Simulation System of Arrhythmia and Artificial Pacemaker using ActiveX Control

Akihiro Takeuchi^a, Minoru Hirose^b, Mototake Taguchi^b, Atsushi Hamada^a, and
Noriaki Ikeda^a

^aDept. of Medical Informatics, Kitasato University Graduate School,
^bDept. of Clinical Engineering, School of Allied Health Sciences, Kitasato University, Japan

Correspondence: A Takeuchi, Dept. of Medical Informatics, Kitasato University, 1-15-1, Sagamihara, Kanagawa, 228-8555, Japan.
E-mail: take@bme.ahs.kitasato-u.ac.jp

1.    Introduction

Two mechanisms that produce arrhythmias are automaticity and conduction. These physiological properties of cardiac cells are represented by a phase response curve and an excitability recovery curve, respectively. Some simulation systems including the curves were developed by the standard programming style [Ikeda et al., 1997, Abramovich-Sivan et al., 1998]. The cells and its mathematical functions can be considered as objects and its properties from a point of view of object-oriented programming. The aim of this study is to develop a simulation system using a window-based software technology, ActiveX control, and to reproduce various arrhythmias.

2.  System Overview

The simulation system consisted of the cardiac module and the artificial pacemaker module (Figure 1). The cardiac module (tkp2.exe 130 kB, Visual Basic 6.0) was composed of normal cardiac cells (the sinus and the atrium, the AV-node, and the ventricle) and ectopic focuses (in the atrium, in the ventricle). The cells were implemented as a set of the ActiveX controls and placed in a form of cardiac module. The automaticity and activity of the cells were modeled by a phase response curve (PRC) (Figure 2). PRC defined the next firing time of the cell due to the last stimulated timing. Each ActiveX control calculated new dynamic state at every timer event from the cardiac window. The antegrade and/or retrograde conduction between these cells were controlled by the user’s operation on the check boxes in the cardiac window.

The artificial pacemaker module had two electrodes to sense the cardiac impulses, and recognized the rhythm disturbances automatically. This module stimulated the atrium and/or the ventricle through the electrode according to the user operation, ICHD modes, pacing rate, and output level. The electrodes were implemented using the ActiveX control.

These ActiveX controls run independently, responded to various events generated from the module, and communicated with another ActiveX control by the user operation.

3.  Sample Run

The application runs under MS-Windows (98 or higher) with a wide screen on a high performance computer (CPU: Pentium III, 500 MHz or higher).

Figure 3 showed the control panel and the ECG panel of the cardiac module, with two PRCs of cardiac cells on the other windows. The ECG waveforms were drawn in real time with a ladder diagram simultaneously. The demonstration showed a Wenckebach rhythm with three waves, and two retrograde conductions from ectopic focus to the sinus, and the sinus to the AV-node in the latter part. In addition, the dynamic state of contraction and relaxation of the atrium and the ventricle were presented graphically. Figure 4 showed a simulation of cardiac rhythm disturbances and heart-pacemaker interactions.

4.  Discussion

Although the previous simulation systems have been generally processed in a batch mode, current computer technology can now support real-time cardiac electrophysiological model [Bauch, 2001]. Object-oriented programming has changed the rules in the development of computer programs. An ActiveX control is a component program object that can be re-used by many application programs such as our two modules. This reusable component approach reduces development time and improves program capability and quality.

Our simulation system can theoretically reproduce many aspects of cardiac electrophysiology in real time. User of the system can interactively modify the antegrade and retrograde conductions, the conduction velocity and the refractory periods. The ladder diagram explains reentrant circuits better than a standard textbook. The interactive pacemaker module is able to clarify various pacing concepts. The interactive learning tool may improve students’ comprehension.