we discuss about ecg signal,types of noises, why only wavelet, what is wavelet etc

1. BY:
U.RESHMI

2. Objectives :
• To explore ecg signal processing
• To perform denoising of the ecg signal using wavelet
transformations
• Verifying the results using MATLAB.

3. Electrocardiograph :
• ECG (Electrocardiography) is graphical presentation of electrical
activity of heart in reference to time.
• An ECG signal is due to ionic current flow causing the cardiac
fibers to contract and relax, subsequently, generating a time
variant periodic signal.
• The ECG signal allows for the analysis of anatomic and
physiologic aspects of the whole cardiac muscle.
• The normal heart rate value is 60-100 beats per minute.

4. Components in ECG wave :
ECG consists of P-wave, QRS-complex, the
T-wave .
P-wave-depolarization of atria.
QRS-complex-depolarization of ventricles.
T-wave-repolarization of ventricles.
Repolarization of the atria not visible.
QRS complex detection-most important task in
automatic ECG analysis.

5. ECG signal often gets contaminated
by various types of noise as:
1. Baseline wandering - caused due to respiration .
2. Electromyogram noise (EMG) -If the electrodes are left
loose then it leads to electrode contact noise.
3. Muscle contraction- artifactual potentials is generated by
muscle contraction.
4. Power line interference -electromagnetic field generated
inside the device leads to generation of harmonics .

6. Discrete Wavelet transform :
• Wavelet transform provides good time resolution and poor
frequency resolution at high frequencies and good frequency
resolution and poor time resolution at low frequencies
• ECG signal is not strictly a periodic signal but it differs in both
period and amplitude level at each beat.
• Thus wavelet transform can be very useful approach for analysis
the ECG signal.

7. Wavelet Thresholding :
 Assume that small coefficients are due to noise and can be set to zero
 Signal is stored in a few large coefficients
 Soft thresholding by which all the coefficients below are discarded
and all the coefficients above a fixed threshold T are shrunk.
 The soft threshold signal is s(x)= (/x/-T) if /x/>T and is 0 if /x/<T.

8. Simple de-noising algorithms that
use DWT consist of three steps:
• WT is adopted to decompose the noisy signal and get the wavelet coefficients.
• These wavelet coefficients are denoised with wavelet soft threshold.
• Inverse transform is applied to the modified coefficients and get denoised signal.

9. Why only wavelet ?
• We also have various enhancement techniques like sgolay
filter, median filter, adaptive methods etc.
• The wavelet Transform denoising is much better than
filters.The reason is that spectrum of the noise interfere with
spectrum of the ECG signal.
• By wavelet, filtering are filtrated some frequency levels
independent each other, whereas by classical filtration isn’t
possible to separate the signal and noise.
• Therefore using wavelet denoising more useful then filtering.

10. Calculation of SNR and PRD -
SNR : (Signal to noise ratio)
PRD : (Percentage root mean square difference)

11. Expected output :
Graph showing original and enhanced ECG signal
Original signal
Enhanced signal

12. Conclusion :
1. We have analyzed a very important signal, the electrocardiography by
applying an advanced filtering tool called discrete wavelet transform
2. From simulation result we can observe that the wavelet transform can remove
the noise effectively and improve the PSNR and low PRD
3. The reason why DWT is ,spectrum of the noise interfere with spectrum of the
ECG signal. By wavelet filtering are filtrated some frequency levels
independent each other, whereas by classical filtration isn’t possible to
separate the signal and noise.