Peter van Dam
Research interests
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InterestsNon-Invasive Imaging
Publications
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A toolkit for forward/inverse problems in electrocardiography within the SCIRun problem solving environment.
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference. 08/2011; 2011:267-70.
Computational modeling in electrocardiography often requires the examination of cardiac forward and inverse problems in order to non-invasively analyze physiological events that are otherwise inaccessible or unethical to explore. The study of these models can be performed in the open-source SCIRun p... [more] Computational modeling in electrocardiography often requires the examination of cardiac forward and inverse problems in order to non-invasively analyze physiological events that are otherwise inaccessible or unethical to explore. The study of these models can be performed in the open-source SCIRun problem solving environment developed at the Center for Integrative Biomedical Computing (CIBC). A new toolkit within SCIRun provides researchers with essential frameworks for constructing and manipulating electrocardiographic forward and inverse models in a highly efficient and interactive way. The toolkit contains sample networks, tutorials and documentation which direct users through SCIRun-specific approaches in the assembly and execution of these specific problems.
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Analysis of the criteria of activation-based inverse electrocardiography using convex optimization.
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference. 08/2011; 2011:3913-6.
In inverse electrocardiography (ECG), the problem of finding activation times on the heart noninvasively from body surface potentials is typically formulated as a nonlinear least squares optimization problem. Current solutions rely on iterative algorithms which are sensitive to the presence of local... [more] In inverse electrocardiography (ECG), the problem of finding activation times on the heart noninvasively from body surface potentials is typically formulated as a nonlinear least squares optimization problem. Current solutions rely on iterative algorithms which are sensitive to the presence of local minima. As a result, improved initialization approaches for this problem have been of considerable interest. However, in experiments conducted on a subject with Wolff-Parkinson-White syndrome, we have observed that there may be a mismatch between favorable solutions of the optimization problem and solutions with the desired physiological characteristics. In this work, we use a method based on a convex optimization framework to explore the solution space and analyze whether the optimization criteria target their intended objective.
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Spatiotemporal estimation of activation times of fractionated ECGs on complex heart surfaces.
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference. 08/2011; 2011:5884-7.
Identification of electrical activation or depolarization times on sparsely-sampled complex heart surfaces is of importance to clinicians and researchers in cardiac electrophys-iology. We introduce a spatiotemporal approach for activation time estimation which combines prior results using spatial an... [more] Identification of electrical activation or depolarization times on sparsely-sampled complex heart surfaces is of importance to clinicians and researchers in cardiac electrophys-iology. We introduce a spatiotemporal approach for activation time estimation which combines prior results using spatial and temporal methods with our own progress on gradient estimation on triangulated surfaces. Results of the method applied to simulated and canine heart data suggest that improvements are possible using this novel combined approach.
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1.08Impact points
Potential applications of the new ECGSIM.
Journal of electrocardiology. 07/2011; 44(5):577-83.
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 tho... [more] 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. These examples include simulation of the atrial electrocardiogram, improved accessibility of endocardial source locations, and an explanation of ST elevations accompanying true TQ depressions.
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4.56Impact points
Mechanoelectrical coupling enhances initiation and affects perpetuation of atrial fibrillation during acute atrial dilation.
Heart rhythm : the official journal of the Heart Rhythm Society. 11/2010; 8(3):429-36.
Acute atrial dilation increases the susceptibility to atrial fibrillation (AF). However, the mechanisms by which atrial stretch may contribute to the initiation and perpetuation of AF remain to be determined. The purpose of this study was to use a novel multiscale model of atrial electromechanics an... [more] Acute atrial dilation increases the susceptibility to atrial fibrillation (AF). However, the mechanisms by which atrial stretch may contribute to the initiation and perpetuation of AF remain to be determined. The purpose of this study was to use a novel multiscale model of atrial electromechanics and mechanoelectrical feedback to test the hypothesis that acute stretch increases vulnerability to AF by heterogeneous activation of stretch-activated channels. Human atria were represented by a triangular mesh obtained from magnetic resonance imaging data. Atrial trabecular bundle structure was incorporated by varying thicknesses of the atrial wall. Atrial membrane behavior was modeled by the Courtemanche-Ramirez-Nattel model with the addition of a nonselective stretch-activated cation current (I(sac)). Mechanical behavior was modeled by a series elastic, a contractile, and a parallel elastic element in which contractile force was related to intracellular concentration of free calcium and sarcomere length. Acute atrial dilation was simulated by increasing stretch throughout the atrial wall. Stimulation near the pulmonary vein ostia at an interval of 600 ms induced AF at an overall stretch ratio of 1.10. Initiation and perpetuation of AF in our model were related to increased dispersion of effective refractory period, conduction slowing, and local conduction block, all related to heterogeneous activation of I(sac). Upon local contraction, mechanoelectrical coupling affects perpetuation of AF by temporarily changing local excitability. During acute atrial dilation, heterogeneous activation of I(sac) enhances initiation and can affect perpetuation of AF.
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1.08Impact points
Improving sensing and detection performance in subcutaneous monitors.
Journal of electrocardiology. 09/2009;
Implantable loop recorders (ILRs) are used for continuous assessment of patients at risk for syncope and arrhythmia. Device accuracy depends on appropriate sensing of the patient's electrocardiogram (ECG) signal. However, current methods for sensing cardiac electrical activity rely on simple thr... [more] Implantable loop recorders (ILRs) are used for continuous assessment of patients at risk for syncope and arrhythmia. Device accuracy depends on appropriate sensing of the patient's electrocardiogram (ECG) signal. However, current methods for sensing cardiac electrical activity rely on simple threshold detectors that are computationally efficient but nonspecific. We test the hypothesis that better ILR implant positions will increase detection accuracy. Ten healthy subjects were studied as they assumed 12 different postures. Body surface potential map (BSM) recordings were used to estimate bipolar R-wave amplitudes for 64 potential implant sites at 360 orientations per site. Optimal sites were identified as the combination of position and orientation that consistently gave the largest signal and the lowest variability during posture changes. Results showed that posture impacts the R-wave amplitude in both BSM and derived bipolar ECGs in healthy subjects. Specific postures are associated with significant drops in R-wave signal amplitude that could cause loss of signal detection in ILRs, especially in positions likely to displace the diaphragm. R-wave changes occurred abruptly as posture was changed. Optimal implant locations cluster near the center of the chest, aligned with the cardiac axis, consistent with the steeper isoelectric gradients known to be associated with these positions.
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2.41Impact points
Non-Invasive Imaging of Cardiac Activation and Recovery.
Annals of biomedical engineering. 07/2009;
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, ... [more] 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. The parameter estimation procedure involved is non-linear, and consequently requires the specification of initial estimates of its solution. Those of the timing of depolarization were based on the fastest route algorithm, taking into account properties of anisotropic propagation inside the myocardium. Those of recovery were based on electrotonic effects. Body surface potentials and individual geometry were recorded on: a healthy subject, a WPW patient and a Brugada patient during an Ajmaline provocation test. In all three cases, the inversely estimated timing agreed entirely with available physiological knowledge. The improvements to the inverse procedure made are attributed to our use of initial estimates based on the general electrophysiology of propagation. The quality of the results and the required computation time permit the application of this inverse procedure in a clinical setting.
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Application of the fastest route algorithm in the interactive simulation of the effect of local ischemia on the ECG.
Med. Biol. Engineering and Computing. 01/2009; 47:11-20.
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1.76Impact points
Application of the fastest route algorithm in the interactive simulation of the effect of local ischemia on the ECG.
Medical & biological engineering & computing. 10/2008;
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. with a response time in the order of a second. The timing of ventricular ischemi... [more] 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. with a response time in the order of a second. The timing of ventricular ischemic activation was computed by using the fastest route algorithm, based on locally reduced values of the propagation velocities derived from a standard, normal activation sequence. The effect of these local reductions of the velocities on the total activation sequence, as well as the changes in the electrocardiogram that these produce, are presented.
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1.87Impact points
Analysing the potential of Reveal for monitoring cardiac potentials.
Europace : European pacing, arrhythmias, and cardiac electrophysiology : journal of the working groups on cardiac pacing, arrhythmias, and cardiac cellular electrophysiology of the European Society of Cardiology. 12/2007; 9 Suppl 6:vi119-23.
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 inve... [more] 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. Additionally, the model is used for determining the optimal implant location of the device. METHODS AND RESULTS: Sinus rhythm ECG of a complete heart cycle was simulated by means of a biophysical model. Different volume conductors were created to investigate the effect of the insulating boundary of the ILR. The Elg closely matched the nearby bipolar ECG, both in morphology and in amplitude. The optimal localization and orientation of the ILR was found to depend on the Elg signal feature of interest, e.g. PQ, QRS, or STT waveforms. CONCLUSION: The differences between the bipolar ECG on the surface and the subcutaneous electrogram are negligible. The optimal implant location may be based on nearby surface recordings. The simulation model is an eligible tool for determining the optimal implant location for the ILR, for all signal features of interest.
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1.87Impact points
Volume conductor effects involved in the genesis of the P wave.
Europace : European pacing, arrhythmias, and cardiac electrophysiology : journal of the working groups on cardiac pacing, arrhythmias, and cardiac cellular electrophysiology of the European Society of Cardiology. 10/2005; 7 Suppl 2:30-8.
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, hear... [more] 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.
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3.70Impact points
Atrial excitation assuming uniform propagation.
Journal of cardiovascular electrophysiology. 11/2003; 14(10 Suppl):S166-71.
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, an... [more] 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.
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Mechanoelectrical coupling enhances initiation and affects perpetuation of atrial fibrillation during acute atrial dilation
Heart Rhythm.
BackgroundAcute atrial dilation increases the susceptibility to atrial fibrillation (AF). However, the mechanisms by which atrial stretch may contribute to the initiation and perpetuation of AF remain to be determined.ObjectiveThe purpose of this study was to use a novel multiscale model of atrial e... [more] BackgroundAcute atrial dilation increases the susceptibility to atrial fibrillation (AF). However, the mechanisms by which atrial stretch may contribute to the initiation and perpetuation of AF remain to be determined.ObjectiveThe purpose of this study was to use a novel multiscale model of atrial electromechanics and mechanoelectrical feedback to test the hypothesis that acute stretch increases vulnerability to AF by heterogeneous activation of stretch-activated channels.MethodsHuman atria were represented by a triangular mesh obtained from magnetic resonance imaging data. Atrial trabecular bundle structure was incorporated by varying thicknesses of the atrial wall. Atrial membrane behavior was modeled by the Courtemanche-Ramirez-Nattel model with the addition of a nonselective stretch-activated cation current (Isac). Mechanical behavior was modeled by a series elastic, a contractile, and a parallel elastic element in which contractile force was related to intracellular concentration of free calcium and sarcomere length.ResultsAcute atrial dilation was simulated by increasing stretch throughout the atrial wall. Stimulation near the pulmonary vein ostia at an interval of 600 ms induced AF at an overall stretch ratio of 1.10. Initiation and perpetuation of AF in our model were related to increased dispersion of effective refractory period, conduction slowing, and local conduction block, all related to heterogeneous activation of Isac. Upon local contraction, mechanoelectrical coupling affects perpetuation of AF by temporarily changing local excitability.ConclusionDuring acute atrial dilation, heterogeneous activation of Isac enhances initiation and can affect perpetuation of AF.
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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 investiga... [more] 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. Additionally, the model is used for determining the optimal implant location of the device. Methods and results Sinus rhythm ECG of a complete heart cycle was simulated by means of a biophysical model. Different volume conductors were created to investigate the effect of the insulating boundary of the ILR. The Elg closely matched the nearby bipolar ECG, both in morphology and in amplitude. The optimal localization and orientation of the ILR was found to depend on the Elg signal feature of interest, e.g. PQ, QRS, or STT waveforms. Conclusion The differences between the bipolar ECG on the surface and the subcutaneous electrogram are negligible. The optimal implant location may be based on nearby surface recordings. The simulation model is an eligible tool for determining the optimal implant location for the ILR, for all signal features of interest.
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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. with a response time in the order of a second. The timing of ventricular ischemi... [more] 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. with a response time in the order of a second. The timing of ventricular ischemic activation was computed by using the fastest route algorithm, based on locally reduced values of the propagation velocities derived from a standard, normal activation sequence. The effect of these local reductions of the velocities on the total activation sequence, as well as the changes in the electrocardiogram that these produce, are presented.
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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, ... [more] 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. The parameter estimation procedure involved is non-linear, and consequently requires the specification of initial estimates of its solution. Those of the timing of depolarization were based on the fastest route algorithm, taking into account properties of anisotropic propagation inside the myocardium. Those of recovery were based on electrotonic effects. Body surface potentials and individual geometry were recorded on: a healthy subject, a WPW patient and a Brugada patient during an Ajmaline provocation test. In all three cases, the inversely estimated timing agreed entirely with available physiological knowledge. The improvements to the inverse procedure made are attributed to our use of initial estimates based on the general electrophysiology of propagation. The quality of the results and the required computation time permit the application of this inverse procedure in a clinical setting.
Following (1)
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Thom Oostendorp
Radboud Universiteit Nijmegen
