Effects of Artefacts on ECG Recording Abnormal patterns of ECG may be due to pathological states or on occasion they may be due to artefacts. To diagnose the presence of undesirable artefacts on the ECG trace, a few recordings are illustrated below: فقط التأثيرات نقاط تعداد مع مثالك Interference from the Power Line: Power line interference is easily recognizable since the interfering voltage in the ECG would have a frequency of 50 Hz. This interference may be due to the stray effect of the alternating current on the patient or because of alternating (b) current fields due to loops in the patient cable. Other causes of interference are loose contacts on the patient cable as well as dirty electrodes. When the machine or the patient is not properly grounded, power line interference may even completely obscure the ECG waveform. ECG recording with regular spreading of the curve with super imposed 50 Hz power line interference signals. Recording with irregular trembling of the ECG trace without wandering of the base line but otherwise normal ECG trace. This noise is very difficult to remove except in those machines which have very high CMRR. The noise can be reduced by partially shielding the patient by means of the bed springs. Connection of the springs to the instrument case helps to compensate for a poor CMRR. 30 Assist Lec: Athra'a Sabeeh 1st Semester 2023-2 Electromagnetic interference from the power lines also results in poor quality tracings. Electrical equipment such as air-conditioners. elevators and X-ray units draw heavy powerline current, which induce 50 Hz signals in the input circuits of ECG machines. Due to unbalanced linkages, common mode rejection circuits almost prove ineffective against them. A practical solution to minimize this problem is physical separation between the interference causing sources and the patient. Shifting of the Baseline A wandering baseline but otherwise normal ECG trace is usually due to the movement of the patient or electrodes. The baseline shift can be eliminated by ensuring that the patient lies relaxed and the electrodes are properly attached. Baseline wander is usually observed immediately after application of
Effects of Artefacts on ECG Recording Abnormal patterns of ECG may be due to pathological states or on occasion they may be due to artefacts. To diagnose the presence of undesirable artefacts on the ECG trace, a few recordings are illustrated below: فقط التأثيرات نقاط تعداد مع مثالك Interference from the Power Line: Power line interference is easily recognizable since the interfering voltage in the ECG would have a frequency of 50 Hz. This interference may be due to the stray effect of the alternating current on the patient or because of alternating (b) current fields due to loops in the patient cable. Other causes of interference are loose contacts on the patient cable as well as dirty electrodes. When the machine or the patient is not properly grounded, power line interference may even completely obscure the ECG waveform. ECG recording with regular spreading of the curve with super imposed 50 Hz power line interference signals. Recording with irregular trembling of the ECG trace without wandering of the base line but otherwise normal ECG trace. This noise is very difficult to remove except in those machines which have very high CMRR. The noise can be reduced by partially shielding the patient by means of the bed springs. Connection of the springs to the instrument case helps to compensate for a poor CMRR. 30 Assist Lec: Athra'a Sabeeh 1st Semester 2023-2 Electromagnetic interference from the power lines also results in poor quality tracings. Electrical equipment such as air-conditioners. elevators and X-ray units draw heavy powerline current, which induce 50 Hz signals in the input circuits of ECG machines. Due to unbalanced linkages, common mode rejection circuits almost prove ineffective against them. A practical solution to minimize this problem is physical separation between the interference causing sources and the patient. Shifting of the Baseline A wandering baseline but otherwise normal ECG trace is usually due to the movement of the patient or electrodes. The baseline shift can be eliminated by ensuring that the patient lies relaxed and the electrodes are properly attached. Baseline wander is usually observed immediately after application of
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Transcribed Image Text:Effects of Artefacts on ECG Recording
Abnormal patterns of ECG may be due to pathological states or on
occasion they may be due to artefacts. To diagnose the presence of
undesirable artefacts on the ECG trace, a few recordings are illustrated
below:
فقط التأثيرات نقاط تعداد مع مثالك
Interference from the Power Line:
Power line interference is easily recognizable since the interfering voltage in
the ECG would have a frequency of 50 Hz. This interference may be due to the
stray effect of the alternating current on the patient or because of alternating b
current fields due to loops in the patient cable. Other causes of interference are
loose contacts on the patient cable as well as dirty electrodes. When the
machine or the patient is not properly grounded, power line interference may
even completely obscure the ECG waveform. ECG recording with regular
spreading of the curve with super imposed 50 Hz power line interference
signals. Recording with irregular trembling of the ECG trace without
wandering of the base line but otherwise normal ECG trace. This noise is very
difficult to remove except in those machines which have very high CMRR.
The noise can be reduced by partially shielding the patient by means of the bed
springs. Connection of the springs to the instrument case helps to compensate
for a poor CMRR.
30 Assist Lec: Athra'a Sabeeh
(a)
(c)
31 Assist Lec: Athra'a Sabeeh
CANTAR
1st Semester 2023-2024
Electromagnetic interference
from the power lines also results in poor quality tracings. Electrical equipment such as air-conditioners,
elevators and X-ray units draw heavy powerline current, which induce 50 Hz signals in the input circuits
of ECG machines. Due to unbalanced linkages, common mode rejection circuits almost prove ineffective
against them. A practical solution to minimize this problem is physical separation between the interference
causing sources and the patient.
Shifting of the Baseline
A wandering baseline but otherwise normal ECG trace is usually due to the movement of the patient
or electrodes. The baseline shift can be eliminated by ensuring that the patient lies relaxed and the
electrodes are properly attached. Baseline wander is usually observed immediately after application of
the electrodes. It is due to a relatively slow establishment of electrochemical equilibrium at the
electrode-skin interface. This can be minimized by selecting the proper electrode material, which will
reach equilibrium quickly with a good electrode jelly.
1st Semester 2023-2024
Muscle Tremor
Irregular trembling of the ECG trace, without wandering of the baseline occurs when the patient is not
relaxed or is cold. It is generally found in the case of older patients. Muscle tremor signals are especially
bothersome on limb leads when a patient moves or the muscles are stretched. Therefore, for long-term
monitoring, the electrodes are applied on the chest and not on the limbs. For normal routine ECG
recordings, the patient must be advised to get warm and to relax so that muscle tremor from shivering or
tension is eliminated. The most critical component of the ECG recorder is the patient cable. The
conventional PVC insulation gets degraded and becomes rigid and breakable because of the antifiction of
the softener. Some manufacturers supply a patient-cable made of silicon-rubber, which provides better
elasticity over long periods.
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