International Journal of Bioelectromagnetism 2003, Vol. 5, No. 1 pp. 150 - 151
www.ijbem.org
Juho Väisänena, Pentti Korhonenb, Juha Nousiainena, Jaakko Malmivuoa a
Ragnar Granit Institute, Tampere University of Technology, Tampere, Finland b Tampere University Hospital,Tampere, Finland
Correspondence: J Väisänen, Ragnar Granit Institute, Tampere University of Technology, P.O. Box 692, FIN-33101 Tampere, Finland. E-mail:
[email protected], phone +358 3 3115 2117, fax +358 3 3115 2162
Abstract. The interest to study atrial activity of the heart has been increasing along with the development of new treatment methods and digital signal prosessing tools. Analysis softwares have to be developed for clinicians for the effective study of low amplitudes in ECG and VCG signals. A tailored analysis software for ECG P-wave analysis is introduced in this paper. Keywords: ECG; VCG; P-wave; Analysis Software; Signal Processing; Graphical User Interface
1. Introduction Electrical activity of the heart has been studied with ECG recordings for over 100 years. The biggest interest has been in the QRS complex and ventricular functions. Other parts of the ECG like P-wave and atrial activity have been left for minor attention particularly because the atrial malfunctions are seldom fatal and not as harmful as the ventricular-based abnormalities. Also the lacks of the effective treatment methods of atrial diseases and possibilities to study low amplitude signals in the ECG recordings have reduced the interest. During the last years clinicians’ interest to study the atrial abnormalities and malfunctions has been increasing through the new treatment methods and digital data processing possibilities. Digital signal processing offers possibilities to study and process signals and therefore better opportunities to solve the problems related to the low amplitudes like P-waves in ECG signals. Analysis software presented in this paper is developed for the posterior ECG P-wave analysis. The purpose of the software is to aid the analysis of long-term dynamic changes in the P-waves. The analysis software contains the calculation of the parameters and graphical user interface (GUI) to present the results. The patient data used in the analysis is collected with MIDA™ (Ortivus AB, Sweden) measurement system based on the Frank lead system to get three orthogonal (X, Y, Z) components of the VCG. MIDA™ is used in clinical diagnosis and analysis of ischemia. This system enables long-term recordings, which contains data from couple of hours up to 24 hours.
2. Development of the Software The analysis software was created with Matlab® (The MathWorks, Inc, USA) because it serves an easy way to carry out signal processing and development of the GUI with the same software and the data collected by MIDA can be converted to suitable form for Matlab®. The developing of the software contained two main phases: developing calculation of the parameters and presentation of the results. The calculation part was developed in close context with the GUI. The GUI is an important part of the software and it has to be usable and illustrative so that the user can easily adopt the software and use it effectively in research. The development of an application must be based on end users needs and requirements. This software was tailored for one user and thereby the user requirements were more easily carried out. Designing and development of the GUI was based on the methods introduced by Jacob Nielsen [Nielsen, 1993] The main problem in developing this software was to make the detection of the P-waves valid and reliable. If the P-wave detection quality is poor then the validity of the whole software significantly decreases. The other main factor
of the validity is the quality of the data. If the quality of the data is poor the detection of the waveforms can’t be performed effectively, and thereby the reliability of the analysis results decreases.
3. Analysis Software The software contains two main parts: analysis of the data and illustration of the results. The phases of the analysis are presented in the Figure 1. During the analysis signal is processed with low-pass filter and waveforms are detected before actual parameter calculation. The P-wave parameters are extracted from the detected P-waves to calculate different kind of P-wave dependent parameters. The parameters include for example time-related parameters, like P-wave duration and parameters from the changes of the space-related characteristics of the P-waves. Parameters can be calculated from each individual P-wave or from the time-averaged P-wave based on the user’s choice.
Figure 1. Data processing flow chart.
A view from the analysis software’s GUI is presented in Figure 2. In this solution the GUI gives the observer an opportunity to choose a parameter he wants to study. The view illustrates dynamic changes of the parameter over the time. The user has an opportunity to select a single time instant from the graph and study closer the P-waves used in calculation. Each component of the P-wave and VCG 3D-loop in that time instant is plotted in a smaller window.
Figure 2. Screenshot of the analysis software’s main view.
References Nielsen J. Usability Engineering. Academic Press, Inc., London, 1999
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