Lead system transformation of body surface map data

Body Surface Potential Mapping: Contemporary Applications and Future Perspectives

Body surface potential mapping (BSPM) is a noninvasive modality to assess cardiac bioelectric activity with a rich history of practical applications for both research and clinical investigation. BSPM provides comprehensive acquisition of bioelectric signals across the entire thorax, allowing for more complex and extensive analysis than the standard electrocardiogram (ECG). Despite its advantages, BSPM is not a common clinical tool. BSPM does, however, serve as a valuable research tool and as an input for other modes of analysis such as electrocardiographic imaging and, more recently, machine learning and artificial intelligence. In this report, we examine contemporary uses of BSPM, and provide an assessment of its future prospects in both clinical and research environments. We assess the state of the art of BSPM implementations and explore modern applications of advanced modeling and statistical analysis of BSPM data. We predict that BSPM will continue to be a valuable research tool, and will find clinical utility at the intersection of computational modeling approaches and artificial intelligence.

Beat-to-beat interplay of heart rate, ventricular depolarization, and repolarization

To improve malignant arrhythmia risk stratification, the causal and random components of spatiotemporal dynamics of heart rate (RR distances), ventricular depolarization sequence, and repolarization disparity were studied based on body surface potential map records taken for 5 minutes, in resting, supine position on 14 healthy subjects (age range, 20-65 years) and on 6 arrhythmia patients (age range, 59-70 years). Beat-to-beat QRS and QRST integral maps, Karhunen-Loève (KL) coefficients, RR, and nondipolarity index time series were computed. Tight relationship was found between RR and QRS integrals in healthy subjects with less association in arrhythmia patients. Tight KL-domain multiple linear association (r(2) > 0.72) was found between the QRS and QRST integral dynamics (ie, depolarization sequence and repolarization disparity). Beat-to-beat probability of the generation of significant nondipolarity index spikes was proportional to the QRST KL-component standard deviations (SD(i)) and inversely proportional with the mean dipolar KL components (M(i)) of the average QRST integral map.

Methods of Solving Reduced Lead Systems for Inverse Electrocardiography

In the context of inverse electrocardiography, we examine the problem of using measurements from sets of electrocardiographic leads that are smaller than the number of nodes in the associated geometric models of the torso. We compared several methods to estimate the solution from such reduced-lead measurements sets both with and without knowledge of prior statistics of the measurements. We present here simulation results that indicate that deleting rows of the forward matrix corresponding to the unmeasured leads performs best in the absence of prior statistics, and that Bayesian (or least-squares) estimation performs best in the presence of prior statistics.

The effect of intrathoracic heart position on electrocardiogram autocorrelation maps

We studied the influence of the heart position in the thorax on the autocorrelation (AC) maps consisting of correlation coefficients between each pair of instantaneous electrocardiogram potential distributions over a time interval. We used a thorax-shaped electrolytic-filled tank with an isolated and perfused dog heart placed at positions spanning 5 cm on each space direction. The correlation coefficient between QRST AC maps was in the range of 0.92 to 0.99, whereas the correlation coefficient between the corresponding QRST integral maps was in the range of 0.55 to 0.87, proving that AC maps are less influenced by the heart position than integral maps. Thus, diagnostic indexes computed from the AC maps can be expected to be more specific to phenomena taking place in the myocardium than to criteria based directly on electrocardiogram amplitudes in various leads.

Gender differences in stability of the instantaneous patterns of body surface potentials during ventricular repolarisation

Women have a higher risk of developing torsade de pointes under OT-prolonging conditions. The electrophysiological differences between the sexes that could account for this are largely unknown. The objective of the work was to evaluate gender differences in repolarisation potentials using a method that is independent of the specific electrical properties of the thorax. 1410 normal recordings from the Glasgow 12-lead ECG database and 52 normal ECG maps obtained separately in Milan were analysed. The average difference between 1 and the correlation coefficient of the instantaneous pattern at the peak of T with that at every other instant is called the early repolarisation deviation index (ERDI) for J-T peak and the late repolarisation deviation index (LRDI) for T peak-T end. In standard ECG recordings, the ERDI was 0.42 +/- 0.22 in females compared with 0.19 +/- 0.16 in males (p < 10(-6)). The LRDI was higher in males under the age of 50. In body surface maps, the ERDI was 0.32 +/- 0.21 in females against 0.16 +/- 0.17 in males (p < 0.01), and the LRDI was non-significantly higher in males. The pattern of instantaneous body surface potentials showed gender differences during repolarisation with a method that is independent of the electrical properties of the thorax.

Software design for analysis of multichannel intracardial and body surface electrocardiograms

Analysis of multichannel ECG recordings (body surface maps (BSMs) and intracardial maps) requires special software. We created a software package and a user interface on top of a commercial data analysis package (MATLAB) by a combination of high-level and low-level programming. Our software was created to satisfy the needs of a diverse group of researchers. It can handle a large variety of recording configurations. It allows for interactive usage through a fast and robust user interface, and batch processing for the analysis of large amounts of data. The package is user-extensible, includes routines for both common and experimental data processing tasks, and works on several computer platforms. The source code is made intelligible using software for structured documentation and is available to the users. The package is currently used by more than ten research groups analysing ECG data worldwide.

The use of the spatial covariance in computing pericardial potentials

This paper investigates the incorporation of the spatial covariance of the pericardial potentials, assumed known a priori as a regularization function, when computing the pericardial potential distribution from observed body surface potentials. The resulting inverse solutions are compared with those using as a regularization function: 1) the norm of the solution, 2) the norm of the surface Laplacian of the solution, as well as with those based on using the truncated singular value decomposition. The study uses a realistic source model to simulate potentials throughout the QRS-interval. This source is placed in an anatomically accurate inhomogeneous volume conductor model of the torso. The use of a single value of the regularization parameter is shown to be feasible: for data incorporating 2% noise, the use of the spatial covariance is demonstrated to result in a relative error over the entire QRS interval as low as 10%. Major errors are demonstrated to result if the effect of the inhomogeneity of the lungs is ignored. The spatial covariance based inverse is shown to be more robust with respect to the perturbations (noise; inhomogeneity) than the other estimators included in this study.

Body surface potential field representation fidelity: analysis of map estimation procedures

The first part of this study analyzed the spatial-temporal error distribution of the Lux-type limited lead system. Quantitative new evidence is reported that the 32-lead anterior subset estimates the further 160 leads with an average amplitude error less than 38.5 microV. The spatial error distribution revealed 8 sites where the error is the highest, primarily on the anterior side, independent of the clinical classification. The second part of the study examined inter-lead-system conversion strategies for interpolating the Lux-192 lead maps from the Montreal-63 data. The methodology based on the Laplacian interpolation yielded an average amplitude error of 143.7 microV and an average correlation of 0.87 for pattern fidelity. In this specific case a modified linear interpolation surpassed the Laplacian method. A presented example illustrates that even in cases when the fidelity of the signal information is heavily compromised the diagnostic information may remain less influenced.