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Determining limits of P and T wave in ECG waveform

Determining limits of P and T wave in ECG waveform. By Ashwin Panchbhai Sudheer Poojary. Objective. Study/Implement an adaptive algorithm to determine limits of P and T wave. The following criteria dictate the use of an adaptive algorithm Oscillations in the baseline of the typical ECG.

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Determining limits of P and T wave in ECG waveform

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  1. Determining limits of P and T wave in ECG waveform By Ashwin Panchbhai Sudheer Poojary

  2. Objective • Study/Implement an adaptive algorithm to determine limits of P and T wave. • The following criteria dictate the use of an adaptive algorithm • Oscillations in the baseline of the typical ECG. • Adoption of different criteria among cardiologists.

  3. Approach: • In the filtered ECG, the end of T wave is near to the minimum • Using Adaptive filtering, this minimum is shifted to the location of end of the T wave.

  4. The transfer function for the filter is given by E(z)/P(z) = (1 + z-1)/(1 – (1 – m).z-1) where m is the adaptation constant. • The initial value of m is determined by the cardiologist’s criterion. • Using this initial value, filtering is carried out which gives new value of m .

  5. Contd… • After second filtering, the points where the derivative of error signal is zero gives the desired limits for T wave. • Assumptions made : • The sampling rate is large enough so that m is sufficiently small. • In the segments from peak of T wave to the limits of T wave, the derivatives of close samples are similar.

  6. Mathematical development e(n) – b.e(n-1) = ecg(n)–ecg(n-1) e’(n) = (b-1).e(n-1) + d(n) d(n) = derivative of the ecg signal e’(n) is equated to 0 to give minimum which gives m = d(n)/e(n-1) From the recursive equation for d(n) we get the time constant for the exponential averaging as t = 1 / m

  7. contd … • In the segments from the peak of T to the limits of the wave, the derivative of ecg signal (close symbols) are similar. • d(n) ≈ d(n-r-1) 0≤r≤N • Hence we can have an approximation of m by making t = N • Hence first approximation is- m ≈ 1/N • The cardiologist marks the limit of T wave which is used in determining N.

  8. References • Application of Adaptive Signal Processing for Determining the Limits of P and T Waves in an ECG Emilio Soria-Olivas, Marcelino Martinez-Sober,Javier Calpe-Maravilla,Juan Francisco Guerrero-Martınez, Javier Chorro-Gasco, and Jose Espı-Lopez.

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