256-channel Electrocardiography in arrhythmia analysis and validation of model investigations

H. G. Puurtinen, M. Sipilä, P. Kauppinen, J. Hyttinen, J. Malmivuo
Ragnar Granit Institute, Tampere University of Technology,
P.O. Box 692, 33101 Tampere, FINLAND

Abstract: The purpose of this study is to introduce a highly accurate 256-channel electrocardiography (ECG) instrumentation employed for e.g. arrhythmia analysis.  For modeling purposes, the multichannel ECG is accompanied with an MR image set of the thorax as well as reference measurements of the arrhythmia location provided by local catheter laboratory. So far, one full test 256-channel (ECG) measurement has been recorded. Several  pre-operative 120-channel or 64-channel ECG measurements have been performed on patients suffering from the Wolff-Parkinson-White (WPW) syndrome. The 256-channel measurement comprised of 142 anteriorly placed individual spot electrodes and 114 posterior electrodes. For the 120-channel measurement, the Dalhousie electrode montage comprising of 76 individual electrodes on the anterior side and 41 electrodes on the posterior side of the torso is used. In addition, the three limb leads are measured. In all measurements, the electrode locations are 3D digitized in order to serve modeling purposes. The information obtained from these recordings will be used to investigate issues related to   localization of arrhythmic foci as well as to investigate and verify theoretical calculations performed in our previous model studies.

INTRODUCTION

The measurement of the electrocardiogram (ECG) provides non-invasively obtained data for the electrical functioning of the heart thus giving important information regarding the state of the heart and possible pathological conditions. Although the information content of the standard 12-lead ECG recording suffices for most clinical applications, it is inevitable that increasing the number of electrodes increases also the accuracy of information obtained resulting to the development of body surface mapping (BSM). Also the redundancy of electrodes in the ECG in various applications has been widely studied [1,2,3,4].

In addition to clinical purposes, BSM procedures are widely used in modeling approaches concentrated on determining the electrical cardiac activity that generates the ECG. These approaches include e.g. solving the inverse problem using the information obtained from the surface ECG and volume conductor models. The level of anatomical detail included in a volume conductor model affects the results obtained with the model. Recently, increased computing capacity has allowed the construction of anatomically detailed, inhomogeneous thorax models [5,6,7].

In this paper, we present a highly accurate method for obtaining detailed information regarding the electrical function of the heart, namely the multichannel ECG measurement using up to 256 channels. The information obtained from these recordings will be used in our laboratory in connection with previously developed anatomically and dynamically detailed patient tailored thorax models in order to investigate issues related to both impedance cardiography and localization of arrhythmic foci in terms of solving the inverse problem.

METHODS

So far, one test measurement with 256 ECG channels has been recorded from one healthy male subject using the ESI-256 EEG system (NeuroScan, Neurosoft, Inc.) also capable of ECG recordings situated in our laboratory. In addition, several 120-channel or 64-channel ECG measurements have been performed on patients suffering from the Wolff-Parkinson-White syndrome. The 256-channel recording was implemented using individual spot electrodes covering the whole upper torso such that 142 electrodes were placed on the anterior side and 114 electrodes on the posterior side (Figure 1). For the 120-channel measurements, the Dalhousie electrode montage [1] comprising of 76 individual electrodes on the anterior side and 41 electrodes on the posterior side of the torso is used. In addition, the three limb leads were measured. The leads included in the 64-channel measurement are selected among the 120 Dalhousie leads according to their information content and lead reconstruction [4].

In all measurements, the electrode locations were digitized using the sophisticated 3-dimensional digitizing feature (Fastrakâ digitizer, Polhemus, Inc.) provided with the measurement device. The electrode montage of the 120-channel measurement and a 3D image of the torso with digitized electrode locations are depicted in Figure 2.

Figure 1. The recording arrangement for the 256-channel ECG measurement

         

Figure 2. The 120-channel electrode configuration and a 3D image of the torso including the digitized electrode locations

RESULTS

Several ECG recordings including 256-lead, 120-lead, and 64-leads systems were performed using the 256-channel EEG/ECG measurement device. An example of the resulting 256-channel measurement signal is shown in Figure 3.

Figure 3. Channels 193-256 of the total of 256 channels from the recorded ECG signal

DISCUSSION

A highly accurate method, multichannel ECG recording was used to obtain information regarding the electrical function of the heart and the body surface potential distributions. Accompanied with patient tailored anatomically and dynamically detailed thorax models these measurements provide accurate and versatile means for investigating a variety of bioelectromagnetic phenomena.

The multichannel ECG in connection with thorax model can further be used for different kind of simulations like conductivity and anisotropy studies, source localization studies, impedance studies etc. Recognizing the inter- and intraindividual variability of the ECG [3,8], it is also evident that if the individual multichannel ECG recording of the patient is available, more accurate diagnosis can be obtained regarding e.g. the pre-operative location of the arrhythmic sources inside the heart. 

Furthermore, if the aim of the research is e.g. to solve the inverse problem, anatomically and dynamically highly accurate, patient tailored models are needed. Thus, the multichannel recordings performed in our laboratory on patients suffering form WPW have been accompanied by taking MR-image data sets of the torso. Previously, the modeling approach has been applied in studying the effects of the number and location of electrodes on the information content of the ECG. Thus, the multichannel ECG recordings enable the validation of model investigations in various respects. Additionally, the ability to digitalize the electrode locations used in each measurement serves the modeling purposes in terms of obtaining exact electrode locations used in the measurements.

The technological improvement of ECG recording devices, imaging methods, and software development provides various new possibilities to gain understanding of the human body. We can conclude that the methods introduced in this study are feasible and applicable to a variety of applications ranging from electrophysiological to bio-impedance and modeling studies.

Acknowledgments: This work has been kindly supported by The Finnish Cultural Foundation and The Ragnar Granit Foundation.

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