A comparison of electrocardiographic imaging based on two source types.

The aim of the study to compare the performance of two major source types involved in the imaging of the electric activity of the heart on the basis of potential differences observed on the thorax. The images depict either the timing of activation and repolarization of the myocardium or the potential field on a surface closely encompassing the myocardium. The depolarization and repolarization timing on a closed surface bounding the ventricular myocardium was derived from measured body surface potentials (BSPs), an MRI-based electric volume conductor model comprising the geometry of thorax, lungs, heart surface Sh, and cavities.

The case of the QRS-T angles versus QRST integral maps.

This contribution discusses the QRS-T angle as well as the QRST integral map. Both of these topics have been tested in their application in extracting the major features of depolarization and repolarization: their spatio-temporal behaviour, and how much of their global or local nature might be deduced from signals that can be observed clinically. Recently, it is in particular the QRS-T angle that has received considerable attention, a method that stems directly from vectorcardiography, a subdomain of electrocardiography.

Repolarization features as detectable from electrograms and electrocardiograms.

This contribution discusses the feasibility of extracting the major features of repolarization: its spatio-temporal behaviour, and how much of its global or local behaviour might be deduced from signals that can be observed experimentally. The analysis presented is based on source-volume-conductor configurations ranging from the classic cable theory, with sources derived from reaction diffusion computations, to a realistic thorax model comprising a whole heart model with electric sources represented by the equivalent electric double layer. The analysis focuses on the fact that the local activation recovery interval (ARI) at regions activated by expanding wave fronts is significantly longer than those activated by contracting ones.

The inverse problem of bioelectricity: an evaluation.

This invited paper presents a personal view on the current status of the solution to the inverse problem of bioelectricity. Its focus lies on applications in the field of electrocardiography. The topic discussed is also relevant in other medical domains, such as electroencephalography, electroneurography and electromyography.

Closed-form analytical expressions for the potential fields generated by triangular monolayers with linearly distributed source strength.

The solution of the mixed boundary value problem of potential theory involves the computation of the potential field generated by monolayer and double layer source distributions on surfaces at which boundary conditions are known. Closed-form analytical expressions have been described in the literature for the potential field generated by double layers having a linearly distributed strength over triangular source elements. This contribution presents the corresponding expression for the linearly distributed monolayer strength.

Potential applications of the new ECGSIM.

This contribution demonstrates some applications of the most recent release of ECGSIM, an interactive simulation program that enables the user to study the relationship between the electric current sources of the heart and the resulting electrocardiographic signals on the body surface as well as those on the surface of the heart. It aims to serve as an educational tool as well as a research tool. The examples are drawn from the topics discussed by the participants of the Magnetic Anatomic and eLectrical Technology meeting in Maastricht, the Netherlands (February 2011), reports of which are to be found in the current issue of the Journal of Electrocardiology.

ECG-based prediction of atrial fibrillation development following coronary artery bypass grafting.

In patients undergoing coronary artery bypass grafting (CABG) surgery, post-operative atrial fibrillation (AF) occurs with a prevalence of up to 40%. The highest incidence is seen between the second and third day after the operation. Following cardiac surgery AF may cause various complications such as hemodynamic instability, heart attack and cerebral or other thromboembolisms.

Development of a toolbox for electrocardiogram-based interpretation of atrial fibrillation.

Background: Atrial fibrillation (AF) develops as a consequence of an underlying heart disease such as fibrosis, inflammation, hyperthyroidism, elevated intra-atrial pressures, and/or atrial dilatation. The arrhythmia is initiated by, or depends on, ectopic focal activity. Autonomic dysfunction may also play a role.

Non-invasive imaging of cardiac activation and recovery.

The sequences of activation and recovery of the heart have physiological and clinical relevance. We report on progress made over the last years in the method that images these timings based on an equivalent double layer on the myocardial surface serving as the equivalent source of cardiac activity, with local transmembrane potentials (TMP) acting as their strength. The TMP wave forms were described analytically by timing parameters, found by minimizing the difference between observed body surface potentials and those based on the source description.

Application of the fastest route algorithm in the interactive simulation of the effect of local ischemia on the ECG.

A method is described to determine the effect on the ECG of a reduced propagation velocity within an ischemic zone. The method was designed to change the activation sequence throughout the ventricles interactively, i.e.

Analysing the potential of Reveal for monitoring cardiac potentials.

Aims: The implantable loop recorder (ILR) continuously monitors the heart's electric activity by means of a subcutaneous bipolar electrogram (Elg). Currently, the relationship between the Elg and the surface electrocardiogram (ECG) has been poorly documented. This model-based study aimed at investigating the differences between the bipolar surface and subcutaneous signals, as well as the effect of the insulating boundary of the ILR on these signals.

Spatial dynamics of atrial activity assessed by the vectorcardiogram: from sinus rhythm to atrial fibrillation.

Aim: This study aims at developing methods for extracting spatiotemporal information about the electric activity of the atria from electrocardiographic signals, in particular during atrial fibrillation.

Methods: A biophysical model of the atria and a volume conductor model of the thorax were used to simulate the atrial electrical activity as expressed on the atrial surface as well as on the thorax surface. In all, 22 different types of atrial electric activity were generated, 20 of which related to atrial fibrillation (AF).

Cancellation of ventricular activity in the ECG: evaluation of novel and existing methods.

Due to the much higher amplitude of the electrical activity of the ventricles in the surface electrocardiogram (ECG), its cancellation is crucial for the analysis and characterization of atrial fibrillation. In this paper, two different methods are proposed for this cancellation. The first one is an average beat subtraction type of method.

ECGSIM: an interactive tool for the study of the relation between the electric activity of the heart and the QRST waveforms at the body surface.

ECGSIM is an interactive computer program that solves the forward problem of electrocardiology. The user may set the depolarization and repolarization times at the heart surface, as well as the transmembrane potential amplitude. The program computes the resulting ECGs at the body surface.

Adaptation of the standard 12-lead electrocardiogram system dedicated to the analysis of atrial fibrillation.

Objective: The objective of the study was to design a lead system aimed at studying atrial fibrillation (AF), while being anchored to the standard 12-lead system.

Methods: The location of 4 of the 6 precordial electrodes was optimized while leaving the remaining 5 of the 9 electrodes of the standard 12-lead system in place. The analysis was based on episodes of 11 different variants of AF simulated by a biophysical model of the atria positioned inside an inhomogeneous thorax.

Vectorcardiographic lead systems for the characterization of atrial fibrillation.

Objective: The aim of the study was to design a vectorcardiographic lead system dedicated to the analysis of atrial fibrillation (AF).

Methods: Body surface potentials during AF were simulated by using a biophysical model of the human atria and thorax. The XYZ components of the equivalent dipole were derived from the Gabor-Nelson equations.

The surface Laplacian operator of the potentials on a bounded volume conductor has a unique inverse.

In the discussion on the use of the surface Laplacian (SL) of the distribution of bioelectric potentials on the body surface, the question remained open whether a complete specification of the SL of the potential over the surface bounding a volume conductor would uniquely specify the potential on that surface up to a constant. This paper reports that this is indeed the case. In addition, it is shown that the integral of the SL over a closed surface is zero, a property that may serve as a check on the accuracy of any numerical approximation of the SL.

Atrial repolarization as observable during the PQ interval.

Objective: We aimed to study the involvement of atrial repolarization in body surface potentials.

Methods: Electrocardiograms of healthy subjects were recorded using a 64-lead system. The data analysis focused on the PQ intervals while devoting special attention to the low-amplitude signals during the PQ segment: the segment from the end of the P wave until onset QRS.

Report of the first virtual visualization of the reconstructed electrocardiographic display symposium.

In August 2004, a group of scientists and clinicians with a deep interest in electrocardiography met to discuss the present and future of the electrocardiogram as an imaging modality. Motivated by a set of challenges to the field, they each presented and discussed their ideas about the basic electrophysiology, the computational approaches required, and the clinical state of the art and where it might go in the future. In this paper, we present a summary of these presentations and discussions, starting with a statement of the challenges and a motivating case study that illustrates the inadequacies of electrocardiography as it is current practiced.

Volume conductor effects involved in the genesis of the P wave.

Aim: To assess the effect of inhomogeneities in the conductivity of different tissues, such as blood and lung tissue, on the body surface potentials generated by atrial electrical activity.

Methods: A 64-lead ECG from a healthy subject was recorded. The subject's geometries of torso, lungs, heart, and blood cavities were derived by magnetic resonance imaging.

Genesis of the P wave: atrial signals as generated by the equivalent double layer source model.

Aim: To assess the effectiveness of the equivalent surface source model in the simulation of atrial signals as observed in ECG leads.

Methods: P waves were extracted from 64-lead ECGs recorded in healthy subjects. The geometries of torso, lungs, heart, and blood cavities of a healthy subject, derived from magnetic resonance imaging, were used to position a detailed, thick-walled 3D model of the atria consisting of a set of 800,000 units representing the activity of all atrial myocytes.

The dominant T wave and its significance.

Introduction: The shapes of the T waves as observed in different leads placed on the thorax are very similar. The dominant T wave is introduced as a means to characterize this general signal shape. Its relationship to the transmembrane potentials of cardiac myocytes is discussed.