A Review on FPGA-Based Digital Filters for De-Noising ECG Signal

Overview Of Ecg

Electrocardiogram (ECG) signal is the most important electrical signal in the field of medical science which has a great need to be processed before further analysis for diagnostic and research purpose. An electrocardiogram is a display of the electrical activity of the heart (cardiac) muscle as obtained from the surface of the skin. Specific feature extraction from an ECG with precise computation and interpretation is always a challenging task. For the correct diagnosis of the heart, the ECG signal should be free from the noise/artifacts. It is necessary to remove these noises/artifacts from the signal for further processing and analysis.

Normally, the frequency range of an ECG signal is of 0.05–100 Hz and its amplitude ranges from 1–10 mV. The ECG signal is characterized by five peaks and valleys labelled by the letters P, Q, R, S, T as shown in Figure 1 and in some cases (especially in infants) another peak called U, may also be seen. The performance of ECG analyzing system depends mainly on the accurate and reliable detection of the QRS complex, as well as T and P waves. The P-wave represents the activation of the upper chambers of the heart, the atria, while the QRS complex and T-wave represent the excitation of the ventricles or the lower chamber of the heart. The detection of the QRS complex is the most important task in automatic ECG signal analysis. Once the QRS complex has been identified a more detailed examination of ECG signal including the heart rate, the ST segment etc. can be performed.

Figure 1.

Typical ECG signal

The electrical activity of the heart is generally sensed by monitoring electrodes placed on the skin surface. Unfortunately, other artifactual signals of similar frequency and often larger amplitude reach the skin surface and mix with the ECG signals. The challenge lies in the removal of these frequencies from the ECG signal for its usefulness.

ECG signals are often contaminated by noise from diverse resources which degrade ECG signals significantly. The ECG signal need to be noise free or low noisy (Zaman et al. 2012). As a clean ECG signal gives full detailed information about the electrophysiology of the heart diseases and ischemic changes that may occur. ECG signal contains high and low frequency noise components that must be filtered before further analysis (Tawfik and Kamal 2010).

Typical examples of noise interference in an ECG signal are:

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  Power line interference

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  Electrode contact noise.

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  Motion artifacts.

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  Muscle contraction.

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  Base line drift.

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  Instrumentation noise generated by electronic devices.

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  Electrosurgical noise.