In vivo validation of electrocardiographic imaging

Objective The purpose of this study was to evaluate the accuracy of noninvasive reconstructions of epicardial potentials, electrograms, activation and recovery isochrones, and beat origins by simultaneously performing electrocardiographic imaging (ECGI) and invasive epicardial electrography in intact animals.

Background Noninvasive imaging of electrical potentials at the epicardium, known as ECGI, is increasingly applied in patients to assess normal and abnormal cardiac electrical activity.

Methods Body-surface potentials and epicardial potentials were recorded in normal anesthetized dogs. Computed tomography scanning provided a torso-heart geometry that was used to reconstruct epicardial potentials from body-surface potentials.

Results Electrogram reconstructions attained a moderate accuracy compared with epicardial recordings (median correlation coefficient: 0.71), but with considerable variation (interquartile range: 0.36 to 0.86). This variation could be explained by a spatial mismatch (overall resolution was <20 mm) that was most apparent in regions with electrographic transition. More accurate derivation of activation times (Pearson R: 0.82), recovery times (R: 0.73), and the origin of paced beats (median error: 10 mm; interquartile range: 7 to 17 mm) was achieved by a spatiotemporal approach that incorporates the characteristics of the respective electrogram and neighboring electrograms. Reconstruction of beats from repeated single-site pacing showed a stable localization of origin. Cardiac motion, currently ignored in ECGI, correlates negatively with reconstruction accuracy.

Conclusions ECGI shows a decent median accuracy, but variability in electrogram reconstruction can be sizable. At present, therefore, clinical interpretations of ECGI should not be made on the basis of single electrograms only. Incorporating local spatiotemporal characteristics allows for accurate reconstruction of epicardial activation and recovery patterns, and beat origin localization to a 10-mm precision. Even more reliable interpretations are expected when the influences of cardiac motion are accounted for in ECGI.

Please find a pre-print of the paper here.

Reference: Matthijs J.M. Cluitmans, Pietro Bonizzi, Joël M.H. Karel, Marco Das, Bas L.J.H. Kietselaer, Monique M.J. de Jong, Frits W. Prinzen, Ralf L.M. Peeters, Ronald L. Westra, Paul G.A. Volders. In Vivo Validation of Electrocardiographic Imaging. 

Physiology-based regularization of the electrocardiographic inverse problem

The inverse problem of electrocardiography aims at noninvasively reconstructing electrical activity of the heart from recorded body-surface electrocardiograms. A crucial step is regularization, which deals with ill-posedness of the problem by imposing constraints on the possible solutions. We developed a regularization method that includes electrophysiological input. Body-surface potentials are recorded and a computed tomography scan is performed to obtain the torso–heart geometry. Propagating waveforms originating from several positions at the heart are simulated and used to generate a set of basis vectors representing spatial distributions of potentials on the heart surface. The real heart-surface potentials are then reconstructed from the recorded body-surface potentials by finding a sparse representation in terms of this basis. This method, which we named ‘physiology-based regularization’ (PBR), was compared to traditional Tikhonov regularization and validated using in vivo recordings in dogs. PBR recovered details of heart-surface electrograms that were lost with traditional regularization, attained higher correlation coefficients and led to improved estimation of recovery times. The best results were obtained by including approximate knowledge about the beat origin in the PBR basis.

Please find the paper here.

Reference: Matthijs Cluitmans, Michael Clerx, Nele Vandersickel, Ralf Peeters, Paul Volders and Ronald Westra. Physiology-based regularization of the electrocardiographic inverse problem. In Medical & Biological Engineering & Computing, Nov 2016. Pubmed

Review: Noninvasive reconstruction of cardiac electrical activity

Recently, we have published a review about noninvasive reconstruction of cardiac electrical activity. In this review, we aim at providing both an overview of the technical background and clinical application of a broad range of noninvasive inverse imaging techniques.

Cluitmans MJ, Peeters RL, Westra RL, Volders PG. Noninvasive reconstruction of cardiac electrical activity: update on current methods, applications and challenges. Neth Heart J. 2015 Apr 21. [Epub ahead of print]

Please find the pdf here and the Pubmed entry here.

Forward/inverse models