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Analysis of electrocardiogram

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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

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