Dakun Lai

Equivalent Moving Dipole Localization of Cardiac Ectopic Activity in a Swine Model During Pacing

Localization of the initial site of cardiac ectopic activity has direct clinical benefits for treating focal cardiac arrhythmias. The aim of the present study is to experimentally evaluate the performance of the equivalent moving dipole technique on noninvasively localizing the origin of the cardiac ectopic activity from the recorded body surface potential mapping (BSPM) data in a well-controlled experimental setting. The cardiac ectopic activities were induced in four well-controlled intact pigs by either single-site pacing or dual-site pacing within the ventricles. In each pacing study, the initiation sites of cardiac ectopic activity were localized by estimating the locations of a single moving dipole (SMD) or two moving dipoles (TMDs) from the measured BSPM data and compared with the precise pacing sites (PSs). For the single-site pacing, the averaged SMD localization error was 18.6 ± 3.8 mm over 16 sites, while the averaged distance between the TMD locations and the two corresponding PSs was slightly larger (24.9 ± 6.2 mm over five pairs of sites), both occurring at the onset of the QRS complex (10-25 ms following the pacing spike). The obtained SMD trajectories originated near the stimulus site and then traversed across the heart during the ventricular depolarization. The present experimental results show that the initial location of the moving dipole can provide the approximate site of origin of a cardiac ectopic activity in vivo, and that the migration of the dipole can portray the passage of an ectopic beat across the heart.

A novel non-model-based 6-DOF electromagnetic tracking method using non-iterative algorithm

Electromagnetic tracking, a non-fluoroscopic image navigation method most often used in minimally invasive therapy, has prominent advantages and features over the traditional X-ray radioscopy. Using two rotating coils and one 3-axis magnetic sensor, a novel 6 degree of freedom (DOF) electromagnetic tracking method is proposed in this paper. Two alternate rotating magnetic fields are generated in turns by these coils and the moving-around sensor simultaneously detects the magnetic filed flux density in 3 orthogonal directions. As the magnitude of a magnetic field comes to the maximum only when the rotating coil directly points toward the sensor, the spatial position and orientation of the sensor can be determined using triangulation measurement. An embodiment and the corresponding system framework of this method are developed and a non-model-based non-iterative algorithm is presented to calculate the 6-DOF of position and orientation. Moreover, simulation experiments are performed to validate the proposed method. The obtained results show that the averaged position error is 0.2365 cm and the averaged orientation error is below 1 degree away from low resolution area.

Localization of endocardial ectopic activity by means of noninvasive endocardial surface current density reconstruction.

Localization of the source of cardiac ectopic activity has direct clinical benefits for determining the location of the corresponding ectopic focus. In this study, a recently developed current-density (CD)-based localization approach was experimentally evaluated in noninvasively localizing the origin of the cardiac ectopic activity from body-surface potential maps (BSPMs) in a well-controlled experimental setting. The cardiac ectopic activities were induced in four well-controlled intact pigs by single-site pacing at various sites within the left ventricle (LV). In each pacing study, the origin of the induced ectopic activity was localized by reconstructing the CD distribution on the endocardial surface of the LV from the measured BSPMs and compared with the estimated single moving dipole (SMD) solution and precise pacing site (PS). Over the 60 analyzed beats corresponding to ten pacing sites (six for each), the mean and standard deviation of the distance between the locations of maximum CD value and the corresponding PSs were 16.9 mm and 4.6 mm, respectively. In comparison, the averaged distance between the SMD locations and the corresponding PSs was slightly larger (18.4 ± 3.4 mm). The obtained CD distribution of activated sources extending from the stimulus site also showed high consistency with the endocardial potential maps estimated by a minimally invasive endocardial mapping system. The present experimental results suggest that the CD method is able to locate the approximate site of the origin of a cardiac ectopic activity, and that the distribution of the CD can portray the propagation of early activation of an ectopic beat.

Successive ECG telemetry monitoring for preventing sudden cardiac death

In this paper, a novel successive ECG telemetry monitoring prototype is developed to evaluate the effect of monitoring for those out-of-hospital patient who has serious arrhythmia and/or possesses the risk of sudden cardiac death (SCD). This system has such features as: real-time, continuous, telemetry monitoring, wide range, long distance, and long term etc. The developed prototype consists a pocket-size patient-side monitor and a monitoring center placed in a hospital, which continually collects every patient’s ECG through GPRS mobile network and automatically analyzes it, if any danger found, instantly send medical warning message to patient. Based on the subsequent experiments on three volunteers in daily activity situation, the preliminary results indicate three-channel ECGs of each volunteer and his localization information can be real-timely and continuously monitored in the center.

A Real-Time Continuous ECG Transmitting Method through GPRS with Low Power Consumption

In this paper, a novel real-time continuous electrocardiogram (ECG) transmitting method through GPRS network is presented, which is based on a packet-level forward error correction (PFEC) method with simultaneously considering low power consumption. This novel method is used on the user datagram protocol (UDP) for data transmission. Furthermore, a series of communication tests based on a developed experiment platform are carried out to validate this method. Results indicate that the transmitting protocol using the PFEC with a packet size of 450 bytes, 3 seconds of transmission interval per packet would achieve about 0.1% to 0.3% packet loss rate, which is more effective transmission and has lower power consumption, and conclusively match actually the requirement of the clinical mobile monitoring.

A shockable rhythm detection algorithm for automatic external defibrillators by combining a slope variability analyzer with a band-pass digital filter

To make automatic external defibrillators (AEDs) easy to use by the public who is not familiar with emergency treatment and electrocardiogram (ECG) analysis, it is critical to have an accurate shockable rhythm recognition algorithm. This paper presents a novel compositive algorithm by combining a slope variability analyzer with a band-pass digital filter so as to accurately distinguish shockable rhythms from non-shockable rhythms for automatic external defibrillators (AEDs). A total of 35 ECG records from the widely recognized Creighton University Ventricular Tachyarrhythmia Database (CUDB) were used to test the performance of the proposed algorithm. The obtained sensitivity of 94.2% and the specificity of 96.6% both satisfy requirements by the AHA rules on the arrhythmias detection for AEDs, and show a higher performance comparing with the previous HILB algorithm and the slope variability method only. As a conclusion, the proposed compositive algorithm would potentially provide a useful tool for AED systems with a higher accuracy and lower computation requirements.

A multi-criteria evaluation method for assessing the defibrillation outcome of different electrode placements in swine.

Compared with clinical and experimental approaches, numerical modeling of defibrillation offers a great opportunity to optimize the defibrillation strategy in a more individualized way. Through numerical simulation of the shock-induce electric field distribution, the outcome of a certain defibrillation shock could be predicted according to several different metrics. In this paper, we propose a novel evaluation method, in which four defibrillation criteria are assigned with separate weighting factors to quantitatively assess the efficiency of a certain defibrillation shock. Three anatomically realistic finite element models of swine were constructed for the evaluation study of 8 electrode pairs in different placements. In addition, corresponding animal experiments were performed to determine the defibrillation threshold of 8 electrode placements. Both computational and experimental results suggest that the clinical recommended anterior-lateral position is the most efficient electrode displacement for transthoracic defibrillation in swine. In conclusion, the good agreement between stimulations and experiments indicates that the present multi-criteria evaluation method would be potentially useful for optimizations of cardiac defibrillation outcome.Compared with clinical and experimental approaches, numerical modeling of defibrillation offers a great opportunity to optimize the defibrillation strategy in a more individualized way. Through numerical simulation of the shock-induce electric field distribution, the outcome of a certain defibrillation shock could be predicted according to several different metrics. In this paper, we propose a novel evaluation method, in which four defibrillation criteria are assigned with separate weighting factors to quantitatively assess the efficiency of a certain defibrillation shock. Three anatomically realistic finite element models of swine were constructed for the evaluation study of 8 electrode pairs in different placements. In addition, corresponding animal experiments were performed to determine the defibrillation threshold of 8 electrode placements. Both computational and experimental results suggest that the clinical recommended anterior-lateral position is the most efficient electrode displacement for transthoracic defibrillation in swine. In conclusion, the good agreement between stimulations and experiments indicates that the present multi-criteria evaluation method would be potentially useful for optimizations of cardiac defibrillation outcome.

Numerical modeling and simulation based on finite element method for internal cardiac defibrillation in a human torso

Since the inability of clinical approaches to measure the shock-induced electric field distribution of internal cardiac defibrillation, current clinical applications of the implantable cardioverter defibrillator (ICD) still stay largely empirical. In this study, a finite element modeling and simulation method for solving internal cardiac defibrillation field was proposed. Using this method, the defibrillation shock-induced potential field distribution was solved numerically in the torso of a patient implanted with a widely used transvenous ICD system. Moreover, the defibrillation energy threshold (DFT) for this patient was pre-surgically calculated using the critical mass hypothesis of cardiac defibrillation studies. The obtained results showed a high agreement between the predicted defibrillation thresholds with records observed in clinical. As a conclusion, the proposed method would be a feasible approach for using a further patient-specific optimization of ICD implantation, as part of preoperative planning.

Cardiac source localization by means of a single moving dipole solution during endocardial pacing in an animal model

The accuracy of localizing the initiation site of cardiac activation by noninvasively estimating a single moving dipole (SMD) was investigated in a swine model. Body surface potential mapping (BSPM) and intracavitary noncontact mapping (NCM) were performed simultaneously during acute left ventricular (LV) endocardial pacing. For each animal, the boundary element model was constructed from preoperative magnetic resonance images (MRI). In each pacing study, the initiation site was localized by inversely estimating the location of an SMD from BSPM data. The results were compared with the precise pacing sites recorded by the NCM system. In total, four pacing sites from two pigs were analyzed, and the averaged source localization error was 16.8 ± 2.3 mm. The present results indicate the potential of localizing focal cardiac events by estimating single moving dipole.

Modeling and Simulation of Three Orthogonal Transthoracic Electrical-Fields for Localization Method of Intracardiac Catheter

The objective of this study is to numerically investigate the three orthogonal transthoracic electrical-fields of a newly developed catheter localization method in guiding radiofrequency catheter ablation (RFCA) procedures. Based on an assumption of quasistatic current field, the problem of the three orthogonal transthoracic electrical-fields in this novel localization method can be formulated using the basic Laplaces equation. With the finite element method, the three electrical-fields including X axis, Y axis, and Z axis, are then modeled and solved with a detail finite element model of human torso, respectively. Moreover, the obtained electrical-field distributions within the heart are depicted spatially and compared detailedly to determine the effects of different axis on the localization accuracy. Results indicate that there are more nonuniform distribution at X axis and the more possible location error than others axes in clinical catheter positioning.