Equivalent Double Layer Research Articles

Electrocardiographic imaging to guide ablation of ventricular arrhythmias and agreement between two different systems.

A recent study using an epicardial-only electrocardiographic imaging (ECGI), suggests that the agreement of ECGI activation mapping and that of the contact mapping for ventricular arrhythmias (VA) is poor. The aim of this study was to assess the diagnostic value of two endo-epicardial ECGI systems using different cardiac sources and the agreement between them. We performed 69 ECGI procedures in 52 patients referred for ablation of VA at our center. One system based on the extracellular potentials was used in 26 patients, the other based on the equivalent double layer model in 9, and both in 17 patients. The first uses up to 224 leads and the second just the 12‑lead ECG. The localization of the VA was done using a segmental model of the ventricles. A perfect match (PM) was defined as a predicted location within the same anatomic segment, whereas a near match (NM) as a predicted location within the same segment or a contiguous one. 44 patients underwent ablation, corresponding to 58 ECGI procedures (37 with the first and 21 with the second system). The percentage of PMs and NMs was not significantly different between the two systems, respectively 76% and 95%, p=0.077, and 97% and 100%, p=1.000. In 14 patients that underwent ablation and had the ECGI performed with both systems, raw agreement for PMs was 79%, p=0.250 for disagreement. ECGI systems were useful to identify the origin of the VAs, and the results were reproducible regardless the cardiac source.

Non-invasive electrocardiographic ventricular mapping based on the equivalent double layer model: different workflows, same accuracy

Abstract Funding Acknowledgements Type of funding sources: None. Background and aim Electrocardiographic imaging (ECGI) is capable of performing activation maps with a single premature beat. The endo-epicardial ECGI system based on the equivalent double layer model (EDL), is a portable system that uses a patient-specific heart torso geometry obtained from a CT-scan or cardiac magnetic resonance (CMR), and a conventional 12-lead ECG. The simplicity of the system allows for its use either as a pre-procedural or intra-procedural tool. The aim of this study was to assess the accuracy of the system in centres using different workflows. Methods We studied consecutive patients referred for ablation of ventricular arrhythmias that had an ECGI performed with the endo-epicardial system based on the EDL model to guide mapping and catheter ablation, at four centres. Three centres performed the ECGI pre-procedurally, two with the use of a bedside portable ECG recorder and one on ambulatory basis with a 12-lead Holter recorder, and ablation was performed either manually or with remote magnetic navigation (RMN). The fourth centre performed the ECGI intra-procedurally, recording the ECG directly from the electrophysiology digital multichannel system, and the ablation was performed manually with the use of intracardiac echo (ICE) in all cases. VAs were localised using a segmental model, which included 22 left ventricular segments (classical 17-segment model, plus the aortic cusps and the papillary muscles), and 12 segments on the right ventricle including 4 on the right ventricular outflow tract (RVOT): Anterior, lateral, right septum and left septum. A perfect match (PM) was defined as a predicted location within the same anatomic segment, whereas a near match (NM) was defined as a predicted location within the same segment or a contiguous one. We studied the three different workflows. Results Sixty-three arrhythmias were studied in 58 patients. The ECGI was performed pre-procedurally with a bedside ECG recorder in 26 cases, pre-procedurally with a Holter recorder in 27 cases and intra-procedurally in 10 cases. The results according to each group are presented in the Table. The accuracy of the ECGI was not different between groups. The system correctly identified the SOO of the VAs in the same or a contiguous segment when compared to the invasive mapping in all patients, regardless of the approach used. The percentage of PM was also not significantly different. The group with ICE guidance had lower fluoroscopy and mapping times, but the success and recurrence rates were similar. Conclusions The results of this multicentre experience show that this ECGI system, using a conventional 12 -lead ECG is simple and accurate across different clinical workflows, and presents a useful and versatile tool to facilitate planning the ablation strategy as well as intra-procedural guidance for mapping and ablation of patients with VAs.

Abstract 12106: Electrocardiographic Imaging Accuracy and Coherence Between Two Different Systems

Introduction: Previous studies reporting on electrocardiographic imaging (ECGI), using an epicardial-only system, have suggested a bad accuracy Hypothesis: Assess the accuracy and coherence of two endo-epicardial ECGI systems using different cardiac sources. Methods: We performed 61 ECGI procedures in 48 patients referred for ablation of frequent idiopathic premature ventricular contractions (PVCs) at our center. The Amycard (EP Solutions SA, Switzerland) system based on the extracellular potential, was used in 26 patients, the VIVO (Catheter Precision, NJ USA) systems based on the equivalent double layer model in 9, and both in 13 patients. The localisation of the PVCs based on ECGI was done using a segmental model with 22 segments on the left ventricle, to include the classical 17 segment model plus the aortic cusps and the papillary muscles, and 12 segments on the right ventricle including 4 on the right ventricular outflow tract (RVOT). A perfect match (PM) was defined as a predicted location within the same anatomic segment, whereas a near match (NM) as a predicted location within the same segment or a contiguous one. Results: Ablation was performed in 42 patients, successful in 76%. The origin of the PVCs was the RVOT in 22 patients, right ventricle in 5, coronary cusps in 3, left ventricle in 3, LV summit in 3, LVOT in 2, papillary muscles in 2, moderator band in 1 and aortomitral continuity in 1. The agreement between the predicted site and the invasive mapping with both systems is depicted in the table. The percentage of PM and NM was not significantly different. In the 13 patients that had the ECGI performed with both systems, we found a NM in 100% and a PM in 70%. (Figure). Conclusions: ECGI is an accurate diagnostic tool with reproducible results regardless the cardiac source used for analysis.

Electrocardiographic imaging a valid tool or an inaccurate toy?

Abstract Funding Acknowledgements Type of funding sources: Private hospital(s). Main funding source(s): Learning Health Background and aim Electrocardiographic imaging (ECGI) is capable of performing an activation map with a single beat. However, previous studies using the epicardial-only system, have suggested a bad accuracy for the assessment of the epicardial breakthrough. Recent systems using endo-epicardial analysis have shown promising results. The aim of this study was to assess the accuracy and reproducibility of two endo-epicardial ECGI systems using different cardiac sources one based on the extracellular-potential, and the other on the equivalent double layer model, respectively the AMYCARD (EP Solutions SA, Switzerland) and VIVO (Catheter Precision, NJ USA) systems. Methods We studied 11 consecutive patients referred for ablation of frequent idiopathic premature ventricular contractions at our center that had an ECGI performed using both systems on the same day. The AMYCARD system uses a dense array of body-surface electrocardiograms with up to 224 leads and VIVO uses just the 12-leads ECG. Both systems use a patient-specific heart torso geometry obtained with a CT-scan or cardiac magnetic resonance. The localisation of the PVCs based on ECGI was done using a segmental model with 22 segments on the left ventricle, to include the classical 17 segment model plus the aortic cusps and the papillary muscles, and 12 segments on the right ventricle including 4 on the right ventricular outflow tract (RVOT): (anterior, lateral, right septum and left septum). A perfect match was defined as a predicted location within the same anatomic segment, whereas a near match as a predicted location within the same segment or a contiguous one. Results The median (Q1-Q3) number of leads used for the AMYCARD was 131 (118-144). Seven patients underwent ablation and in 4 ablation is pending. The predicted locations and the ablation site are depicted on the Table. We found a perfect match between both systems in 73% (Figure) and near match in 91% of cases. In patients that underwent ablation the systems localised the site of origin of the PVCs within the same segment or the contiguous segment in all patients with VIVO and in six out of seven with AMYCARD. Conclusions ECGI is an accurate diagnostic tool with reproducible results regardless the cardiac source used for analysis.

Accuracy of non-invasive anatomical lead localization in CRT patients: BSPM vs 12-lead ECG

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Grant agency AZV, Ministry of Health of the Czech Republic Background Non-invasive, inverse ECG (iECG), estimating the cardiac activation from ECG signals, may be useful both to support CRT implant and optimization. However, most iECG strategies require a 32-250 electrode body surface potential mapping (BSPM), limiting their clinical utility. Objective This proof of concept study evaluates the accuracy of our novel PaceView iECG method to localize the LV/RV pacemaker lead to the cardiac anatomy using either a 96-electrode BSPM or the 12-lead ECG. Methods PaceView generates activation sequences in combination with the equivalent double layer source model to simulate the corresponding ECG signals. An initial activation sequence is iteratively optimized to match simulated and measured ECG signals. A BSPM with 96 electrodes and CT were recorded for every patient with implanted CRT. The CT was used to create patient-specific heart/torso model and to localize the ECG electrodes and CRT leads. From a BSPM, 9 signals were selected to obtain the 12-lead ECG. Both BSPM and 12-lead ECG were used to localize the RV/LV lead as the earliest ventricular activation site. Results In this study 14 consecutive patients with dilated cardiomyopathy were enrolled: mean age 58±9 years, 7 females. The localization error for the RV/LV lead was 10.4±5.4 (max 22) / 11.3±5.5 (max 20.4) mm using the 12 lead ECG and 11.7±6.1 (max 26.2) / 13.5±5.8 (max 24.5) mm for the BSPM. The time used for a 3D activation map computation was 0.9-1.8 s. Conclusion Our preliminary results show that the non-invasive lead localization error, using the 12-lead ECG, is small and comparable with a 96-lead BSPM. Therefore PaceView might be clinically beneficial, by actively localizing the LV/RV pacing sites during CRT implant, and optimize AV or VV delays at CRT follow-ups.

In-vivo endocardial and epicardial quantitative comparison of multi-wave based non-invasive inverse electrocardiography

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): This work was supported by the Dutch Heart Foundation Introduction Non-invasive mapping of ventricular activation using inverse electrocardiography (iECG) in patients with cardiomyopathy during sinus rhythm, may improve risk stratification for sudden cardiac death. However, iECG is complicated by multiple simultaneous endocardial activation waves (multi-wave) mediated by the His-Purkinje system, especially when the QRS complex is narrow. The activation estimation should be based on a realistic physiological model of the His-Purkinje system combining multiple waves initiated at His-Purkinje associated endocardial locations. Equivalent double layer based iECG provides an estimation of both the endocardial and epicardial surface. To improve accuracy, equivalent double layer based iECG was supplemented with electro-anatomical structures associated with the His-Purkinje system to test initial ventricular activation (Figure, Panel C). Multi-wave iECG local activation timing (LAT) maps and invasive LAT maps during sinus rhythm were quantitatively compared. Purpose Quantitative comparison of multi-wave iECG in His-Purkinje mediated cardiac activation using invasive activation maps in patients. Methods Thirteen patients referred for invasive electro-anatomical mapping (EAM) of the endocardial and epicardial surface were included. Prior to EAM, each subject underwent 64 electrode body surface potential mapping, cardiac computed tomography (CT) imaging, and 3D imaging of electrode positions. Anatomical models of the ventricles, lungs and thorax were created using CT images and supplemented with electrode positions (Figure, Panel A-B). Electro-anatomical structures associated with the His-Purkinje system were incorporated in ventricular anatomical models (Figure, Panel C) and multiple simultaneous activation waves were simulated. Invasive endocardial and epicardial LAT maps were quantitatively compared to iECG LAT maps. Invasive EAM LAT maps were quantitatively compared to estimated iECG LAT maps (Figure, Panel D) using inter-map correlation coefficients (CC, Pearson’s) and absolute differences (AD). Results Mean inter-map CC and AD were 0.54 ± 0.19 and 18 ± 7 ms respectively for the epicardial surface (n = 13). Similar to the RV endocardial surface (n = 10, CC = 0.50 ± 0.29, AD = 20 ± 8 ms) and the LV endocardial surface (n = 4, CC = 0.44 ± 0.26, AD = 25 ± 7 ms). Conclusion(s): Quantitative comparison of the multi-wave iECG method showed overall moderate performance. This novel iECG method provides a physiologically more realistic and more robust estimation of sinus rhythm and may serve as a tool for detection of electro-anatomical substrates and risk stratification. Compared to other available non-invasive ECG methods, multi-wave iECG captures His-Purkinje mediated ventricular activation better. This method might also be useful for the accurate detection and localization of structural conduction disorders. Abstract Figure. Multi-Wave inverse electrocardiography

In-vivo validation of non-invasive electrocardiographic imaging based on the equivalent double layer source model using epicardial and endocardial electroanatomical mapping

Abstract Background Noninvasive electrocardiographic imaging (ECGi) using the equivalent double layer (EDL) source model enables both epicardial and endocardial reconstruction of electroanatomical activation patterns during sinus rhythm. The EDL source model has been validated in torso-tank models and animal experiments, however validation in humans using invasive electroanatomical mapping is limited. Purpose Validation of EDL based ECGi using invasive electroanatomical mapping. Methods Ten patients referred for epicardial and endocardial electroanatomical mapping underwent 67 electrode body surface potential mapping (BSPM), cardiac CT imaging and 3D imaging of electrode positions. Anatomical models of the ventricles, lungs and thorax were created and supplemented with electrode positions. Invasive epicardial (4020±1514 contact points), right ventricle endocardial (724±113 contact points) and left ventricle endocardial (459±117 contact points) local activation timing (LAT) maps were compared to ECGi derived LAT maps. Results Included patients (mean age 48±21 years, 80% males) were diagnosed with either arrhythmogenic cardiomyopathy (N=4), dilated cardiomyopathy (N=1), symptomatic premature ventricular complexes (N=3) or myocarditis (N=2). Measured BSMP highly correlated with simulated BSPM (97±2%) with a relative difference of 24% ± 6%. Source models consisted of a mean of 2614±214 nodes with a mean distance between nodes of 8.3±1 mm. Overall, invasive LAT maps and ECGi derived LAT maps showed reasonable correlation for epicardial maps (49% ± 18%) and endocardial maps of the right ventricle (48% ± 27%). Endocardial left ventricular LAT maps showed less correlation (23% ± 28). The absolute difference between invasive and ECGi LAT maps was 16.7±14.2 ms for epicardial maps, 17.2±12.9 ms for right ventricle endocardial maps and 34.0±19.8 ms for left ventricle endocardial maps. Visual comparison showed corresponding areas of breakthrough and regions of latest activation in all cases (Figure). Quantitative comparison of these areas showed a mean absolute difference of 33±7mm or 19±10 ms for epicardial maps, 25±10 mm or 17±13 ms for right ventricle endocardial maps and 39±16 mm or 20±6 ms for left ventricular endocardial maps. Conclusion Overall agreement was observed between EDL based ECGi LAT maps and electroanatomical LAT maps. Future research will focus on further quantification of this agreement and improvement of ECGi mapping accuracy. Funding Acknowledgement Type of funding source: Foundation. Main funding source(s): Netherlands Cardiovascular Research Initiative, an initiative with support of the Dutch Heart Foundation and UCL Hospitals NIHR Biomedical Research Centre.

Correcting Undersampled Cardiac Sources in Equivalent Double Layer Forward Simulations.

Electrocardiographic Imaging (ECGI) requires robust ECG forward simulations to accurately calculate cardiac activity. However, many questions remain regarding ECG forward simulations, for instance: there are not common guidelines for the required cardiac source sampling. In this study we test equivalent double layer (EDL) forward simulations with differing cardiac source resolutions and different spatial interpolation techniques. The goal is to reduce error caused by undersampling of cardiac sources and provide guidelines to reduce said source undersampling in ECG forward simulations. Using a simulated dataset sampled at 5 spatial resolutions, we computed body surface potentials using an EDL forward simulation pipeline. We tested two spatial interpolation methods to reduce error due to undersampling triangle weighting and triangle splitting. This forward modeling pipeline showed high frequency artifacts in the predicted ECG time signals when the cardiac source resolution was too low. These low resolutions could also cause shifts in extrema location on the body surface maps. However, these errors in predicted potentials can be mitigated by using a spatial interpolation method. Using spatial interpolation can reduce the number of nodes required for accurate body surface potentials from 9,218 to 2,306. Spatial interpolation in this forward model could also help improve accuracy and reduce computational cost in subsequent ECGI applications.

Localization of Activation Origin on Patient-Specific Endocardial Surface by the Equivalent Double Layer (EDL) Source Model With Sparse Bayesian Learning.

Ablation treatment of ventricular arrhythmias can be facilitated by pre-procedure planning aided by electrocardiographic inverse solution, which can help to localize the origin of arrhythmia. Our aim was to improve localization accuracy of the inverse solution for activation originating on the left-ventricular endocardial surface, by using a sparse Bayesian learning (SBL). The inverse problem of electrocardiography was solved by reconstructing endocardial potentials from time integrals of body-surface electrocardiograms and from patient-specific geometry of the heart and torso for three patients with structurally normal ventricular myocardium, who underwent endocardial catheter mapping that included pace mapping. Complementary simulations using dipole sources in patient-specific geometry were also performed. The proposed method is using sparse property of the equivalent-double-layer (EDL) model of cardiac sources; it employs the SBL and makes use of the spatio-temporal features of the cardiac action potentials. The mean localization error of the proposed method for pooled pacing sites ( n=52) was significantly smaller ( p=0.0039) than that achieved for the same patients in the study of Erem etal. Simulation experiments localized the source dipoles ( n=48) from forward-simulated potentials with the error of 9.4 ± 4.5mm (mean ± SD). The results of our clinical and simulation experiments demonstrate that localization of left-ventricular endocardial activation by means of the Bayesian approach, based on sparse representation of sources by EDL, is feasible and accurate. The proposed approach to localizing endocardial sources may have important applications in pre-procedure assessment of arrhythmias and in guiding their ablation treatment.

Influence of Modeling Errors on the Initial Estimate for Nonlinear Myocardial Activation Times Imaging Calculated With Fastest Route Algorithm.

Noninvasive reconstruction of cardiac electrical activity has a great potential to support clinical decision making, planning, and treatment. Recently, significant progress has been made in the estimation of the cardiac activation from body surface potential maps (BSPMs) using boundary element method (BEM) with the equivalent double layer (EDL) as a source model. In this formulation, noninvasive assessment of activation times results in a nonlinear optimization problem with an initial estimate calculated with the fastest route algorithm (FRA). Each FRA-simulated activation sequence is converted into the ECG. The best initialization is determined by the sequence providing the highest correlation between predicted and measured potentials. We quantitatively assess the effects of the forward modeling errors on the FRA-based initialization. We present three simulation setups to investigate the effects of volume conductor model simplifications, neglecting the cardiac anisotropy and geometrical errors on the localization of ectopic beats starting on the ventricular surface. For the analysis, 12-lead ECG and 99 electrodes BSPM system were used. The areas in the heart exposing the largest localization errors were volume conductor model and electrode configuration specific with an average error <10mm. The results show the robustness of the FRA-based initialization with respect to the considered modeling errors.

Computer simulations to investigate the causes of T-wave notching

Drugs that cause strong hERG potassium channel block (e.g., dofetilide, quinidine) cause T-wave notching. It has been suggested that this is due to prolongation of mid-myocardial (M) cells’ action potential duration relative to endocardial and epicardial cells. However, the role of M cells in intact human hearts is debated. We simulated 2025 electrocardiograms representing changes in ventricular action potentials using the equivalent double layer mode that does not include M-cells. Action potential changes included prolongation, triangularization, squaring, and bumps in late repolarization, which have been observed experimentally and in single cell models with block of the hERG potassium channel. Changes were applied globally and spatially dispersed. Action potential bumps (slowing in late repolarization) produced T-wave notching similar to that observed clinically in healthy subjects receiving dofetilide or quinidine. Conversely, all other action potential changes (i.e., prolongation, triangularization, squaring), either global or spatially dispersed, resulted in T-wave changes, but did not cause T-wave notching. This study demonstrates that M-cells are not required to simulate T-wave notching.

Faradaic Impedance Spectroscopy for Detection of Small Molecules Binding using the Avidin-Biotin Model

The changes in the Faradaic impedance of gold/biomolecules system due to specific binding of small molecule to a significantly larger binding protein molecule were investigated. The biotin (244.31Da) - avidin (66000Da) couple was used as a model for small ligand - binding protein biorecognition. The study was carried out under open circuit potential in the presence of [Fe(CN)6]−3/−4 redox couple. An equivalent electrical circuit was proposed and used for the interpretation of the recorded impedance spectra.Adsorption of thiolated avidin increased the electron transfer resistance, Rct, by a factor of about 7.5 while subsequent addition of biotin within the concentration range of 4.1-40.9nM reduced the value of Rct by amount proportional to the biotin concentration. The addition of biotin did not affect, however, the equivalent double layer capacitance or other equivalent circuit parameters.A simple model based on effective surface coverage by the avidin molecules and the effect of the added biotin on electron transfer through the coated surface is proposed. A model for the minimum detection limit based on the random distribution of the binding protein and its dimensions is proposed.

Modelling of a novel high-impedance matching layer for high frequency (>30 MHz) ultrasonic transducers

This work describes a new approach to impedance matching for ultrasonic transducers. A single matching layer with high acoustic impedance of 16MRayls is demonstrated to show a bandwidth of around 70%, compared with conventional single matching layer designs of around 50%. Although as a consequence of this improvement in bandwidth, there is a loss in sensitivity, this is found to be similar to an equivalent double matching layer design. Designs are calculated by using the KLM model and are then verified by FEA simulation, with very good agreement Considering the fabrication difficulties encountered in creating a high-frequency double matched design due to the requirement for materials with specific acoustic impedances, the need to accurately control the thickness of layers, and the relatively narrow bandwidths available for conventional single matched designs, the new approach shows advantages in that alternative (and perhaps more practical) materials become available, and offers a bandwidth close to that of a double layer design with the simplicity of a single layer design. The disadvantage is a trade-off in sensitivity. A typical example of a piezoceramic transducer matched to water can give a 70% fractional bandwidth (comparable to an ideal double matched design of 72%) with a 3dB penalty in insertion loss.

Repolarization features as detectable from electrograms and electrocardiograms

This contribution discusses the feasibility of extracting the major features of repolarization: its spatio-temporal behaviour, and how much of its global or local behaviour might be deduced from signals that can be observed experimentally. The analysis presented is based on source-volume-conductor configurations ranging from the classic cable theory, with sources derived from reaction diffusion computations, to a realistic thorax model comprising a whole heart model with electric sources represented by the equivalent electric double layer. The analysis focuses on the fact that the local activation recovery interval (ARI) at regions activated by expanding wave fronts is significantly longer than those activated by contracting ones. The consequences of this effect on observed magnitude and wave form of recorded signals are illustrated.

Simulation study of a magnetocardiogram based on a virtual heart model: effect of a cardiac equivalent source and a volume conductor**Project supported by the State Key Development Program for Basic Research of China (Grant Nos. 2007CB512100 and 2006CB601007), the National Natural Science Foundation of China (Grant No. 10674006), the National High Technology Research and Development Program of China (Grant No.

In this paper, we present a magnetocardiogram (MCG) simulation study using the boundary element method (BEM) and based on the virtual heart model and the realistic human volume conductor model. The different contributions of cardiac equivalent source models and volume conductor models to the MCG are deeply and comprehensively investigated. The single dipole source model, the multiple dipoles source model and the equivalent double layer (EDL) source model are analysed and compared with the cardiac equivalent source models. Meanwhile, the effect of the volume conductor model on the MCG combined with these cardiac equivalent sources is investigated. The simulation results demonstrate that the cardiac electrophysiological information will be partly missed when only the single dipole source is taken, while the EDL source is a good option for MCG simulation and the effect of the volume conductor is smallest for the EDL source. Therefore, the EDL source is suitable for the study of MCG forward and inverse problems, and more attention should be paid to it in future MCG studies.

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, 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.

Model-based inferences for clinical applications of the ECG

Doctor Macchi reported on the progress of an animal model study of electric propagation initiated by electric stimuli. Doctor Oostendorp first gave an introduction to the inverse problem of cardiac activation time mapping (ATM), the determination of the depolarization times at the myocardial surface as computed from the equivalent double layer (EDL) source model, and a biophysical model of the volume conductor involved: the passive conductive tissues inside the thorax. Doctor van Oosterom presented some results from an ongoing study aimed at extracting more information about the atrial electric activity from potentials observed on the body surface: the ECG. Doctor Zabel discussed the potential of using a standard 12-lead ECG device for estimating body surface potential maps.

Genesis of the P wave: Atrial signals as generated by the equivalent double layer source model

To assess the effectiveness of the equivalent surface source model in the simulation of atrial signals as observed in ECG leads. 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. 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. 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.

Volume conductor effects involved in the genesis of the P wave

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. 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. 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. The inhomogeneities of lungs and atrial blood cavities need to be incorporated in volume conductor models linking atrial electric activity to body surface potentials.

A RECONCILIATION OF MATHEMATICAL MODELS FOR SPONTANEOUS MINERALIZATION POTENTIALS1

AbstractTwo methods for computing spontaneous mineralization potentials in the region external to the source body are reviewed. The first of these is a long‐established technique in which the causation is assumed to be a distribution of simple current source on the boundary of the mineralization. The second is a more recent technique which assumes a surface distribution of current dipole moment (double layer) along the boundary of the source body.The former technique is a special case of a more general spontaneous potential (SP) model in which the source is a density of current dipole moment (current polarization) distributed throughout the mineralization. As far as the potentials in the region external to the source body are concerned this current polarization can be simply related to an equivalent double layer source function, i.e. the potential discontinuity produced over the boundary of the mineralization by an equivalent double layer model.This simple relationship suggests an integral equation technique for the exact numerical solution of boundary value problems appropriate to the polarization model for spontaneous mineralization potentials. The technique is applied to exploring the justification of interpreting mineralization self‐potentials by the traditional approach.