A Morphology-Preserving Algorithm for Denoising of EMG-Contaminated ECG Signals.

Goal: Clinical interpretation of an electrocardiogram (ECG) can be detrimentally affected by noise. Removal of the electromyographic (EMG) noise is particularly challenging due to its spectral overlap with the QRS complex. The existing EMG-denoising algorithms often distort signal morphology, thus obscuring diagnostically relevant information. Methods: Here, a new iterative regeneration method (IRM) for efficient EMG-noise suppression is proposed. The main hypothesis is that the temporary removal of the dominant ECG components enables extraction of the noise with the minimum alteration to the signal. The method is validated on SimEMG database of simultaneously recorded reference and noisy signals, MIT-BIH arrhythmia database and synthesized ECG signals, both with the noise from MIT Noise Stress Test Database. Results: IRM denoising and morphology-preserving performance is superior to the wavelet- and FIR-based benchmark methods. Conclusions: IRM is reliable, computationally non-intensive, fast and applicable to any number of ECG channels recorded by mobile or standard ECG devices.

A Database of Simultaneously Recorded ECG Signals With and Without EMG Noise.

Goal: Noise on recorded electrocardiographic (ECG) signals may affect their clinical interpretation. Electromyographic (EMG) noise spectrally coincides with the QRS complex, which makes its removal particularly challenging. The problem of evaluating the noise-removal techniques has commonly been approached by algorithm testing on the contaminated ECG signals constructed ad hoc as an additive mixture of a noise-free ECG signal and noise. Consequently, there is an absence of a unique/standard database for testing and comparing different denoising methods. We present a SimEMG database recorded by a novel acquisition method that allows for direct recording of the genuine EMG-noise-free and -contaminated ECG signals. The database is available as open source.

A novel pulsed field ablation system using linear and spiral ablation catheters can create large and durable endocardial and epicardial ventricular lesions in vivo.

BACKGROUND: We investigated the preclinical safety and efficacy of ventricular pulsed field ablation (PFA) using a family of novel, 6-/8-Fr, linear, and spiral PFA/mapping catheters (CRC EP, Inc). METHODS: QRS-gated, bipolar PFA (>2.0 kV) was performed in 10 healthy swine. Altogether, 20 endocardial and epicardial right and left ventricular applications were delivered. The catheters were inserted through an 8.5-Fr steerable introducer. The intensity of skeletal muscle activation was quantified using an accelerometer. Lesions were assessed by pre- versus post-PFA electrogram analysis, pacing threshold, 3D voltage mapping, necropsy, and histology. The swine rete mirabile, liver and kidneys were examined for embolic events. RESULTS: All applications were single-shot (56 ± 18 s) without catheter repositioning. Minimal microbubbling was observed without significant skeletal muscle stimulation (mean acceleration 0.05 m/s2) or ventricular tachyarrhythmias. There was significant reduction in post- versus pre-PFA electrogram amplitude (0.5 ± 0.2 mV versus 3.2 ± 0.9 mV, P < 0.001) with a marked increase in pacing threshold (>20 mA versus 7.5 ± 2.9 mA, P < 0.001). All lesions were large and durable up to 28 days, measuring 32 ± 5 mm (length), 27 ± 8 mm (width), and 8 ± 3 mm (depth) using the spiral catheters and 43 ± 1 mm (length), 7 ± 1 mm (width), and 8 ± 1 mm (depth) using the linear catheters. Despite higher waveform voltages and prolonged applications, no thermal effects were detected at necropsy/histology. Moreover, gross and microscopic examinations revealed no evidence of thromboembolism, vascular or collateral injury. CONCLUSIONS: A novel, QRS-gated PFA system using linear and spiral PFA catheters is capable of creating large and durable ventricular lesions in vivo without significant microbubbling, ventricular arrhythmias or thromboembolism.

Preclinical evaluation of a novel single-shot pulsed field ablation system for pulmonary vein and atrial ablation.

INTRODUCTION: Pulsed field ablation (PFA) is a nonthermal ablative strategy that achieves cell death via electroporation. Herein, we investigated the preclinical safety and efficacy of PFA using two novel 8-French, 16-electrode spiral PFA/mapping catheters (ElePulse; CRC EP, Inc.). METHODS: Bipolar PFA (>1.8 kV) was performed using 30 s, single-shot, QRS-gated applications. Altogether, 94 atrial structures were ablated in 23 swine, one canine, and one ovine, including right and left atria and atrial appendages, pulmonary veins, and superior and inferior (IVC) vena cavae. We also examined the impact of PFA on the phrenic nerve (14 swine) and on a deviated esophagus after delivery of PFA from inside the IVC (five swine). RESULTS: All applications were single-shot without catheter repositioning. Minimal microbubbling was observed without significant skeletal muscle twitching/activation (mean acceleration: 0.05 m/s2 ). There was a marked reduction in post-PFA versus pre-PFA atrial electrogram amplitude (0.17 ± 0.21 vs. 1.18 ± 1.08 mV; p < .0001). Lesion durability was demonstrated up to 3 months in all targeted tissues. Histologically, lesions were contiguous and transmural, except in the atrial appendage, and without any thermal effects. Magnetic resonance, gross, and histologic examinations of the brain, rete mirabile, and kidneys revealed no thromboembolism. No acute/long-term phrenic nerve dysfunction was encountered. Although within 2 h of ablation, histologic examinations of the esophagus revealed acute PFA-related changes in the muscular layer, these completely resolved by 21 ± 5 days. CONCLUSION: A novel, single-shot, spiral PFA system is capable of safely creating large, durable atrial lesions without significant adverse effects on the phrenic nerve or the esophagus.

Electrocution Risk of Capacitive Discharge Shocks: Application to Electric Vehicle Charging.

It is difficult to electrocute (induce ventricular fibrillation) with capacitive discharge shocks. With small capacitance values, the high voltages required for the necessary charge are rarely seen in industrial situations (e.g. electric vehicle charging stations). On the other hand, with large capacitance values, the discharge time is so great that the shock couples inefficiently with the cardiac cells. The update to IEC 60479-2 sets the C1 "mostly-safe" charge limit of 3 mC for a short "impulse function" pulse. We calculated the equivalent capacitor stored charge for an arbitrary capacitance value using the simple single membrane time constant model for the cardiac response. The peak membrane response was set equal to that of the 3 mC impulse function response to calculate the safe values for stored charge, voltage, and energy. The total stored charge, per se, cannot be used simplistically to estimate the danger of a capacitive discharge shock. A capacitive-discharge shock cannot be accurately compared to a rectangular shock with a duration equal to the shock time constant. The greater the capacitance, the larger the fraction of wasted charge in coupling to the heart and thus the shorter equivalent duration compared to the shock time constant. For a capacitive discharge shock this translates to a stored charge of 3 mC increasing up to 9 mC for a 10 capacitor using the assumed 575 load for an electric-vehicle (EV) charging station. In the area of interest for 1 - 10 the safe voltage ranges from 1300 to 4700 V, which includes the 1500-VDCscope of EV charger standard IEC 61851-23. For C > 100 the voltage asymptote is 700 V.

Estimation of Physiological Impedance from Neuromuscular Pulse Data.

INTRODUCTION: A Conducted Electrical Weapon (CEW) deploys 2, or more, probes to conduct current via the body to induce motor-nerve mediated muscle contractions, but the inter-probe resistances can vary and this can affect charge delivery. For this reason, newer generation CEWs such as the TASER® X3, X2 and X26P models have feed-forward control circuits to keep the delivered charge constant regardless of impedance. Our main goal was to explore the load limits for this "charge metering" system. A secondary goal was to evaluate the reliability of the "Pulse Log" stored data to estimate the load resistance. METHODS: We tested 10 units each of the X2 (double shot), X26P, and X26P+ (single-shot) CEW models. We used non-inductive high-voltage resistor assemblies of 50, 200, 400, 600, 1k, 2.5k, 3.5k, 5k, and 10k Ω, a shorted output (nominal 0 Ω), and arcing open-circuits. The Pulse Log data were downloaded to provide the charge value and stimulation and arc voltages for each of the pulses in a 5 s standard discharge cycle. RESULTS: The average reported raw charge was 65.4 ± 0.2 µC for load resistances < 1 kΩ consistent with specifications for the operation of the feed-forward design. At load resistances ≥ 1 kΩ, the raw charge decreased with increasing load values. Analyses of the Pulse Logs, using a 2-piece multiple regression model, were used to predict all resistances. For the resistance range of 0 - 1 kΩ the average error was 53 Ω; for 1 kΩ - 10 kΩ it was 16%. Muzzle arcing can be detected with a model combining parameter variability and arcing voltage. CONCLUSIONS: The X2, X26P, and X26P+ electrical weapons deliver an average charge of 65 µC with a load resistance < 1 kΩ. For loads ≥ 1 kΩ, the metered charge decreased with increasing loads. The stored pulse-log data for the delivered charge and arc voltage allowed for methodologically-reliable forensic analysis of the load resistance with useful accuracy.

Detection of Arcing and High Impedance with Electrical Weapons.

INTRODUCTION: Conducted electrical weapons are primarily designed to stop subjects from endangering themselves or others by deploying 2, or more, probes to conduct current via the body to induce motor-nerve mediated muscle contractions, but probe impedance can vary significantly including open circuits from probes failing to complete or maintain a circuit. METHODS: We tested 10 units of the TASER® 7 model with a range of impedances and open circuit conditions. Pulse data (stored in the device's memory) were used to predict the load resistances and detect arcing conditions. Acoustical data (recorded externally) was evaluated on an exploratory basis as a secondary goal. RESULTS: The average error of predicted resistance, over the physiological load range of 400-1000 Ω, was 8%. Arcing conditions was predicted with an accuracy of 97%. An arcing condition increases the duration of the sound generation. CONCLUSIONS: The TASER 7 electronic control device stored pulse-log data for charge and arc voltage yielded forensic analysis of the load resistance with reliable accuracy.

Ventricular Fibrillation Threshold vs Alternating Current Shock Duration.

INTRODUCTION: International basic safety limits for utility-frequency electrical currents have long been set by the International Electrotechnical Commission 60479-1 standard. These were inspired by a linear-section plot proposed by Biegelmeier in 1980 with current given as a function of the shock duration. This famous plot has contributed to safe electrical circuit design internationally and has properly earned significant amount of respect over its 35 years of life. However, some possible areas for improvement have been suggested. METHODS: We searched for all animal studies of ventricular fibrillation threshold versus duration that used a forelimb to hindlimb connection that had at least 3 durations tested. We found 6 such studies and they were then used to calculate a new C3 curve after normalizing the data. RESULTS: A rational function model fit the animal data with r2 = .96. Such a correlation calculation tends to underweight the smaller values, so we also correlated the log threshold values and this had a correlation of r2=.94. CONCLUSION: Existing ventricular fibrillation threshold current versus duration data can be fitted with a simple rational function. This can provide a useful update to IEC 60479-1.

Output of Electronic Muscle Stimulators: Physical Therapy and Police Models Compared.

INTRODUCTION: Both physical therapists and police officers use electrical muscle stimulation. The typical physical therapist unit is attached with adhesive patches while the police models use needle-based electrodes to penetrate clothing. There have been very few papers describing the outputs of these physical therapy EMS (electrical muscle stimulator) units. METHODS: We purchased 6 TENS/EMS units at retail and tested them with loads of 500 Ω, 2 kΩ, and 10 kΩ. RESULTS: For the typical impedance of 500 Ω, the EMS units delivered the most current followed by the electrical weapons; TENS units delivered the least current. At higher im-pedances (> 2 kΩ) the electrical weapons delivered more current than the EMS units, which is explained by the higher voltage-compliance of their circuits. Some multi channel EMS units deliver more calculated muscle stimula tion than the multi-channel weapons. CONCLUSION: Present therapeutic electrical muscle stimula-tors can deliver more current than present law-enforcement muscle stimulators.

Humidity and Ventricular Fibrillation: When Wet Welding can be Fatal.

INTRODUCTION: Arc welding is generally considered very safe electrically. There have been electrocution cases with welders in high humidity environments. When dry, the flux coatings tend to have sufficient electrical resistance to limit the current below that required for the induction of VF (ventricular fibrillation). METHODS: We tested 4 welding electrodes for resistance in both dry and wet conditions. To estimate the cardiac current density - in a worst-case scenario - we used a 20k element finite-element bioimpedance model with 1 cm of skin and fat along with 1 cm of muscle before the heart of 5 cm dimensions. Between the heart and a metal plate we assumed 5 cm of lung and 1 cm of skin and fat. RESULTS: Welding electrode flux is highly resistive when dry. However, when saturated with moisture the resistance is almost negligible as far as dangerous currents in a human. The FEM model calculated a current density of > 7 mA/cm2 on the ventricular epicardium with a source of 80 V at the welding rod. CONCLUSION: In conditions of high humidity, a supine operator, in contact with a coated welding electrode to the precordial region of the body can be fibrillated with the AC open-circuit voltage. Most reported DC fatalities were probably due to pseudo-DC outputs that were merely rectified AC without smoothing.

Computer simulations of an irrigated radiofrequency cardiac ablation catheter and experimental validation by infrared imaging.

PURPOSE: To develop and validate a three-dimensional (3-D) computer model based on accurate geometry of an irrigated cardiac radiofrequency (RF) ablation catheter with microwave radiometry capability, and to test catheter performance. METHODS: A computer model was developed based on CAD geometry of a RF cardiac ablation catheter prototype to simulate electromagnetic heating, heat transfer, and computational fluid dynamics (blood flow, open irrigation, and natural convection). Parametric studies were performed; blood flow velocity (0-25 cm/s) and irrigation flow (0-40 ml/min) varied, both with perpendicular (PE) and parallel (PA) catheter orientations relative to tissue. Tissue Agar phantom studies were performed under similar conditions, and temperature maps were recorded via infrared camera. Computer model simulations were performed with constant voltage and with voltage adjusted to achieve maximum tissue temperatures of 95-105 °C. RESULTS: Model predicted thermal lesion width at 5 W power was 5.8-6.4 mm (PE)/6.5-6.6 mm (PA), and lesion depth was 4.0-4.3 mm (PE)/4.0-4.1 mm (PA). Compared to phantom studies, the mean errors of the computer model were as follows: 6.2 °C(PE)/4.3 °C (PA) for maximum gel temperature, 0.7 mm (10.9%) (PE)/0.1 mm (0.8%) (PA) for lesion width, and 0.3 mm (7.7%)(PE)/0.7 mm (19.1%) (PA) for lesion depth. For temperature-controlled ablation, model predicted thermal lesion width was 7-9.2 mm (PE)/8.6-9.2 mm (PA), and lesion depth was 4.3-5.5 mm (PE)/3.4-5.4 mm (PA). CONCLUSIONS: Computer models were able to reproduce device performance and to enable device evaluation under varying conditions. Temperature controlled ablation of irrigated catheters enables optimal tissue temperatures independent of patient-specific conditions such as blood flow.

Computational models for contact current dosimetry at frequencies below 1 MHz.

Electric contact currents (CC) can cause muscle contractions, burns, or ventricular fibrillation which may result in life-threatening situations. In vivo studies with CC are rare due to potentially hazardous effects for participants. Cadaver studies are limited to the range of tissue's electrical properties and the utilized probes' size, relative position, and sensitivity. Thus, the general safety standards for protection against CC depend on a limited scientific basis. The aim of this study was therefore to develop an extendable and adaptable validated numerical body model for computational CC dosimetry for frequencies between DC and 1 MHz. Applying the developed model for calculations of the IEC heart current factors (HCF) revealed that in the case of transversal CCs, HCFs are frequency dependent, while for longitudinal CCs, the HCFs seem to be unaffected by frequency. HCFs for current paths from chest or back to hand appear to be underestimated by the International Electrotechnical Commission (IEC 60479-1). Unlike the HCFs provided in IEC 60479-1 for longitudinal current paths, our work predicts the HCFs equal 1.0, possibly due to a previously unappreciated current flow through the blood vessels. However, our results must be investigated by further research in order to make a definitive statement. Contact currents of frequencies from DC up to 100 kHz were conducted through the numerical body model Duke by seven contact electrodes on longitudinal and transversal paths. The resulting induced electric field and current enable the evaluation of the body impedance and the heart current factors for each frequency and current path.

Safety of a High-Efficiency Electrical Fence Energizer.

INTRODUCTION: Our primary goal was to evaluate the performance of a new high-efficiency electric fence energizer unit using resistive load changes. Our secondary goal was to test for compliance with the classical energy limits and the newer charge-based limits for output. METHODS: We tested 4 units of the Nemtek Druid energizer with 2 channels each. We used a wide load-resistance range to cover the worst-case scenario of a barefoot child making a chest contact (400 Ω) up to an adult merely touching the fence (2 kΩ). RESULTS: The energy output was quite consistent between the 8 sources. Even at the lowest resistance, 400 Ω, the outputs were well below the IEC 60335-2-76 limit of 5 J/pulse. The charge delivered was also quite consistent. Even at the lowest resistance, 400 Ω, the outputs (679 ± 23 µC) were well below the proposed limits of 4 mC for short pulses. CONCLUSIONS: The high-efficiency electric fence energizers satisfied all relevant safety limits. Charge, energy, voltage, and current outputs were consistent between channels and units.

Therapeutic Systems and Technologies: State-of-the-Art Applications, Opportunities, and Challenges.

In this review, we present current state-of-the-art developments and challenges in the areas of thermal therapy, ultrasound tomography, image-guided therapies, ocular drug delivery, and robotic devices in neurorehabilitation. Additionally, intellectual property and regulatory aspects pertaining to therapeutic systems and technologies are addressed.

Protocols for documentation of electrical injuries for electrical safety inspectors and emergency medical practitioners.

BACKGROUND: Electric shocks are common, and victims report difficulty in finding practitioners with knowledge of the injury. Medical Practitioners, especially in private practice, report lack of knowledge of the injury and lack of expertise in assessing and treating the injury. The authors are often requested to suggest investigation protocols, assessment protocols, and treatment protocols, and to provide educational information. METHODS: The international body establishing electrical standards on the effects of current on the body (International Electrotechnical Commission, Maintenance Team 4 (MT4) of Technical Committee 64 (TC64)) have established protocols for the factors which require documentation and reporting of the injury. This article provides a narrative approach to using these protocols in accord with the standards (IEC 60479). The level of evidence is Level III (US/Canada classification). TYPE: This article collects together and collates physical and medical aspects of investigating electric shocks, and summarizes those of importance, and which are potentially forgotten. The thoroughness of initial assessment is emphasized. SUBSTANCE: Summaries are set out to guide first attenders and emergency medical personnel as to findings and observations which must be recorded for later comprehensive medicolegal reporting and which are often overlooked. CONCLUSION: Wider teaching in the nature of electric shocks will enhance assessment of victims and thorough recording of pertinent information and thus will enhance later medicolegal reporting. Many such factors are initially overlooked and lead to inadequate reporting for forensic purposes.

High Impedance Electrical Accidents: Importance of Source and Subject Impedance.

In most cases, the diagnosis of an electrical injury or electrocution is straightforward. However, there is a necessity for much closer analysis in many cases. There exist sophisticated electrical safety standards that predict outcomes for shocks of various currents applied to different parts of the body. Unfortunately, the actual current is almost never known in an accident investigation. A common source of errors is the assumption that the source (including the return) has zero impedance. Another surprisingly common problem is the erroneous assumption that the body current is equal to the source current capability. METHODS: We used the following methodology for analyzing such cases: (1) Determine body pathway, (2) Estimate body pathway impedance, (3) Determine source voltage, (4) Determine source impedance, (5) Calculate delivered current using total pathway impedance, and (6) Ignore available current as it is largely confounding in most cases. RESULTS: We analyzed 6 difficult cases using the above methodology. This includes 2 subtle situations involving pairs of matched case-control subjects where a subject was electrocuted while his work partner was not. CONCLUSIONS: Careful calculations of the amplitude and duration of the shock is required for understanding the limits and potential causation of such electrical injury. This requires the determination of both the source and body pathway impedance. Available current is usually irrelevant and overemphasized.

Dosimetry for Ventricular Fibrillation Risk with Short Electrical Pulses: History and Future.

Electrical safety limits for unidirectional pulses with short durations are increasingly important due to the proliferation of electric-car and factory energy storage systems with potentially dangerous voltages. Electrocution by a short-duration direct-current pulse is not understood as well as that by alternating current and the data are limited. The primary international guidance comes from IEC 60479-2 section 11. METHODS: We have analyzed the dosimetry for short pulse safety limits based on a fuller understanding of the scientific principles involved and human data. Implantable defibrillators have been tested by externally delivering short-duration pulses giving us human data which we analyze for this paper. RESULTS: The present IEC current limit (60479-2:11) for short pulse durations is based on an exponent of -0.68 in the equation I = d-0.68, (d being pulse width), while the correct exponent should be -1.0 given the constant charge for the VF threshold of short pulses. We also propose a baseline charge value based on the human data. CONCLUSIONS: Charge-based VF thresholds give the correct dosimetry for short-duration pulses. Results from this paper should be considered in support of revising the IEC 60479-2 standard section 11.

Electrical Safety and Performance of the G.L.O.V.E Relative to Relevant Requirements of International Electrical Standards.

The G.L.O.V.E (Generated Low Output Voltage Emitter) is a tool for law-enforcement professionals operating in a wider band of the force continuum than other intermediate weapons. The goal of this paper was to analyze the G.L.O.V.E electrical output and to compare it to safety and efficacy requirements of relevant international standards. Methods - Four G.L.O.V.Es were tested. Measurements on fresh, skinned animal tissue established a G.L.O.V.E operational impedance range of 140 - 300 Ω. Their voltage, current, charge, pulse duration and rate were measured when applied to loads from 140 to 330 Ω. Measurements were also taken with two G.L.O.V.E devices simultaneously applied to a resistive network which simulated a hand-hand, or shoulder-shoulder, currentflow path. Such path may involve cardiac risk. The measurement results were compared to relevant safety and efficacy requirements of following standards: UL 69, IEC 60335-7-26, IEC 60479-1 and -2, and ANSI/CPLSO-17. Results - Within its operational load range, the G.L.O.V.E device delivers maximum voltages in the range of 210 - 320 V, maximum currents of 0.9 - 1.5 A, charge levels of 84 - 125 µC with pulse durations between 105 - 115 µs, with repetition rates of 29.7 - 30.8 pps and duty cycles of 0.32 - 0.35%. These parameters were all within relevant ranges required by UL 69, IEC 60335-7-26, IEC 60479-1 and -2, and ANSI/CPLSO-17. Conclusion - Based on our measurement data, the G.L.O.V.E device is in compliance with relevant requirements for safety and efficacy stated by standards such as UL 69, IEC 60335-7-26, IEC 60479-1 and -2, and ANSI/CPLSO-17.

Electrical Weapon Charge Delivery With Arcing.

INTRODUCTION: Human electronic control with the Conducted Electrical Weapon (CEW) has gained widespread acceptance as the preferred law enforcement force option technology due to its dramatic injury and fatal shooting reduction. However, with bulky or baggy clothing, a CEW probe may fail to make direct skin contact and thus arcing is critical to complete the circuit. The goal of the study was to evaluate the ability of modern CEWs to deliver their pulse charges across typical required arcing distances. METHODS: Popular TASER® CEW models X26E (openloop output), and the X2 and X26P (with closed-loop outputs) were activated using a cartridge connected to a custom polymer air-gap fixture. For each model 5 units were tested. The raw and normalized charge delivery were evaluated according to ANSI-CPLSO-17. RESULTS: All 5 units of each model satisfied ANSICPLSO-17 even at maximum arcing length. The X26P CEW had the greatest arcing gap capability. CONCLUSIONS: The stabilized closed-loop charge output feedback of modern electrical weapons (X2 and X26P CEWs) provides a significantly improved output consistency under arcing conditions. With arc lengths of 10-20 mm per probe, the X2 CEW normalized output charge exceeds that of some units of the older higher output X26E CEW model.