Marie Turzova

Influence of individual torso geometry on inverse solution to 2 dipoles.

BACKGROUND The purpose of this study was to observe the influence of variety in individual torso geometries on the results of inverse solution to 2 dipoles. METHODS The inverse solution to 2 dipoles was computed from the measured data on 8 patients using either standard torso with various shapes and sizes of the heart and lungs in it or using various outer torso geometries with the same inhomogeneities. The vertical position of the heart relative to the fourth intercostal level was kept constant in all models. The results were compared with the reference solution computed in standard torso. RESULTS The inverse solution was influenced in 4 of 8 cases by changes of torso geometry and only in 1 of 8 cases by changes of internal inhomogeneities. CONCLUSIONS The use of individual torso geometry with the knowledge of the true heart position is very important for correct inverse results.

A model study of the sensitivity of body surface potential distribution to variations of electrode placement

The effect of electrode displacement as one of the sources of reproducibility errors in body surface potential maps was studied using a realistic computer model of the cardiac electric field. A uniform dipole layer model of the cardiac generator and a realistic geometry of the torso, heart, and lungs was adopted for the simulation of surface potentials during ventricular activation. The effect of systematic electrode displacement in terms of longitudinal shifts and variations of longitudinal size (height) of the mapped area was studied. The map reconstruction error of three different limited lead systems and the variability of maps measured on all points of the mapping grid, as well as maps reconstructed from limited lead systems, were investigated and quantified. A mean relative error of map reconstruction of less than 3.5% was found for longitudinal shifts from -4.4 to +1.7 cm, and for longitudinal size changes from 65 to 108% of the initial area. For vertical displacements of electrodes between the limits of +/- 2.0 cm for full grid maps and +/- 1.4 cm if limited lead systems were used, the mean relative error of the maps remained under 5%.

Forward modeling of the cardiac electric field

In the paper an approach to simple forward modeling of the cardiac electric field is presented enabling to compute surface potential distribution and to analyze the influence of selected intra- and extracardial factors. Geometry of inhomogeneous torso and heart is represented by a set of closed surfaces, volume inside one surface is described by identical electrical properties. Propagation of the activation within the myocardium volume is simulated by a finite element model supposing isotropic tissue and enabling definition of excitable heart elements with different propagation velocities. From the simulated activation sequence, parameters of an equivalent multidipole or uniform dipole layer generator are derived and used for computation of body surface potentials. In the paper simulated potential maps for normal case, for old antero-septal myocardial infarction and for preexcitation in WPW syndrome are presented.

PC-based system for cardiac potential mapping

A PC-based ecg mapping device designed for electrophysiological experiments and for clinical use is presented. Up to 6 4 signals from the body surface or from the epicardium can be measured simultaneously, A full grid lead set or three diEerent limited lead arrays are uscd for body surface potential mapping, niensuremcnt of the standard 12-lead ecg and R a n k vcg i s also possible. The system was used for stratiflcation of patients with myocardial infarction. A modifled memuring iiiiit and a polyester-silon sleeve formed mesh with 16 electrodes can be used for epicardial measurements. This version was used in arrhythmogenesis study during induced ischemia in

Simulation study of possibilities of using limited lead mapping data for inverse solution based on multipole cardiac generator

Forward simulation was used for computing body surface potential distribution. Three different limited lead systems have been studied using the simulated surface potential data. The electrical field of computed equivalent multipolar generators was studied in relation to the simulated one. From the results it implies that the multipolar generator equivalent in sense of surface potentials seems not sufficient for recovery of the electrical field near the spatially distributed generator and that limited lead systems give enough accurate maps for judgment about the model acceptability.

A Personal Computer-Based System for Cardiac Electric Field Investigation in the Clinic and in Research

The results of using a special minicomputer-based system EKKG-80 for measuring and modelling the cardiac electrical field (Tysler et al., 1984) showed that it would be desirable to have some more convenient system for clinical studies and, at the same time, for additional studies in electrocardiological research. After some analysis of the clinical needs we decided to develop a personal computer-based system which enables different methods of the heart state analysis to be used, such as classical ECG and VCG recording methods, computerised ECG and VCG classifications and also some newer methods based on body surface potential mapping.