1. Analysis of electrocardiogram
5th practice
Medical Informatics Biomedical Signal Processing
TAMUS, Zoltán Ádám

2. The electrocardiogram (ECG)
The electrical manifestation of the contractile activity of the heart
The ECG can be easily recorded with surface electrodes on the limbs or chest (Einthoven’s triangle)
The waveshape is altered by cardiovascular diseases

3. The electrocardiogram (ECG)
Einthoven’s triangle

4. The electrocardiogram (ECG)
The ECG is an electrical signal (function of time)

5. The electrocardiogram (ECG)
The SA node fires

6. The electrocardiogram (ECG)
Slow-moving depolarization (contraction) of the atria
The P wave in ECG mV
60-80 ms

7. The electrocardiogram (ECG)
Propagation delay at atrio-venricular (AV) node
Normally iso-electric segment
PQ segment
60-80 ms

8. The electrocardiogram (ECG)
His bundle, the bundle branches, and the Purkinje system of specialized conduction fibers propagate the stimulus to the ventricles at high rate

9. The electrocardiogram (ECG)
The wave of stimulus spreads rapidly from the apex of the heart upwards
Rapid depolarization (contraction) of ventricles
QRS wave
1 mV
80 ms

10. The electrocardiogram (ECG)
The ventricular muscle cells possess a relatively long action potential ms
Result: iso-electric segment
ST segment ms

11. The electrocardiogram (ECG)
Repolarization (relaxation) of ventricles causes slow T wave mV ms

12. Artifacts in ECG Physiological interference
Respiration, squirms, coughs etc.
Mother’s ECG appearing with the ECG of the fetus
Electromagnetic interference
TV and radiostations, CRTs, computers, fluorescent lamps
Result: noise in the ECG signal

13. Noise in ECG
Signal
Deterministic signal:
the value at a given instance of time may be computed using a closed-form mathematical function of time or
Predicted from a knowledge of a few past values of the signal
Nondeterministic signal (random signal):
That does not meet the conditions of the deterministic signal
The noise may be random, structured (deterministic) and physiological

14. Noise filtering Random noise Reduction: Moving Average (MA) filter
ensemble average: 0
Reduction: Moving Average (MA) filter
general form:
bk:filter coefficients

15. Noise filtering Examples of MA filters von Hann or Hanning filter:
8-point average:

16. Reference
Rangaraj M. Rangayyan: Biomedical Signal Analysis, IEEE Press/Wiley, New York, NY, 2002.

17. Exercises 1. Observation of noisy ECG signal
2. Filtering the noisy ECG signal by MA filter
von Hann or Hanning filter
8-point MA filter
sample files:
software: MS Excel