The diagnostic accuracy of a shock advisory algorithm in automated external defibrillators in the presence of real-world artifacts.

BACKGROUND: The current standards for shock advisory algorithms in AEDs require performance testing on artifact-free ECGs. However, AED analysis in the real world is more challenging due to potential artifacts from various sources (e.g., patient handling, and electromagnetic interference). This retrospective data analysis reports the real-world performance and behavior of a shock advisory algorithm used in three AED models with the presence of artifacts. METHODS: ECG rhythm analyses recorded during the use of three AED models (HS1, FRx and FR3) were reviewed. The shock recommendations made in the AEDs were compared to the expert annotations of reviewers. The effects of real-world artifacts and the handling by the algorithm were analyzed. RESULTS: Among the 3,941 analyses, 619 were annotated as shockable rhythms, and 2,912 were non-shockable. The overall sensitivity and specificity were 97.1% (601/619), and 99.9% (2,908/2,912), respectively. Artifacts were detected by the algorithm in 23.3% (918/3,941) of the analysis periods. The algorithm performance for the analysis periods with artifacts detected was 95.2% (80/84) for sensitivity and 100.0% (687/687) for specificity. In the remaining analysis periods with no artifacts detected, the sensitivity was 97.4% (521/535), and specificity was 99.8% (2,221/2,225). CONCLUSIONS: The performance of this shock advisory algorithm during real-world resuscitations with or without artifacts, exceeded AHA recommendations and the requirements in international standards. The high sensitivity and specificity demonstrate the effectiveness and safety of this algorithm in all three AED models.

Characterization of non-cardiac arrest PulsePoint activations in public and private settings.

BACKGROUND: Geospatial smartphone application alert systems are used in some communities to crowdsource community response for out-of-hospital cardiac arrest (OHCA). Although the clinical focus of this strategy is OHCA, dispatch identification of OHCA is imperfect so that activation may occur for the non-arrest patient. The frequency and clinical profile of such non-arrest patients has not been well-investigated. METHODS: We undertook a prospective 3-year cohort investigation of patients for whom a smartphone geospatial application was activated for suspected OHCA in four United States communities (total population ~1 million). The current investigation evaluates those patients with an activation for suspected OHCA who did not experience cardiac arrest. The volunteer response cohort included off-duty, volunteer public safety personnel (verified responders) notified regardless of location (public or private) and laypersons notified to public locations. The study linked the smartphone application information with the EMS records to report the frequency, condition type, and EMS treatment for these non-arrest patients. RESULTS: Of 1779 calls where volunteers were activated, 756 had suffered OHCA, resulting in 1023 non-arrest patients for study evaluation. The most common EMS assessments were syncope (15.9%, n=163), altered mental status (15.5%, n=159), seizure (14.3%, n=146), overdose (13.0%, n=133), and choking (10.5%, n=107). The assessment distribution was similar for private and public locations. Overall, the most common EMS interventions included placement of an intravenous line (43.1%, n=441), 12-Lead ECG(27.9%, n=285), naloxone treatment (9.8%, n=100), airway or ventilation assistance (8.7%, n=89), and oxygen administration (6.6%, n=68). CONCLUSIONS: More than half of patients activated for suspected OHCA had conditions other than cardiac arrest. A subset of these conditions may benefit from earlier care that could be provided by both layperson and public safety volunteers if they were appropriately trained and equipped.

A pilot evaluation of respiratory mechanics during prehospital manual ventilation.

INTRODUCTION: Respiratory mechanics, such as tidal volume (VT) and inspiratory pressures, may affect outcome in hospitalized patients with respiratory failure. Little is known about respiratory mechanics in the prehospital setting. METHODS: In this prospective, pilot investigation of patients receiving prehospital advanced airway placement, paramedics applied a device to measure respiratory mechanics. We evaluated tidal volume (VT) per predicted body weight (VTPBW) to determine the proportion of breaths within the lung-protective range of 4-10 mL/kg per PBW overall, according to ventilation bag volume (large versus small) and cardiac arrest status (active CPR, post-ROSC, non-arrest). RESULTS: Over 16-months, 7371 post-intubation breaths were measured in 54 patients, 32 patients with cardiac arrest and 22 with other conditions. Paramedics ventilated 19 patients with a small bag and 35 patients with a large bag. Overall, mean VT was 435 mL (95% CI 403, 467); VTPBW was 7.0 mL/kg (95% CI 6.4, 7.6) with 75% within the lung-protective range. Mean VTPBW and peak pressure differed according to arrest status (absolute difference -0.36 mL/kg and 32 cmH2O for active CPR compared to post-ROSC), though not according to bag size. CONCLUSIONS: We observed that measuring respiratory mechanics in the prehospital setting was feasible. Tidal volumes were generally delivered within a safe range. Respiratory mechanics varied most significantly with active CPR with lower VTPBW and higher peak pressures, though did not seem to be affected by bag size. Future work might examine the relationship between respiratory mechanics and outcomes, which may identify opportunities to improve clinical outcomes.

Improving response to out-of-hospital cardiac arrest: The verified responder program pilot.

BACKGROUND: Survival following out-of-hospital cardiac arrest (OHCA) decreases as the interval from collapse to CPR and defibrillation increases. Innovative approaches are needed to reduce response intervals, especially for private locations. METHODS: We undertook the Verified Responder Program in 5 United States communities during 2018, whereby off-duty EMS professionals volunteered and were equipped with automated external defibrillators (AEDs). Volunteers were alerted using a geospatial smartphone application (PulsePoint) and could respond to nearby private and public suspected OHCA. The study evaluated the frequency of Verified Responder notification, response, scene arrival, and initial care prior to EMS arrival. OHCA surveillance used the CARES registry. RESULTS: Of the 651 OHCA events (475 private, 176 public), Verified Responders were notified in 7.4% (n = 49). Among the 475 in a private location, volunteers were alerted in 8% (n = 38), responded in 2.7% (n = 13), arrived on scene in 2.3% (n = 11), and provided initial care in 1.7% (n = 8). Among the 176 in a public location, volunteers were alerted in 6.3% (n = 11), responded in 2.3% (n = 4), arrived on-scene in 2.3% (n = 4), and provided initial care in 2.3% (n = 4). Over 96% surveyed had positive impression of the program and intended to continue participation. No responder reported any adverse event. CONCLUSIONS: In this initial US-based experience of a smartphone program for suspected OHCA in private and public locations, Verified Responders reported a positive experience, though were only involved in a small fraction of OHCA. Studies should determine how this type of program could be enhanced to involve more OHCA events.

Strategy to Address Private Location Cardiac Arrest: A Public Safety Survey.

OBJECTIVE: Most cardiac arrests occur in the private setting where response is often delayed and outcomes are poor. We surveyed public safety personnel to determine if they would volunteer to respond into private locations and/or be equipped with a personal automated external defibrillator (AED) as part of a vetted responder program that would use smart geospatial technology. METHODS: We conducted an anonymized survey among personnel from fire-based emergency medical services (EMS) and search and rescue organizations from Washington State. The goal of the survey was to evaluate whether there was interest among cardiopulmonary resuscitation (CPR)-trained, public safety personnel to respond with or without an AED to private-residence cardiac arrest outside of working hours using a smartphone platform. We used a 5-point Likert scale to assess responses. RESULTS: Overall the response rate was 73.7% (527/715). Two-thirds of respondents were between the ages of 30-59 with a similar proportion certified as a firefighter-emergency medical technician (EMT). Most were male (80%). As a vetted volunteer responder, the majority would "almost always" or "often" respond to private (79.7%) or public locations (85.2%) outside of work hours. The majority (54.1%) would store the AED in their vehicle while 38% would plan to keep the AED on their person. A total of 83% were "definitely' or "probably interested" in participating in the program. CONCLUSION: The results of this survey indicate that public safety personnel are willing to respond to suspected cardiac arrest during off-hours using geospatial smart technology to private locations with or without an AED.

Carotid Doppler blood flow measurement during cardiopulmonary resuscitation is feasible: A first in man study.

OBJECTIVE: High quality chest compressions are the cornerstone of effective cardiopulmonary resuscitation (CPR). There is no available method of real time noninvasive hemodynamic measurement and feedback to inform rescuers of the efficacy of compressions. Ultrasound-based measures of blood flow may provide immediate, noninvasive hemodynamic information. Our objective was to determine the feasibility and safety of using ultrasound to measure blood flow on patients with cardiac arrest. METHODS: Study design This was a prospective cohort study in an emergency department setting. Subjects Included were patients receiving ongoing manual chest compressions for cardiac arrest. Excluded were those less than 18 years of age, incarcerated, pregnant, with neck injury, or obvious traumatic cause of arrest. Scan protocol Physicians recorded blood flow over the common carotid arteries during chest compressions with transverse and longitudinal color flow and Doppler using a portable ultrasound machine (CX30, Philips Healthcare., Andover, MA). Measurements Duration of scan time, and the median values for peak systolic (PSV), end-diastolic (EDV) and mean diastolic (MDV) carotid blood flow velocities were captured. Feasibility was defined as the proportion of eligible subjects upon whom ultrasound was initiated Safety was defined as availability of at least 5 min of scanning time. RESULTS: Nineteen patients (56% of eligible) where enrolled and had ultrasound measurements attempted during manual compressions. In one patient, scanning was not initiated because ongoing CPR efforts were terminated. Three patients were enrolled but had no images available for review. A total of 15 patients (78% of attempted) had ultrasound imaging saved. Most (n=10, 66%) had scanning times greater than 5 min (median 5 min 59s, interquartile range 3 min 15s to 8 min 25s), median PSV was 67 cms(-1) (IQR 55-106), median EDV was 18 cms(-1) (IQR 12-27), and median MDV was 14 cms(-1) (IQR 9-18). CONCLUSIONS: Ultrasound measurement of common carotid artery blood flow during CPR is feasible. Further studies are necessary to correlate carotid blood flow to other hemodynamic measures and its effects on patient outcomes.

Waveform analysis-guided treatment versus a standard shock-first protocol for the treatment of out-of-hospital cardiac arrest presenting in ventricular fibrillation: results of an international randomized, controlled trial.

BACKGROUND: Ventricular fibrillation (VF) waveform properties have been shown to predict defibrillation success and outcomes among patients treated with immediate defibrillation. We postulated that a waveform analysis algorithm could be used to identify VF unlikely to respond to immediate defibrillation, allowing selective initial treatment with cardiopulmonary resuscitation in an effort to improve overall survival. METHODS AND RESULTS: In a multicenter, double-blind, randomized study, out-of-hospital cardiac arrest patients in 2 urban emergency medical services systems were treated with automated external defibrillators using either a VF waveform analysis algorithm or the standard shock-first protocol. The VF waveform analysis used a predefined threshold value below which return of spontaneous circulation (ROSC) was unlikely with immediate defibrillation, allowing selective treatment with a 2-minute interval of cardiopulmonary resuscitation before initial defibrillation. The primary end point was survival to hospital discharge. Secondary end points included ROSC, sustained ROSC, and survival to hospital admission. Of 6738 patients enrolled, 987 patients with VF of primary cardiac origin were included in the primary analysis. No immediate or long-term survival benefit was noted for either treatment algorithm (ROSC, 42.5% versus 41.2%, P=0.70; sustained ROSC, 32.4% versus 33.4%, P=0.79; survival to admission, 34.1% versus 36.4%, P=0.46; survival to hospital discharge, 15.6% versus 17.2%, P=0.55, respectively). CONCLUSIONS: Use of a waveform analysis algorithm to guide the initial treatment of out-of-hospital cardiac arrest patients presenting in VF did not improve overall survival compared with a standard shock-first protocol. Further study is recommended to examine the role of waveform analysis for the guided management of VF.

Impacting sudden cardiac arrest in the home: a safety and effectiveness study of privately-owned AEDs.

BACKGROUND: Sudden cardiac arrest (SCA) remains a major public health problem. The majority of SCA events occur in the home; however, scant data has been published regarding the effectiveness of privately owned AEDs. METHODS: The study, initiated in 2002 under prescription labeling, continued with over the counter availability in 2004 and was completed in 2009. Surveillance methods included annual surveys, follow-up phone calls, media reports, and use queries upon order of replacement pads. AED owners reporting emergency use of the device were contacted for an in-depth interview, and the ECG and event data in the device's internal memory were evaluated. RESULTS: 25 cases were identified in which an AED was used on a patient in SCA. Two uses were on children. The SCA was witnessed in 76% (19/25) of the cases. In 56% (14/25), the patient presented in VF and at least one shock was delivered. All 14 patients who were shocked had termination of VF; 6 (43%) required more than one shock due to refibrillation. Shock efficacy was 100% (25/25) for termination of VF for all delivered shocks. Of the patients with a witnessed arrest who were shocked, 67% (8/12) survived to hospital discharge. There were no circumstances of unsafe emergency use of the AED or harm to the patient, responder, or bystanders. CONCLUSIONS: People who purchase an AED for their home, even without previous AED experience, are able to use the device successfully in both adults and children. The high survival rate observed in this study demonstrates that lay responders with privately owned AEDs can successfully and safely use the devices.

Minimal interruption of cardiopulmonary resuscitation for a single shock as mandated by automated external defibrillations does not compromise outcomes in a porcine model of cardiac arrest and resuscitation.

OBJECTIVES: Current automated external defibrillations require interruptions in chest compressions to avoid artifacts during electrocardiographic analyses and to minimize the risk of accidental delivery of an electric shock to the rescuer. The earlier three-shock algorithm, with prolonged interruptions of chest compressions, compromised outcomes and increased severity of postresuscitation myocardial dysfunction. In the present study, we investigated the effect of timing of minimal automated external defibrillation-mandated interruptions of chest compressions on cardiopulmonary resuscitation outcomes, using a single-shock algorithm. We hypothesized that an 8-sec interruption of chest compressions for a single shock, as mandated by automated external defibrillations, would not impair initial resuscitation and outcomes of cardiopulmonary resuscitation. DESIGN: Randomized prospective animal study. SETTING: University affiliated research laboratory. SUBJECTS: Domestic pigs. MEASUREMENTS AND MAIN RESULTS: In 24 domestic male pigs weighing 41 +/- 2 kg, ventricular fibrillation was induced by left anterior descending coronary artery occlusion and untreated for 7 min. Cardiopulmonary resuscitation, including chest compressions and ventilation with oxygen, was then performed for an interval of 2 min before attempted defibrillation. Animals were randomized into three groups: A) interruption immediately before defibrillation; B) interruption after 1 min of cardiopulmonary resuscitation; or C) no interruption. Chest compressions were delivered with the aid of a mechanical chest compressor at a rate of 100 compressions/min and compression/ventilation ratio of 30:2. Defibrillation was attempted with a single biphasic 150-J shock. Each animal was successfully resuscitated and survived for >72 hr. No differences in the number of shocks before return of spontaneous circulation, frequency of recurrent ventricular fibrillation, duration of cardiopulmonary resuscitation, and severity of postresuscitation myocardial dysfunction were observed. CONCLUSIONS: In this experimental model of cardiac arrest and cardiopulmonary resuscitation, minimal automated external defibrillation-mandated interruption of chest compressions for a single-shock algorithm did not have adverse effects on postresuscitation myocardial or neurologic function. All animals, whether subjected to cardiopulmonary resuscitation interruptions or not, survived.

The quality of chest compressions during cardiopulmonary resuscitation overrides importance of timing of defibrillation.

BACKGROUND: We address the quality of chest compressions and the impact on initial defibrillation or initial chest compressions after sudden death. METHODS: Ventricular fibrillation was induced by occlusion of the left anterior descending coronary artery in 24 domestic pigs with a mean (+/- SD) weight of 40 +/- 2 kg. Cardiac arrest was left untreated for 5 min. Animals were then randomized to receive chest compressions-first or defibrillation-first and were further randomized to "optimal" or "conventional" chest compressions. A total of four groups of animals were investigated using a factorial design. For optimal chest compressions, the anterior posterior diameter of the chest was reduced by 25%, representing approximately 6 cm. Only 70% of this depth, or approximately 4.2 cm, represented conventional chest compressions. Chest compressions were delivered with a mechanical chest compressor. Defibrillation was attempted with a single biphasic 150-J shock. Postresuscitation myocardial function was echocardiographically assessed. RESULTS: Coronary perfusion pressures and end-tidal Pco(2) were significantly lower with conventional chest compressions. With optimal chest compressions, either as an initial intervention or after defibrillation, each animal was successfully resuscitated. Fewer shocks were required prior to the return of spontaneous circulation after initial optimal chest compressions. No animals were resuscitated when conventional chest compressions preceded the defibrillation attempt. When defibrillation was attempted as the initial intervention followed by conventional chest compressions, two of six animals were resuscitated. CONCLUSIONS: In this animal model of cardiac arrest, it was the quality of the chest compressions, rather then the priority of either initial defibrillation or initial chest compressions, that was the predominant determinant of successful resuscitation.

Outcome prediction for guidance of initial resuscitation protocol: Shock first or CPR first.

BACKGROUND: Ventricular fibrillation (VF) is treated optimally with a defibrillation shock shortly after patient collapse, but may benefit from initial cardiopulmonary resuscitation (CPR) if the shock is delayed. An objective measure of potential responsiveness to defibrillation could help decide optimal initial therapy. METHODS AND RESULTS: a new electrocardiogram (ECG) analysis algorithm was compared with response interval (call-to-shock) for prediction of patient outcome in a population of 87 VF patients in the Rochester, Minnesota area. In a retrospective analysis, both call-to-shock interval (p = 0.009) and ECG analysis (p < 0.001) predicted neurologically intact survival, with ECG analysis the stronger predictor (p = 0.034). When applied to advising initial patient treatment, ECG analysis compared favorably with the call-to-shock interval. Using a 7 min call-to-shock time criterion, 69% of patients would receive shocks first treatment using ECG analysis versus 67% using the call-to-shock interval (p = NS), 94% of survivors would retain successful shocks first treatment versus 85% (p = NS), and 48% of non-survivors receive alternate CPR-first treatment versus 45% (p = NS). Similarly, no significant differences were observed between ECG analysis and call-to-shock interval using an 8 min criterion. CONCLUSIONS: Both call-to-shock interval and a real-time ECG analysis are predictive of patient outcome. The ECG analysis is more predictive of neurologically intact survival. Moreover, the ECG analysis is dependent only upon the patient's condition at the time of treatment, with no need for knowledge of the response interval, which may be difficult to estimate at the time of treatment.

Comparison of current densities measured in a pig heart during states of ventricular fibrillation and post-mortem for different defibrillation electrode positions.

Current density imaging (CDI) is an MRI technique used to quantitatively measure current density vectors in biological tissue. A fast CDI sequence was developed that can image the whole body of a 4 kg pig in about 15 minutes. A state of ventricular fibrillation (VF) can be sustained for nearly 30 minutes allowing two complete CDI scans of the same subject. A single parameter, i.e. electrode position, is adjusted between the two scans for comparative analysis. This study compares the current density vector directions and current density magnitudes measured for two typical electrode positions, i.e. apex anterior (AA) and apex posterior (AP). The comparative experiment is repeated on the same subjects for states of immediate post-mortem and one hour post-mortem. Further, the acquired vector datasets are used to compute conductivity images of the heart.

Attenuated pediatric electrode pads for automated external defibrillator use in children.

OBJECTIVE: This post-market, observational study is intended to evaluate reported uses of pediatric pads that reduce the energy delivered by some adult automated external defibrillators (AEDs) so that they may be used with pediatric patients. METHODS: Users of the pediatric pads were asked to report any use of the pads, even if no shock was delivered and to provide detailed information about the event, caregiver and the patient. RESULTS: Reports of the use of pediatric pads have been received and confirmed for 27 patients, age range 0 days to 23 years, median 2 years. Ventricular fibrillation (VF) was reported in eight cases, age range 4.5 months to 10 years, median 3 years. Shocks were delivered to all VF patients, the average shock number was 1.9, range 1-4. All patients had termination of VF, were admitted to the hospital and five survived to hospital discharge. Non-shockable rhythms were reported in 16 patients, and the AED appropriately did not advise a shock. Eleven of these patients had asystole or PEA as their initial rhythm and did not survive to hospital discharge. One report contained no additional information other than that the patient did not survive, and in two other reports, the pads were not applied to patients. CONCLUSIONS: Voluntary reports of the use of attenuated pediatric defibrillation pads indicate the devices performed appropriately. All eight VF patients had termination of VF and five survived to hospital discharge. These data support the rapid deployment of AEDs for young children as well as adolescents and adults. Since the pediatric pads are available and deliver an appropriate dose for children, their use should be strongly encouraged.

Transthoracic impedance does not affect defibrillation, resuscitation or survival in patients with out-of-hospital cardiac arrest treated with a non-escalating biphasic waveform defibrillator.

OBJECTIVE: This is a study of the influence of transthoracic impedance (TTI) on defibrillation, resuscitation and survival in patients with out-of-hospital cardiac arrest (OHCA), treated with a non-escalating impedance-compensating 150 J biphasic waveform defibrillator. METHODS: Cardiac arrest data from two EMS systems were analyzed retrospectively. All witnessed arrests from patients who presented with a shockable rhythm and were treated initially by BLS personnel were included (n = 102). For each defibrillation and resuscitation outcome variable, we tested differences in mean TTI for successful versus unsuccessful outcome. The effect of call-to-shock time on overall outcome was also examined. RESULTS: Initial shocks defibrillated 90% [83-95%] (95% confidence interval) of patients. Cumulative success with two shocks was 98% [93-100%] and with three shocks was 99% [95-100%]. TTI averaged 90 +/- 23 Omega. First-shock success, cumulative success through two shocks and cumulative success through the first-shock series were unrelated to TTI, as were BLS ROSC, pre-hospital ROSC, hospital admission and discharge. In contrast and consistent with previous findings, call-to-shock time was highly predictive of survival. CONCLUSIONS: High impedance patients were defibrillated by the biphasic waveform used in this study at high rates with a fixed energy of 150 J and without energy escalation. Rapid defibrillation rather than differences in patient impedance accounts for resuscitation success.

Body weight does not affect defibrillation, resuscitation, or survival in patients with out-of-hospital cardiac arrest treated with a nonescalating biphasic waveform defibrillator.

BACKGROUND: This is a study of the influence of body weight on defibrillation, resuscitation, and survival in patients with out-of-hospital cardiac arrest treated with a nonescalating impedance-compensating 150-J biphasic waveform defibrillator. METHODS: Cardiac arrest data from Rochester, MN, emergency medical services over a 6-yr period was retrospectively analyzed. Patient weight data were available for 62 of the 68 patients who were treated initially by basic life support personnel and who presented with a shockable rhythm. For each defibrillation and resuscitation outcome variable, we tested for differences in body weight for successful vs. unsuccessful outcome. RESULTS: Initial shocks defibrillated 92% (83% to 97%) of patients. Cumulative success with two shocks was 98% (confidence interval, 92% to 100%) and with three shocks was 100% (confidence interval, 95% to 100%). The mean shock impedance was 90 +/- 21 ohms. The average body weight was 84 +/- 17 kg (minimum, 53 kg; maximum, 135 kg) and was normally distributed. Based on the body mass index for 46 patients, approximately 41% were classified as overweight (body mass index, > or = 25), 24% obese (body mass index, > or = 30), and 4% extremely obese (body mass index, > or = 40). The remaining 31% were classified as normal or underweight. First-shock success, cumulative success through two shocks, and cumulative success through the first-shock series were unrelated to body weight, as were basic life support restoration of spontaneous circulation, prehospital restoration of spontaneous circulation, hospital admission, and discharge. CONCLUSIONS: Overweight patients were defibrillated by the biphasic waveform used in this study at high rates, with a fixed energy of 150 J, and without energy escalation.

Human factors impact successful lay person automated external defibrillator use during simulated cardiac arrest.

OBJECTIVE: With the dissemination of automated external defibrillators in the community, there is increasing lay person use, along with less formal automated external defibrillator training and retraining. Therefore, the "ease of use" factors related to the human-device interface may be vital for successful use. We sought to determine whether human factor differences would result in differences in parameters of successful or safe use by lay persons in the setting of simulated cardiac arrest. METHODS: We measured parameters of successful and safe use with two automated external defibrillator devices among two groups of volunteers, those trained with a brief video tape and those without any training (completely naive). Both devices (the Philips FR2 or the HS1) are used in public access defibrillator settings. Volunteers entered a mock cardiac arrest scenario after randomization to either the naive (untrained) group or to a video-trained group. RESULTS: Both the FR2 and HS1 were found to be completely safe when used by video-trained and by naive groups of participants, with no adverse events observed (total, n = 256). For both devices, video-trained participants demonstrated high rates of successful defibrillation in the simulated testing (86% for FR2 and 89% for HS1). With the FR2, video-trained participants were significantly more successful compared with naive, untrained participants (86% vs. 48% successful use; p < .001). However, for the HS1, there was no significant difference in success rates for the video-trained vs. naive, untrained groups (89% vs. 87%; p = .79). CONCLUSIONS: Both devices are safe with either video-trained or naive users. The successful use of each device is high when participants view the training videotape designed for the device. An important difference in successful use was observed for naive users where the HS1 showed improved successful use compared with the FR2. Because defibrillation in the community may increasingly be attempted by lay persons whose training is remote or who have not been trained at all, the "naive" scenario may be increasingly relevant to automated external defibrillator use. Collectively, these data support the notion that human factors associated with ease of use may play a critical factor in survival rates achieved by specific devices.