NEktal-16 lead system for noninvasive display of the cardioelectric field on an imaging sphere

L.I. Titomir¹, A.A. Mikhnev², V.G. Trunov¹, E.A.I. Aidu^1
1Institute for Information Transmission Problems, Russian Academy of Sciences 19 B. Karetny, Moscow, Russia
²All-Russian Research Institute of Automatics,  22 Sushсhevskaya, Moscow, Russia

Abstract: Results of mathematical modeling and preliminary experimental investigation of the lead system NEKTAL-16 are presented. This system includes 16 electrodes and allows constructing maps of the cardioelectric potential distribution on a spherical imaging surface.

INTRODUCTION

In connection with the requirement of simplifying the measurement procedure and improving the methods of data processing and imaging for ECG mapping, we have previously carried out a comparative investigation of several “reduced” lead systems for noninvasive ECG mapping on a standard imaging sphere enclosing the heart [1, etc.]. These investigations have showed that the demands imposed on the technique are most fully achieved by the lead system NEKTAL-16 and data processing method based on the multipole expansion of the potential with using some lower-order  terms. Here we present a short description of this lead system and the data processing concept, as well as some results of mathematical modeling and experimental measurement with the use of the NEKTAL-16 system.

METHODS

The lead system NEKTAL-16 under consideration includes the classical Frank electrodes 1(I), 3(E), 4(C), 5(A), 7(M), 15(H), 16(F) and the following additional electrodes: electrode 2 between 1 and 3, electrode 6 between 5 and 7, electrodes 8 and 12 on the arms, electrodes 9, 10, 11, 13, 14 above 2, 3, 4, 6, 7, respectively (Fig. 1). Unipolar signals with respect to the Wilson terminal are generated for each electrode. The electrode coordinates are defined according to a realistic geometric model of the chest individually adapted on the basis of three principal anthropometric parameters.

The body surface potential distribution is approximated by the 0th  to 2nd order terms of the spatial spherical harmonics (adaptive quasimultipole approximation technique [2]). Then the true dipole and quadrupole components of the cardiogenerator are calculated by the well-known relations involving the weighted integration of the potential over the chest surface. From these components, the potential over a standard imaging sphere (SIS) is determined on the assumption that the medium inside the sphere is conductive and homogeneous, and outside it is dielectric.

The accuracy of this method was investigated by mathematical modeling on a simplified homogeneous chest model having parallelepipedal shape. The modeling was carried out for several typical structures of the elementary cardioelectric generators, including dipole and quadrupole configurations. As well, the method was tested using ECG measurements on several normal subjects with the NEKTAL-16 system and NEKTAL-48 as an accurate reference system.

RESULTS

The results of modeling are presented in Fig. 2. Here at the left the generator structures (bold arrows) are shown in the heart region (bounded by the dashed circle). To the right of the generator models, there are shown the calculated potential maps on SIS cut along the right meridian (x0z plane), unrolled and projected onto the plane in the equiareal projection format. An example of application of the method in actual measurements is presented in Fig. 3, where the maps on SIS are shown for several time instants of the QRS period.

Figure 2: Model generator structures (left) and corresponding SIS maps obtained by exact calculation (True) and by use of the NEKTAL-16 lead system. The interval between the equipotential lines is 250 μV

Figure 3: Instantaneous SIS maps obtained by using the NEKTAL-48 and NEKTAL-16 lead systems for the time instants of the QRS period (left) in a normal subject. The interval between the equipotential lines is 500  μV

It is seen that the SIS maps obtained with the use of the NEKTAL-16 lead system retain the main features of the true potential distribution, including extension and situation of the principal positive and negative regions, relations between the extrema, and so on; these features are rather important for diagnostical interpretation of the maps.

DISCUSSION

The NEKTAL-16 lead system and the ECG mapping method proposed possess the following favourable features. The data are represented in a map-like form closely related to the anatomical parts of the heart, so that the visual (heuristic) analysis of the data becomes more efficient. The effects of asymmetric position of the heart in the chest and of the chest shape are significantly reduced. The measurement is rather simple as compared to conventional ECG mapping with the use of much greater number of lead electrodes.

Acknowledgements: Work supported by the Russian Foundation of Basic Research, Project No. 01-01-00104

REFERENCES

[1] L.I. Titomir, A.A. Mikhnev. V.G. Trunov, and E.A.I. Aidu, “Practical ECG mapping with few-lead systems: A new approach and mathematical modeling”, Measurement 2001, 2001, pp. 219-222.

[2] L.I. Titomir and P. Kneppo, Bioelectric and Biomagnetic Fields. Theory and Applications in Electrocardiology. Boca Raton etc.: CRC Press, 1994.