Milan Tysler - Academia.edu (original) (raw)
Papers by Milan Tysler
Journal of Electrocardiology, Nov 1, 2021
Computing in Cardiology (CinC), 2012, Sep 14, 2016
Comparison of the localization error of inverse estimation of the origin of premature ventricular... more Comparison of the localization error of inverse estimation of the origin of premature ventricular contraction using three different formulations of transfer matrix between the equivalent source and the surface potentials was performed in this study. Body surface potential maps measured in 63 precordial leads during nine spontaneous PVCs in one patient provided by Karlsruhe Institute of Technology in EDGAR database were used as input data. The localization error was evaluated with respect to two reference points PVC1 and PVC2 assigned during the ablation procedure. The transfer matrices for epicardial potentials, transmembrane voltages and dipoles situated on the joined endo-and-epicardial surface were used for inverse computation searching the best single point generator representing the input data For all nine considered PVCs the locations of the inverse results were very stable-for particular transfer matrix they resulted in the same point or in adjoining points for all cases. Mean localization error with respect to PVC1 or PVC2 was from 21.3 to 26.2 mm and from 15.0 to 26.4 mm respectively. The results obtained by inverse solution supposing single point source were similar regardless of the source formulation.
The activation propagation characteristics obtained when using homogeneous monodomain model (MM) ... more The activation propagation characteristics obtained when using homogeneous monodomain model (MM) of the cardiac ventricles and the model based on cellular automaton (CA) are compared in this study. The MM comprises the reaction — diffusion equation of the propagation and the modified FitzHugh-Nagumo equations of the electrical excitation of cardiac cells. This model was simulated in Comsol Multiphysics environment. Model based on CA was simulated in Matlab program environment. Realistic activation time of about 80 ms was obtained for the whole ventricles when activation was started in nine analytically defined points. Differences in activation times obtained from the numerical solutions using MM and CA models were less than ±10 ms.
Advances in Electrical and Electronic Engineering, Jun 28, 2011
Elektronika : konstrukcje, technologie, zastosowania, 2005
Frontiers in Physiology, Jun 9, 2023
Introduction: Localization of premature ventricular contraction (PVC) origin to guide the radiofr... more Introduction: Localization of premature ventricular contraction (PVC) origin to guide the radiofrequency ablation (RFA) procedure is one of the prominent clinical goals of non-invasive electrocardiographic imaging. However, the results reported in the literature vary significantly depending on the source model and the level of complexity in the forward model. This study aims to compare the paced and spontaneous PVC localization performances of dipole-based and potential-based source models and corresponding inverse methods using the same clinical data and to evaluate the effects of torso inhomogeneities on these performances.Methods: The publicly available EP solution data from the EDGAR data repository (BSPs from a maximum of 240 electrodes) with known pacing locations and the Bratislava data (BSPs in 128 leads) with spontaneous PVCs from patients who underwent successful RFA procedures were used. Homogeneous and inhomogeneous torso models and corresponding forward problem solutions were used to relate sources on the closed epicardial and epicardial–endocardial surfaces. The localization error (LE) between the true and estimated pacing site/PVC origin was evaluated.Results: For paced data, the median LE values were 25.2 and 13.9 mm for the dipole-based and potential-based models, respectively. These median LE values were higher for the spontaneous PVC data: 30.2–33.0 mm for the dipole-based model and 28.9–39.2 mm for the potential-based model. The assumption of inhomogeneities in the torso model did not change the dipole-based solutions much, but using an inhomogeneous model improved the potential-based solutions on the epicardial–endocardial ventricular surface.Conclusion: For the specific task of localization of pacing site/PVC origin, the dipole-based source model is more stable and robust than the potential-based source model. The torso inhomogeneities affect the performances of PVC origin localization in each source model differently. Hence, care must be taken in generating patient-specific geometric and forward models depending on the source model representation used in electrocardiographic imaging (ECGI).
De Gruyter eBooks, Dec 31, 1988
During multi-lead ECG recording, some electrodes can be identified as broken and thus information... more During multi-lead ECG recording, some electrodes can be identified as broken and thus information from those electrodes cannot be used for the inverse problem of electrocardiography. The objective of this study is to explore the significance of individual ECG electrodes derived from the patient-specific transfer matrix for homogeneous volume conductor. Four multi-lead ECG measurement datasets with corresponding geometries were used for this study. The transfer matrices were computed using the boundary element method. The significance of individual torso electrodes for a given position of the dipole as the equivalent heart generator was assessed by the singular value decomposition of the transfer matrices for the forward and inverse problem of electrocardiography, respectively. The study showed that the position of the most significant electrodes depends on the position of the heart within the chest and the position of the dipole as an equivalent heart generator. The positions of the first 20% of the most significant electrodes for the forward and inverse problem differ from 0% to 16%.
High-resolution multichannel bioelectric potential measurement is required for diagnostic methods... more High-resolution multichannel bioelectric potential measurement is required for diagnostic methods of various cardiac and brain diseases. The systems previously developed in our lab are streaming measured data to PC over an optical USB cable. Disadvantages of these systems are that the personnel should be careful when manipulating with the cables and difficulty of mounting the electrodes on the patients. New wireless standards enable high data rate transmission. The newest wireless Bluetooth and Wi-Fi standards were studied and specifications of these standards were evaluated for possible usage in multichannel battery powered measuring systems.
Advanced electrocardiographic diagnostic methods of various cardiovascular diseases need high res... more Advanced electrocardiographic diagnostic methods of various cardiovascular diseases need high resolution multichannel measurement of ECG signals that offer much more information than the standard 12-lead ECG. To obtain such ECG signals in required quality a special multichannel electrocardiograph ProCardio 8 was developed. The system is designed as a virtual instrument consisting of an external intelligent measuring unit connected via optical USB interface to a controlling PC running the measuring and data analyzing software. The system can be configured for measurement of up to 144 standard and/or mapping ECG leads using active or passive Ag-AgCl or carbon electrodes. Most of the measuring and newly designed data processing software is written in MATLAB and its compiled version can be deployed as a stand-alone application on any computer running Windows. The modular software architecture consists of real-time modules for the control and checking of the measuring system, data acquisition and signal monitoring as well as modules for off-line data analysis including ECG processing, body surface potential mapping, integral mapping and data preparation for non-invasive model-based electrocardiographic imaging based on inverse solutions and serving as an advanced diagnostic tool.
Computing in Cardiology Conference, Sep 1, 2014
In this simulation study an identification of the latest depolarized site of the ventricles from ... more In this simulation study an identification of the latest depolarized site of the ventricles from integral body surface potential maps (BSPMs) using an inverse solution in terms of one or two dipoles was tested on models of a normal heart. The input data for the inverse solution were integral BSPMs computed from the interval of the last 5 or 10 ms of depolarization. It was assumed that such integral BSPMs represents a small activated area so that they can be approximated by a single dipole. The BSPMs were produced by two types of normal heart-torso models. The very last activated points on the surfaces of the ventricular models were known. If there was a single latest activated area, the localization error was between 0.5 and 3.5 cm. If there were two distinct latest activated areas, the localization error was between 1.7 and 2.9 cm. The proposed method could be used for the preliminary noninvasive assessment of the latestactivated ventricular areas, which are of great interest for cardiac resynchronization therapy.
Computing in Cardiology (CinC), 2012, Dec 30, 2020
In real experiments with body surface potential mapping, it is usual that the measuring electrode... more In real experiments with body surface potential mapping, it is usual that the measuring electrodes cannot be placed regularly because of other patches of sensors used on the torso during the procedure. The influence of accidentally missing the most powerful ECG signals on the inverse localization of the pacing site using a single dipole was studied. Body surface potential maps from three tank experiments on the pig or dog heart and one measurement from the patient's torso were used for inverse computation of the known pacing site position using the full electrodes setup and setups omitting 10% and 20% of the signals with the largest power. The sensitivity of the inverse method was evaluated by localization error between the true and computed pacing site. The localization error did not change (13mm or 7mm) or changed from 13 to 24 mm for tank data, but it increased rapidly from 19 to 41/68 mm for human data. The largest effect of electrodes' omission using human data can be explained by the largest complexity of the human torso what is not fully included in the computational torso model.
Computing in Cardiology (CinC), 2012, Sep 14, 2017
Localization of seven intraventricular pacing sites in the left ventricle was performed using a s... more Localization of seven intraventricular pacing sites in the left ventricle was performed using a single dipole as equivalent heart generator. The used data were provided by Karlsruhe Institute of Technology in EDGAR database. Body surface potential maps were measured in 63 precordial leads during intraventricular pacing with recorded position of the stimulating catheter. The inverse solution was computed for instantaneous and integral maps from the initial 30 ms time interval of ventricular activation. The role of the relative residual error between the input map and the map computed from the resulting dipole was studied with respect to the accuracy of the inverse solution. The localization error of the obtained results for the initial 30 ms was dependent on the position of the pacing site and varied from 20-30 mm for anterior and lateral sites to 45-55 mm for inferior sites. The results were improved considerably when the considered time interval was prolonged and the inverse solution was computed for the time instant when the residual error reached its minimum. The proper time instant for computation of the input data for localization of pacing sites should be chosen individually for each ECG signal.
In this simulation study various characteristics of difference STT integral body surface potentia... more In this simulation study various characteristics of difference STT integral body surface potential maps (DI BSPMs) were used to discriminate cases with single and double modelled lesions with changed repolarization. One or two lesions in different positions in the ventricular myocardium were modelled and corresponding BSPMs were calculated. DI BSPM was computed by subtraction of BSPM computed from normal activation from the BSPM computed from the activation with the presence of one or two lesions. Various morphological and statistical properties of DI BSPM were used as features for a discriminant analysis. Quadratic Fisher discriminant analysis with cross-validation was then used to determine the number of lesions in each case. Taking into account just one best performing feature, the overall error rate for distinguishing the number of lesions was 25.2%. Feature dimensionality was reduced by a feature selection algorithm resulting in 12 features as the optimal number for distinguishing DI BSPMs representing two lesions from maps representing a single lesion. The overall error rate was 4.1%, with partial errors 9.6% and 1.2% for misclassification of single or double lesions, respectively. Discriminant analysis based on exploitation of geometrical and statistical properties of integral BSPMs may be helpful in correct identification of the number of ischemic lesions.
An updated program for modeling simplified heart geometry and simulation of action potentials pro... more An updated program for modeling simplified heart geometry and simulation of action potentials propagation is presented. The implemented model allows simulation of geometry changes as well as changes in action potentials amplitude and duration. In propagation simulation real conduction velocities can be considered. Two different pathological situations were simulated using the model. First, only geometrical changes were applied simulating the left ventricular hypertrophy, second, only action potentials properties simulating activation propagation velocity were changed. The resulting ECG signals on the torso were very similar. It is shown that modeling and simulation is useful for explaining of discrepant observations in clinical diagnostics.
Journal of Electrocardiology, May 1, 2012
We studied the implementation of a patient-specific torso model created without the use of magnet... more We studied the implementation of a patient-specific torso model created without the use of magnetic resonance imaging in the inverse problem of electrocardiology. Three types of inhomogeneous numerical torso models were created, with different degrees of adjustment of the outer surface to patients, whereas the heart and lung models remained unchanged. The torso models were used in the inverse localization of small areas with repolarization changes from simulated difference integral QRST maps. The localization error (LE) was evaluated as the distance between the centers of the modeled and the inversely found area with repolarization changes. The mean LE was 1.88 cm with the standard torso model. After adapting the torso shape, the mean LE was 1.83 cm, whereas after adapting both, the shape and electrode positions, the mean LE was 1.02 cm. If torso imaging is not available, a torso model with adapted shape and electrode positions gives only slightly less accurate results.
Journal of Electrocardiology, Nov 1, 2021
Computing in Cardiology (CinC), 2012, Sep 14, 2016
Comparison of the localization error of inverse estimation of the origin of premature ventricular... more Comparison of the localization error of inverse estimation of the origin of premature ventricular contraction using three different formulations of transfer matrix between the equivalent source and the surface potentials was performed in this study. Body surface potential maps measured in 63 precordial leads during nine spontaneous PVCs in one patient provided by Karlsruhe Institute of Technology in EDGAR database were used as input data. The localization error was evaluated with respect to two reference points PVC1 and PVC2 assigned during the ablation procedure. The transfer matrices for epicardial potentials, transmembrane voltages and dipoles situated on the joined endo-and-epicardial surface were used for inverse computation searching the best single point generator representing the input data For all nine considered PVCs the locations of the inverse results were very stable-for particular transfer matrix they resulted in the same point or in adjoining points for all cases. Mean localization error with respect to PVC1 or PVC2 was from 21.3 to 26.2 mm and from 15.0 to 26.4 mm respectively. The results obtained by inverse solution supposing single point source were similar regardless of the source formulation.
The activation propagation characteristics obtained when using homogeneous monodomain model (MM) ... more The activation propagation characteristics obtained when using homogeneous monodomain model (MM) of the cardiac ventricles and the model based on cellular automaton (CA) are compared in this study. The MM comprises the reaction — diffusion equation of the propagation and the modified FitzHugh-Nagumo equations of the electrical excitation of cardiac cells. This model was simulated in Comsol Multiphysics environment. Model based on CA was simulated in Matlab program environment. Realistic activation time of about 80 ms was obtained for the whole ventricles when activation was started in nine analytically defined points. Differences in activation times obtained from the numerical solutions using MM and CA models were less than ±10 ms.
Advances in Electrical and Electronic Engineering, Jun 28, 2011
Elektronika : konstrukcje, technologie, zastosowania, 2005
Frontiers in Physiology, Jun 9, 2023
Introduction: Localization of premature ventricular contraction (PVC) origin to guide the radiofr... more Introduction: Localization of premature ventricular contraction (PVC) origin to guide the radiofrequency ablation (RFA) procedure is one of the prominent clinical goals of non-invasive electrocardiographic imaging. However, the results reported in the literature vary significantly depending on the source model and the level of complexity in the forward model. This study aims to compare the paced and spontaneous PVC localization performances of dipole-based and potential-based source models and corresponding inverse methods using the same clinical data and to evaluate the effects of torso inhomogeneities on these performances.Methods: The publicly available EP solution data from the EDGAR data repository (BSPs from a maximum of 240 electrodes) with known pacing locations and the Bratislava data (BSPs in 128 leads) with spontaneous PVCs from patients who underwent successful RFA procedures were used. Homogeneous and inhomogeneous torso models and corresponding forward problem solutions were used to relate sources on the closed epicardial and epicardial–endocardial surfaces. The localization error (LE) between the true and estimated pacing site/PVC origin was evaluated.Results: For paced data, the median LE values were 25.2 and 13.9 mm for the dipole-based and potential-based models, respectively. These median LE values were higher for the spontaneous PVC data: 30.2–33.0 mm for the dipole-based model and 28.9–39.2 mm for the potential-based model. The assumption of inhomogeneities in the torso model did not change the dipole-based solutions much, but using an inhomogeneous model improved the potential-based solutions on the epicardial–endocardial ventricular surface.Conclusion: For the specific task of localization of pacing site/PVC origin, the dipole-based source model is more stable and robust than the potential-based source model. The torso inhomogeneities affect the performances of PVC origin localization in each source model differently. Hence, care must be taken in generating patient-specific geometric and forward models depending on the source model representation used in electrocardiographic imaging (ECGI).
De Gruyter eBooks, Dec 31, 1988
During multi-lead ECG recording, some electrodes can be identified as broken and thus information... more During multi-lead ECG recording, some electrodes can be identified as broken and thus information from those electrodes cannot be used for the inverse problem of electrocardiography. The objective of this study is to explore the significance of individual ECG electrodes derived from the patient-specific transfer matrix for homogeneous volume conductor. Four multi-lead ECG measurement datasets with corresponding geometries were used for this study. The transfer matrices were computed using the boundary element method. The significance of individual torso electrodes for a given position of the dipole as the equivalent heart generator was assessed by the singular value decomposition of the transfer matrices for the forward and inverse problem of electrocardiography, respectively. The study showed that the position of the most significant electrodes depends on the position of the heart within the chest and the position of the dipole as an equivalent heart generator. The positions of the first 20% of the most significant electrodes for the forward and inverse problem differ from 0% to 16%.
High-resolution multichannel bioelectric potential measurement is required for diagnostic methods... more High-resolution multichannel bioelectric potential measurement is required for diagnostic methods of various cardiac and brain diseases. The systems previously developed in our lab are streaming measured data to PC over an optical USB cable. Disadvantages of these systems are that the personnel should be careful when manipulating with the cables and difficulty of mounting the electrodes on the patients. New wireless standards enable high data rate transmission. The newest wireless Bluetooth and Wi-Fi standards were studied and specifications of these standards were evaluated for possible usage in multichannel battery powered measuring systems.
Advanced electrocardiographic diagnostic methods of various cardiovascular diseases need high res... more Advanced electrocardiographic diagnostic methods of various cardiovascular diseases need high resolution multichannel measurement of ECG signals that offer much more information than the standard 12-lead ECG. To obtain such ECG signals in required quality a special multichannel electrocardiograph ProCardio 8 was developed. The system is designed as a virtual instrument consisting of an external intelligent measuring unit connected via optical USB interface to a controlling PC running the measuring and data analyzing software. The system can be configured for measurement of up to 144 standard and/or mapping ECG leads using active or passive Ag-AgCl or carbon electrodes. Most of the measuring and newly designed data processing software is written in MATLAB and its compiled version can be deployed as a stand-alone application on any computer running Windows. The modular software architecture consists of real-time modules for the control and checking of the measuring system, data acquisition and signal monitoring as well as modules for off-line data analysis including ECG processing, body surface potential mapping, integral mapping and data preparation for non-invasive model-based electrocardiographic imaging based on inverse solutions and serving as an advanced diagnostic tool.
Computing in Cardiology Conference, Sep 1, 2014
In this simulation study an identification of the latest depolarized site of the ventricles from ... more In this simulation study an identification of the latest depolarized site of the ventricles from integral body surface potential maps (BSPMs) using an inverse solution in terms of one or two dipoles was tested on models of a normal heart. The input data for the inverse solution were integral BSPMs computed from the interval of the last 5 or 10 ms of depolarization. It was assumed that such integral BSPMs represents a small activated area so that they can be approximated by a single dipole. The BSPMs were produced by two types of normal heart-torso models. The very last activated points on the surfaces of the ventricular models were known. If there was a single latest activated area, the localization error was between 0.5 and 3.5 cm. If there were two distinct latest activated areas, the localization error was between 1.7 and 2.9 cm. The proposed method could be used for the preliminary noninvasive assessment of the latestactivated ventricular areas, which are of great interest for cardiac resynchronization therapy.
Computing in Cardiology (CinC), 2012, Dec 30, 2020
In real experiments with body surface potential mapping, it is usual that the measuring electrode... more In real experiments with body surface potential mapping, it is usual that the measuring electrodes cannot be placed regularly because of other patches of sensors used on the torso during the procedure. The influence of accidentally missing the most powerful ECG signals on the inverse localization of the pacing site using a single dipole was studied. Body surface potential maps from three tank experiments on the pig or dog heart and one measurement from the patient's torso were used for inverse computation of the known pacing site position using the full electrodes setup and setups omitting 10% and 20% of the signals with the largest power. The sensitivity of the inverse method was evaluated by localization error between the true and computed pacing site. The localization error did not change (13mm or 7mm) or changed from 13 to 24 mm for tank data, but it increased rapidly from 19 to 41/68 mm for human data. The largest effect of electrodes' omission using human data can be explained by the largest complexity of the human torso what is not fully included in the computational torso model.
Computing in Cardiology (CinC), 2012, Sep 14, 2017
Localization of seven intraventricular pacing sites in the left ventricle was performed using a s... more Localization of seven intraventricular pacing sites in the left ventricle was performed using a single dipole as equivalent heart generator. The used data were provided by Karlsruhe Institute of Technology in EDGAR database. Body surface potential maps were measured in 63 precordial leads during intraventricular pacing with recorded position of the stimulating catheter. The inverse solution was computed for instantaneous and integral maps from the initial 30 ms time interval of ventricular activation. The role of the relative residual error between the input map and the map computed from the resulting dipole was studied with respect to the accuracy of the inverse solution. The localization error of the obtained results for the initial 30 ms was dependent on the position of the pacing site and varied from 20-30 mm for anterior and lateral sites to 45-55 mm for inferior sites. The results were improved considerably when the considered time interval was prolonged and the inverse solution was computed for the time instant when the residual error reached its minimum. The proper time instant for computation of the input data for localization of pacing sites should be chosen individually for each ECG signal.
In this simulation study various characteristics of difference STT integral body surface potentia... more In this simulation study various characteristics of difference STT integral body surface potential maps (DI BSPMs) were used to discriminate cases with single and double modelled lesions with changed repolarization. One or two lesions in different positions in the ventricular myocardium were modelled and corresponding BSPMs were calculated. DI BSPM was computed by subtraction of BSPM computed from normal activation from the BSPM computed from the activation with the presence of one or two lesions. Various morphological and statistical properties of DI BSPM were used as features for a discriminant analysis. Quadratic Fisher discriminant analysis with cross-validation was then used to determine the number of lesions in each case. Taking into account just one best performing feature, the overall error rate for distinguishing the number of lesions was 25.2%. Feature dimensionality was reduced by a feature selection algorithm resulting in 12 features as the optimal number for distinguishing DI BSPMs representing two lesions from maps representing a single lesion. The overall error rate was 4.1%, with partial errors 9.6% and 1.2% for misclassification of single or double lesions, respectively. Discriminant analysis based on exploitation of geometrical and statistical properties of integral BSPMs may be helpful in correct identification of the number of ischemic lesions.
An updated program for modeling simplified heart geometry and simulation of action potentials pro... more An updated program for modeling simplified heart geometry and simulation of action potentials propagation is presented. The implemented model allows simulation of geometry changes as well as changes in action potentials amplitude and duration. In propagation simulation real conduction velocities can be considered. Two different pathological situations were simulated using the model. First, only geometrical changes were applied simulating the left ventricular hypertrophy, second, only action potentials properties simulating activation propagation velocity were changed. The resulting ECG signals on the torso were very similar. It is shown that modeling and simulation is useful for explaining of discrepant observations in clinical diagnostics.
Journal of Electrocardiology, May 1, 2012
We studied the implementation of a patient-specific torso model created without the use of magnet... more We studied the implementation of a patient-specific torso model created without the use of magnetic resonance imaging in the inverse problem of electrocardiology. Three types of inhomogeneous numerical torso models were created, with different degrees of adjustment of the outer surface to patients, whereas the heart and lung models remained unchanged. The torso models were used in the inverse localization of small areas with repolarization changes from simulated difference integral QRST maps. The localization error (LE) was evaluated as the distance between the centers of the modeled and the inversely found area with repolarization changes. The mean LE was 1.88 cm with the standard torso model. After adapting the torso shape, the mean LE was 1.83 cm, whereas after adapting both, the shape and electrode positions, the mean LE was 1.02 cm. If torso imaging is not available, a torso model with adapted shape and electrode positions gives only slightly less accurate results.