Delineation of ECG characteristic features using multiresolution wavelet analysis method S. Banerjee, R. Gupta, M. Mitra ⇑ Department of Applied Physics, University of Calcutta, 92, APC Road, Calcutta 700 009, India article info Article history: Received 13 June 2011 Received in revised form 20 October 2011 Accepted 25 October 2011 Available online 9 November 2011 Keywords: ECG fiducial points Discrete wavelet transform Multiresolution analysis Denoising Feature extraction abstract A discrete wavelet transform (DWT) based feature extraction technique in the QT segment of digitized electrocardiograph recordings is proposed. At first, the signal is denoised by decomposing it using DWT technique and discarding the coefficients corresponding to the noise components. A multiresolution approach along with an adaptive thresholding is used for the detection of R-peaks. Then Q, S peak, QRS onset and offset points are iden- tified. Finally, the T wave is detected. By detecting the baseline of the ECG data, height of R, Q, S and T wave are calculated. For R-peak detection, proposed algorithm yields sensitivity and positive predictivity of 99.8% and 99.6% respectively with MIT BIH Arrhythmia data- base, 99.84% and 99.98% respectively with PTB diagnostic ECG database. For time plane fea- tures, an average coefficient of variation of 3.21 is obtained over 150 leads tested from PTB data, each with 10,000 samples. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Electrocardiogram (ECG) is widely used for diagnosing many cardiac diseases, which are one of the prime causes of mortality all over the world. The origin of ECG is the electrical activation of heart muscle cell causing sequence of depolarization and repolarization of its membrane. The electrical pulses generated due to this electrical activation are propagated along the cell fiber and transmitted to adjoining cells. The result is generation of electrical im- pulses, which travels through the cardiac surface. These electrical impulses can be detected by surface electrodes, amplified and displayed as the ECG. From electrical point of view, the heart is situated at the center of the electrical field it generates. The intensity of its electric field dimin- ishes with the distance from its origin. A 12-lead electrode system is used for ECG recording, exploring an overall view of the heart’s electrical activity. ECG waveform consists of five different component waves, namely P, Q, R, S and T wave followed by a conditional U wave. A typical ECG beat is shown in Fig. 1. The durations and intervals of the con- stituent waves and amplitudes of the wave peaks reveal clinically significant information to the cardiologists for diagnosis [1]. Computerized processing of ECG for assisted diagnosis is an established area of biomedical research from long time. Performance of an automatic ECG analyzing system depends upon the reliable and accurate detection of the QRS complex and P and T waves along with the measure- ment of the QT segment. Detection and measurement of characteristic waves are related to diagnosis of various car- diac functions. For example, QRS detection is necessary to determine the heart rate and is used as reference for beat alignment. Likewise, ST segment elevation or depression is related to Myocardial Infarction. The automatic delineation of the ECG is widely studied and algorithms are developed for QRS detection and wave detection [2–4]. A real time QRS detection algorithm, implemented in assembly language is developed by Pan and Tomkins [5]. Some early software based QRS detec- tors are presented [6–8]. ECG signal is normally corrupted with several noises, some of which are of physiological 0263-2241/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.measurement.2011.10.025 ⇑ Corresponding author. E-mail addresses: swatibanerjee29@yahoo.com (S. Banerjee), rgaphy@caluniv.ac.in (R. Gupta), mmitra@ieee.org (M. Mitra). Measurement 45 (2012) 474–487 Contents lists available at SciVerse ScienceDirect Measurement journal homepage: www.elsevier.com/locate/measurement