Automated External Defibrillator Shock Advisement Discordance Among Multiple Electrocardiographic Rhythms and Devices: A Preliminary Report

Background: The early use of automated external defibrillators (AEDs) can save lives by correcting lethal ventricular arrhythmias with minimal operator intervention. AED shock advisements also play a role in termination of resuscitation strategies. AED function is dependent on the accuracy of their shock advisement algorithms, which may differ between manufacturers. We sought to compare the shock advisement performance characteristics of several AEDs. Methods: We conducted a prospective, laboratory-based simulation study evaluating five commercially available AEDs from Cardiac Science, Defibtech, Medtronic, Philips, and Zoll. Shock advisement performance was evaluated for eight ECG rhythms {ventricular fibrillation (VF), ventricular tachycardia (VT), toursades de pointes (TdP), sinus rhythm (SR), atrial fibrillation (AF), atrial flutter (AFL), idioventricular rhythm (IDV), and asystole} that were generated using the SimMan Classic Manikin and the LLEAP Simulator software (Laerdal Medical Inc., Norway). We recorded shock advisement decisions for each of the ECG rhythms three times per device. Shock advisements were coded as discordant if a shock was advised for a non-shockable rhythm or not advised for a shockable rhythm. Results: We analyzed 330 rhythm trials in total (66 per device), finding 28 (8.5%) discordant shock advisements overall. Discordance ranged from 6% to 11% among the five AED models. VF rhythm variants were the most frequent (43%) source of discordant advisements. No shocks were advised for any of the sinus rhythms, AFL, AF with QRS > 40, IDV, or asystole. Conclusions: Discordant shock advisements were observed for each AED and varied between manufacturers, most often involving VF. There may be implications for termination of resuscitation decision making.     

Automated external defibrillators appropriately recognize ventricular fibrillation in electromagnetic fields

Objectives. Automated external defibrillators (AEDs) are increasingly available in industrial settings, but many industries have high electromagnetic fields (EMFs), which can interfere with the function of electronic devices. This study evaluated the performance of several AEDs when exposed to high EMFs. Methods. Three commercially available AEDs were evaluated in the setting of a public utility coal-fired electrical generation plant. Each AED was placed in three areas of high EMF ranging from 310 to 1,600 milligauss. A signal generator, used to simulate various cardiac rhythms, was connected to the AEDs. Rhythms simulated were ventricular fibrillation, asystole, and normal sinus rhythm. Each of the AED's interpretations of various rhythms were evaluated in the different EMF settings. Results. Rhythms of ventricular fibrillation, asystole, and normal sinus rhythm were correctly recognized by each AED in each of the three areas of high EMF. Each AED appropriately recommended defibrillation when presented with ventricular fibrillation. No misinterpretations or inappropriate defibrillations were observed. Conclusion. Electromagnetic fields generated by an electrical power plant did not interfere with three commercial AEDs' abilities to correctly interpret simulated rhythms and recommend appropriate defibrillation. PREHOSPITAL EMERGENCY CARE 2002;6:65-66     

Susceptibility of automated external defibrillators to train overhead lines and metro third rails

INTRODUCTION: Immediate accessibility to automated external defibrillators (AED) is recommended for highly frequented public areas. In train terminals and metro stations electromagnetic interference (EMI) is present. In preparation for a public access defibrillation (PAD) programme in this environment possible effects on AED safety and accuracy were studied. METHODS: In typical public transportation settings 11 different AED models were bench tested for their sensitivity and specificity of ECG analysis with shockable and nonshockable rhythms provided by an ECG simulator. The devices were exposed to the electromagnetic interference of a rail system operating with 15 kV alternating current (ac) with a frequency of 16 2/3 Hz and a subway system powered with 750 V direct current (dc). AED cables were setup parallel and perpendicular to the tracks, the tests were carried out at 3 m distance from the rails in an empty station and with incoming trains. RESULTS: A total of 5280 tests were recorded, each device was tested a total of 480 times. Fifteen kilovolts 16 2/3 Hz ac interfered more than 750 V dc with the tachyarrhythmia detection systems (P < 0.0001). An AED setup with electrode cables perpendicular to track and power line reduced interference (P < 0.0001), while incoming trains had no significant effect on ECG analysis (P = 0.19). Depending on the AED model, sensitivity ranged from 60 to 100% and specificity from 54 to 100%, representing a positive likelihood-ratio from 1.3 to 241 and a negative likelihood-ratio from 0.7 to 0.0. In the public transportation setting tested, four AED models were unsuitable for automated defibrillation as these devices demonstrated an unacceptable performance in respect of accuracy and safety. In the train setting two devices performed with an accuracy of 57 and 65%. One AED recommended shocks for sinus rhythm at normal frequency. In the metro setting one AED did not advise shocks for ventricular tachycardia. CONCLUSION: Shock advisory systems of some AED models are susceptible to electromagnetic interference, especially in terminals with 15 kV 16 2/3 Hz ac power supplies. Interference is minimized, if patient position is parallel and electrode cables are perpendicular to overhead line. The choice of AED model for train or metro stations depends on its lack of susceptibility to typical electromagnetic interference.     

Inconsistent shock advisories for monomorphic VT and Torsade de Pointes – A prospective experimental study on AEDs and defibrillators

BackgroundCardiovascular disease and sudden cardiac arrest are the leading causes of death in the United States. Early defibrillation is key to successful resuscitation for patients who experience shockable rhythms during a cardiac arrest. It is therefore vital that the shock advisory of AEDs (automated external defibrillators) or defibrillators in AED mode be reliable and appropriate. The goal of this study was to better understand the performance of multiple lay-rescuer and hospital professional defibrillators in AED mode in their analysis of ventricular arrhythmias. The measurable objectives of this study sought to quantify:

• 1.No shock advisory for sinus rhythms at any rate.
• 2.Recognition and shock advisory for ventricular fibrillation (VF).
• 3.Recognition and shock advisory for monomorphic ventricular tachycardia (VT).
• 4.Recognition and shock advisory for Torsades de Pointes (TdP).

MethodsThis is a prospective evaluation of two AEDs and four semi-automatic, hospital professional defibrillators. This study represents post-marketing evaluation of FDA approved devices. Each defibrillator was connected to multiple rhythm simulators and presented with simulated ECG waveforms 20 consecutive times at various rates when possible.ResultsAll four defibrillators and both AEDs tested consistently recognized normal sinus rhythm (NSR) from all rhythm sources, and did not recommend a shock for NSR at any rate (from 80 to 220 bpm). All four defibrillators and both AEDs recognized VF from all rhythm sources tested and recommended a shock 100% of the time. Variations were found in the shock advisory rates among defibrillators when testing simulated VT heart rates at or below 150 bpm. One AED tested did not consistently advise a shock for monomorphic VT or TdP at any tested rate.ConclusionLay-rescuer AEDs and professional hospital defibrillators tested in AED mode did not reliably recommend a shock for sustained monomorphic VT or TdP at certain rates, despite the fact that it is a critical component of the currently recommended treatment. These findings require further examination of the risk benefit analysis of shocking or not shocking rhythms such as TdP or pulseless VT.     

Performance of an automated external defibrillator during simulated rotor-wing critical care transports

Objective

This study aimed to evaluate whether an automated external defibrillator (AED) was accurate enough to analyze the heart rhythm during a simulated rotor wing critical care transport. We hypothesized that AED analysis of the simulated rhythms during a helicopter flight would result in significant errors (i.e., inappropriate shocks, analysis delay).

Methods

Three commercial AEDs were tested for analyzing the heart rhythm in a helicopter using a manikin and a human volunteer. Ventricular fibrillation (VF), sinus rhythm, and asystole were simulated by using an arrhythmia simulator of the manikin. The intervals from analysis to shock recommendation were collected on a stationary and in-motion helicopter. Sensitivity and specificity of three AEDs were also calculated. Vibration intensities were measured with a digital vibration meter placed on the chest of the manikin/human volunteer both on the stretcher and on the floor of the helicopter.

Results

All AEDs correctly recommended shock delivery for the cardiac rhythms of the manikin. Sensitivity for VF was 100.0% (95% CI 91.2-100.0) and specificity for sinus rhythm and asystole were 100.0% (95% CI 91.2-100.0). Although the recorded ECG rhythms of the volunteer in an in-motion helicopter showed baseline artifacts, all AEDs analyzed the cardiac rhythm of the volunteer correctly and did not recommend shock delivery. On the floor of the helicopter, the median measured vibration intensity was 6.6 m/s² (IQR 5.5-7.7 m/s²) with significantly less vibrations transmitted to the manikin/human volunteer chest (manikin median 3.1 m/s², IQR 2.2-4.0 m/s²; human volunteer median 0.95 m/s², IQR 0.65-1.25 m/s²).

Conclusion

This study suggested that current AEDs could analyze the heart rhythm correctly during simulated helicopter transport. Further studies using an animal model would be needed before applying to patients.     

Efficacy of out of hospital defibrillation by ambulance technicians using automated external defibrillators. The Heartstart Scotland Project.

During the Heartstart Scotland project all 407 ambulances in Scotland were equipped with automated external defibrillators (AEDs). All cases of chest pain or collapse aged over 10 years were monitored and multiple 3-s rhythm strips recorded in a solid state memory module. A shockable rhythm was defined as an organised rhythm of > or = 180 beats/min or a disorganised rhythm of > or = 100 beats/min and amplitude > 0.1 mV. We analysed all the stored rhythm strips in two patient populations to determine the ability of the AED and ambulance crews to detect a shockable rhythm and to initiate appropriate defibrillation. The first population comprised 493 patients, all of whom had received shocks. A total of 4741 rhythm strips were analysed, of which 1461 were true positives, 33 false positives, 3161 true negatives and 86 false negatives. Overall sensitivity of the AED was 94.4% and specificity 99.0%. The second population comprised a random sample of 200 shocked and 200 non-shocked arrests. The combined group contained 4154 rhythm strips of which 562 were true positives, 12 false positives, 3460 true negatives and 120 false negatives. Overall sensitivity of the system (AED+crew) was 82.4% and specificity 99.7%. However, only 66 of the 120 false negatives were attributable to the AED giving a sensitivity of 90.3% for the AED. The sensitivity of the AED is dependent on the prevalence of shockable rhythms, but will be within the range 90.3-94.4% for most emergency medical services. We conclude that early management of potentially lethal arrhythmias by ambulance technicians using AEDs is practical with acceptable sensitivity and specificity.     

Moderate sea states do not influence the application of an AED in rigid inflatable boats

PURPOSE: This study was to determine if the AED can be operated correctly on board rigid inflatable rescue boats (RIBs), and if downloading of data later for quality control is possible. METHODS: Six AEDs were tested for their reliability, robustness and stability. Data were collected on three different types of RIBs, in a harbour and at sea. Each AED was connected to a volunteer and a manikin simulating VF. Data from the AED were continuously collected. RESULTS: At one of the RIBs each AED became wet; no AED had a technical problem. When connected to the volunteer, the ECGs delivered by the AEDs showed a regular sinus rhythm. When connected to a manikin in VF, each AED was able to recognise VF and to provide a shock. There were differences in the time between first analysis and the shock. The voice prompt of the Zoll AED Plus was 'understandable', while the other AEDs were 'difficult to understand'. We had a problem with the infrared connection, which means that evaluation and quality control afterwards may be difficult. CONCLUSION: The use of AEDs on RIBs during patient transport over calm water is possible and effective. The AED should have a screen and better features to download data. However, AEDs are only worthwhile when they fit well in the Chain of Survival (fast arrival, immediately availability of an AED, trained provider and advanced life support).     

Esophageal electric fields are predictive of atrial defibrillation thresholds

Background: Atrial fibrillation (AF) is a common cardiac arrhythmia characterized by disorganized cardiac electrical activity. Defibrillation electrode placement has been shown to affect the amount of energy and number of shocks required to defibrillate. The objective of this study was to investigate the relationship between esophageal electric fields (EEFs) and atrial defibrillation thresholds (ADFTs) to determine the feasibility of using EEFs during a low‐strength shock to predict patient‐specific defibrillation electrode placements. Methods: AF was induced and defibrillated according to a Bayesian four‐shock protocol for 12‐electrode placements in six pigs. EEFs were measured during each of the four shocks of the protocol and during a 1‐J shock for each electrode placement. Squared EEFs (EEF²s) during all shocks were compared to the ADFTs using a linear regression. Results: There was a negative relationship between EEF²s during the 1‐J shocks and ADFTs, with median R² values of 0.863 and 0.840 for anterior–anterior (AA) and anterior–posterior (AP) electrode placements, respectively. There was a strong, positive relationship between applied energy and EEF²s, with median R² values of at least 0.866 for all animals. The placement with the highest EEF² resulted in the lowest ADFT for both AA and AP placements in four of six pigs. In the other two animals, this held for one electrode set but not both. Conclusions: There was a strong negative relationship between EEF²s during 1‐J shocks and ADFTs for both AA and AP electrode placements. These preliminary results suggest that using EEF²s to predict patient‐specific electrode placements is feasible. (PACE 2011;1–6)     

Optimal Response to Cardiac Arrest study: defibrillation waveform effects.

INTRODUCTION: Advances in early defibrillation access, key to the "Chain of Survival", will depend on innovations in defibrillation waveforms, because of their impact on device size and weight. This study compared standard monophasic waveform automatic external defibrillators (AEDs) to an innovative biphasic waveform AED. MATERIAL AND METHODS: Impedance-compensated biphasic truncated exponential (ICBTE) and either monophasic truncated exponential (MTE) or monophasic damped sine (MDS) AEDs were prospectively, randomly assigned by date in four emergency medical services. The study design compared ICBTE with MTE and MDS combined. This subset analysis distinguishes between the two classes of monophasic waveform, MTE and MDS, and compares their performance to each other and to the biphasic waveform, contingent on significant overall effects (ICBTE vs. MTE vs. MDS). Primary endpoint: Defibrillation efficacy with < or =3 shocks. Secondary endpoints: shock efficacy with < or =1 shock, < or =2 shocks, and survival to hospital admission and discharge. Observations included return of spontaneous circulation (ROSC), refibrillation, and time to first shock and to first successful shock. RESULTS: Of 338 out-of-hospital cardiac arrests, 115 had a cardiac aetiology, presented with ventricular fibrillation, and were shocked by an AED. Defibrillation efficacy for the first "stack" of up to 3 shocks, for up to 2 shocks and for the first shock alone was superior for the ICBTE waveform than for either the MTE or the MDS waveform, while there was no difference between the efficacy of MTE and MDS. Time from the beginning of analysis by the AED to the first shock and to the first successful shock was also superior for the ICBTE devices compared to either the MTE or the MDS devices, while again there was no difference between the MTE and MDS devices. More ICBTE patients achieved ROSC pre-hospital than did MTE patients. While the rates of ROSC were identical for MTE and MDS patients, the difference between ICBTE and MDS was not significant. Rates of refibrillation and survival to hospital admission and discharge did not differ among the three populations. CONCLUSIONS: ICBTE was superior to MTE and MDS in defibrillation efficacy and speed and to MTE in ROSC. MTE and MDS did not differ in efficacy. There were no differences among the waveforms in refibrillation or survival.     

In-hospital use of automated external defibrillators does not improve survival

The use of automated external defibrillators (AEDs) following a cardiac arrest in the out-of-hospital setting has demonstrated increased survival rates, likely because up to 71% of out-of-hospital cardiac arrests are associated with rhythm disturbances that are able to be treated with defibrillation. ^{[1] , [2] and [3]} It is less clear whether the use of AEDs in the hospital setting would be effective because fewer patients (approximately 25%) have initial cardiac rhythms that respond to defibrillation⁴ and because survival may be compromised if the use of AEDs contributes to interruptions in the delivery of chest compressions.

Methods

The authors of this study⁵ used data from the National Registry of Cardiopulmonary Resuscitation (NRCPR) to evaluate the association between survival after an in-hospital cardiac arrest and use of an AED. Data was drawn from patients 18 years of age or older, who had an index pulseless, in-hospital cardiac arrest in clinical area where an AED was available for patient treatment. The sample comprised 11,695 patients from 204 hospitals. The primary outcome measure was survival to hospital discharge. The authors also reported secondary outcomes such as return of spontaneous circulation (ROSC) for at least 20 min during the acute resuscitation; survival at 24 h; and neurological status among those patients surviving to hospital discharge.

Results

Of the 11,695 patients with cardiac arrests, the majority (82.2%; n = 9616) were in a nonshockable rhythm, such as asystole or pulseless electrical activity (PEA). Only 17.8% (n = 2079) of patients in the study were in a shockable rhythm (ventricular fibrillation and pulseless ventricular tachycardia). AEDs were used on 4515 patients (38.6%). An overall survival to discharge rate of 18.1% (n = 2117) was reported. The use of an AED was associated with lower survival rates (16.3% vs 19.3%; adjusted rate ratio [RR], 0.85; 95% confidence interval [CI], 0.78–0.92; P < 0.001). AED use in those patients with asystole or PEA (unshockable rhythms) was associated with lower survival (10.4% vs 15.4%; adjusted RR, 0.74; 95% CI, 0.65–0.83; P < 0.001). Where shockable rhythms, such as ventricular tachycardia or ventricular fibrillation, were present, AED use did not increase survival (38.4% vs 39.8%; adjusted RR, 1.00; 95% CI, 0.88–1.13; P = 0.99). These trends were consistent for AED use in both monitored and nonmonitored hospital units (p > .10).For cardiac arrest due to asystole or PEA the use (or not) of an AED did not influence the rates of ROSC. For cardiac arrests due to ventricular fibrillation or pulseless ventricular tachycardia the rates of ROSC and survival at 24 h did not differ by AED use. AED use did not shorten the time to defibrillation and for those patients with ROSC, and was not associated with shorter CPR times or fewer administered defibrillations.Overall the authors concluded that the use of AEDs in hospitalised patients following cardiac arrest was not associated with improved survival.     

Automated external defibrillators and in-hospital cardiac arrest: patient survival and device performance at an Australian teaching hospital

Aims

To evaluate the effect of automated external defibrillators (AEDs) on patient survival and to describe the performance of AEDs after in-hospital cardiac arrest.

Methods

Prospectively collected data were analysed for cardiac arrests in the general patient care areas of a teaching hospital during the 3 years before and the 3 years after the deployment of AEDs. The association between availability of an AED and survival to hospital discharge was assessed using multivariate logistic regression. AED performance during automated management of the initial rhythms was assessed using information captured by the AEDs.

Results

There were 84 cardiac arrests in the AED period and 82 in the pre-AED period. Patient and event characteristics were similar in each period. The initial rhythm was shockable in 16% of cases. Return of spontaneous circulation was higher in the AED period (54% vs. 35%, P = 0.02) but the proportion of hospital survivors in each period was similar (22% vs. 19%, P = 0.56). The adjusted odds ratio for hospital survival when an AED was available was 1.22 (95% CI 0.53-2.84, P = 0.64). An AED was applied in 77/84 (92%) possible cases. Median interruption to chest compressions was 12 s (inter-quartile range 12-13). An automated shock was delivered in 8/13 (62%) possible cases.

Conclusions

Availability of AEDs was not independently associated with hospital survival. Shockable presenting rhythms were not common and, in keeping with the manufacturer's specifications, the AEDs did not shock all potentially shockable rhythms. The hands-off time associated with automated rhythm management was considerable.     

Defibrillation threshold and cardiac responses using an external biphasic defibrillator with pediatric and adult adhesive patches in pediatric-sized piglets

Before recommendations for using an automatic external defibrillator on pediatric patients can be made, a protocol for the energy of a biphasic waveform energy dosing needs to be determined that will allow ventricular defibrillation of 8 year olds while causing only a minimal amount of cardiac damage to infants. Pediatric- and adult-sized electrode patches were alternately applied to 10 isoflurane-anesthetized piglets weighing 3.8-20.1 kg to approximate the body weights of newborns to children < 8 years old. The defibrillation threshold (DFT) was determined for biphasic truncated exponential waveform shocks. Additional shocks, varying from the DFT to 360 Joules (J), were delivered during sinus rhythm or following 30 s of ventricular fibrillation (VF). The DFT was 2.4+/-0.81 and 2.1+/-0.65 J/kg for pediatric and adult patches, respectively (P = N.S.). The change in left ventricular (LV) dP/dt from baseline as a function of shock strength was significantly different at 1 and 10 s after shocks of increasing energy that were delivered in sinus rhythm, and 1, 10, 20, and 30 s after defibrillation shocks. There was no significant difference in LV dP/dt with increasing shock energy at 60 s with either patch size. The time to return of sinus rhythm, ST-segment deviation, and cardiac output were also not significantly different from baseline 60 s following shocks of up to 360 J delivered during sinus rhythm or VF with either patch. The same amount of energy delivered with a biphasic external defibrillator successfully defibrillated VF whether adult or pediatric patches were used. Cardiac rhythm and hemodynamic variables were unaltered at 60 s after shocks delivered at energies of up to 360 J. These data suggest that there is a substantial safety margin above a DFT strength shock for this biphasic waveform in piglets.     

A prospective,randomised and blinded comparison of first shock success of monophasic and biphasic waveforms in out-of-hospital cardiac arrest

BACKGROUND: Evidence suggests that biphasic waveforms are more effective than monophasic waveforms for defibrillation in out-of-hospital cardiac arrest (OHCA), yet their performance has only been compared in un-blinded studies. METHODS AND RESULTS: We compared the success of biphasic truncated exponential (BTE) and monophasic damped sine (MDS) shocks for defibrillation in OHCA in a prospective, randomised, double blind clinical trial. First responders were equipped with MDS and BTE automated external defibrillators (AEDs) in a random fashion. Patients in ventricular fibrillation (VF) received BTE or MDS first shocks of 200 J. The ECG was recorded for subsequent analysis continuously. The success of the first shock as a primary endpoint was removal of VF and required a return of an organized rhythm for at least two QRS complexes, with an interval of <5 s, within 1 min after the first shock. The secondary endpoint was termination of VF at 5 s. VF was the initial recorded rhythm in 120 patients in OHCA, 51 patients received BTE and 69 received MDS shocks. The success rate of 200 J first shocks was significantly higher for BTE than for MDS shocks, 35/51 (69%) and 31/69 (45%), P=0.01. In a logistic regression model the odds ratio of success for a BTE shock was 4.01 (95% CI 1.01-10.0), adjusted for baseline cardiopulmonary resuscitation, VF-amplitude and time between collapse and first shock. No difference was found with respect to the secondary endpoint, termination of VF at 5 s (RR 1.07 95% CI: 0.99-1.11) and with respect to survival to hospital discharge (RR 0.73 95% CI: 0.31-1.70). CONCLUSION: BTE-waveform AEDs provide significantly higher rates of successful defibrillation with return of an organized rhythm in OHCA than MDS waveform AEDs.     

The Los Angeles public access defibrillator (PAD) program: Ten years after

Background

Public access automated external defibrillator (PAD) programs have been shown to be successful in several municipalities. This study sought to determine the usage of and survival rate from a large, urban PAD program in the first 10 years since its implementation.

Methods

This was a prospective, longitudinal, observational study from January 2002–2012 conducted in Los Angeles, California, a city with a population of 3.8 million. An incremental rollout resulted in a current total of 1300 automated external defibrillators (AEDs) in place in city-owned buildings and other public places, including all 3 area airports, golf-courses, and public pools. All instances where an AED was applied were included in the study.

Results

There were 59 incidents of cardiac arrest with a public access AED applied, of which 42 (71%) occurred at an airport. 51 (86%) of the patients were male, with a median age of 64 years (interquartile range, 56.5 to 70 years). A shockable rhythm was detected and shocks were applied in 39 (66%) patients, with 30 (77%) of these patients achieving a return of spontaneous circulation (ROSC). Of those patients who received shock(s) by public access AED, 27 (69%) survived to hospital discharge. The youngest survivors were a 25 year old male and a 34 year old female.

Conclusion

While the majority of PAD cases occurred at an airport, there were also survivors from other public locations. AEDs deployed as part of a large PAD program resulted in a very high survival rate for patients with cardiac arrest.     

Validation of a Predictive Model for Automated External Defibrillator Placement in Rural America

Objective. The development of Automated External Defibrillators (AEDs) to treat out-of-hospital cardiac arrest (OOHCA) has greatly expanded the availability of life saving defibrillatory shocks in various settings. However, placement of AEDs in rural areas remains perplexing since OOHCAs are rare andunpredictable. We set out to develop a cost-effective rural AED placement model andto test the validity of the resulting model using OOHCAs attended by EMS. Methods. Design: A population-based cross-sectional study. Analytic Plan: An exhaustive literature search was conducted to identify community attributes correlated with successful placement of AEDs in rural regions. Identified attributes were characterized using U.S. Census andCDC heart disease mortality data to estimate the potential risk for AED use andapplied this estimate to rural census tracts in all 50 states. Based upon risk, AEDS were assigned to each tract using a first responder model andcost effectiveness was assessed. Using Utah State EMS data, the predicted placement of AEDs in each tract was validated using the actual number of OOHCAs attended by EMS. Results. A total of 14,586 rural census tracts in 50 U.S. states were evaluated. On average, 2,600 AEDs were situated within each state. AED placement in rural areas proved as cost effective as health screening programs. In Utah, predicted AED placement correlated with the frequency of OOHCAs attended by EMS personnel (ρ = 0.55, p < 0.001). Conclusions. The resulting model illustrates one potential way to determine the most beneficial location for rural AED placement.     

Layperson’s performance on an unconversant type of AED device: A prospective crossover simulation experimental study

BACKGROUND:Diverse models of automated external defibrillators (AEDs) possess distinctive features. This study aimed to investigate whether laypersons trained with one type of AED could intelligently use another initial contact type of AED with varying features.METHODS:This was a prospective crossover simulation experimental study conducted among college students. Subjects were randomly trained with either AED1 (AED1 group) or AED2 (AED2 group), and the AED operation performance was evaluated individually (Phase I test). At the 6-month follow-up AED performance test (Phase II test), half of the subjects were randomly switched to use another type of AED, which formed two switches (Switch A: AED1-1 group vs. AED2-1 group; Switch B: AED2-2 group vs. AED1-2 group).RESULTS:A total of 224 college students participated in the study. In the phase I test, a significantly higher proportion of successful defibrillation and shorter shock delivery time to achieve successful defibrillation was observed in the AED2 group than in the AED1 group. In the phase II test, no statistical differences were observed in the proportion of successful defibrillation in Switch A (51.4% vs. 36.6%, P=0.19) and Switch B (78.0% vs. 53.7%, P=0.08). The median shock delivery time within participants achieving successful defibrillation was significantly longer in the switched group than that of the initial group in both Switch A (89 [81–107] s vs. 124 [95–135] s, P=0.006) and Switch B (68 [61.5–81.5] s vs. 95.5 [55–131] s, P<0.001).CONCLUSION:College students were able to effectively use AEDs different from those used in the initial training after six months, although the time to shock delivery was prolonged.     

Local lay rescuers with AEDs,alerted by text messages,contribute to early defibrillation in a Dutch out-of-hospital cardiac arrest dispatch system

Aim

Public access defibrillation rarely reaches out-of-hospital cardiac arrest (OHCA) patients in residential areas. We developed a text message (TM) alert system, dispatching local lay rescuers (TM-responders). We analyzed the functioning of this system, focusing on response times and early defibrillation in relation to other responders.

Methods

In July 2013, 14 112 TM-responders and 1550 automated external defibrillators (AEDs) were registered in a database residing with the dispatch center of two regions of the Netherlands. TM-responders living <1000 m radius of the patient received a TM to go to the patient directly, or were directed to retrieve an AED first. We analyzed 1536 OHCA patients where a defibrillator was connected from February 2010 until July 2013. Electrocardiograms from all defibrillators were analyzed for connection and defibrillation time.

Results

Of all OHCAs, the dispatcher activated the TM-alert system 893 times (58.1%). In 850 cases ≥1 TM-responder received a TM-alert and in 738 cases ≥1 AED was available. A TM-responder AED was connected in 184 of all OHCAs (12.0%), corresponding with 23.1% of all connected AEDs. Of all used TM-responder AEDs, 87.5% were used in residential areas, compared to 71.6% of all other defibrillators. TM-responders with AEDs defibrillated mean 2:39 (min:sec) earlier compared to emergency medical services (median interval 8:00 [25–75th percentile, 6:35–9:49] vs. 10:39 [25–75th percentile, 8:18–13:23], P < 0.001). Of all shocking TM-responder AEDs, 10.5% delivered a shock ≤6 min after call.

Conclusion

A TM-alert system that includes local lay rescuers and AEDs contributes to earlier defibrillation in OHCA, particularly in residential areas.     

Multiple Shocks Affect Thoracic Electrical Impedance During External Cardioversion of Atrial Fibrillation

Background: Thoracic impedance (TI) influences the success of external cardioversion (ECV) or defibrillation because current intensity traversing the heart is inversely related to TI. Experimental data suggest that TI decreases after multiple shocks. We undertook a clinical study to determine changes of TI values in patients with atrial fibrillation or flutter requiring ECV. Methods: We enrolled 222 consecutive patients (age 73 ± 11 years; males 67%; body weight 75 ± 13 kg) who underwent ECV between January 2004 and February 2007. Biphasic shocks were delivered through adhesive pads placed in the anteroposterior position. The initial energy was set at 1 J/kg, with progressive increases up to a maximum of 180 J in case of failure. In the last 39 elective patients, plasma concentration of interleukin‐6 (IL‐6) and tumor necrosis factor (TNF)‐α were determined before and 6 hours after ECV. Results: Sinus rhythm was restored in 202 patients (91.0%). Of these, 155 (69.8%) required more than one shock (on average, 2.5 ± 1.5 shocks/patient). Final values of energy and peak current intensity were 136 ± 47 J and 50 ± 14 A, respectively. TI decreased significantly by 6.2% from baseline after ≥2 shocks (P < 0.001). The absolute reduction was correlated with baseline TI, number of delivered shocks, and hemoglobin oxygen saturation. IL‐6 and TNF‐α increased with ECV (P < 0.001 and P = 0.014, respectively). Conclusions: TI decreases significantly after multiple shocks, possibly by activation of acute inflammation.