ARTIFACTS ON ECG RECORDING

ARTIFACTS ON ECG RECORDING

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  1 POWER LINE INTERFERENCE ARTIFACTS INECG RECORDING
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  ARTIFACTS ■ Artifact onthe electrocardiogram can result from a variety of internal and external causes. ■ Artifact and troubleshooting the problem will be straight forward. ■ When artifact mimics ECG abnormalities that can cause problems for patient care. 2
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  BASIC ELECTRONIC RECORDINGSYSTEM 3
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  EFFECTS OF ARTIFACTSON ECG RECORDINGS (OR) POWER LINE INTERFERENCE Power line interference Shifting of the Baseline Muscle Tremor 4
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  Interference from PowerLine ❖ Power line interference is easily recognizable since the interfering voltage in the ECG ❖ This interference may be due to the stray effect of the alternating current on the patient or because of alternating 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. ❖ The most common cause of 50 Hz interference is the disconnected electrode resulting in a very strong disturbing signal. 5
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  ❖ Electromagnetic interferencefrom the power lines also results in poor quality tracings. Electrical equipment such as air-conditioners and X-ray units draw heavy power-line current, which induce 50 Hz signals in the input circuits of ECG machines ❖ This noise is very difficult to remove except in those machines which have very high CMRR. ❖ A practical solution to minimize this problem is physical separation between the interference causing sources and the patient. ■ The noise can be reduced by partially shielding the patient 6
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  a) ECG recordingwith regular spreading of the curve with super-imposed 50Hz power line interference signals. b)Recording with irregular trembling of the ECG trace with wandering of the base line but otherwise normal ECG trace. c) ECG trace without wandering of the baseline. 7
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  Problem solved by: ■Use of transient suppressor in the mains lead of the machines helps to solve this problem. 8
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  Shifting of theBaseline ❖ A wandering baseline [Fig. (b)] 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. 9
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  Muscle Tremor ❖ Irregulartrembling of the ECG trace [Fig.(c)], 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 aerification of the softener. 10
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  Problem solved by: ❖Some manufacturers supply a patient-cable made of silicon-rubber, which provides better elasticity over long periods. 11
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