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PubMed2006

Wavefront-based models for inverse electrocardiography.

We introduce two wavefront-based methods for the inverse problem of electrocardiography, which we term wavefront-based curve reconstruction (WBCR) and wavefront-based potential reconstruction (WBPR). In the WBCR approach, the epicardial activation wavefront is modeled as a curve evolving on the heart surface, with the evolution governed by factors derived phenomenologically from prior measured data. The body surface potential/wavefront relationship is modeled via an intermediate mapping of wavefront to epicardial potentials, again derived phenomenologically. In the WBPR approach, we iteratively construct an estimate of epicardial potentials from an estimated wavefront curve according to a simplified model and use it as an initial solution in a Tikhonov regularization scheme. Initial simulation results using measured canine epicardial data show considerable improvement in reconstructing activation wavefronts and epicardial potentials with respect to standard Tikhonov solutions. In particular the WBCR method accurately finds the anisotropic propagation early after epicardial pacing, and the WBPR method finds the wavefront (regions of sharp gradient of the potential) both accurately and with minimal smoothing.

Action Potentials↗
PubMed2006

Sensitivity- and effort-gain analysis: multilead ECG electrode array selection for activation time imaging.

Methods for noninvasive imaging of electric function of the heart might become clinical standard procedure the next years. Thus, the overall procedure has to meet clinical requirements as an easy and fast application. In this paper, we propose a new electrode array which improves the resolution of methods for activation time imaging considering clinical constraints such as easy to apply and compatibility with routine leads. For identifying the body-surface regions where the body surface potential (BSP) is most sensitive to changes in transmembrane potential (TMP), a virtual array method was used to compute local linear dependency (LLD) maps. The virtual array method computes a measure for the LLD in every point on the body surface. The most suitable number and position of the electrodes within the sensitive body surface regions was selected by constructing effort gain (EG) plots. Such a plot depicts the relative attainable rank of the leadfield matrix in relation to the increase in number of electrodes required to build the electrode array. The attainable rank itself was computed by a detector criterion. Such a criterion estimates the maximum number of source space eigenvectors not covered by noise when being mapped to the electrode space by the leadfield matrix and recorded by a detector. From the sensitivity maps, we found that the BSP is most sensitive to changes in TMP on the upper left frontal and dorsal body surface. These sensitive regions are covered best by an electrode array consisting of two L-shaped parts of approximately 30 cm x 30 cm and approximately 20 cm x 20 cm. The EG analysis revealed that the array meeting clinical requirements best and improving the resolution of activation time imaging consists of 125 electrodes with a regular horizontal and vertical spacing of 2-3 cm.

Action Potentials↗
PubMed1997

Noninvasive electrocardiographic imaging: reconstruction of epicardial potentials, electrograms, and isochrones and localization of single and multiple electrocardiac events.

BACKGROUND: The goal of noninvasive electrocardiographic imaging (ECGI) is to determine electric activity of the heart by reconstructing maps of epicardial potentials, excitation times (isochrones), and electrograms from data measured on the body surface. METHODS AND RESULTS: Local electrocardiac events were initiated by pacing a dog heart in a human torso-shaped tank. Body surface potential measurements (384 electrodes) were used to compute epicardial potentials noninvasively. The accuracy of reconstructed epicardial potentials was evaluated by direct comparison to measured ones (134 electrodes). Protocols included pacing from single sites and simultaneously from two sites with various intersite distances. Body surface potentials showed a single minimum for both single- and double-site pacing (intersite distances of 52, 35, and 17 mm). Noninvasively reconstructed epicardial electrograms, potentials, and isochrones closely approximated the measured ones. Single pacing sites were reconstructed to within < or = 10 mm of their measured positions. Dual sites were located accurately and resolved for the above intersite distances. Regions of sparse and crowded isochrones, indicating spatial nonuniformities of epicardial activation spread, were also reconstructed. CONCLUSIONS: The study demonstrates that ECGI can reconstruct epicardial potentials, electrograms, and isochrones over the entire epicardial surface during the cardiac cycle. It can provide detailed information on local activation of the heart noninvasively. Its uses could include localization of cardiac electric events (eg, ectopic foci), characterization of nonuniformities of conduction, characterization of repolarization properties (eg, dispersion), and mapping of dynamically changing arrhythmias (eg, polymorphic VT) on a beat-by-beat basis.

Animals↗
PubMed2003

The temporal prior in bioelectromagnetic source imaging problems.

The multiplicity of temporal priors proposed for regularization of the bioelectromagnetic source imaging problems [e.g., the inverse electrocardiogram (ECG) and inverse electroencephalogram (EEG) problems], is discordant with the fact that fundamental statistical principles sharply limit the choice. Thus, our objective is to derive the form of the prior consistent with the general unavailability of temporal constraints. Writing linear formulations of the inverse ECG and inverse EEG problems as H = FG + N (where the ith columns of matrices H, G, and N, are data, signal, and noise vectors at time step i, and F is the transfer matrix), and using the noninformative principle that features of the spatiotemporal prior not supplied a posteriori should be invariant under temporal transformations, we show that the implied spatiotemporal signal autocovariance matrix (of the vector formed by the entries of G) is given in block matrix form [equation in text] where Cg is a matrix of unit trace proportional to the autocovariance matrix of any column of G (representing supplied information regarding the spatial prior), epsilon[.] denotes expectation, superscript ' indicates transpose, [symbol in text] is the Kronecker product, [symbol in text] is Frobenius norm, and the "matrix scalar product" [symbol in text] indicates the inner product of the two vectors formed by the entries of the two adjacent matrices (i.e., A [symbol in text] B [triple bond] trace[A'B]). This result eliminates some uncertainties and ambiguities that have characterized spatiotemporal regularization methods--including eight methods previously introduced in this transactions. Ultimately, the result derives from an implied symmetry principle under which the form of a nontrivial noninformative temporal component of the prior can be identified. Among other things, separability of the spatiotemporal prior in terms of the above Kronecker product can be thought of as the expression of the lack of "entanglement" of the spatial and temporal contributions (a consequence of noninformativity). The approach is generalized to the important cases of non-Gaussian spatial priors, and signal and noise that are not independent (transfer matrix noise). We also demonstrate a means for computational complexity reduction, related to the application of a particular orthogonal transformation, having features dependent on whether or not the transfer matrix represents a surjective mapping.

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PubMed1995

[QRST isointegral map in dilated cardiomyopathy].

To evaluate the diagnostic usefulness and prognostic significance of QRST isointegral map in dilated cardiomyopathy (DCM), we performed body surface mapping, signal averaged electrocardiogram and thallium-201 myocardial scintigraphy in 41 DCM patients. Late potentials (LP) were detected in 17 patients (41%). QRST isointegral subtraction map (QRST I-sub map: departure map, calculated from 40 normal subjects) showed -2 standard deviation area and departure indices at minimal point (DImin) were calculated in each case. Significant coefficients of correlation were observed between the DImin and root mean square voltage in last 40 ms (r = -0.435, p < 0.001). The abnormal scintigraphic patterns were discriminated into 3 groups: anteroseptal, inferoapical and posterolateral defects, which revealed separate distribution of minimal point in QRST I-sub map: F-G 4, G-H 2 and I-J 4, respectively. These results suggest that QRST isointegral map is useful for detecting the presence of LP (prognostic value) and the location of scintigraphic perfusion defect (diagnostic value) in DCM.

Body Surface Potential Mapping↗
PubMed2004

Recent advances in magnetocardiography.

New developments in instrumentation, in clinical application, as well as in data analysis and visualization have provided new momentum to magnetocardiography (MCG). On one hand robust, easy to use and budget-priced MCG-systems entered the market and are applied to a multi-centred clinical study. On the other hand highly sophisticated vectormagnetometer systems with >300 SQUID sensors are opening new perspectives in electrocardiology research. Several parameters have recently been introduced to evaluate MCG-signals in order to support diagnosis, therapy follow-up and risk stratification. Particularly interesting is the renaissance of the Hosaka-Cohen-transformation which allows to visualize so-called pseudo current density (PCD) maps. A few examples are given to emphasise the value of these maps.

Animals↗
PubMed1995

Variability maps of body surface ECG in normal subjects.

A method for quantifying the fluctuations of the QRS electrocardiogram over the flat (unrolled) thoracic surface in normal subjects is presented. Serial comparisons were performed on 32-lead ECG recordings and body surface maps from seven healthy men, using as similarity measures correlation and RMS-difference in both time-signal and 2D map domain. Recordings were made on one and the same day, and on different days. The time-signal correlation and RMS-differences were plotted as 2D distributions. Correlation was higher on the front of the torso and RMS-differences were largest in the precordial area. The average time-signal correlation calculated over the QRS in comparisons of signals taken on different days was 0.9717, whereas the corresponding RMS-difference was 57.8 microV. Additionally, 2D comparisons between reconstructed map frames at different time instants in the QRS were carried out, using the 2D versions of the correlation and RMS-difference. The averaged results of the 2D comparisons were close to the time-signal comparison values (respectively 0.9696 and 68.9 microV). Finally, 2D comparisons between isointegral maps (mapping the QRS signal integral) were performed. They yielded even higher correlations (0.98, 3.453 microV s). Although the number of subjects studied was not large, the investigation brought to light important variability ranges that may serve as a basis when detecting pathologies. In addition, the topology of normal ECG variability on the body surface was revealed. This study confirmed the pertinence of correlation and RMS-difference as measures of time-signal and map similarity.

Adult↗
PubMed1995

[The utility of body surface isochrone mapping of recovery time in diagnosing effort angina].

Myocardial ischemia is characterized by ST depression on a standard electrocardiogram caused by shortening of the action potential duration (APD). We investigated whether shortening of the APD can be used as a screening criterion, in place of ST depression, to diagnose effort angina. Estimation of APD was made based on recovery time (RT) on a 16-lead system signal-averaged electrocardiogram (SAE). RT was defined as the interval between the onset of the QRS complex and the maximum positive value during the T wave of SAE. The values of RT measured at each lead were plotted on a graph to produce an electrocardiographic isochrone map. RT were significantly shortened in all electrocardiographic leads in patients with effort angina. Shortening in RT was especially marked in the right precordal leads and was shown to be a highly specific criterion for screening effort angina.

Aged↗
PubMed1991

Signal-averaged body surface mapping for the assessment of low-amplitude potentials. Detailed maps during early ventricular activation in normal subjects.

Body surface isopotential maps around early ventricular activation were investigated in 30 normal subjects by the use of the authors' signal-averaged body surface mapping system. The number of beats averaged was 96-154 (mean, 127). Two distinct patterns were recognized in the appearance of a maximum at the onset of ventricular activation: the maximum in the first type (n = 16) was located on the right anterior chest; the maximum in the second type (n = 14) was on the central or left anterior chest. The site of the earliest ventricular activation was considered to be different in each of these types. During early ventricular activation, 25 subjects (83%) had two minima: one was on the left lateral chest and the other was on the left back. The two minima probably reflect two different receding activation fronts in the ventricles. The data in the present study are important to the understanding of the early ventricular activation process, as well as the diagnosis of heart diseases in which this process is disturbed.

Adolescent↗
PubMedDate not supplied

[Localization of infarction of the anterior and inferior myocardial wall by body surface mapping].

11 patients after anterior myocardial infarction and 7 patients inferior myocardial infarction were subjected to potentials mapping from 87 body surface electrode system. The reference group was made up by 15 healthy individuals. The analysis referred to isopotential and isointegral maps during the 20 ms and 40 ms of the QRS onset and for the entire QRS. It was stated that the occurrence of abnormal potential minimum might be the essential diagnostic criterion. In the case of anterior infarction, the abnormal negative potentials is located in the vicinity of the sternum, whereas in inferior infarction in right and lower part of the chest. The diagnostics of inferior infarction requires additional criteria, ventricular activation time maps especially.

Action Potentials↗