PubMed Health⌕ Search

Biomedical subjects

Adriaan van Oosterom

Publications and source records attributed to Adriaan van Oosterom.

11 recordsLinked to original sources
PubMed2006

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. The optimization criterion used was derived from the singular value decomposition of the data matrices. RESULTS: While maintaining VR, VL, VF, V1 and V4, the 4 new electrode positions increased the ratio of the eighth and the first singular values of the data matrices of the new configuration about 5-fold compared with that of the conventional electrode positions. CONCLUSION: The adapted lead system produces a more complete view on AF compared with that of the standard 12-lead system.

Atrial Fibrillation↗
PubMed2006

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. These served as the gold standard while searching for an optimal orthogonal lead system for the estimation of the heart vector while using a limited number of electrode positions. Six electrode configurations and their dedicated transfer matrices were tested by using 10 different episodes of simulated AF and 25 different thorax geometries. RESULTS: Root-mean-square-based relative estimation error of the vectorcardiogram using the Frank electrodes was 0.39. An adaptation of 4 of the 9 electrode locations of the standard electrocardiogram, with 1 electrode moved to the back, reduced the error to 0.24. CONCLUSION: The Frank lead system is suboptimal for estimating the equivalent dipole components (VCG) during AF. Alternative electrode configurations should include at least 1 electrode on the back.

Action Potentials↗
PubMed2006

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. The data were analyzed by inspecting body surface potential maps and the XYZ signals of the vectorcardiogram. RESULTS: Standard P-wave features exhibited normal values. The local potential extremes were found at positions not sampled by the standard leads. The PQ segment was found to be not isoelectric, the time course of the potential distribution being very similar to that during the P wave but for a reversed polarity and about 3-fold lower magnitudes. CONCLUSION: The results demonstrate a significant involvement of atrial repolarization during the PQ interval and essentially discordant "atrial T waves," suggesting a small dispersion of atrial action potential durations.

Atrial Function↗
PubMed2006

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.

Algorithms↗
PubMed2005

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. These geometries were used to construct a numerical volume conductor model. The boundary element method was applied to simulate the potentials on the surface of the thorax generated by the atria. The equivalent double layer served as the source description during depolarization. Recorded body surface potentials were used as a check on the simulations. Subsequently, the conductivities in the model were varied to determine their influence on P wave morphology and amplitude. RESULTS: The model with realistic conductivity values for blood and lungs produced potentials that closely matched the measured ones (correlation 98%). The subsequent variation of conductivity of blood and lungs revealed a major influence on P wave morphology and amplitude: a mean reduction in amplitude by 42%, with pronounced inter-lead differences. CONCLUSION: The inhomogeneities of lungs and atrial blood cavities need to be incorporated in volume conductor models linking atrial electric activity to body surface potentials.

Action Potentials↗
PubMed2005

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 ion-kinetics of the units was based on the formulation of Courtemanche et al. The simulated transmembrane potentials following a normal sinus beat, as well as those during atrial fibrillation, were projected on the 1297 nodes of the surface encapsulating all atrial myocytes (endocardium and epicardium). The transmembrane potentials at these nodes formed the source strengths of the elements of the equivalent generator, which were used to compute body surface potentials. RESULTS: After invoking slight adaptations of the timing of depolarization of the transmembrane potentials, the simulated signals during the P wave closely corresponded to recorded ones. The correspondence during the entire PR interval improved markedly after the inclusion of early repolarization effects in the interval between the end of the P wave and onset of QRS. This demanded a shortening of the mean action potential duration generated by the Courtemanche model. The simulated ECGs related to atrial fibrillation demonstrated the characteristic features of those clinically observed. CONCLUSIONS: The equivalent double layer is a useful source model for the genesis of atrial signals observed on the thorax. The interval from the end of the P wave to onset of QRS is not iso-electric. The Courtemanche model of the ion-kinetics of atrial cells needs to be adapted when applied to represent the activity of healthy, 'common' atrial myocytes.

Adult↗
PubMed2005

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. Following this introduction are overviews of the present state of the inverse problem of electrocardiography and the underlying assumptions of this form of simulation and modeling. We conclude with a summary of the needs that we feel must be addressed to achieve the full potential of electrically based imaging of the heart.

Computer Graphics↗
PubMed2003

Brain symmetry and topographic analysis of lateralized event-related potentials.

OBJECTIVE: We investigated the influence of symmetry assumptions implicit in the derivation and the use of event-related lateralized potentials (ERLs), such as the lateralized readiness potential (LRP). We describe these assumptions and demonstrate several alternative computational methods. METHODS: Using analytical methods and forward simulations, we computed the error in the ERL topography that results from deviations in symmetry between homologous brain areas. Based on analytical considerations we show that, for source analysis, the ERL derivation provides no benefits compared to a single subtraction of the two (left-lateralized and right-lateralized) conditions underlying the ERL. RESULTS: Relative errors of 10% in the ERL topography are found if the location of an active region in one hemisphere differs by 10 mm from the symmetric location as compared to the other hemisphere A difference of 30 degrees in orientation results in a relative error of the ERL of 40%. Differences in source strength between hemispheres result in an ERL error that is half the size of the relative strength difference. CONCLUSIONS: We estimate that, due to violations of the symmetry assumption underlying the ERL, errors in the ERL topography of 10-40% can be expected. Source analysis does not benefit from the ERL. In topographic mapping and source analysis, the double subtraction of the ERL should be approached with caution and the single subtraction of the ERPs of two lateralized conditions should be first analyzed whenever possible. We suggest that analyses based on the topography of the ERL should only be performed after the assumption of symmetry has been validated.

Brain↗
PubMed2003

Atrial excitation assuming uniform propagation.

INTRODUCTION: We investigated the spread of the excitation wave over the atria following initiation in a given focus in an atrial model containing its overall geometry only, i.e., without atrial bundles. METHODS AND RESULTS: The propagation velocity of the excitation wave was taken to be uniform, and the wall thickness was discarded. The timing of excitation of any point on the atrium thus becomes directly proportional to its shortest distance over the atrial wall to the focus. Despite these gross simplifications, the general nature of the excitation sequence found corresponded closely to clinical data reported in the literature. This suggests that the complex overall geometry of the atria dominates the timing of the excitation. A highly intriguing observation from this study was that, when looking at the pathways from the sinus node to all other points on the atrium, prominent routes became visible even though no such pathways formed part of the model of the atrial geometry used. The locations of these prominent routes coincide with those of various distinct bundles in the atria. Possible inferences of these observations are discussed. CONCLUSION: Based upon comparison with data from other studies, it is concluded that, during stable heart rhythms, propagation of the atrial excitation wave is well approximated by an assumption of uniform velocity, even though no atrial bundles were included in the model. The overall geometry seems to be the dominant factor in the spread of excitation.

Algorithms↗
PubMed2003

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. METHODS AND RESULTS: The source description of a biophysical model that previously was shown to yield realistic T waveforms was analyzed in order to exploit its relation to the transmembrane potentials of the cardiac myocytes at the surface bounding the myocardium. The product of this analysis is the dominant T wave: a waveform that describes the slope of the transmembrane potential. It is shown that the dominant T wave can be estimated easily from the matrix of sampled lead potentials. The timing of its peak reveals the mean of the repolarization times of the involved transmembrane potentials. The amplitude of the peak is the maximum downward slope of the transmembrane potential. This amplitude is independent of the volume conductor effects of the tissues surrounding the heart. The estimate of the dominant T wave retains this property. CONCLUSION: The dominant T wave reflects the derivative of the recovery phase of a generalized transmembrane potential. Its amplitude is independent of the volume conductor properties of the tissues surrounding the heart. This is a unique feature that greatly facilitates the interpretation and application of the other signal features of the dominant T wave.

Algorithms↗