Safety aspects for public access defibrillation using automated external defibrillators near high-voltage power lines

In vitro assessment of the immunity of implantable cardioverter-defibrillators to magnetic fields of 50/60 Hz

Public concern for the compatibility of electromagnetic (EM) sources with active implantable medical devices (AIMD) has prompted the development of new systems that can perform accurate exposure studies. EM field interference with active cardiac implants (e.g. implantable cardioverter-defibrillators (ICDs)) can be critical. This paper describes a magnetic field (MF) exposure system and the method developed for testing the immunity of ICD to continuous-wave MFs. The MFs were created by Helmholtz coils, housed in a Faraday cage. The coils were able to produce highly uniform MFs up to 4000 µT at 50 Hz and 3900 µT at 60 Hz, within the test space. Four ICDs were tested. No dysfunctions were found in the generated MFs. These results confirm that the tested ICDs were immune to low frequency MFs.

Bench study of the accuracy of a commercial AED arrhythmia analysis algorithm in the presence of electromagnetic interferences

This paper presents a bench study on a commercial automated external defibrillator (AED). The objective was to evaluate the performance of the defibrillation advisory system and its robustness against electromagnetic interferences (EMI) with central frequencies of 16.7, 50 and 60 Hz. The shock advisory system uses two 50 and 60 Hz band-pass filters, an adaptive filter to identify and suppress 16.7 Hz interference, and a software technique for arrhythmia analysis based on morphology and frequency ECG parameters. The testing process includes noise-free ECG strips from the internationally recognized MIT-VFDB ECG database that were superimposed with simulated EMI artifacts and supplied to the shock advisory system embedded in a real AED. Measurements under special consideration of the allowed variation of EMI frequency (15.7-17.4, 47-52, 58-62 Hz) and amplitude (1 and 8 mV) were performed to optimize external validity. The accuracy was reported using the American Heart Association (AHA) recommendations for arrhythmia analysis performance. In the case of artifact-free signals, the AHA performance goals were exceeded for both sensitivity and specificity: 99% for ventricular fibrillation (VF), 98% for rapid ventricular tachycardia (VT), 90% for slow VT, 100% for normal sinus rhythm, 100% for asystole and 99% for other non-shockable rhythms. In the presence of EMI, the specificity for some non-shockable rhythms (NSR, N) may be affected in some specific cases of a low signal-to-noise ratio and extreme frequencies, leading to a drop in the specificity with no more than 7% point. The specificity for asystole and the sensitivity for VF and rapid VT in the presence of any kind of 16.7, 50 or 60 Hz EMI simulated artifact were shown to reach the equivalence of sensitivity required for non-noisy signals. In conclusion, we proved that the shock advisory system working in a real AED operates accurately according to the AHA recommendations without artifacts and in the presence of EMI. The results may be affected for specificity in the case of a low signal-to-noise ratio or in some extreme frequency setting.

Interference of 16.7-Hz electromagnetic fields on measured electrocardiogram

The extent of electromagnetic interference (EMI) from 16.7-Hz alternate current power lines in the human surface electrocardiogram (ECG) was evaluated. Results showed a direct linear correlation between mean EMI and magnetic induction of 5.8-21 microT on a railroad platform (electric field: 270 V/m). EMI inside a railroad car (10 microT, 0 V/m) was comparable to the electromagnetic field at the platform. Inside a voltage transformer substation (0 microT, 2000 V/m) EMI occurred only when the ECG device was closer to the power line than the test person. Magnetic induction caused 16.7-Hz EMI to a degree that proper diagnosis of ECG-rhythms was rendered impossible.

Clinical testing of cellular phone ringing interference with automated external defibrillators

OBJECTIVE

This study examined cellular phone ringing interference with automated external defibrillators (AED).

METHODS

The phone systems tested were two single band handheld telephones: (1) a Global System for Mobile Communication (GSM) receiver; and (2) a Personal Communication Services (PCS) receiver. The ringing phase of a digital cellular phone includes a brief burst of peak-emitted power. The GSM had a maximum power output of 2 W, operating on a 900 MHz carrier frequency, and the PCS had a maximum output of 1 W, operating on a 1800 MHz carrier frequency. During AED monitoring, the digital cellular telephone was placed successively in three positions: (1) on the AED; (2) on the patient's chest between the electrodes; and (3) on the connector between the electrodes and the AED cable. After positioning the cellular phone, calls were placed during the AED analyzing phase.

RESULTS

Three AED models were tested using their original electrodes: (1) LifePak 20 monitor/defibrillator device; (2) Lifepak 20 P monitor/defibrillator/stimulator (Medtronic Emergency Response Systems, Redmond, WA, USA); and (3) HeartStart XL M4735A monitor/defibrillator (Philips Medical Systems, Andover, MA, USA). The first two devices had Quik-Combo electrodes and the third device had Adults Plus multifunction electrodes. Ninety-one tests were performed on 13 patients. The only disturbance provoked by testing was noise emitted by the AED speaker when the receiver was close to the device. The noise began 2-4 s before the first audible ringing tone and persisted throughout the ringing phase. The distance at which this effect could be prevented was 15 cm.

CONCLUSION

Clinical testing during ECG monitoring by an AED during call from a cellular phone did not show any analysis dysfunction during unshockable rhythms and provoked only transient dysfunction of the speaker device.

Automated external defibrillators do not recommend false positive shocks under the influence of electromagnetic fields present at public locations

Electromagnetic fields (EMF) reduce the signal quality of electrocardiograms and may lead to the misinterpretation by automated external defibrillators (AED). We designed this investigation as a prospective study, with a randomized sequence of AED applications on healthy volunteers. We chose busy public places where public access defibrillation was possible as test locations. Strong EMF were sought and found at train stations next to accelerating and decelerating trains. The primary outcome variable was the absolute number of shocks advised in the presence of sinus rhythm by five commonly used AED in Austria. For data analysis, the statistician was blinded in regard to the AED models tested. Data analysis was based on a per protocol evaluation. Of 390 tests run, 0 cases of false positive results occurred (95% CI: 0-0.77). AED can be regarded as safe, even with the interference of EMF present at train stations.

Future shock: automatic external defibrillators

PURPOSE OF REVIEW

This review provides a practical overview of the performance capabilities of automatic external defibrillators (AEDs), and of advances in technology and dissemination programmes for these devices.

RECENT FINDINGS

Arrhythmia analysis by AEDs is extremely reliable in most settings (sensitivity 81-100%, specificity 99.9-97.6%). Accurate detection of arrhythmias has also been demonstrated in children, leading the US Food and Drug Administration to approve the use of several AEDs in children aged 8 years or younger. Factors that potentially may reduce the quality of arrhythmia detection are the presence of wide complex supraventricular tachycardia and location of an arrythmic event near to high-power lines. AED use by professional basic life support providers resulted in increased survival in the prehospital setting. However, provision of AEDs to nonmedical rescue services did not result in universal improvement in patient outcome. Public access defibrillation programmes have led to higher rates of survival from cardiac arrest. The role of AEDs in hospitals has yet to be elucidated, although in-hospital mortality from ventricular arrhythmias has been shown to decrease following AED deployment.

SUMMARY

Given the correct setting, AEDs can ensure that defibrillation is not limited by lack of medical knowledge or difficulties in decision making. However, event-related variables and operator-related factors, that are yet to be determined, can significantly affect the efficacy of automatic external defibrillation.

Influence of electromagnetic fields on function of automated external defibrillators

OBJECTIVES

In this study, the authors tested whether electromagnetic interference (EMI) is able to impair correct electrocardiogram analysis and produce false-positive shock advice from automated external defibrillators (AEDs) when the true rhythm is sinus.

METHODS

Nineteen healthy subjects were used to test five AEDs available on the Austrian market in a prospective, open, and sequence-randomized study. The primary outcome variable was the absolute number of shocks advised in the presence of EMI. The secondary outcome was the number of impaired analyses caused by incorrectly detected patient movements or electrode failure.

RESULTS

Of 760 tests run, 18 (2.37%) cases of false-positive results occurred, and two of five AEDs recommended shocks in the presence of sinus rhythm. Of 760 tests run, no electrode failures occurred. There were 27 occurrences (3.55%) of motion detected by an AED in the presence of strong electromagnetic fields.

CONCLUSIONS

AED models differ in their response to EMI; it may be useful to consider specific safety requirements for areas with such fields present. Working personnel and emergency medical services staff should be informed about potential risks and the possible need for patient evacuation before AEDs are attached and shock recommendations are followed.

Suppression of AC railway power-line interference in ECG signals recorded by public access defibrillators

Background

Public access defibrillators (PADs) are now available for more efficient and rapid treatment of out-of-hospital sudden cardiac arrest. PADs are used normally by untrained people on the streets and in sports centers, airports, and other public areas. Therefore, automated detection of ventricular fibrillation, or its exclusion, is of high importance. A special case exists at railway stations, where electric power-line frequency interference is significant. Many countries, especially in Europe, use 16.7 Hz AC power, which introduces high level frequency-varying interference that may compromise fibrillation detection.

Method

Moving signal averaging is often used for 50/60 Hz interference suppression if its effect on the ECG spectrum has little importance (no morphological analysis is performed). This approach may be also applied to the railway situation, if the interference frequency is continuously detected so as to synchronize the analog-to-digital conversion (ADC) for introducing variable inter-sample intervals. A better solution consists of rated ADC, software frequency measuring, internal irregular re-sampling according to the interference frequency, and a moving average over a constant sample number, followed by regular back re-sampling.

Results

The proposed method leads to a total railway interference cancellation, together with suppression of inherent noise, while the peak amplitudes of some sharp complexes are reduced. This reduction has negligible effect on accurate fibrillation detection.

Conclusion

The method is developed in the MATLAB environment and represents a useful tool for real time railway interference suppression.

Subtraction of 16.67 Hz railroad net interference from the electrocardiogram: application for automatic external defibrillators

The widespread application of automatic external defibrillators (AEDs) for treating out-of-hospital cardiac arrest incidents and their particular use at railway stations defines the task for 16.67 Hz power line interference elimination from the electrocardiogram (ECG). Although this problem exists only in five European countries, it has to be solved in all AEDs, which must comply with the European standard for medical equipment requirements for interchangeability and compatibility between rail systems. The elimination of the railroad interference requires a specific approach, since its frequency band overlaps with a significant part of the frequencies in the QRS spectra. We present a method based only on one channel ECG signal processing, which effectively subtracts the interference components. The computation procedure is based on simple signal processing tools, which include: (i) bi-directional band-pass filtering (13-23 Hz) of the analyzed ECG segment; (ii) estimation of adequate linearity thresholds; (iii) frequency measurement and calculation of dynamic interference buffer in linear segments and (iv) phase synchronization and subtraction technique in nonlinear segments. The developed method has proved advantageous in providing sufficient quality of the output interference free ECG signal for seven defined arrhythmia types (normal sinus rhythm, normal rhythm, supraventricular tachicardia, slow/rapid ventricular tachycardia, and coarse/fine ventricular fibrillation), and simulated interferences with constant or variable frequencies and amplitudes, which cover the entire amplitude range of the input channel. The procedure is suitable to be embedded in AEDs as a preprocessing branch, which proves reliable for analysis of ECG signals, thus guaranteeing the specified accuracy of the AED automatic rhythm analysis algorithms.

Public access defibrillation: suppression of 16.7 Hz interference generated by the power supply of the railway systems

BACKGROUND

A specific problem using the public access defibrillators (PADs) arises at the railway stations. Some countries as Germany, Austria, Switzerland, Norway and Sweden are using AC railroad net power-supply system with rated 16.7 Hz frequency modulated from 15.69 Hz to 17.36 Hz. The power supply frequency contaminates the electrocardiogram (ECG). It is difficult to be suppressed or eliminated due to the fact that it considerably overlaps the frequency spectra of the ECG. The interference impedes the automated decision of the PADs whether a patient should be (or should not be) shocked. The aim of this study is the suppression of the 16.7 Hz interference generated by the power supply of the railway systems.

METHODS

Software solution using adaptive filtering method was proposed for 16.7 Hz interference suppression. The optimal performance of the filter is achieved, embedding a reference channel in the PADs to record the interference. The method was tested with ECGs from AHA database.

RESULTS

The method was tested with patients of normal sinus rhythms, symptoms of tachycardia and ventricular fibrillation. Simulated interference with frequency modulation from 15.69 Hz to 17.36 Hz changing at a rate of 2% per second was added to the ECGs, and then processed by the suggested adaptive filtering. The method totally suppresses the noise with no visible distortions of the original signals.

CONCLUSION

The proposed adaptive filter for noise suppression generated by the power supply of the railway systems has a simple structure requiring a low level of computational resources, but a good reference signal as well.