Pace mapping using body surface potential maps to guide catheter ablation of accessory pathways in patients with Wolff-Parkinson-White syndrome

Nonlocal based FISTA network for noninvasive cardiac transmembrane potential imaging

Objective. The primary aim of our study is to advance our understanding and diagnosis of cardiac diseases. We focus on the reconstruction of myocardial transmembrane potential (TMP) from body surface potential mapping.Approach. We introduce a novel methodology for the reconstruction of the dynamic distribution of TMP. This is achieved through the integration of convolutional neural networks with conventional optimization algorithms. Specifically, we utilize the subject-specific transfer matrix to describe the dynamic changes in TMP distribution and ECG observations at the body surface. To estimate the TMP distribution, we employ LNFISTA-Net, a learnable non-local regularized iterative shrinkage-thresholding network. The coupled estimation processes are iteratively repeated until convergence.Main results. Our experiments demonstrate the capabilities and benefits of this strategy. The results highlight the effectiveness of our approach in accurately estimating the TMP distribution, thereby providing a reliable method for the diagnosis of cardiac diseases.Significance. Our approach demonstrates promising results, highlighting its potential utility for a range of applications in the medical field. By providing a more accurate and dynamic reconstruction of TMP, our methodology could significantly improve the diagnosis and treatment of cardiac diseases, thereby contributing to advancements in healthcare.

Data analysis in cardiac arrhythmias

Cardiac arrhythmias are an increasingly present in developed countries and represent a major health and economic burden. The occurrence of cardiac arrhythmias is closely linked to the electrical function of the heart. Consequently, the analysis of the electrical signal generated by the heart tissue, either recorded invasively or noninvasively, provides valuable information for the study of cardiac arrhythmias. In this chapter, novel cardiac signal analysis techniques that allow the study and diagnosis of cardiac arrhythmias are described, with emphasis on cardiac mapping which allows for spatiotemporal analysis of cardiac signals.Cardiac mapping can serve as a diagnostic tool by recording cardiac signals either in close contact to the heart tissue or noninvasively from the body surface, and allows the identification of cardiac sites responsible of the development or maintenance of arrhythmias. Cardiac mapping can also be used for research in cardiac arrhythmias in order to understand their mechanisms. For this purpose, both synthetic signals generated by computer simulations and animal experimental models allow for more controlled physiological conditions and complete access to the organ.

An electrical heart model incorporating real geometry and motion

This paper describes an electrical model of the ventricles incorporating real geometry and motion. Cardiac geometry and motion is obtained from segmentations of multiple-slice MRI time sequences. A static heart model developed previously is deformed to match the observed geometry using a novel shape registration algorithm. The resulting electrocardiograms and body surface potential maps are compared to a static simulation in the resting heart. These results demonstrate that introducing motion into the cardiac model modifies the ECG during the T wave at peak contraction of the ventricles.

Late QRS activity in signal-averaged magnetocardiography, body surface potential mapping, and orthogonal ECG in postinfarction ventricular tachycardia patients

BACKGROUND

Delayed electrical activity necessary for re-entrant ventricular tachycardia (VT) is detectable noninvasively with high resolution techniques. We compared high resolution signal-averaged analysis of magnetocardiography (MCG), body surface potential mapping (BSPM), and orthogonal three-lead ECG (SA-ECG) in the identification of patients prone to VT after myocardial infarction (MI).

METHODS

Patients with remote myocardial infarction and cardiac dysfunction were studied, 22 with (VT group) and 22 without VT (control group). MCG with seven channels and BSPM with 63 and SA-ECG with three orthogonal leads were registered. After signal-averaging and highpass filtering, three time domain analysis (TDA) parameters describing late electrical activity were computed: QRS duration (QRSd), root mean square amplitude (RMS) of the last 40 ms of QRS, and the duration of the low-amplitude QRS end (LAS).

RESULTS

All parameters by each method were significantly different between the patients' groups. For example, LAS parameter in MCG was 59 (SD 22) ms in the VT group vs. 37 (SD 13) ms in controls (P < 0.001), 77 (SD 22) ms vs. 56 (SD 19) ms in BSPM (P = 0.002), and 60 (SD 24) ms vs. 39 (SD 22) ms in SA-ECG (P = 0.005). The combination of LAS parameter in MCG and SA-ECG resulted in improved performance in comparison to any single parameter with 95% sensitivity and 68% specificity.

CONCLUSIONS

All three high resolution methods identified VT propensity among post-MI patients with cardiac dysfunction and between-method differences were small. Information in MCG and SA-ECG may be complementary and their combination could be of value in postinfarction arrhythmia risk assessment.

How many ECG leads do we need?

The number of leads needed in clinical electrocardiography depends on the clinical problem to be solved. The standard 12-lead ECG is so well established that alternative lead systems must prove their advantage through well-conducted clinical studies to achieve clinical acceptance. Certain additional leads seem to add valuable information in specific patient groups. The use of a large number of leads (eg, in body surface potential mapping) may add clinically relevant information, but it is cumbersome and its clinical advantage is yet to be proven. Reduced lead sets emulate the 12-lead ECG reasonably well and are especially advantageous in emergency situations.

Noninvasive imaging of cardiac transmembrane potentials within three-dimensional myocardium by means of a realistic geometry anisotropic heart model

We have developed a new approach for imaging cardiac transmembrane potentials (TMPs) within the three-dimensional (3-D) myocardium by means of an anisotropic heart model. The cardiac TMP distribution is estimated from body surface electrocardiograms by minimizing objective functions of the "measured" body surface potential maps (BSPMs) and the heart-model-generated BSPMs. Computer simulation studies have been conducted to evaluate the present 3-D TMP imaging approach using pacing protocols. Simulations of single-site pacing at 24 sites throughout the ventricles, as well as dual-site pacing at 12 pairs of sites in the vicinity of atrio-ventricular ring were performed. The present simulation results show that the correlation coefficient (CC) and relative error (RE) between the "true" and inversely estimated TMP distributions were 0.9915 +/- 0.0041 and 0.1266 +/- 0.0326, for single-site pacing, and 0.9889 +/- 0.0034 and 0.1473 +/- 0.0237 for dual-site pacing, respectively, when 10 microV Gaussian white noise (GWN) was added to the BSPMs. The effects of heart and torso geometry uncertainty were also evaluated by shifting the heart position by 10 mm and altering the torso size by 10%. The CC between the "true" and inversely estimated TMP distributions was above 0.97 when these geometry uncertainties were considered. The present simulation results demonstrate the feasibility of noninvasive estimation of TMP distribution throughout the ventricles from body surface electrocardiographic measurements, and suggest that the present method may become a useful alternative in noninvasive imaging of distributed cardiac electrophysiological processes within the 3-D myocardium.

Noninvasive localization of the site of origin of paced cardiac activation in human by means of a 3-D heart model

A recently developed heart-model-based localization approach is experimentally evaluated in noninvasively localizing the site of origin of cardiac activation in a patient with a pacemaker. The heart-torso model of the patient was constructed from the contrast ultrafast computed tomography images. The site of initial paced activation in the patient was quantitatively localized and compared with the tip position of the pacemaker lead. The localization error of the inverse estimation was found to be 5.2 mm with respect to the true lead tip position. The promising result of this pilot experimental study suggests the feasibility of localizing the site of origin of cardiac activation in an experimental setting. The heart-model-based localization approach may become an alternative tool in localizing the site of origin of cardiac activation.

Noninvasive three-dimensional activation time imaging of ventricular excitation by means of a heart-excitation model

We propose a new method for imaging activation time within three-dimensional (3D) myocardium by means of a heart-excitation model. The activation time is estimated from body surface electrocardiograms by minimizing multiple objective functions of the measured body surface potential maps (BSPMs) and the heart-model-generated BSPMs. Computer simulation studies have been conducted to evaluate the proposed 3D myocardial activation time imaging approach. Single-site pacing at 24 sites throughout the ventricles, as well as dual-site pacing at 12 pairs of sites in the vicinity of atrioventricular ring, was performed. The present simulation results show that the average correlation coefficient (CC) and relative error (RE) for single-site pacing were 0.9992+/-0.0008/0.9989+/-0.0008 and 0.05+/-0.02/0.07+/-0.03, respectively, when 5 microV/10 microV Gaussian white noise (GWN) was added to the body surface potentials. The average CC and RE for dual-site pacing were 0.9975+/-0.0037 and 0.08+/-0.04, respectively, when 10 microV GWN was added to the body surface potentials. The present simulation results suggest the feasibility of noninvasive estimation of activation time throughout the ventricles from body surface potential measurement, and suggest that the proposed method may become an important alternative in imaging cardiac electrical activity noninvasively.

Noninvasive myocardial activation time imaging: a novel inverse algorithm applied to clinical ECG mapping data

Linear approaches like the minimum-norm least-square algorithm show insufficient performance when it comes to estimating the activation time map on the surface of the heart from electrocardiographic (ECG) mapping data. Additional regularization has to be considered leading to a nonlinear problem formulation. The Gauss-Newton approach is one of the standard mathematical tools capable of solving this kind of problem. To our experience, this algorithm has specific drawbacks which are caused by the applied regularization procedure. In particular, under clinical conditions the amount of regularization cannot be determined clearly. For this reason, we have developed an iterative algorithm solving this nonlinear problem by a sequence of regularized linear problems. At each step of iteration, an individual L-curve is computed. Subsequent iteration steps are performed with the individual optimal regularization parameter. This novel approach is compared with the standard Gauss-Newton approach. Both methods are applied to simulated ECG mapping data as well as to single beat sinus rhythm data from two patients recorded in the catheter laboratory. The proposed approach shows excellent numerical and computational performance, even under clinical conditions at which the Gauss-Newton approach begins to break down.

Conversion of left ventricular endocardial positions from patient-independent co-ordinates into biplane fluoroscopic projections

Electrocardiographic body surface mapping is used clinically to guide catheter ablation of cardiac arrhythmias by providing an estimate of the site of origin of an arrhythmia. The localisation methods used in our group produce results in left-ventricular cylinder co-ordinates (LVCCs), which are patient-independent but hard to interpret during catheterisation in the electrophysiology laboratory. It is preferable to provide these results as three-dimensional (3D) co-ordinates which can be presented as projections in the biplane fluoroscopic views that are used routinely to monitor the catheter position. Investigations were carried out into how well LVCCs can be converted into fluoroscopic projections with the limited anatomical data available in contemporary clinical practice. Endocardial surfaces from magnetic resonance imaging (MRI) scans of 24 healthy volunteers were used to create an appropriate model of the left-ventricular endocardial wall. Methods for estimation of model parameters from biplane fluoroscopic images were evaluated using simulated biplane data created from these surfaces. In addition, the conversion method was evaluated, using 107 catheter positions obtained from eight patients, by computing LVCCs from biplane fluoroscopic images and reconstructing the 3D positions using the model. The median 3D distance between reconstructed positions and measured positions was 4.3mm.

Noninvasive characterisation of multiple ventricular events using electrocardiographic imaging

Distributions of epicardial potentials, calculated from body surface electrocardiograms (ECGs), were investigated to determine if they could enable detection of multiple sites of ventricular activity. An anatomical model of the human ventricular myocardium was used to simulate activation sequences initiated at nine different ventricular pairs of sites. From these sequences, body surface ECGs were simulated at 352 sites on the torso surface and then used to reconstruct epicardial potentials at 202 sites. The criterion for detection of dual ventricular events was the presence of two distinct primary potential minima in the reconstructed epicardial potentials. The shortest distance between the two events in the right ventricle that resulted in the reconstruction of epicardial potential patterns, featuring two minima, was 27 mm; the distance between the two events in the left ventricle was 23 mm. When Gaussian white noise in the simulated body surface potentials was increased from 3 microV to 15 microV and 50 microV, dual events became more difficult to distinguish. Findings indicate that calculated epicardial potentials provide useful visual information about the presence of multiple ventricular events that is not apparent in features of body surface ECGs, and could be particularly helpful in optimising mapping procedures during difficult or unsuccessful radiofrequency ablations of accessory pathways.

Localization of the site of origin of cardiac activation by means of a heart-model-based electrocardiographic imaging approach

We have developed a new approach to solve the inverse problem of electrocardiography in terms of heart model parameters. The inverse solution of the electrocardiogram (ECG) inverse problem is defined, in the present study, as the parameters of the heart model, which are closely related to the physiological and pathophysiological status of the heart, and is estimated by using an optimization system of heart model parameters, instead of solving the matrix equation relating the body surface ECGs and equivalent cardiac sources. An artificial neural network based preliminary diagnosis system has been developed to limit the searching space of the optimization algorithm and to initialize the model parameters in the computer heart model. The optimal heart model parameters were obtained by minimizing the objective functions, as functions of the observed and model-generated body surface ECGs. We have tested the feasibility of the newly developed technique in localizing the site of origin of cardiac activation using a pace mapping protocol. The present computer simulation results show that, the present approach for localization of the site of origin of ventricular activation achieved an averaged localization error of about 3 mm [for 5-muV Gaussian white noise (GWN)] and 4 mm (for 10-muV GWN), with standard deviation of the localization errors of being about 1.5 mm. The present simulation study suggests that this newly developed approach provides a robust inverse solution, circumventing the difficulties of the ECG inverse problem, and may become an important alternative to other ECG inverse solutions.

Continuous localization of cardiac activation sites using a database of multichannel ECG recordings

Monomorphic ventricular tachycardia and ventricular extrasystoles have a specific exit site that can be localized using the multichannel surface electrocardiogram (ECG) and a database of paced ECG recordings. An algorithm is presented that improves on previous methods by providing a continuous estimate of the coordinates of the exit site instead of selecting one out of 25 predetermined segments. The accuracy improvement is greatest, and most useful, when adjacent pacing sites in individual patients are localized relative to each other. Important advantages of the new method are the objectivity and reproducibility of the localization results.

Localization of intramural necrotic regions using electrocardiographic imaging

Recent studies have demonstrated that electrocardiographic imaging (ECGI) is a novel noninvasive modality for exploring the spread of electrical activation within the ventricular wall. In this study, our goal was to explore the ability of ECGI in reconstructing epicardial potentials and electrograms in the ventricles damaged by localized necroses (<2 cm2). An anatomical model of the human ventricular myocardium was used to simulate activation sequences initiated at 428 epicardial and endocardial pacing sites distributed over the right ventricular and left ventricular free walls. From these realistic sequences, we simulated extracardiac potentials at epicardial (202 sites) and torso surfaces (352 sites) using boundary element model of the human torso. ECGI in terms of the L-curve was applied to compute epicardial potentials and unipolar electrograms (202 sites). Inversely computed electrograms correlated well with those simulated by an anatomical model (r > 0.9 at 68% of sites). Specifically, ECGI accurately reconstructed the following features that have been observed during measurements on the exposed canine hearts: (a) an epicardial potential pattern with a central minimum and two maxima, with the minimum positioned above the pacing site; (b) a complete transient loss of one of the positive areas in the epicardial potential pattern when the necrosis was located subepicardially; and (c) a transient gap in the expanding positive areas of the epicardial potential pattern when the necrosis was located intramurally or subendocardially. Findings of our study indicate that ECGI provides detailed reconstruction of patterns of myocardial activation in the presence of localized necroses and may be useful in the assessment of arrhythmogenic substrate in the clinical setting.

Bioelectromagnetic localization of a pacing catheter in the heart

The accuracy of localizing source currents within the human heart by non-invasive magneto- and electrocardiographic methods was investigated in 10 patients. A non-magnetic stimulation catheter inside the heart served as a reference current source. Biplane fluoroscopic imaging with lead ball markers was used to record the catheter position. Simultaneous multichannel magnetocardiographic (MCG) and body surface potential mapping (BSPM) recordings were performed during catheter pacing. Equivalent current dipole localizations were computed from MCG and BSPM data, employing standard and patient-specific boundary element torso models. Using individual models with the lungs included, the average MCG localization error was 7+/-3 mm, whereas the average BSPM localization error was 25+/-4 mm. In the simplified case of a single homogeneous standard torso model, an average error of 9+/-3 mm was obtained from MCG recordings. The MCG localization accuracies obtained in this study imply that the capability of multichannel MCG to locate dipolar sources is sufficient for clinical purposes, even without constructing individual torso models from x-ray or from magnetic resonance images.

Value of magnetocardiographic QRST integral maps in the identification of patients at risk of ventricular arrhythmias

It has been shown that regional ventricular repolarization properties can be reflected in body surface distributions of electrocardiographic QRST deflection areas (integrals). We hypothesize that these properties can be reflected also in the magnetocardiographic QRST areas and that this may be useful for predicting vulnerability to ventricular tachyarrhythmias. Magnetic field maps were obtained during sinus rhythm from 49 leads above the anterior chest in 22 healthy (asymptomatic) control subjects (group A) and in 29 patients with ventricular arrhythmias (group B). In each subject, the QRST deflection area was calculated for each lead and displayed as an integral map. The mean value of maximum was significantly larger in the control group A than in the patient group B (1,626+/-694 pTms vs. 582+/-547 pTms, P<0.0001). To quantitatively assess intragroup variability in the control group A and intergroup variability of the control and patient groups, we used the correlation coefficient r and covariance sigma. These indices showed significantly less intragroup than intergroup variation (e.g., in terms of sigma, 28.0x10(-6)+/-12.3x10(-6) vs. 3.4x10(-6)+/-12.5x10(-6), P<0.0001). Each QRST integral map was also represented as a weighted sum of 24 basis functions (eigenvectors) by means of Karhunen-Loeve transformation to calculate the contribution of the nondipolar eigenvectors (all eigenvectors beyond the third). This percentage nondipolar content of magnetocardiographic QRST integral maps was significantly higher in the patient group B than in the control group A (13.0%+/-9.1 % vs. 2.6%+/-2.0%, P<0.0001). Discriminations between control subjects and patients with ventricular arrhythmias based on magnitude of the maximum, covariance sigma, and nondipolar content were 90.2%, 90.2%, and 86.3% accurate, with a sensitivity of 89.7%, 93.1%, and 75.9%, and a specificity of 90.9%, 86.4%, and 100%. We have shown that magnitude of the maximum and indices of variability and nondipolarity of the magnetocardiographic QRST integral maps may predict arrhythmia vulnerability. This finding is in agreement with earlier studies that used body surface potential mapping and suggests that magneticfield mapping may also be a useful diagnostic tool for risk analysis.

Nonfluoroscopic localization of an amagnetic stimulation catheter by multichannel magnetocardiography

This study was performed to: (1) evaluate the accuracy of noninvasive magnetocardiographic (MCG) localization of an amagnetic stimulation catheter; (2) validate the feasibility of this multipurpose catheter; and (3) study the characteristics of cardiac evoked fields. A stimulation catheter specially designed to produce no magnetic disturbances was inserted into the heart of five patients after routine electrophysiological studies. The catheter position was documented on biplane cine x-ray images. MCG signals were then recorded in a magnetically shielded room during cardiac pacing. Noninvasive localization of the catheter's tip and stimulated depolarization was computed from measured MCG data using a moving equivalent current-dipole source in patient-specific boundary element torso models. In all five patients, the MCG localizations were anatomically in good agreement with the catheter positions defined from the x-ray images. The mean distance between the position of the tip of the catheter defined from x-ray fluoroscopy and the MCG localization was 11 +/- 4 mm. The mean three-dimensional difference between the MCG localization at the peak stimulus and the MCG localization, during the ventricular evoked response about 3 ms later, was 4 +/- 1 mm calculated from signal-averaged data. The 95% confidence interval of beat-to-beat localization of the tip of the stimulation catheter from ten consecutive beats in the patients was 4 +/- 2 mm. The propagation velocity of the equivalent current dipole between 5 and 10 ms after the peak stimulus was 0.9 +/- 0.2 m/s. The results show that the use of the amagnetic catheter is technically feasible and reliable in clinical studies. The accurate three-dimensional localization of this multipurpose catheter by multichannel MCG suggests that the method could be developed toward a useful clinical tool during electrophysiological studies.

Assessment of spatial resolution of pace mapping when using body surface potentials

Using computer simulations and statistical methods, the resolution of pace mapping when used in combination with body surface potentials was systematically investigated. In an anatomical model of the human ventricular myocardium, pre-excitation sequences were initiated at 69 sites positioned along the atrioventricular (AV) ring and corresponding body surface potential maps (BSPMs) were calculated at 32 leads placed on the anterior torso. For each time after the onset of pre-excitation (every 4 ms to 40 ms) and each root-mean-square (RMS) noise level (5, 10, 20 and 50 microV), BSPMs were cros-correlated and the spatial resolution defined as the largest pacing site separation at which the differences in correlation coefficients were not statistically significant (level p > or = 0.05). The findings indicate that when random RMS noise of 5 microV was added to the simulated BSPMs, average spatial resolution over all 60 sites was at 20 ms after the onset of pre-excitation within 3.5 +/- 0.9 mm. The results provide theoretical evidence that statistical analysis of BSPMs obtained during pace mapping can offer improved means for subcentimetre identification of accessory pathways located along the AV ring.

Localization of a ventricular tachycardia-focus with multichannel magnetocardiography and three-dimensional current density reconstruction

The objective of this case report is to determine the accurate localization of a malignant ventricular tachycardia (VT) focus by combining multichannel magnetocardiographic (MCG) information with morphologic data. The localization was obtained by calculating the three-dimensional current density distribution (3D-CDD) on the left ventricular surface. To estimate the accuracy of this localization technique, examinations of a healthy volunteer were additionally performed. The MCG-signals were recorded in a magnetically shielded room by a 49-channel magnetogradiometer. The corresponding morphologic information was recorded by magnetic resonance tomography (MRT). The coordinate systems were matched with the help of markers. The 3D-CDD was calculated by the Philips CURRY software package. The origin of a malignant VT determined by X-ray images of the ablation catheter position during the electrophysiological examination (EPE), was used as the gold standard. This was then compared with the localization results obtained by the 3D-CDD. It was found that the localization coordinates showed a difference of less than 10 mm.

A comparison of simulated QRS isointegral maps resulting from pacing at adjacent sites: implications for the spatial resolution of pace mapping using body surface potentials

The precise localization of ventricular tachycardia (VT) foci is a prerequisite for the successful radiofrequency catheter ablation in patients. The purpose of this study was to systematically quantify over what distance adjacent sites in the right ventricular (RV) and left ventricular (LV) epicardium and LV endocardium could be distinguished by inspecting morphological features of QRS isointegral maps using statistical methods. We investigated the spatial resolution of QRS isointegral maps by means of an anatomically accurate computer model of the human ventricular myocardium that incorporates a bidomain model for simulating the realistic activation sequences and the oblique dipole model in combination with the boundary element method for calculating extracardiac potentials. In this model, we initiated activation sequences at a total of 183 epicardial and 75 LV endocardial pacing sites, positioned in three levels (basal, middle, and apical). For each of the 258 pacing sites, we calculated a set of 10 QRS isointegral maps with added Gaussian noise at 117 leads (covering the anterior and posterior torso) and at 32 leads (covering only the anterior torso), respectively. Sets of maps were then cross correlated and root-mean-square (RMS) values of difference maps were calculated for all possible pairs of pacing sites on the same level. We applied the nonparametric unpaired Kolmogorov-Smirnov test and defined the spatial resolution as the pacing site separation at which the differences in correlation coefficients and RMS differences were significant (level P < .05). We observed significant differences in maps when the distances between pacing sites were on average (+/- SD) greater than 4.3 +/- 1.0 mm. In more than 90% of pacing sites, the significant differences in maps were observed within 4 mm even when using a 32-lead mapping system. The findings of our study provide theoretical evidence that QRS isointegral maps may offer noninvasive means for preinterventional planning of the ablative treatment in localizing both endocardial and epicardial sites of origin of VT.

Nonfluoroscopic localization of an amagnetic catheter in a realistic torso phantom by magnetocardiographic and body surface potential mapping

This study was performed to evaluate the accuracy of multichannel magnetocardiographic (MCG) and body surface potential mapping (BSPM) in localizing three-dimensionally the tip of an amagnetic catheter for electrophysiology without fluoroscopy. An amagnetic catheter (AC), specially designed to produce dipolar sources of different geometry without magnetic disturbances, was placed inside a physical thorax phantom at two different depths, 38 mm and 88 mm below the frontal surface of the phantom. Sixty-seven MCG and 123 BSPM signals generated by the 10 mA current stimuli fed into the catheter were then recorded in a magnetically shielded room. Non-invasive localization of the tip of the catheter was computed from measured MCG and BSPM data using an equivalent current dipole source in a phantom-specific boundary element torso model. The mean 3-dimensional error of the MCG localization at the closer level was 2 +/- 1 mm. The corresponding error calculated from the BSPM measurements was 4 +/- 1 mm. At the deeper level, the mean localization errors of MCG and BSPM were 7 +/- 4 mm and 10 +/- 2 mm, respectively. The results showed that MCG and BSPM localization of the tip of the AC is accurate and reproducible provided that the signal-to-noise ratio is sufficiently high. In our study, the MCG method was found to be more accurate than BSPM. This suggests that both methods could be developed towards a useful clinical tool for nonfluoroscopic 3-dimensional electroanatomical imaging during electrophysiological studies, thus minimizing radiation exposure to patients and operators.

Body surface Laplacian mapping in patients with left or right ventricular bundle branch block

Body surface Laplacian maps (BSLMs) have been previously reported to provide enhanced capability in localizing and resolving multiple spatially separate myocardial events. However, only a few studies have been reported on the clinical applications of BSLM. To test the clinical utility of BSLMs, BSLMs and body surface potential maps (BSPMs) during ventricular depolarization for complete right or left ventricular bundle branch block (CRBBB or CLBBB) were studied in ten patients in each group. As a control group, ten healthy subjects were also studied using the same procedure. One hundred and twenty-eight electrodes were placed uniformly over the entire chest and back of the subjects. BSLMs were computed from recorded potentials, using a numerical algorithm. The BSLMs showed multiple and more localized positive and negative activities compared with the BSPMs. In healthy subjects, the BSLMs showed multiple areas of positive activity overlying the RV, LV, and the RV outflow, and negative activity corresponding to RV free-wall breakthrough and LV anterolateral breakthrough sites, whereas the BSPMs could not separate RV and LV activities. In the patients with CRBBB, the BSLMs showed more localized areas of activity corresponding to the LV apex breakthrough and LV lateral breakthrough, and separated LV lateral and posterior activation. In the patients with CLBBB, the BSLMs showed multiple RV activation, and propagating activation of LV from lateral to posterior. The BSLMs appear to provide enhanced capability in detecting multiple ventricular electrical events associated with normal and abnormal conduction and a more detailed activation sequence of both ventricles in healthy subjects and in the patients with CRBBB and CLBBB. BSLM may provide an important alternative to other imaging modalities in localizing cardiac electrical activity noninvasively.

Magnetocardiographic pacemapping for nonfluoroscopic localization of intracardiac electrophysiology catheters

The purpose of the study was to validate, in patients, the accuracy of magnetocardiography (MCG) for three-dimensional localization of an amagnetic catheter (AC) for multiple monophasic action potential (MAP) with a spatial resolution of 4 mm2. The AC was inserted in five patients after routine electrophysiological study. Four MAPs were simultaneously recorded to monitor the stability of endocardial contact of the AC during the MCG localization. MAP signals were band-pass filtered DC-500 Hz and digitized at 2 KHz. The position of the AC was also imaged by biplane fluoroscopy (XR), along with lead markers. MCG studies were performed with a multichannel SQUID system in the Helsinki BioMag shielded room. Current dipoles (5 mm; 10 mA), activated at the tip of the AC, were localized using the equivalent current dipole (ECD) model in patient-specific boundary element torso. The accuracy of the MCG localizations was evaluated by: (1) anatomic location of ECD in the MRI, (2) mismatch with XR. The AC was correctly localized in the right ventricle of all patients using MRI. The mean three-dimensional mismatch between XR and MCG localizations was 6 +/- 2 mm (beat-to-beat analysis). The co efficient of variation of three-dimensional localization of the AC was 1.37% and the coefficient of reproducibility was 2.6 mm. In patients, in the absence of arrhythmias, average local variation coefficients of right ventricular MAP duration at 50% and 90% of repolarization, were 7.4% and 3.1%, respectively. This study demonstrates that with adequate signal-to-noise ratio, MCG three-dimensional localizations are accurate and reproducible enough to provide nonfluoroscopy dependant multimodal imaging for high resolution endocardial mapping of monophasic action potentials.

Spatial resolution of body surface potential maps and magnetic field maps: a simulation study applied to the identification of ventricular pre-excitation sites

The spatial resolution of body surface potential maps (BSPMs) and magnetic field maps (MFMs) is investigated by means of an anatomically accurate computer model of the human ventricular myocardium. BSPMs and MFMs are calculated for the simulated activation sequences initiated at 35 pre-excitation sites located along the atrioventricular (AV) ring of the epicardium. Changes in the BSPMs and MFMs corresponding to different pre-excitation sites are quantified in terms of the correlation coefficient r. The spatial resolution (selectivity) for a given pre-excitation site is defined as the half-distance between those neighbouring locations at which morphological features of maps, in terms of r, become distinct (r < 0.95). It is found that, at 28 ms after the onset of pre-excitation and with no noise added, this distance +/- SD, for all sites along the AV ring for the 117-lead BSPMs, is 0.83 +/- 0.32 cm, and for the 64-lead and 128-lead MFMs it is 1.54 +/- 0.84 cm and 1.15 +/- 0.43 cm, respectively. The findings suggest that, when features of non-invasively recorded electrocardiographic and magnetocardiographic map patterns are used for identifying accessory pathways in patients suffering from WPW syndrome, BSPMs are likely to provide more detailed information for guiding the ablative treatment than MFMs. For some sites MFMs provide more information. Both modalities may provide additional assistance to the cardiologist in locating the site of the accessory pathway.

Value of simulated body surface potential maps as templates in localizing sites of ectopic activation for radiofrequency ablation

Body surface potential maps recorded during catheter pace mapping can facilitate the localization of the site of origin of ventricular tachycardia. In this study, we investigated the value of a realistic computer model of the human ventricular myocardium in generating body surface potential maps as templates for identifying sites of ectopic activation. Our model features an anatomically accurate geometry and an anisotropy due to transmural fibre rotation, that were reconstructed with a spatial resolution of 0.5 mm. It simulates the electrotonic interactions of cardiac cells by solving a nonlinear parabolic partial differential equation, but it behaves as a cellular automaton when the transmembrane potential exceeds the threshold value. We successfully validated our model by comparing the simulated activation sequences--described by isochronal maps, epicardial potential maps and body surface potential maps--with the measured sequences of epicardial and body surface maps reported in the literature. By systematically pacing the left ventricular and right ventricular endocardial surfaces in our ventricular model, we generated a database of 155 QRS-integral maps, which provides a high-resolution reference frame for localizing distinct endocardial pacing sites. This database promises to be a useful tool in improving the performance of catheter pace mapping used in combination with body surface potential mapping. Overall, the results demonstrate that our computer model of the human ventricular myocardium is well suited for complementing a database of QRS-integral maps obtained during clinical pace mapping and can help enhance the efficacy of the ablative treatment of ventricular arrhythmias.

Spatial resolution and role of pacemapping during ablation of accessory pathways

The objectives of this study were: (1) to evaluate quantitatively the spatial resolution of pacemapping; and (2) to assess the predictive value and role of pacemapping for the catheter ablation of overt APs. Sixty-three unipolar leads were used instead of the standard 12-lead ECG to acquire more information and assess the intrinsic accuracy of pacemapping. Spatial resolution was evaluated in 19 patients for whom data were recorded during bipolar ventricular pacing near the AV ring using the three electrode pairs of a quadripolar ablation catheter with a 5-mm interelectrode spacing. The predictive value was assessed in 27 patients with overt APs who underwent RF ablation; their data were recorded during pacing at the site of successful ablation and at one or two sites where RF energy delivery was ineffective. Data from different beats were compared visually by using body surface potential maps and quantitatively by computing average correlation coefficients (r). Reproducibility was high for paced beats (r = 0.98 +/- 0.02). Displacements of 5 mm of the pacing site could be detected with a sensitivity of 90% and a specificity of 87%. Correlation between pacing at successful ablation sites and preexcited sinus rhythm was low (r = 0.79 +/- 0.11) and the ablation outcome could be predicted with a negative prediction accuracy of 87% and a positive prediction accuracy of 49%. Despite an excellent spatial resolution, pacemapping is of limited value for the identification of successful AP ablation sites, probably because APs can be interrupted at some distance from their ventricular insertion point.

A computer heart model incorporating anisotropic propagation. III. Simulation of ectopic beats

With the advent of catheter ablation procedures, it has become an important goal to predict noninvasively the site of origin of ventricular tachycardia. Site classifications based on the observed body surface potential maps (BSPMs) during ventricular endocardial pacing, as well as on the patterns of the QRS integrals of these maps, have been suggested. The goals of this study were to verify these maps and their QRS integral patterns via simulation using a computer heart model with realistic geometry and to determine whether the model could improve clinical understanding of these ectopic patterns. Simulation was achieved by initiating excitation of the heart model at different endocardial sites and their overlying epicardial counterparts. This excitation propagated in anisotropic fashion in the myocardium. Retrograde excitation of the model's His-Purkinje conduction system was necessary to obtain realistic activation durations. Simulated BSPMs, computed by placing the heart model inside a numerical torso model, and their QRS integrals were close to those observed clinically. Small differences in QRS integral map patterns and in the positions of the QRS integral map extrema were noted for endocardial sites in the left septal and anteroseptal regions. The simulated BSPMs during early QRS for an endocardial site and its epicardial counterpart tended to be mirror images about the zero isopotential contour, exchanging positive and negative map regions. The simulation results attest to the model's ability to reproduce accurately clinically recorded body surface potential distributions obtained following endocardial stimulation. The QRS integral maps from endocardial sites in the left septal and anteroseptal regions were the most labile, owing to considerable cancellation effects. Conventional BSPMs can be useful to help distinguish between endocardial and epicardial ectopic sites.

Evaluation of the non-invasive localization accuracy of cardiac arrhythmias attainable by multichannel magnetocardiography (MCG)

The accuracy of multichannel magnetocardiography (MCG) for the non-invasive localization of cardiac arrhythmias was investigated. A non-magnetic catheter was used in phantom studies and for cardiac pacing of 6 patients. In a clinical setting, 32 patients with WPW-syndrome, 37 patients with premature ventricular complexes and 12 patients with ventricular tachycardia were studied and the MCG results compared to reference methods, including invasive electrophysiological mapping. Phantom and pacing studies demonstrated the spatial localization accuracy to be better than 15 mm for a dipole-to-dewar distance below 15 cm. In all patients with structural cardiac disease, the ectopic focus was localized at the margin of the damaged area, serving as a proof of MCG localization. Invasive mapping confirmed the MCG result whenever performed (42 patients). In 11 patients (9 WPW, 2 VT) the MCG localization result was verified by successful HF catheter ablation as a gold standard. MCG permits the non-invasive localization of cardiac arrhythmias with high spatial accuracy. MCG guided HF catheter ablation constitutes a new concept of non-invasive localization and minimally invasive causal therapy.

Magnetocardiographically-guided catheter ablation

After more than 30 years since the first magnetocardiographic (MCG) recording was carried out with induction coils, MCG is now approaching the threshold of clinical use. During the last 5 years, in fact, there has been a growing interest of clinicians in this new method which provides an unrivalled accuracy for noninvasive, three-dimensional localization of intracardiac source. An increasing number of laboratories are reporting data validating the use of MCG as an effective method for preoperative localization of arrhythmogenic substrates and for planning the best catheter ablation approach for different arrhythmogenic substrates. In this article, available data from literature have been reviewed. We consider the clinical use of MCG to localize arrhythmogenic substrates in patients with Wolff-Parkinson-White syndrome and in patients with ventricular tachycardia in order to assess the state-of-the-art of the method on a large number of patients. This article also addresses some suggestions for industrial development of more compact, medically oriented MCG equipments at reasonable cost.

Clinical applications of BSM

Body surface mapping (BSM) has now become a feasible clinical technique, providing useful information applicable to the diagnosis of cardiac arrhythmias and their treatment by surgical and endocardial catheter ablation. In WPW patients, validation of preexcitation patterns has been obtained by computer simulation and by direct epicardial mapping at surgery. BSM pacemapping has subsequently been developed to be used during radiofrequency catheter ablation. This method has been evaluated prospectively and its predictive accuracy assessed. The recognition of two distinct BSM patterns in idiopathic ventricular tachycardia, has led to the application of successful pacemapping for radiofrequency catheter ablation. The use of a realistic tri-dimensional heart-torso computer model has shown that specific sites of endocardial stimulation are related to distinct thoracic map patterns.

Clinical applications of body surface potential mapping

Accumulated evidence suggests that the electrocardiographic information provided by the standard 12-lead electrocardiogram can be improved by use of multilead electrocardiograms. The clinical utility of body surface potential mapping is related to the selective regional information provided by the increased number of leads. That clinical utility includes such things as improved localization of accessory pathways in preexcitation syndromes, improved localization of pacing sites within the ventricles, localization of late potentials, and improved recognition of acute myocardial ischemia. Recording equipment and interpretation schemes are available to make possible more widespread application of potential mapping.

Estimating ECG distributions from small numbers of leads

The utility of body surface potential mapping to improve interpretation of electrocardiographic information lies in the presentation of thoracic surface distributions to characterize underlying electrophysiology less ambiguously than that afforded by conventional electrocardiography. Localized cardiac disease or abnormal electrophysiology presents itself electrocardiographically on the body surface in a manner in which pattern plays an important role for identifying or characterizing these abnormalities. Thus, in myocardial infarction, transient myocardial ischemia, Wolff-Parkinson-White syndrome, or ventricular ectopy, observation of electrocardiographic potential patterns, their extrema, and their magnitudes permits localization and quantization of the abnormal activity. Conventional electrocardiography assesses pattern information incompletely and does not use information of distribution extrema locations or magnitudes. Thus, increases or decreases in the magnitudes of electrocardiographic features (ST-segment potential displacement, amplitude, or morphology of Q, R, S, or T waves) associated with changes in cardiac sources (ischemia, infarction, conduction abnormalities, etc.) as measured from fixed leads have a high likelihood of being misinterpreted if the distribution itself is changing. In this study, the authors demonstrate the utility of estimating distributions from small numbers of optimally selected leads, including conventional leads, to reduce uncertainty in the interpretation of electrocardiographic information. This issue is highly relevant when thresholds are used to detect significance of potential levels (exercise testing, detection of myocardial infarction, and continuous monitoring to assess ST-segment changes). Significance of this work lies in improved detection and characterization of abnormal electrophysiology using conventional or enhanced leadsets and methods to estimate thoracic potential distributions.

Radiofrequency catheter ablation of accessory pathways: a contemporary review

Catheter ablation techniques are now advocated as the first line of therapy for arrhythmias caused by accessory pathways (APs). The most common energy source is radiofrequency current, but technical characteristics vary. Several parameters can be used to determine the optimal target site: AP potential, AV time, atrial or ventricular insertion site, or unipolar morphology. Specific considerations are needed depending on AP location. Despite the different approaches described, there is no significant difference in the reported success rate, which is over 90%. However, the number of radiofrequency applications needed to achieve ablation appears to differ significantly, with median values from 3 to 8 reported. A combination of criteria related to both timing and direction of the activation wavefront or use of subthreshold stimulation could improve the accuracy of mapping. In patients with "resistant" APs, different changes in ablation technique must be considered during the procedure to achieve elimination of AP conduction. The incidence of complications in multicenter reports is close to 4%, with a recurrence rate of 8%. The long-term safety of catheter ablation requires further study.

Radiofrequency catheter ablation of an accessory pathway in a young man with dextroversion

We report an observation of a radiofrequency catheter ablation of an accessory pathway (AP) in a patient with Wolff-Parkinson-White syndrome (WPW) and dextroversion. Atrioventricular rings were mapped by the ablation catheter to locate the shortest local atrioventricular conduction time in sinus rhythm and ventriculoatrial conduction time during orthodromic tachycardia or ventricular pacing. Successful ablation confirmed a right posteroseptal AP localization. Thus, the electrocardiographic modifications due to an AP in this location in the presence of dextroversion were defined.