On mesh refinement and accuracy of numerical solutions

This paper investigates mesh refinement and its relation with the accuracy of the boundary element method (BEM) and the finite element method (FEM). TO this end an isotropic homogeneous spherical volume conductor, for which the analytical solution is available, wag used. The numerical results obtained with the BEM and FEM were compared with the results of the andytical solution. The results show that the accuracy of the numerical solutions is improved by enriching a mesh only if the enriched mesh not only incorporates a greater number of nodes but also follows more closely the actual geometry of the volume conductor involved

Vectorcardiography based analysis of atrial fibrillation

This paper discusses the feasibility and effectiveness of using vectors of the current dipoles representing local electric activity inside the atrial myocardium during atrial fibrillation. The application relates to the search for improving the performance of electric signals observed on the body surface in the diagnoses of this life-threatening arrhythmia. The topics addressed include some historical and basic conceptual notes on the use of the vector, as well as some recent developments in which the vector concept is used in combination with spectral analysis. The invited paper is of a didactic nature

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. AF increases morbidity, duration and expense of medical treatments. This study aims at identifying patients at high risk of post-operative AF. Early prediction of AF would provide timely prophylactic treatment and would reduce the incidence of arrhythmia. Patients at low risk of post-operative AF could be excluded on the basis of the contraindications of anti-arrhythmic drugs. The study included 50 patients in whom lead II electrocardiograms were continuously recorded for 48 h following CABG. Univariate statistical analysis was used in the search for signal features that could predict AF. The most promising ones identified were P wave duration, RR interval duration and PQ segment level. On the basis of these, a nonlinear multivariate prediction model was made by deploying a classification tree. The prediction accuracy was found to increase over time. At 48 h following CABG, the measured best smoothed sensitivity was 84.8% and the specificity 85.4%. The positive and negative predictive values were 72.7% and 92.8%, respectively, and the overall accuracy was 85.3%. With regard to the prediction accuracy, the risk assessment and prediction of post-operative AF is optimal in the period between 24 and 48 h following CABG

The role of atrial modeling in the development of ECG processing tools

The standard ECG remains the most common non-invasive tool for assessing atrial fibrillation. Specific signal processing techniques have been developed to improve the diagnosis. However, validation of such tools is challenging and comprehensive invasive data may not easily be obtained. To facilitate this task, we developed a computer model of the atria. In this electrophysiological model, atrial fibrillation was simulated and the manifestation of its electrical activity on the thorax was computed. The resulting realistic-looking synthetic ECG signals were used as benchmarks for testing, evaluating and comparing ECG processing techniques such as cancellation of the ventricular activity, vectorcardiography and dominant frequency analysis

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. The solution is shown to be valid for all observation points in space, including those on the interior, edges and vertices of the source triangle

Spatial filtering of the fetal electrocardiogram

Peer Reviewe

Measuring the T Wave of the Electrocardiogram; The How and Why

The genesis of the T wave of the electrocardiogram is discussed on the basis of a biophysical model, derived from the underlying electrophysiology. This model is used to scrutinize the commonly-assumed significance of the individual features of this waveform. As is shown, the last word is yet to be said about this topic

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