Future shock: automatic external defibrillators

[Inappropriate analyses of automated external defibrillators used during out-of-hospital cardiac arrests]

Objetivo

Analizar la frecuencia de errores terapéuticos por parte de los desfibriladores externos semiautomáticos y evaluar su validez diagnóstica en el reconocimiento de ritmo desfibrilable.

Diseño

Descriptivo retrospectivo.

Emplazamiento

Nueve unidades de soporte vital básico de Vizcaya.

Participantes

Se incluyeron 201 pacientes asistidos por parada cardiorrespiratoria entre 2006 y 2011.

Mediciones principales

Se estudió la adecuación del tratamiento (desfibrilación o no) tras cada análisis e identificaron los errores terapéuticos. Se calculó la sensibilidad, especificidad y valores predictivos con sus respectivos intervalos de confianza al 95%.

Resultados

Se analizaron 811 ritmos electrocardiográficos donde 120 (14,1%), de 30 pacientes, correspondieron a ritmos desfibrilables. La sensibilidad y especificidad en el reconocimiento por parte de los desfibriladores fue del 85% (IC 95% 77,5-90,3%) y 100% (IC 95% 99,4-100%) respectivamente. Los valores predictivos positivos y negativos fueron del 100% (IC 95% 96,4-100%) y el 97,4% (IC 95% 96-98,4%). Se detectaron 18 (2,2%; IC 95% 1,3-3,5) análisis inadecuados por parte del desfibrilador, correspondiendo todos a errores de omisión de descarga en presencia de taquiarritmias ventriculares. Un error fue dependiente del operador y el resto dependientes del desfibrilador: en 6 por interacción del marcapasos y en 11 no se pudo filiar la causa.

Conclusiones

Los desfibriladores externos semiautomáticos poseen una muy elevada especificidad y moderadamente alta sensibilidad. Los errores dependientes del operador han sido escasos. Los marcapasos implantados parecen interaccionar con el análisis de los dispositivos.

Public access defibrillation: time to access the public

STUDY OBJECTIVE

Public accessible automated external defibrillators (AEDs) are increasingly made available in highly frequented places, allowing coincidental bystanders to defibrillate with minimal delay if necessary. Although the public, as the largest and most readily available group of potential rescuers, is assigned a key role in this concept of "public" access defibrillation, it is unknown whether bystanders are actually sufficiently prepared. We therefore investigate knowledge and attitudes toward AEDs among the public.

METHODS

Standardized interviews were conducted at the Central Railway Station of Amsterdam, the Netherlands, a highly frequented and AED-equipped public place with a high number of travelers and visitors from all over the world.

RESULTS

Surveys from 1,018 participants from a total of 38 nations were analyzed, revealing a considerable lack of knowledge among the public. Less than half of participants (47%) would be willing to use an AED, and more than half (53%) were unable to recognize an AED. Overall, only a minority of individuals have sufficient knowledge and would be willing to use an AED. Differences between subgroups were identified, which may aid to tailor public information campaigns to specific target audiences.

CONCLUSION

Only a minority of individuals demonstrate sufficient knowledge and willingness to operate an AED, suggesting that the public is not yet sufficiently prepared for the role it is destined for. Wide-scale public information campaigns are an important next step to exploit the lifesaving potential of public access defibrillation.

Survival after application of automatic external defibrillators before arrival of the emergency medical system: evaluation in the resuscitation outcomes consortium population of 21 million

OBJECTIVES

The purpose of this study was to assess the effectiveness of contemporary automatic external defibrillator (AED) use.

BACKGROUND

In the PAD (Public Access Defibrillation) trial, survival was doubled by focused training of lay volunteers to use an AED in high-risk public settings.

METHODS

We performed a population-based cohort study of persons with nontraumatic out-of-hospital cardiac arrest before emergency medical system (EMS) arrival at Resuscitation Outcomes Consortium (ROC) sites between December 2005 and May 2007. Multiple logistic regression was used to assess the independent association between AED application and survival to hospital discharge.

RESULTS

Of 13,769 out-of-hospital cardiac arrests, 4,403 (32.0%) received bystander cardiopulmonary resuscitation but had no AED applied before EMS arrival, and 289 (2.1%) had an AED applied before EMS arrival. The AED was applied by health care workers (32%), lay volunteers (35%), police (26%), or unknown (7%). Overall survival to hospital discharge was 7%. Survival was 9% (382 of 4,403) with bystander cardiopulmonary resuscitation but no AED, 24% (69 of 289) with AED application, and 38% (64 of 170) with AED shock delivered. In multivariable analyses adjusting for: 1) age and sex; 2) bystander cardiopulmonary resuscitation performed; 3) location of arrest (public or private); 4) EMS response interval; 5) arrest witnessed; 6) initial shockable or not shockable rhythm; and 7) study site, AED application was associated with greater likelihood of survival (odds ratio: 1.75; 95% confidence interval: 1.23 to 2.50; p < 0.002). Extrapolating this greater survival from the ROC EMS population base (21 million) to the population of the U.S. and Canada (330 million), AED application by bystanders seems to save 474 lives/year.

CONCLUSIONS

Application of an AED in communities is associated with nearly a doubling of survival after out-of-hospital cardiac arrest. These results reinforce the importance of strategically expanding community-based AED programs.

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.

[Technical requirements for early defibrillation: what are the capabilities of automated external defibrillators]

Modern automated external defibrillators (AEDs) offer a variety of technical improvements which increase the efficacy of early defibrillation, facilitate the application by not or minimally trained persons and improve safety. The development of biphasic shocks allows better myocardial protection, the use of lithium batteries, and a marked decrease of AEDs, in size. Microprocessors realize complex acoustic and visual prompts which lead the user through all steps of cardiopulmonary resuscitation (CPR) according to current guidelines. The design of AEDs has been simplified; many devices provide only a single button which can be used for all active processes. Memory functions record the whole CPR with all details which can be transferred to other computers and analyzed off-line. The introduction of AEDs has reduced the delay between collapse and defibrillation to less than 4 min in several studies thus increasing the success of CPR and the proportion of patients dismissed from hospital alive and without neurological deficit. Up to 93% of untrained volunteers were able to successfully complete defibrillation with the use of an AED, sixth-form pupils without experience in CPR were only few sec slower with an AED than staff of emergency medical services. The ability to perform CPR after defibrillation guided by the AED depends primarily on the clarity of acoustic prompts which have to consider the terms and abbreviations of the respective language. Currently available AEDs surpass performance goals of the AHA. However, all devices exhibit advantages and disadvantages which will be discussed in this review.