%0 Journal Article
%T A Method for Ventricular Late Potentials Detection Using Time-Frequency Representation and Wavelet Denoising
%A Matteo Gadaleta
%A Agostino Giorgio
%J ISRN Cardiology
%D 2012
%R 10.5402/2012/258769
%X This study proposes a method for ventricular late potentials (VLPs) detection using time-frequency representation and wavelet denoising in high-resolution electrocardiography (HRECG). The analysis is performed both with the signal averaged electrocardiography (SAECG) and in real time. A comparison between the temporal and the time-frequency analysis is also reported. In the first analysis the standard parameters QRSd, LAS40, and RMS40 were used; in the second normalized energy in time-frequency domain was calculated. The algorithm was tested adding artificial VLPs to real ECGs. 1. Introduction The ventricular late potentials (VLP) are high-frequency (in relation to the bandwidth of the electrocardiographic signal) and very-low-intensity signals. The presence of VLPs in the electrocardiographic signal has been associated with damages in the ventricular myocardial tissues. The necrosis or ischemic death of myocardial cells causes the formation of high-resistivity areas, where the propagation of cardiac action potential is delayed. This phenomenon affects the electrocardiographic signal with the presence of electrical activity, although of low intensity, between the end of the QRS complex and the initial part of the ST segment, where it should not be (Figure 1) [1]. Figure 1: Schematic ECG without (a) and with very exalted VLPs (b). Some characteristic points are also marked. VLPs are localized at the end of QRS complex and in the initial part of the ST segment. Their intensity is at least two orders of magnitude smaller than the electrocardiographic signal, so they are usually ¡°hidden¡± below the noise produced by the acquisition hardware and the electrical activity not related to the heart. For these reasons VLPs are not easily visible on the ECG. Several statistical studies demonstrated a correlation between the presence of VLPs and the possibility of sudden cardiac death due to arrhythmia, often tachycardia. Patients with previous ischemic events are the most at risk. A correct VLPs detection makes the prevention of this serious malignant arrhythmias possible. A classic electrocardiographic signal has amplitude of the order of a few mV and it contains most of the information at frequencies below 100£¿Hz. VLPs, if present, are considered nonstationary and non-Gaussian signals with an amplitude between 1 and 20£¿¦ÌV. Table 1 summarizes the main features of the VLP. Table 1: Characteristics of VLPs. The low-amplitude and high-frequency dispersion makes VLPs detection very difficult, often the signal is dominated by the noise. It is therefore necessary to
%U http://www.hindawi.com/journals/isrn.cardiology/2012/258769/