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

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

Cardiac Safety Profile for Random Complex Waveforms

Introduction: A rigorous method for assessing the Ventricular Fibrillation (VF) risk of a Random Complex Waveform (RCW) has not been previously available. Real-life hazardous events motivated us to develop such method. An RCW is observable and recordable. It consists of multiple different components randomly added one to the other. Assessment for VF risk exists for non-random waveforms, particularly VF thresholds for 50/60 Hz alternating currents, but not for RCWs

Transthoracic ventricular fibrillation charge thresholds

Standards, including IEC 60479-1 and -2, provide current-based ventricular fibrillation thresholds (VFT) for stimuli durations between 0.1 ms and 10 s. It has been established that the amount of electrical charge, not the current calculated by root-mean-square, is most representative of the effects of cardiac stimulation. There are no unified models that present transthoracic charge VFTs for a wide range of stimuli durations. This work proposes a new unified charge model applicable to transthoracic stimuli durations ranging over 1 μs - 300 s. VFTs were compiled from our previous animal work and from other published reports, including from the studies that provided the raw data for IEC 60479-1 and -2. Our study goal was to cover a wide range of stimuli durations, for which reliable data exists. Consistent data were found for stimuli durations covering the range of 1 μs - 300 s where VFTs were expressed as charge. The model predicted a transthoracic charge VFT of 1 mC at 1 μs duration. The charge VFT increased with stimulus duration and reached 10 C at 300 s. Presenting the first charge-based transthoracic VFT model covering stimuli durations over 1 μs - 300 s, we found 3 behavioral regions of charge VFT vs. duration. For short stimuli durations, 1 μs - 10 ms, VFTs followed a classic Weiss charge strength-duration curve. For long stimuli, longer than 5 s, charge VFTs can be approximated using a 38 mArms constant current model. From 10 ms to 5 s, charge VFTs tracked through a transition zone that could be approximated as a constant charge model Q≈100 mC

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, (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

Wireless Remote Monitoring of Atrial Fibrillation Using Reconstructed 12-Lead ECGs

Remote surveillance is important for patients with atrial fibrillation (AF). Atrial signal recognition with conventional monitoring devices is difficult; remote AF detection is predominantly accomplished by R-R interval analysis. Twelve lead ECG (12L) displays atrial activity and remains the gold standard for AF diagnosis. CardioBip is a portable wireless patient-activated event monitor providing signal reconstruction of a 12L waveform (12CB) using 5 leads and patient-specific transformation matrices. We hypothesized that atrial signal analysis with 12CB can detect atrial activity and improve AF detection. METHODS: 18 patients with AF undergoing DC cardioversion (CV) were studied. Separate 12-lead P and QRS patient-specific transformation matrices were created at baseline AF. Multiple wireless 12CB transmissions were performed 3-7 days before and up to 2 weeks after CV. Rhythm was confirmed with 12-lead ECGs (12L). In SR the number of leads with visible P waves (atrial signal GT 0.05 mV), and P wave polarity were analyzed. In AF, the number of leads with AF signal were compared (fibrillatory [f] waves GT 0.025 mV). RESULTS: Fourteen of 18 patients successfully cardioverted to SR and 4 failed; thus, 14 SR and 22 AF transmissions were analyzed. SR P wave was visible on 141/168 leads on 12L and 137/168 on 12CB (126 true pos [TP] and 11 false pos [FP] relative to 12L; p=0.26). In 126 leads with P waves in both 12L and 12CB, the methods agreed on P wave polarity in 125. In AF, F waves were visible in 178/264 leads on 12L and 189/264 leads on 12CB (144 TP, 45 FP; p=0.27). All 5 AF relapses were successfully detected by 12CB based on atrial activity. CONCLUSION: 12CB is not inferior to 12L in detecting atrial signal in SR and AF, and shows excellent potential for remote wireless monitoring of AF patients.IEEE Engineering in Medicine and Biology Society Conference Proceedings, 32nd Annual International Conference of the IEEE Engineering-in-Medicine-and-Biology-Society (EMBC 10), Aug 30-Sep 04, 2010, Buenos Aires, Argentin

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

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