Peter Kneppo

Integral Characteristics of the Human Cardiac Electrical Generator from Electric Field Measurements by Means of an Automatic Cylindrical Coordinator

An automated electronic system based upon a cylindrical coordinator was constructed for measurement and preliminary computational processing of the heart electrical potentials on the surface of a human torso and of the coordinates of this surface. The potential distribution on the body surface at consecutive instants of time and the geometrical parameters of the body received as the output of the measuring system can be used for investigation of various types of mathematical descriptions, or models of the cardiac electrical generator. One such mathematical description, a set of integral characteristics of the cardiac electrical generator, is studied in this work. These characteristics are: three components of the heart dipole moment, three coordinates of the moving cardiac electrical center and the complexity parameter of the cardiac generator. The results of experimental measurement of the cardiac electrical field and calculation of the integral characteristics of the cardiac generator are presented for a group of healthy men. Physical and electrophysiological significance of the results is briefly discussed.

Influence of Torso Model Complexity on the Noninvasive Localization of Ectopic Ventricular Activity

Abstract Location of premature ectopic ventricular activity was assessed noninvasively in five patients using integral body surface potential maps and inverse solution in terms of a single dipole. Precision of the inverse solution was studied using three different torso models: homogeneous torso model, inhomogeneous torso model including lungs and heart ventricles and inhomogeneous torso model including lungs, heart ventricles and atria, aorta and pulmonary artery. More stable results were obtained using the homogeneous model. However, in some patients the location of the resulting dipole representing the focus of ectopic activity was shifted between solutions using the homogeneous and inhomogeneous models. Comparison of solutions with inhomogeneous torso models did not show significantly different dispersions, but localization of the focus was better when a torso model including atria and arteries was used. The obtained results suggest that presented noninvasive localization of the ectopic focus can be used to shorten the time needed for successful ablation and to increase its success rate.

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%.

On the Possibility to Determine Integral Characteristics of the Cardiac Electric Generator from Extracardiac Electric and Magnetic Measurements

The relation between the electric and magnetic fields of the heart outside the body is considered on the assumption that the primary bioelectric generators impressed membrane currents may be represented as geometrically curvilinear thread-like flows. An approach based substantially upon the multipole expansion of scalar potentials is developed for distinguishing between two parts of a measured total magnetic field, the first part being uniquely joint with the electric field, and the second being independent and containing information about curvilinearity of the elementary generators.

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.

A method for description of the vectorcardiographic loop in space

Abstract A method of mathematical expression for the VCG loop in space is described. After expressing the three nonharmonic scalar functions in the x, y, and z axes by means of Fourier series, a vectoranalytical expression is obtained for the time vector by means of complex determining constiuents in a simple form. The constants in this equation represent the digital description of the VCG loop in space. The geometrical interpretation of his equation is a set of ellipses. The method is applied in a concrete recorded VCG loop. A sampling method was used in order to decrease the number of harmonics. For the description of the spatial QRS loop a relatively low number of harmonics (3–5) may be used, enabling a sufficiently correct expressing of the loop.

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

Modular Measuring System for Assessment of the Thyroid Gland Functional State

Distributed modular system BioLab for biophysical examinations enabling assessment of the thyroid gland functional state is presented. Two smart sensors modules measuring 4 different biosignals are connected to an Ethernet based network and enable to obtain peripheral indicators of human cardiovascular and neuromuscular functions. Personal notebook or desktop computer with a network interface controls the sensors and performs processing and evaluation of measured biosignals

Multipolar generator capability to represent the heart activation process

Abdruct Some multipolar equivalent generator properties were studied. Forward simulations of the depolarization wave in heart were used to get reference surface and epicardial data. Multipolar generators of different orders were inversely calculated and were used to compute epicardial potential and isochrone maps. In several experiments the comparison of these maps with the reference data showed their ability to characterize the original simulated depolarization. sphere or torso, in the eccentric model there was a 5 cm distance between the heart and the sphere or torso cencer (surface of the torso model or heart surface created the volume conductor boundaries). The resultant epicardial and quasiepicardial potential and isochrone maps were compared with the reference maps obtained from the forward solution. Finally, correlation coefficients between the resultant and reference maps were computed.

Multichannel Measurement and Analysis of the Cardiac Electric Field

INTRODUCTION: Multichannel measurements of cardiac signals contribute to more detailed knowledge about the cardiac electric Held [4]. Analysis and topographic Pr sentation of this Information can be a valuable tool for nonivasive diagnostics of the heart state [3]. Technology of personal Computers brings new possibilities to cardiac electric field studies. Detailed Information about myocardium activation obtained form the torso surface by mapping techniques can be compared with simulated data where models of heart activation are used in forward and inverse compulations, A personal Computer based flexible measuring and processing System CardioPC was developed to enable the use of mapping techniques in electrophysiological and clinical studies. Its hardware and Software enables recording and processing of heart electrograms or surface ecg signals. Body surface potential mapping, integral mapping or departure integral mapping is possible from a 24-lead system [1] and two 32-lead Systems [3, 5]. Using additional Software, forward Simulation of body surface potential maps (BSPMs) or potentials on an arbitrary surface within the torso is possible using the boundary element method. The myocardium depolarization spreading through the cardiac muscle can be approximated by a multidipole, uniform dipole layer or by multipole model. Estimation of the model parameters from BSPMs by an inverse solution could contribute to the ability of nonivasive localization of cardiac electrical events and identification of the electrical disturbances of the myocardium activation. Multipole equivalent generator is a superposition of multipole sources. The basic problem is to make some transition from multipolar series s an theoretical characteristic to another more physiological representation [3] of the heart excitation process.