation & Measurement Magazine 24-2

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