Single Equivalent Moving Dipole Research Articles

Use of the inverse solution guidance algorithm method for RF ablation catheter guidance.

We previously introduced the inverse solution guidance algorithm (ISGA) methodology using a Single Equivalent Moving Dipole model of cardiac electrical activity to localize both the exit site of a re-entrant circuit and the tip of a radiofrequency (RF) ablation catheter. The purpose of this study was to investigate the use of ISGA for ablation catheter guidance in an animal model. Ventricular tachycardia (VT) was simulated by rapid ventricular pacing at a target site in eleven Yorkshire swine. The ablation target was established using three different techniques: a pacing lead placed into the ventricular wall at the mid-myocardial level (Type-1), an intracardiac mapping catheter (Type-2), and an RF ablation catheter placed at a random position on the endocardial surface (Type-3). In each experiment, one operator placed the catheter/pacing lead at the target location, while another used the ISGA system to manipulate the RF ablation catheter starting from a random ventricular location to locate the target. The average localization error of the RF ablation catheter tip was 0.31 ± 0.08 cm. After analyzing approximately 35 cardiac cycles of simulated VT, the ISGA system's accuracy in locating the target was 0.4 cm after four catheter movements in the Type-1 experiment, 0.48 cm after six movements in the Type-2 experiment, and 0.67 cm after seven movements in the Type-3 experiment. We demonstrated the feasibility of using the ISGA method to guide an ablation catheter to the origin of a VT focus by analyzing a few beats of body surface potentials without electro-anatomic mapping.

Accuracy of cardiac ablation catheter guidance by means of a single equivalent moving dipole inverse algorithm to identify sites of origin of cardiac electrical activation.

We have developed a system that could potentially be used to identify the site of origin of ventricular tachycardia (VT) and to guide a catheter to that site to deliver radio-frequency ablation therapy. This system employs the Inverse Solution Guidance Algorithm based upon Single Equivalent Moving Dipole (SEMD) localization method. The system was evaluated in in vivo swine experiments. Arrays consisting of 9 or 16 bipolar epicardial electrodes and an additional mid-myocardial pacing lead were sutured to each ventricle. Focal tachycardia was simulated by applying pacing pulses to each epicardial electrode at multiple pacing rates during breath hold at the end-expiration phase. Surface potentials were recorded from 64 surface electrodes and then analyzed using the SEMD method to localize the position of the pacing electrodes. We found a close correlation between the locations of the pacing electrodes as measured in computational and real spaces. The reproducibility error of the SEMD estimation of electrode location was 0.21 ± 0.07cm. The vectors between every pair of bipolar electrodes were computed in computational and real spaces. At 120bpm, the lengths of the vectors in the computational and real space had a 95% correlation. Computational space vectors were used in catheter guidance simulations which showed that this method could reduce the distance between the real space locations of the emulated catheter tip and the emulated arrhythmia origin site by approximately 72% with each movement. We have demonstrated the feasibility of using our system to guide a catheter to the site of the emulated VT origin.

On the efficiency and accuracy of the single equivalent moving dipole method to identify sites of cardiac electrical activation.

We have proposed an algorithm to guide radiofrequency catheter ablation procedures. This algorithm employs the single equivalent moving dipole (SEMD) to model cardiac electrical activity. The aim of this study is to investigate the optimal time instant during the cardiac cycle as well as the number of beats needed to accurately estimate the location of a pacing site. We have evaluated this algorithm by pacing the ventricular epicardial surface and inversely estimating the locations of pacing electrodes from the recorded body surface potentials. Two pacing electrode arrays were sutured on the right and left ventricular epicardial surfaces in swine. The hearts were paced by the electrodes sequentially at multiple rates (120-220bpm), and body surface ECG signals from 64 leads were recorded for the SEMD estimation. We evaluated the combined error of the estimated interelectrode distance and SEMD direction at each time instant during the cardiac cycle, and found the error was minimum when the normalized root mean square (RMS n ) value of body surface ECG signals reached 15% of its maximum value. The beat-to-beat variation of the SEMD locations was significantly reduced (p<0.001) when estimated at 15% RMS n compared to the earliest activation time (EAT). In addition, the 5-95% interval of the estimated interelectrode distance error decreased exponentially as the number of beats used to estimate a median beat increased. When the number of beats was 4 or larger, the 5-95% interval was smaller than 3.5mm (the diameter of a commonly used catheter). In conclusion, the optimal time for the SEMD estimation is at 15% of RMS n , and at that time instant a median beat estimated from 4 beats is associated with a beat-to-beat variability of the SEMD location that is appropriate for catheter ablation procedures.

A Method to Noninvasively Identify Cardiac Bioelectrical Sources

We have introduced a method to guide radiofrequency catheter ablation (RCA) procedures that estimates the location of a catheter tip used to pace the ventricles and the target site for ablation using the single equivalent moving dipole (SEMD). To investigate the accuracy of this method in resolving epicardial and endocardial electrical sources. Two electrode arrays, each of nine pacing electrodes at known distances from each other, sutured on the left- and right-ventricular (LV and RV) epicardial surfaces of swine, were used to pace the heart at multiple rates, while body surface potentials from 64 sites were recorded and used to estimate the SEMD location. A similar approach was followed for pacing from catheters in the LV and RV. The overall (RV & LV) error in estimating the interelectrode distance of adjacent epicardial electrodes was 0.38 ± 0.45 cm. The overall endocardial (RV & LV) interelectrode distance error, was 0.44 ± 0.26 cm. Heart rate did not significantly affect the error of the estimated SEMD location (P > 0.05). The guiding process error became progressively smaller as the SEMD approached an epicardial target site and close to the target, the overall absolute error was ∼ 0.28 cm. The estimated epicardial SEMD locations preserved their topology in image space with respect to their corresponding physical location of the epicardial electrodes. The proposed algorithm suggests one can efficiently and accurately resolve epicardial electrical sources without the need of an imaging modality. In addition, the error in resolving these sources is sufficient to guide RCA procedures.

The Single Equivalent Moving Dipole Model Does Not Require Spatial Anatomical Information to Determine Cardiac Sources of Activation

Radio-frequency catheter ablation (RCA) is an established treatment for ventricular tachycardia (VT). A key feature of the RCA procedure is the need for a mapping approach that facilitates the identification of the target ablation site. In this study, we investigate the effect of the location of the reference potential and spatial anatomical constraints on the accuracy of an algorithm to identify the target site for ablation therapy of VT. This algorithm involves processing body surface potentials using the single equivalent moving dipole (SEMD) model embedded in an infinite homogeneous volume conductor to model cardiac electrical activity. We employed a swine animal model and an electrode array of nine electrodes that was sutured on the epicardial surface of the right ventricle. We identified two potential reference electrode locations: at an electrode most far away from the heart (R1) and at the average of all 64 body surface electrode potentials (R2). Also, we developed three spatial "constraining" schemes of the algorithm used to obtain the SEMD location: one that does not impose any constraint on the inverse solution (S1), one that constrains the solution into a volume that corresponds to the heart (S2), and one that constrains the solution into a volume that corresponds to the body surface (S3). We have found that R2S1 is the most accurate approach (p < 0.05 versus R1S1 at earliest activation time-EAT) for localizing epicardial electrical sources of known locations in vivo. Although the homogeneous volume conductor introduces systematic error in the estimated compared to the true dipole location, we have observed that the overall error of the estimated interelectrode distance compared to the true one was 0.4 ± 0.4cm and 0.4 ± 0.1cm for the R1S1 and R2S1 combinations, respectively, at the EAT (p = N.S.) and 1.0 ± 0.6 and 0.5 ± 0.4cm, respectively, at the pacing spike time (PST, ). In conclusion, our algorithm to estimate the SEMD parameters from body surface potentials can potentially be a useful method to rapidly and accurately guide the catheter tip to the target site during a RCA procedure without the need for spatial anatomical information obtained by conventional imaging modalities.

Cardiac Ablation Catheter Guidance by Means of a Single Equivalent Moving Dipole Inverse Algorithm

We developed and evaluated a novel system for guiding radiofrequency catheter ablation therapy of ventricular tachycardia. This guidance system employs an inverse solution guidance algorithm (ISGA) using a single equivalent moving dipole (SEMD) localization method. The method and system were evaluated in both a saline tank phantom model and in vivo animal (swine) experiments. A catheter with two platinum electrodes spaced 3 mm apart was used as the dipole source in the phantom study. A 40-Hz sinusoidal signal was applied to the electrode pair. In the animal study, four to eight electrodes were sutured onto the right ventricle. These electrodes were connected to a stimulus generator delivering 1-ms duration pacing pulses. Signals were recorded from 64 electrodes, located either on the inner surface of the saline tank or on the body surface of the pig, and then processed by the ISGA to localize the physical or bioelectrical SEMD. In the phantom studies, the guidance algorithm was used to advance a catheter tip to the location of the source dipole. The distance from the final position of the catheter tip to the position of the target dipole was 2.22 ± 0.78 mm in real space and 1.38 ± 0.78 mm in image space (computational space). The ISGA successfully tracked the locations of electrodes sutured on the ventricular myocardium and the movement of an endocardial catheter placed in the animal's right ventricle. In conclusion, we successfully demonstrated the feasibility of using an SEMD inverse algorithm to guide a cardiac ablation catheter.

Novel catheter guidance technique to the site of origin of the arrhythmia

The purpose of this study was to evaluate the accuracy of our catheter guidance system using Single Equivalent Moving Dipole (SEMD) method to guide the tip of the cardiac ablation catheter to the site of origin of the arrhythmia. 3 different patterns of 8 bipolar electrodes were sutured on the right ventricular myocardium of 3 swine through a standard thoracotomy. Electrode cables passed subcutaneously to a ventral interscapular position were exteriorized, fixed by stay sutures, and the chest closed in layers. The animals' heart rate, pulse oximetry, femoral artery blood pressure, and body temperature were continuously monitored. As the epicardial electrodes connected to a stimulator delivered pacing spikes simulating focal ventricular tachycardia at a rate of 120 bpm, the BioSemi ActiveTwo system at a frequency of 1Khz with a symmetrically patterned array of 64 electrodes placed on the chest measured body surface potentials. A paralytic drug was used to reduce error in cardiac mapping by minimizing muscular activity and allowing for full respirator control of breathing. Both simulation and real catheter's movements were well detected (R=0.95) and the final localization error of a simulation catheter to a pre‐defined target was less than 1 cm in imaginary space, which is equal to 0.4 cm in real space. These data support the validity of SEMD method for localizing the origin of arrhythmia in swine model.

Method for guiding the ablation catheter to the ablation site: a simulation and experimental study

Radiofrequency catheter ablation (RCA) procedures for treating ventricular arrhythmias have evolved significantly over the past several years; however, the use of RCA has been limited due to the difficulty in identifying the appropriate site for ablation. In this study, we investigate the accuracy of a computer algorithm to guide the tip of an ablation catheter to the exit site of the scar tissue or the site of abnormal automaticity (the "target site"). This algorithm involves modeling the body surface potentials corresponding to the wavefront at the target site for ablation and current pulses generated from a pair of electrodes at the tip of the ablation catheter with a single equivalent moving dipole (SEMD) in an infinite homogeneous volume conductor. Despite the fact that the use of the homogeneous volume conductor introduces systematic error in the estimated compared to the true dipole location, we find that the systematic error had minor influence in the ability of the algorithm to accurately guide the tip of the ablation catheter to the ablation site and the overall error (1.9 +/- 1.1 mm) in the left ventricle is adequate for RCA procedures. These results were verified, in saline tank studies in which the distance between the dipole due to the catheter tip and the dipole due to the target site was found to be 2.66 +/- 0.52 mm. In conclusion, our algorithm to estimate the SEMD parameters from body surface potentials can potentially be a useful method to rapidly and accurately guide the catheter tip to the arrhythmic site during an RCA procedure.

Sensory Stimulation Triggers Spindles During Sleep Stage 2

Toward understanding the function of sleep spindle, we examined whether sensory stimulation triggers sleep spindles. Eleven normal subjects participated in the experiments. The subjects had a nap in the afternoon, and sensory stimulation was applied during sleep stage 2. 21-channel EEG was recorded during the 2-3 hour experiment carried out between 13:00 and 16:00. Somatosensory, auditory, or visual stimulation was performed over a 5-minute period during stage 2. The frequency and duration of spindles were compared in 2 different segments of 5 minutes, with and without sensory stimulation. The latency from the onset of a sensory stimulus to the succeeding spindle was also analyzed. To estimate the active brain regions during a spindle, the EEG recordings were modeled with a single equivalent moving dipole (SEMD) model. In the period with stimulation, spindle frequency and duration increased compared with the period without stimulation. Statistical tests revealed that with stimulation, the interval between 2 consecutive spindles was significantly shorter (p < 0.05, regardless of the modality) and that the duration of the spindles was significantly longer with stimulation (p < 0.05, regardless of the modality). The latency was approximately 2 s. During a spindle after somatosensory stimulation brain activities were observed near the somatosensory area, while with auditory stimulation active regions were observed near the auditory cortex. A sensory stimulus appeared to trigger a sleep spindle during sleep stage 2. SEMD trajectories suggest that active brain regions during spindle are different according to the modality of the preceding stimulus.

Applicability of the Single Equivalent Moving Dipole Model in an Infinite Homogeneous Medium to Identify Cardiac Electrical Sources: A Computer Simulation Study in a Realistic Anatomic Geometry Torso Model

We have previously proposed an inverse algorithm for fitting potentials due to an arbitrary bio-electrical source to a single equivalent moving dipole (SEMD) model. The algorithm achieves fast identification of the SEMD parameters by employing a SEMD model embedded in an infinite homogeneous volume conductor. However, this may lead to systematic error in the identification of the SEMD parameters. In this paper, we investigate the accuracy of the algorithm in a realistic anatomic geometry torso model (forward problem). Specifically, we investigate the effect of measurement noise, dipole position and electrode configuration in the accuracy of the algorithm. The boundary element method was used to calculate the forward potential distribution at multiple electrode positions on the body surface due to a point dipole in the heart. We have found that the position and not the number of electrodes as well as the site of the origin of the arrhythmia in the heart have a significant effect on the accuracy of the inverse algorithm, while the measurement noise does not. Finally, we have shown that the inverse algorithm preserves the topology of the source distribution in the heart, thus potentially allowing the cardiac electrophysiologist to efficiently and accurately guide the tip of the catheter to the ablation site.

Statistical accuracy of a moving equivalent dipole method to identify sites of origin of cardiac electrical activation

While radio frequency (RF) catheter ablation (RCA) procedures for treating ventricular arrhythmias have evolved significantly over the past several years, the use of RCA has been limited to treating slow ventricular tachycardias (VTs). In this paper, we present preliminary results from computer and animal studies to evaluate the accuracy of an algorithm that uses the single equivalent moving dipole (SEMD) model in an infinite homogeneous volume conductor to guide the RF catheter to the site of origin of the arrhythmia. Our method involves measuring body surface electrocardiographic (ECG) signals generated by arrhythmic activity and by bipolar current pulses emanating from a catheter tip, and representing each of them by a SEMD model source at each instant of the cardiac cycle, thus enabling rapid repositioning of the catheter tip requiring only a few cycles of the arrhythmia. We found that the SEMD model accurately reproduced body surface ECG signals with a correlation coefficients > 0.95. We used a variety of methods to estimate the uncertainty of the SEMD parameters due to measurement noise and found that at the time when the arrhythmia is mostly localized during the cardiac cycle, the estimates of the uncertainty of the spatial SEMD parameters (from ECG signals) are between 1 and 3 mm. We used pacing data from spatially separated epicardial sites in a swine model as surrogates for focal ventricular arrhythmic sources and found that the spatial SEMD estimates of the two pacing sites agreed with both their physical separation and orientation with respect to each other. In conclusion, our algorithm to estimate the SEMD parameters from body surface ECG can potentially be a useful method for rapidly positioning the catheter tip to the arrhythmic focus during an RCA procedure.