The document discusses the electrocardiogram (ECG), which measures and records the electrical activity of the heart. An ECG represents the atrial and ventricular depolarization and repolarization that occurs with each heartbeat. ECGs are obtained via electrodes placed on the skin and measure the potential differences. The ECG signal is analyzed in both the time and frequency domains to study cardiac features. A typical ECG consists of P, Q, R, S, and T waves that represent different electrical events in the heart. Digital signal processing is used to filter noise and detect the heart rate from the ECG signal.

1. ECG
BY:
Kira n R (1 RV1 0 EE0 2 6 )
Sunil Fe rna nd e s (1 RV1 0 EE5 2 )
Sura j K ( 1 RV1 0 EE0 5 3 )

2. Introduction


The electrocardiogram (ECG) is a time-varying signal
reflecting the ionic current flow which causes the cardiac
fibers to contract and subsequently relax. The surface
ECG is obtained by recording the potential difference
between two electrodes placed on the surface of the
skin. A single normal cycle of the ECG represents the
successive atrial depolarisation/repolarisation and
ventricular depolarisation/repolarisation which occurs
with every heart beat.
Simply put, the ECG (EKG) is a device that measures
and records the electrical activity of the heart from
electrodes placed on the skin in specific locations

3. Basic Working




The ECG is nothing but the recording of the hearts electrical activity.
The deviations in the normal electrical patterns indicate various
cardiac disorders. Cardiac cells, in the normal state are electrically
polarized. Their inner sides are negatively charged relative to their
outer sides.
These cardiac cells can lose their normal negativity in a process
called depolarization, which is the fundamental electrical activity of
the heart.
This depolarization is propagated from cell to cell, producing a wave
of depolarization that can be transmitted across the entire heart. This
wave of depolarization produces a flow of electric current and it can
be detected by keeping the electrodes on the surface of the body.
Once the depolarization is complete, the cardiac cells are able to
restore their normal polarity by a process called re-polarization.

4. •
•
•
The earlier method of ECG signal analysis was
based on time domain approach
But this is not always sufficient to study all the
features of ECG signals. So, the frequency
domain analysis is made use of
To accomplish this, FFT (Fast Fourier
Transform) technique is applied.

5. Measuring ECG

ECG commonly measured via 12
specifically placed leads

6. Typical ECG

A typical ECG period consists of P,Q,R,S,T and
U waves

7. P,Q,R,S,T Theory
•ECG is composed of 5 waves - P, Q, R, S and T. This signal could
be measured by electrodes from human body in typical
engagement.
•Signals from these electrodes are brought to simple electrical
circuits with amplifiers and analogue – digital converters.

8. ECG Waves
P wave: the sequential
activation
(depolarization) of the
right and left atria
 QRS comples: right and
left ventricular
depolarization
 T wave: ventricular
repolarization
 U wave: origin not clear,
probably
”afterdepolarizations” in
the ventrices


9. ECG Example

16. Elements of the ECG:
• P wave
• Depolarization
of both atria;
• Relationship between P and QRS helps distinguish
various cardiac arrhythmias
• Shape and duration of P may indicate atrial
enlargement

17. QRS complex:
• Represents ventricular depolarization
• Larger than P wave because of greater muscle mass of ventricles
• Normal duration = 0.08-0.12 seconds
• Its duration, amplitude, and morphology are useful in diagnosing cardiac
arrhythmias, ventricular hypertrophy, MI, electrolyte derangement, etc.
• Q wave greater than 1/3 the height of the R wave, greater than 0.04 sec
are abnormal and may represent MI

18. PR interval
• From onset of P wave to onset of QRS
• Normal duration = 0.12-2.0 sec (120-200 ms) (3-4
horizontal boxes)
• Represents atria to ventricular conduction time
(through His bundle)
• Prolonged PR interval may indicate a 1st degree
heart block

19. ST segment:
• Connects the QRS complex and T wave
• Duration of 0.08-0.12 sec (80-120 ms)
T wave:
• Represents repolarization or recovery of ventricles
• Interval from beginning of QRS to apex of T is referred to as the
absolute refractory period
QT Interval:
• Measured from beginning of QRS to the end of the T wave
• Normal QT is usually about 0.40 sec
• QT interval varies based on heart rate

20. Need for using DSP




A number of emerging medical applications not only
electrocardiography (ECG), but also digital stethoscope,
and pulse oximeters require DSP processing
performance at very low power.
The main problem of digitalized signal is interference
with other noisy signals like power supply network 50 Hz
frequency and breathing muscle artefacts.
These noisy elements have to be removed before the
signal is used for next data processing like heart rate
frequency detection.
Digital filters and signal processing should be designed
very effective for real-time applications in embedded
devices.

21. Steps Involved

Signal acquisition : ECG signal for digital signal
processing and heart rate calculation is acquired by a
measurement card of known sampling frequency.
Analogue signal pre-processing is done by a simple
amplifier circuit designated for ECG signal measurement.
Raw signal acquired by
measuring card with
simple ECG amplifier
circuit.

22. 
Digital signal processing with digital filters: In this part
there is described noise elements filtering and baseline
wander elimination with digital filters. The main noise
elements are power supply network 50 Hz frequency and
breathing muscle movements.

23. Filtered Waveforms
Signal after network 50 Hz and
baseline wander filtering..
Energy signal after R-peaks filtering.

24. Heart rate detection algorithms:
Two Types – 1 ) Sta tis tic a l Co m p uting


2 ) Diffe re ntia l Co m p uting
These algorithms compute heart rate
frequency from the signal energy.
A c o rre la tio n m e tho d can be used because the ECG
uto
signal is quasi-periodical. Matlab provides a very simple
way of using autocorrelation method in signal processing
which is very useful for this purpose.
The second algorithm aims at detecting heart rate as a
difference between R waves in ECG. These waves are
filtrated by band pass filters firstly and then the signal
energy is computed. The wave’s peaks are detected by
peak detector or s ig na l thre s ho ld ing .

25. [1] Autocorrelation of energy signal
Autocorrelation function of signal energy

26. [2] Thresholding of energy signal

27. Which method to adopt?


From the Figures we can see that the differential computing
methods yield better results than statistical computing method
in a way that they adapt well to real-time processing
simulation.
The main problem of autocorrelation function algorithm is that
the quality of signal is under par and fluctuates for fast signal
changes.

28. More about Digital Signal
Processors


Texas Instruments [TI] is a pioneer producer of DSPs.
The TMS320C5515 is the most widely used DSP in
Electro-Cardiograms owing to its good performance and
low power consumption.
The TM 320C5515 Digital signal processor (DS ) board
S
P

29. DSP Software Architecture

30. Front end Architecture

31. Diseases generally diagnosed using
ECG
•
Ischemic Heart Disease
•
AV node blocks Detected on ECG
•
Arrhythmias Detected on ECG
•
Fibrillation Detected on ECG

32. • www.ecglibrary.com/
• library.med.utah.edu/ecg/
• dsp.ti.com

33. 