Assessment of the equivalent dipole layer source model in the reconstruction of cardiac activation times on the basis of BSPMs produced by an anisotropic model of the heart

Arno M Janssen,Olaf Dössel,Thom F Oostendorp,Danila Potyagaylo

doi:10.1007/s11517-017-1715-x

Abstract

Promising results have been reported in noninvasive estimation of cardiac activation times (AT) using the equivalent dipole layer (EDL) source model in combination with the boundary element method (BEM). However, the assumption of equal anisotropy ratios in the heart that underlies the EDL model does not reflect reality. In the present study, we quantify the errors of the nonlinear AT imaging based on the EDL approximation. Nine different excitation patterns (sinus rhythm and eight ectopic beats) were simulated with the monodomain model. Based on the bidomain theory, the body surface potential maps (BSPMs) were calculated for a realistic finite element volume conductor with an anisotropic heart model. For the forward calculations, three cases of bidomain conductivity tensors in the heart were considered: isotropic, equal, and unequal anisotropy ratios in the intra- and extracellular spaces. In all inverse reconstructions, the EDL model with BEM was employed: AT were estimated by solving the nonlinear optimization problem with the initial guess provided by the fastest route algorithm. Expectedly, the case of unequal anisotropy ratios resulted in larger localization errors for almost all considered activation patterns. For the sinus rhythm, all sites of early activation were correctly estimated with an optimal regularization parameter being used. For the ectopic beats, all but one foci were correctly classified to have either endo- or epicardial origin with an average localization error of 20.4 mm for unequal anisotropy ratio. The obtained results confirm validation studies and suggest that cardiac anisotropy might be neglected in clinical applications of the considered EDL-based inverse procedure.

Highlights

The electrocardiogram (ECG) is an important diagnostic tool in cardiology
We performed a realistic model-to-model study to examine the effects of neglecting heart anisotropy on activation times (AT) imaging with the equivalent dipole layer (EDL)-based non-linear inverse procedure and fasted route algorithm (FRA) for calculating the initial estimate
Isotropic and equal anisotropy ratio cases resulted in a better match between the simulated and recovered activation sequences

Summary

Introduction

The electrocardiogram (ECG) is an important diagnostic tool in cardiology. The ECG is the result of electrical currents generated by the myocardial cells that initiate and accompany the contraction of the human heart. Based on the ECG, a cardiologist can assess the patient’s heart condition, but even for experienced clinicians, it is difficult to accurately translate the information obtained from the ECG to cardiac electrograms. The electromagnetic fields originating from electrical activity of the heart are attenuated in the body volume and only low-resolution information content can be detected on the thorax surface. Med Biol Eng Comput (2018) 56:1013–1025 non-invasive electrocardiographic imaging (ECG imaging) [35, 41], called the inverse problem of electrocardiography, is to reconstruct high-resolution maps of cardiac electrical activity from the signals recorded at the body surface (either 12-lead ECGs or multi-lead Body Surface Potential Maps). Despite the progress made in the methodology of ECG imaging over the past decades and the promising application of the technique in clinical studies [3, 39, 48], an accurate estimation of cardiac sources remains a challenging problem

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