Analysis of electrocardiogram 5th practice Medical Informatics Biomedical Signal Processing TAMUS, Zoltán Ádám zoltanadam_tamus@yahoo.com

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

The electrocardiogram (ECG) Einthoven’s triangle

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

The electrocardiogram (ECG) The SA node fires

The electrocardiogram (ECG) Slow-moving depolarization (contraction) of the atria The P wave in ECG 0.1-0.2 mV 60-80 ms

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

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

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

The electrocardiogram (ECG) The ventricular muscle cells possess a relatively long action potential 300-350 ms Result: iso-electric segment ST segment 100-120 ms

The electrocardiogram (ECG) Repolarization (relaxation) of ventricles causes slow T wave 0.1-0.3 mV 120-160 ms

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

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

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

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

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

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: http://zoltanadam.fw.hu software: MS Excel