ECGSIM Manual: Introduction

ECGSIM Manual

Introduction

ECGSIM is an interactive simulation program that enables its users to study the relationship between the electric sources of the ventricular myocardium and the resulting potentials on the thorax (QRST waveforms as well as body surface potential maps) and on the heart surface (electrograms, potential maps, and maps of the local transmembrane potential). Note that both the depolarization and the repolarization phase are covered, but not the electric activity of the atria.

One of our objectives for ECGSIM is to serve as a research tool for those interested in testing any hypothesis they may have regarding the manifestation of cardiac malfunctioning in the electrocardiographic waveforms on the thorax.

Another objective is for it to serve as an educational tool, to be used for students learning the basic aspects of the genesis of the electrocardiogram.

Please note: ECGSIM is not a diagnostic tool. Any diagnostic application is only indirect; ECGSIM provides a forward simulation and does not solve the inverse problem.

ECGSIM simulates electrocardiographic potentials by specifying the distribution of the timing of depolarization, dep(n), and repolarization, rep(n), of the transmembrane potentials at nodes n, (n=1...N), where N is the number of nodes at the surface bounding the ventricles, referred to henceforth as the heart surface. For every node the difference apd(n)=rep(n)-dep(n) is taken a measure of the local action potential duration. The ventricular surface is the closed surface bounding all ventricular mass, i.e., endocardium, epicardium and their connection at the base of the ventricles. The magnitude of the upstroke of the local transmembrane potential, str(n), representing the local source strength, is allowed to be non-uniform. By setting pre-computed values for the parameters dep(n) and rep(n) for each node and using a uniform str(n) values, potentials are simulated that closely resemble the set of reference values recorded on a healthy subject.

The program allows the interactive changing of the local timing of depolarization and repolarization as well as the magnitude of the upstroke of the local transmembrane potentials. The former two sets of parameters allows one to study the effect of changes in local timing, the latter set, the manifestation of local ischemic regions.

The strength of the cardiac equivalent generator involved is the distribution on the heart surface of the local transmembrane potential. The transfer used to determine the expression of these sources as body surface potentials was computed by applying the laws of current flow to an inhomogeneous torso model, the geometry of which was based on MRI data.

The theory used has been developed over the last 30 years, about 20 years of which at the Department of Medical Physics of the University of Nijmegen. The simulation package has had two predecessors. The current version has been inspired by the enthusiastic reactions of the users to which these earlier versions were made available.

ECGSIM was introduced to the scientific community though the paper in HEART included in the reference list: ECGSIM; an interactive tool for studying the genesis of QRST waveforms. The theory behind ECGSIM is explained in the papers shown in the reference list. Whenever you would want to acknowledge the use of ECGSIM, please refer to the paper in HEART.

Any comments and suggestions for improvements will be greatly appreciated. Please e-mail your comments to .

In response, the package will be developed to (even) greater perfection. Updates will be available from www.ecgsim.org. Those of you that have indicated their wish during the downloading procedure will be notified about updates. You can determine which version you are currently working with by selecting About ecgsim from the Help menu.