Abstract
Background
Survival following out-of-hospital cardiac arrest (OHCA) with shockable rhythms can be improved with early defibrillation. Although shockable OHCA accounts for only ~25% of overall arrests, ~60% of public OHCA are shockable, offering the possibility of restoring thousands of individuals to full recovery with early defibrillation by bystanders. We sought to determine the association of bystander automated external defibrillator (AED) use with survival and functional outcomes in shockable-observed-public OHCA.
Methods
From 2011–2015 the Resuscitation Outcomes Consortium prospectively collected detailed information on all cardiac arrests at 9 regional centers. The exposures were shock administration by a bystander-applied AED compared to initial defibrillation by EMS. The primary outcome measure was discharge with normal or near normal (favorable) functional status defined as a modified Rankin Score (mRS) less than or equal to 2. Survival to hospital discharge was the secondary outcome measure.
Results
Among 49,555 OHCA, 4115 (8.3%) observed public OHCA were analyzed of which 2500 (60.8%) were shockable. A bystander shock was applied in 18.8% of the shockable arrests. Patients shocked by a bystander were significantly more likely to survive to discharge (66.5% vs. 43.0%) and be discharged with favorable functional outcome (57.1% vs. 32.7%) than patients initially shocked by EMS. After adjusting for known predictors of outcome the odds ratio associated with a bystander shock was 2.62 (95%CI 2.07–3.31) for survival to hospital discharge and 2.73 (95%CI 2.17–3.44) for discharge with favorable functional outcome. The benefit of bystander shock increased progressively as EMS response time became longer.
Conclusions
Bystander AED use prior to EMS arrival in shockable-observed-public OHCA was associated with better survival and functional outcomes. Continued emphasis on public AED utilization programs may further improve outcomes of OHCA.
Keywords: cardiac arrest, automated external defibrillator, cardiopulmonary resuscitation, public policy
Introduction
Out-of-hospital cardiac arrest (OHCA) remains a significant cause of mortality and morbidity throughout the world,1 and sudden cardiac death is often the first symptom of underlying cardiopulmonary pathology.2–4 Overall survival following OHCA is low.1,5 The presenting arrest rhythm has a strong influence on prognosis. Cardiac arrest presenting with an initial rhythm of ventricular tachycardia and ventricular fibrillation has significantly better odds of survival compared to non-shockable rhythms, particularly when early cardiopulmonary resuscitation and rapid defibrillation are available.6–8 Although the overall prevalence of shockable rhythms in OHCA has decreased over the last 30 years,9,10 the prevalence of such rhythms in observed OHCA occurring in public rather than at home has been reported to be as high as 60%.6,11 The high proportion of shockable rhythms in public OHCA suggests that automatic external defibrillators (AEDs) located in public locations, which can be used by bystanders to decrease the time to defibrillation, may be a particularly effective allocation of resources. Given the potential for extremely rapid defibrillation prior to EMS arrival, the ~18,200 individuals (annually in the US alone) who experience shockable observed public OHCA (SOP-OHCA) represent an ideal population in which public access defibrillation can improve survival.
Indeed, the use of public access defibrillators is consistently shown to improve survival in overall shockable OHCA.12,13 This benefit has been attributed to the decreased time to defibrillation for bystander versus emergency medical services (EMS) shock as survival in shockable OHCA decreases significantly with each minute of delay in defibrillation.14–16 These studies, however, did not report the detailed functional status of the patients at discharge or determine how EMS response might influence the effectiveness of bystander AED use. Recently, three key studies have reported on functional outcomes following bystander AED use. Hansen and colleagues evaluated functional outcome from bystander versus EMS shock for a subset of counties in North Carolina where EMS response was on average >8 minutes.17 Kitamura and colleagues analyzed functional outcomes associated with bystander AED use in Japan in a setting with longer EMS response.18 Kragholm et al., reported bystander interventions were associated with improved 1-year neurological function amongst 30-day survivors of OHCA.19 These studies suggested that bystander AED use was associated with improved functional outcome although the definition of improved functional outcome has varied considerably between studies.
The Resuscitation Outcomes Consortium (ROC) is a collaboration among several large sites with rigorous data collection processes on multiple components of pre- and post-hospital care that presents a unique opportunity to study bystander intervention in the setting of strictly monitored and often rapid EMS response times. This multi-center, international, observational cohort study compared survival and a strictly defined favorable functional outcome between patients treated with initial bystander AED shock versus initial EMS shock among SOP-OHCA from 2011–2015.
METHODS
The data and analytical methods are available to other researchers for purposes of reproducing the results or replicating the procedure. The dataset is available at the National Heart, Lung and Blood Institute bioLINCC program20 and the analysis software is available as online supplementary material.
Study Design and Setting
The Resuscitation Outcomes Consortium (ROC) is a clinical trials network implemented to investigate strategies to improve outcomes in pre-hospital cardiopulmonary resuscitation and severe traumatic injury. This study is a prospectively designed analysis using the ROC Epistry data set that aims to ascertain all treated OHCA for each ROC site. The ROC Epistry defines an OHCA as a case in which CPR was performed by EMS or defibrillation was attempted by EMS or a bystander. The current investigation used data from cases treated in six US regions (Seattle/King County, WA; Dallas/Fort Worth, TX; Pittsburgh, PA; Milwaukee, WI; Birmingham, AL; Portland, OR) and three Canadian regions (Toronto, ON; Ottawa, ON; British Columbia).
Approval for the Epistry and associated investigations was provided by the institutional review boards or research ethics boards at each ROC site. All research was conducted in accordance with US and Canadian regulations on human subjects research.
Inclusion Criteria
This study included all patients at least 18 years of age with non-traumatic shockable observed public OHCA (SOP-OHCA) on whom defibrillation was attempted by EMS or a bystander. Although not a part of the primary study population, additional analyses among patient with unobserved and/or private OHCA was also performed to expand on the generalizability of the findings. Patients who attained return of spontaneous circulation (ROSC) prior to EMS arrival as a result of bystander AED use were included. The study excluded 1) patients on whom CPR was not attempted as a result of “do not resuscitate” orders or clear signs of death, 2) EMS-observed cardiac arrests because bystander AED is not relevant in these cases., and 3) the modest number (n=18) for whom no EMS shock was delivered but subsequent analysis of ECG records indicated an initial shockable rhythm.
Data Collection and Definitions
A detailed description of data collection, quality control and definitions has been reported previously.21 Briefly, data elements from each OHCA were collected by trained study personnel according to a set of predefined and uniform data collection procedures designed to maximize the validity, reproducibility and accuracy of data. Data collection procedures and data definitions were implemented by the study investigators according to the Utstein standards. Canadian sites are not permitted to assess the race of the patient; these individuals are treated as having an unknown race. Random and centralized audits of data collection practices were conducted throughout the study period to ensure the stability and reproducibility of data acquisition. Functional outcomes were assessed from the patient health record by trained study personnel.
The primary comparison groups and outcome measures for the current study were identified prospectively and individuals involved in patient care were not aware of the study intent. A public location was defined as a street or highway, public building, place of recreation, industrial place, or other public property, excluding health care facilities (hospitals, medical clinics, and other health care institutions). All other locations, excluding healthcare facilities as above were defined as private. Bystander observed cardiac arrest was defined as an arrest that was observed by a person who was not a member of the organized EMS response. Police officers were considered bystanders. A shockable rhythm was defined as any patient in whom an AED shock was delivered, an AED rhythm analysis (when available) indicated a shockable rhythm, or when the initial EMS electrocardiogram (ECG) readings indicated a shockable rhythm. All other arrests were considered non-shockable. The incidence of incorrect ECG analysis by an AED is rare.22 A previous study reported the error rate in the ECG rhythm assignment by EMS providers for a portion of this dataset was 3.1%.11 Bystander AED shock was defined as any shock delivered by a bystander-applied AED prior to EMS arrival as reported by the bystander to EMS personnel or when AED records were available and indicated a shock was delivered. EMS shock was defined as any cardiac arrest in which the initial shock was delivered by EMS. Individuals shocked by a bystander applied AED who were later shocked by EMS were still considered bystander shocked. EMS response interval was defined as the time period from receipt of the initial 911 call at the dispatch center to the arrival of the EMS vehicle at the scene.
Functional Outcome
Functional outcomes were assessed from the medical record by trained ROC personnel using the Modified Rankin Score (mRS), a validated, clinician-reported, measure of global disability.23,24 The modified Rankin score (mRS) uses a scoring system from 0 to 6 to quantify functional outcome (0=No symptoms, 1=No significant disability, 2=slight disability, 3=moderate disability, requiring some help but able to walk without assistance, 4=moderately severe disability, unable to walk or attend to bodily needs without assistance, 5=severe disability, 6=death). An MRS ≤2 is a validated dichotomous indicator of favorable functional outcome and was selected a priori as the primary functional outcome.23 Although we chose to identify patients with minimal disability (mRS≤2) as the cutoff for favorable outcome, due to a lack of consensus in the cardiac arrest literature for cutoff mRS we included a sensitivity analysis utilizing the less strict ≤3 cutoff. mRS=3 indicates inability to look after one’s own affairs without assistance.23,24
Statistical Analysis
Subjects’ characteristics and treatment were summarized with proportions, mean and standard deviation, or median and interquartile range as appropriate. The attempt of this study was to analyze the impact of bystander AED utilization while limiting the impact of confounding from patient characteristics, other bystander interventions and pre-hospital treatment. Therefore in the primary analysis, multivariable logistic regression was used to quantify the relationship between bystander AED shock and good functional outcome, adjusted for age, sex, race, bystander CPR, EMS response time, and study site.
A similar analysis was conducted for the secondary outcome measure of survival to hospital discharge. Results are expressed as odds ratios (OR) with 95% confidence Intervals (CI). We undertook a sensitivity analysis that excluded cases from the bystander AED shock group that were treated by police (n=41). In a secondary analysis, we also evaluated whether the potential outcome benefit of bystander AED shock was modified by the EMS response interval by including an interaction term between bystander AED shock and EMS response interval. All statistical analyses were performed with commercially available statistical packages (SAS, version 9.4, Cary, NC; R, version 2.14.1, Vienna, Austria).
RESULTS
Study Population
Between 2011 and 2015 a total of 49,555 cardiac arrests were treated by EMS. Of these, 4115 took place in public and were observed, and 2589 of the observed public cardiac arrests presented with an initial shockable rhythm. A total of 89 SOP-OHCA were excluded for do not resuscitate orders, dead on EMS arrival, missing data, or confirmed shockable rhythms that were not shocked by EMS or a bystander. Consequently, the primary study cohort of SOP-OHCA included the 469 who were shocked by a bystander and 2031 who were initially shocked by EMS (Figure 1).
Figure 1. Patient Inclusion and Exclusion Criteria.
Flowchart of patient inclusion and exclusion criteria. Numbers listed are number of patients in each group.
The bystander- and EMS-shocked patients among the SOP-OHCA group were similar according to the Utstein data elements with the exception of bystander CPR and administration of epinephrine (table 1). Bystander CPR was initiated more often among bystander-shocked OHCA while epinephrine was administered more often among EMS-shocked group. Much of the observed difference in epinephrine administration between EMS and bystander-shocked patients is explained by the 30.9% of bystander-shocked patients achieving return of spontaneous circulation (ROSC) prior to EMS arrival as no patient with ROSC on EMS arrival received epinephrine
Table 1.
Characteristics of Public Cardiac Arrests
| SOP-OHCA | ||||||||
|---|---|---|---|---|---|---|---|---|
| Treated Arrests |
Private Arrests |
Public Arrests |
Public Arrests, Bystander observed |
Public, observed, shockable arrests |
EMS shock |
Bystander AED shock |
||
| N =49,555 |
N =42,473 |
N =6,973 |
N =4,115 | N =2,500 | N =2,031 |
N =469 | ||
| Age (years) | Median (Q1,Q3) | 67 (55, 80) | 69 (56, 81) | 61 (51, 71) | 62 (53, 72) | 61 (53, 72) | 61 (53, 70) | 62 (53, 70) |
| Male | % | 63% | 61% | 80% | 80% | 85% | 84% | 89% |
| Race | ||||||||
| White | % | 25% | 25% | 27% | 27% | 28% | 28% | 26% |
| Black | % | 11% | 11% | 9% | 8% | 6% | 7% | 3% |
| Other | % | 2% | 2% | 2% | 2% | 2% | 2% | 2% |
| Unknown | % | 62% | 62% | 62% | 64% | 64% | 63% | 69% |
| Bystander CPR | ||||||||
| Yes | % | 42% | 40% | 54% | 66% | 73% | 67% | 99% |
| No | % | 56% | 58% | 45% | 33% | 26% | 32% | 1% |
| Missing | % | 2% | 2% | 1% | 1% | 1% | 1% | 0% |
| EMS response time (min) | Median (Q1–Q3) | 5.6 (4.3, 7.2) | 5.6 (4.4, 7.2) | 5.3 (4.0, 7.1) | 5.3 (4.0, 7.1) | 5.2 (4.0, 7.0) | 5.1 (3.9, 6.8) | 5.7 (4.3, 7.6) |
| Epinephrine | % | 81% | 82% | 77% | 73% | 67% | 72% | 43% |
| Dose | Mean (SD) | 3.7 (2.0) | 3.7 (2.0) | 3.7 (2.3) | 3.7 (2.4) | 3.6 (2.5) | 3.5 (2.4) | 3.9 (2.8) |
Min = minutes; CPR = cardiopulmonary resuscitation; EMS = emergency medical services; Q1,Q3 = The boundaries of the interquartile range.
Bystander Applied Shock
Over the entire study period, bystanders initiated CPR in 73% of SOP-OHCA (table 1). Bystanders applied an AED and delivered a shock prior to the arrival of EMS personnel in 18.8% of SOP-OHCA.
Survival and Functional Outcomes
Functionally favorable survival (mRS≤2) was greater among those patients treated with bystander AED shock than EMS shock (57.1% versus 32.7%, p<0.001) with most of the outcome advantage apparent when comparing the group with no disability (MRS=0 for 32.6% of bystander AED shocked versus 14.4% of EMS shocked, p<0.001) (table 2). After multivariable adjustment, the odds ratio for discharge with favorable functional outcome (mRS≤2) associated with initial bystander shock was 2.73 (95% Confidence Interval (CI) 2.17–3.44 p<0.001) (table 3). The relationship between bystander AED use and favorable outcome were similar regardless of the MRS cutoff (mRS ≤3 or mRS≤2). Overall survival to hospital discharge was 66.5% among bystander AED shocked versus 43.0% among EMS shocked, p<0.001. After adjustment, the odds ratio for survival to discharge associated with initial bystander AED shock was 2.62, (95% CI 2.07–3.31) (table 3). No survival benefit of bystander shock compared to EMS shock was seen in subjects with shockable public arrest that was not observed by the bystander. In shockable arrests occurring in private locations there was a significant survival benefit when these arrests were observed by the bystander but not in unobserved arrests (table 3, Supplemental tables 1 and 2).
Table 2.
Outcomes in the Overall and Study Population
| All public arrests | Public, bystander observed arrests |
Public, bystander observed, shockable arrests |
|||||
|---|---|---|---|---|---|---|---|
| No AED Applied |
AED Applied |
No AED Applied |
AED Applied |
EMS shock |
Bystander AED shock |
||
| N =6104 | N =869 | N =3460 | N =655 | N =2031 | N =469 | ||
| Duration of resuscitation (min) | Median (Q1,Q3) | 26.1 (16.7, 34.9) | 24.0 (10.1, 35.0) | 25.2 (14.5, 34.0) | 22.2 (7.3, 34.9) | 23.1 (11.4, 33.0) | 15.4 (4.9, 31.2) |
| Prehospital ROSC | n (%) | 2940 (48.2%) | 562 (64.7%) | 1929 (55.8%) | 480 (73.3%) | 1357 (66.8%) | 382 (81.4%) |
| Pulses at ED arrival | n (%) | 2187 (35.9%) | 464 (53.4%) | 1505 (43.5%) | 408 (62.3%) | 1117 (55.0%) | 338 (72.1%) |
| Admitted to hospital | n (%) | 2508 (41.4%) | 439 (53.7%) | 1707 (49.9%) | 381 (62.8%) | 1233 (61.7%) | 309 (73.4%) |
| Survived to discharge | n (%) | 1295 (21.2%) | 365 (42.0%) | 1004 (29.0%) | 343 (52.4%) | 874 (43.0%) | 312 (66.5%) |
| MRS | |||||||
| 0 | n (%) | 435 (7.1%) | 172 (19.8%) | 339 (9.8%) | 167 (25.5%) | 293 (14.4%) | 153 (32.6%) |
| 1 | n (%) | 318 (5.2%) | 89 (10.2%) | 253 (7.3%) | 85 (13.0%) | 229 (11.3%) | 80 (17.1%) |
| 2 | n (%) | 210 (3.4%) | 42 (4.8%) | 160 (4.6%) | 39 (6.0%) | 142 (7.0%) | 35 (7.5%) |
| 3 | n (%) | 173 (2.8%) | 26 (3.0%) | 127 (3.7%) | 25 (3.8%) | 112 (5.5%) | 23 (4.9%) |
| 4 | n (%) | 99 (1.6%) | 26 (3.0%) | 80 (2.3%) | 18 (2.7%) | 66 (3.2%) | 14 (3.0%) |
| 5 | n (%) | 60 (1.0%) | 8 (0.9%) | 45 (1.3%) | 7 (1.1%) | 32 (1.6%) | 5 (1.1%) |
| 6 (dead) | n (%) | 4809 (78.8%) | 506 (58.2%) | 2456 (71.0%) | 314 (47.9%) | 1157 (57.0%) | 159 (33.9%) |
| MRS≤2 at discharge | n (%) | 963 (15.8%) | 303 (34.9%) | 752 (21.7%) | 291 (44.4%) | 664 (32.7%) | 268 (57.1%) |
| Transported to the ED | N =4958 | N =711 | N =3010 | N =572 | N =1873 | N =431 | |
| Induced hypothermia* | n (%) | 1434 (34.6%) | 211 (39.9%) | 1019 (38.3%) | 174 (42.0%) | 805 (47.2%) | 139 (47.0%) |
| Diagnostic Catheterization* | n (%) | 442 (10.6%) | 91 (17.2%) | 336 (12.6%) | 82 (19.8%) | 301 (17.6%) | 71 (24.0%) |
| PTCA* | n (%) | 597 (14.4%) | 90 (17.0%) | 444 (16.7%) | 79 (19.1%) | 419 (24.6%) | 67 (22.6%) |
| Admitted to hospital | N =2508 | N =439 | N =1707 | N =381 | N =1233 | N =309 | |
| CCU/ICU (days) † | Median (Q1,Q3) | 5.0 (3.0, 10.0) | 6.0 (3.0, 10.0) | 5.0 (3.0, 10.0) | 6.0 (3.0, 10.0) | 6.0 (3.0, 11.0) | 6.0 (3.0, 9.5) |
| Hospitalization (days) † | |||||||
| Survived | Median (Q1,Q3) | 11.0 (7.0, 20.0) | 10.0 (5.0, 19.0) | 11.0 (7.0, 21.0) | 10.0 (5.0, 18.0) | 12.0 (7.0, 21.0) | 9.5 (5.0, 17.5) |
| Did not survive | Median (Q1,Q3) | 3.0 (1.0, 6.0) | 3.0 (1.0, 6.0) | 3.0 (1.0, 7.0) | 3.0 (1.0, 6.0) | 3.0 (1.0, 7.0) | 3.5 (1.0, 7.5) |
Of those transported to the ED.
Initial continuous, of those admitted to the hospital.
AED = automatic external defibrillator; Min = minutes; ROSC = return of spontaneous circulation; CCU= cardiac care unit; ICU = intensive care unit; MRS = modified Rankin score; ED = Emergency Department. Q1,Q3 = The boundaries of the interquartile range.
Table 3.
Associated between Bystander AED use and Outcome in several populations
| Unadjusted | Adjusted | |||
|---|---|---|---|---|
| OR* (95% CI) | p-value | OR* (95% CI) | p-value | |
| Public, bystander observed, shockable arrests | ||||
| Association between MRS≤2 and bystander AED shock | 2.74 (2.24, 3.37) | <0.001 | 2.73 (2.17, 3.44) | <0.001 |
| Association between MRS≤3 and bystander AED shock | 2.64 (2.15, 3.25) | <0.001 | 2.59 (2.05, 3.28) | <0.001 |
| Association between survival and bystander AED shock for selected populations | ||||
| Public, bystander observed, shockable arrest | 2.63 (2.13, 3.25) | <0.001 | 2.62 (2.07, 3.31) | <0.001 |
| Public, unobserved, shockable arrests | 1.32 (0.79, 2.22) | 0.28 | 1.30 (0.74, 2.32) | 0.36 |
| Private, bystander observed, shockable arrests | 2.42 (1.70, 3.45) | <0.001 | 2.07 (1.38, 3.09) | <0.001 |
| Private, unobserved, shockable arrests | 1.33 (0.71, 2.46) | 0.37 | 1.25 (0.66, 2.38) | 0.49 |
| Public, observed, shockable arrests, police AED use excluded | ||||
| Association between MRS≤2 and bystander AED shock | 3.05 (2.47, 3.78) | <0.001 | 3.02 (2.37, 3.78) | <0.001 |
| Association between survival and bystander AED shock | 2.89 (2.32, 3.61) | <0.001 | 2.93 (2.29, 3.78) | <0.001 |
Versus EMS shock without bystander AED shock
Adjusted for age, sex, race, bystander CPR, EMS response time, and study site.
OR = odds ratio; CI = confidence interval
The overall survival and functional status of individuals experiencing SOP-OHCA varied with the location of arrest, and the benefit of bystander AED use versus EMS defibrillation was strongest at industrial locations and places of recreation (table 4).
Table 4.
Association between aOR survival and location of shock among shockable observed OHCA
|
|
|||
|---|---|---|---|
| Adjusted | |||
|
| |||
| Number of arrests |
OR* (95% CI) | p-value | |
| Association between survival and bystander AED shock | |||
| Street/highway | 673 | 1.30 (0.56, 3.03) | 0.54 |
| Public building | 194 | 1.76 (0.85, 3.65) | 0.13 |
| Place of recreation | 472 | 2.79 (1.79, 4.35) | <0.001 |
| Industrial place | 177 | 5.57 (2.30, 13.44) | <0.001 |
| Other public | 1127 | 2.26 (1.56, 3.28) | <0.001 |
| Home/residence | 4043 | 1.75 (1.10, 2.79) | 0.02 |
| Residential institution | 192 | 2.26 (0.80, 6.41) | 0.12 |
| Other private | 60 | 5.46 (1.07, 27.96) | 0.04 |
Versus EMS resuscitation without bystander AED shock
Adjusted for age, sex, race, bystander CPR, EMS response time, and study site.
OR = odds ratio; CI = confidence interval
Test for interaction of bystander AED application and location type has a p-value = 0.14 after adjustment for public vs. private location.
The results for favorable functional outcome and survival to discharge were similar when analyses excluded police AED shock from the bystander shock group (aOR=3.02 [95% CI 2.37–3.78] for favorable functional survival, aOR =2.93 [95% CI 2.29–3.78] for survival to discharge).
EMS Response Time and Survival Following Bystander Shock
We observed that the relative benefit of bystander AED shock was a function of EMS response interval as the fit of the multivariable logistic model was improved with the addition of an interaction term between EMS response interval and bystander AED shock status (p=0.013 for interaction term). As the EMS response interval increased, survival with favorable functional outcome declined more rapidly for EMS shocked individuals than for bystander-shocked individuals (figure 2). For example, according to this multivariable logistic model, the adjusted odds ratio for favorable functional outcome associated with bystander AED shock compared to EMS initial shock was 1.86 (95% CI: 1.03, 3.37) when EMS response interval was 4 minutes, 3.49 (95% CI: 1.59, 7.67) when EMS response was 8 minutes, and 6.54 (95%CI: 2.15, 19.91) when EMS response was 12 minutes.
Figure 2. Logistic Regression of EMS Response Interval and Survival.
Logistic regression model of interaction between initial bystander or EMS shock and EMS response interval on functionally favorable survival. Small dotted line indicates 95% confidence interval of the probability of functionally favorable survival at any given time. Larger dashed line is bystander shock. Solid line is EMS shock.
DISCUSSION
In this prospective contemporary observational cohort study we found that bystanders provided the initial shock in nearly one fifth of SOP-OHCA among ROC sites. We observed that survival and functionally-favorable outcomes were significantly higher when a bystander rather than EMS provided the initial shock. Finally, the relative and absolute survival benefit related to bystander AED shock increased as the EMS response interval became longer. These findings confirm the important role of bystander-provided defibrillation among observed public OHCA.
In a prior investigation using the ROC Epistry spanning the years 2005–2007, Weisfeldt and colleagues observed a lower rate of bystander AED shock for all public OHCA compared to the current more contemporary experience in public OHCA (7.8% vs. 14.2% [see table 2, all public arrests]).25 In this previous publication, it was estimated that nearly 500 additional lives were saved each year in the US and Canada by bystander AED use. Given the increased use of bystander AEDs reported here, we can raise this estimate to approximatly 1,700 additional lives saved each year. Furthermore, extrapolation of our data suggests that among the 350,000 OHCA treated in the US each year, ~18,200 are shockable, observed by a bystander and occur in public locations. According to our results if 100% of these individuals was shocked by a bystander ~3459 additional lives would be saved with good neurologic outcome. This is in comparison to the 2,456 additional lives that the National Highway Traffic Safety Administration estimates would be saved with universal seat-belt usage.26 Clearly continued emphasis on increasing the number of individuals shocked by a bystander is a public health imperative. The temporal increase in the rate of bystander AED use across the ROC sites raises the question of which policy and/or programmatic interventions may be most effective to increase bystander AED use in public OHCA. There are very likely more AEDs available for public use. Analysis of FDA reports indicated that the number of AEDs sold in the US increased 10-fold from 1996–2006 from 18,645 in 1996 to 192,400 in 2006,27 and this trend may have continued since. In a study from the Netherlands, the increase in early AED shock was attributed to police-dispatched AEDs.28 In North America, the role of police AED has been variable with some but not all communities achieving earlier defibrillation and better outcomes with such a program.29–31 Only 8.5% of the SOP OHCA in the current study received a bystander AED shock as a consequence of police response. A limitation to this result however, is the fact that we are unable to determine whether the police who applied the AED were dispatched by the 911 call-center versus those officers who happen to be on scene at the time of cardiac arrest. Regardless, police officers made up a limited proportion of AED applications. Furthermore, in sensitivity analysis, when police AED use was excluded the adjusted odds ratio of favorable outcome was not reduced indicating that non-police bystanders may be as effective in AED use as police. A better understanding of the temporal increase has implications for communities striving to improve their public access AED programs.
The outcome relationships in the current study are consistent with prior investigations including those involving functional outcomes reported from Japan and North Carolina.17,18,32,33 Median EMS response in the current study is about 6 minutes, considerably shorter than prior publications and similar to many US and Canadian metropolitan communities.
We did, however, observe an interaction such that the benefit of bystander shock depended on the EMS response interval. Survival with favorable functional outcome among the bystander AED shock group declined more slowly across EMS response intervals compared to the group initially shocked by EMS. As a consequence the greatest relative and absolute survival benefits of bystander AED shock occurred among cases with a longer EMS response interval. Such information may be useful as systems try to allocate placement of a relatively scarce AED resource.34 The odds of favorable neurological outcome did decrease as EMS response was delayed for those patients shocked by a bystander possibly indicating that rapid transfer to definitive care does improve outcome even with early defibrillation.
Interestingly, when the study population was expanded to include shockable observed private arrests there was a significant survival benefit to bystander AED shock. Although a prior study showed no significant benefit to placing AEDs in the homes of individuals at increased risk for cardiac arrest, many of these arrests were unobserved.35 According to our results, the benefit of bystander shock was not apparent when the arrests, either private or public, was unobserved by the bystander. We propose that the benefit of bystander interventions decreases rapidly following cardiac arrest; therefore, in cases with unobserved arrest the overall time from onset of arrest to defibrillation is longer, potentially reducing the relative time benefit of bystander shock. We chose to analyze only public arrests in the primary analysis as this population is unique in that a substantial proportion of these arrests are shockable and observed compared to private arrest where only about 10% of arrests are shockable and observed. It may be of interest to attempt to identify factors in private arrest that increase the likelihood of an arrest being observed, such as wearable monitoring devices, as this would be a subgroup of private arrest where bystander AED use may be of greatest benefit.
There are several limitations to this study. First the current study is unable to capture functional changes that emerge following hospital discharge. A prior study has demonstrated that better functional status at discharge is associated with better long-term prognosis.36. Thus the current findings suggest that bystander AED shock with its excess of mRS 0 and 1 (none and minimal disability) compared to EMS shock should correspond to favorable long-term prognosis. Furthermore, a recent publication reports that among 30-day survivors of OHCA, bystander interventions were associated with lower 1-year rates of nursing home admission and brain injury, indicating that even after discharge bystander inventions only further improve long-term outcomes.19
The study was observational. Although efforts were made in design and analysis to account for potential confounding, we cannot be certain that the survival advantage of bystander AED shock is solely attributable to this action versus other factors. For example, bystander AED shock was more likely to receive bystander CPR so we adjusted for this covariate in the analysis. There may be unmeasured characteristics or care that could not be incorporated into the evaluation.
A strength of the study is its inclusion of multiple EMS systems from across North America. Nonetheless, the systems are involved in clinical trials so may be higher performing, a circumstance that could limit the generalizability. Moreover we are not able to determine if the “quality” of EMS care influenced the potential survival effects of bystander AED use. The current study demonstrates that the majority of patients who receive a bystander AED shock still require EMS resuscitation and that a proportion of these patients ultimately achieves spontaneous circulation and survives intact,37 suggesting that EMS care in these cases is likely important for prognosis. Moreover, we observed that the relative benefit of bystander AED depends on the EMS response interval, suggesting that bystander AED use may have even greater benefit in communities with slower EMS response. A recently reported meta-analysis of public access defibrillation in OHCA concluded that for 21 accepted studies AED application by a lay bystander resulted in 32.0 % (range 14 to 78 %) survival and AED shock resulted in 53.0 % (14 to 78%) survival.38 This compares to this report with 66.5% survival with bystander shock. ROC results are high but not out of range of other reports. We contend that the results presented here, therefore, are both readily generalizable and serve as an example of the benefit provided by rigorously optimizing the pre- and post-hospital systems as many ROC sites have done.
Conclusion
In this multisystem cohort study of SOP-OHCA, nearly 20% received a shock by bystander AED. An initial shock by a bystander AED compared to an initial EMS shock was associated with a greater than 2-fold increase in the odds of favorable functional survival after adjustment for potential confounders. Furthermore, the relative functional outcome advantage of bystander AED use increased as EMS response interval become longer. Collectively, these findings provide support for ongoing emphasis on strategies to increase public access defibrillation.
Supplementary Material
Clinical Perspective.
What is new?
Bystander automated external defibrillation versus Emergency Medical Services defibrillation in shockable, observed, public out of hospital cardiac arrest is associated with an increased odds of survival with full or nearly full functional recovery.
The benefit of bystander automated external defibrillation use increases as the arrival of emergency medical services is delayed.
Overall bystanders shocked a remarkable 19% of shockable observed public out of hospital cardiac arrest from 2011–2015 at 9 sites across the United States and Canada.
What are the clinical Implications?
Efforts to increase the availability and use of Automated External Defibrillators in public locations are likely the most promising immediate way to improve survival from out of hospital cardiac arrest.
The effective allocation of automated external defibrillators and training may benefit from an emphasis on locations where the response time for emergency medical response is longer.
Acknowledgments
The authors would like to thank the numerous Emergency Medical Services Providers and the Resuscitation Outcomes Consortium staff for their commitment and contribution to this project.
Funding
The ROC is supported by a series of cooperative agreements to 10 regional clinical centers and one Data Coordinating Center (5U01 HL077863-University of Washington Data Coordinating Center, HL077865-University of Iowa, HL077866-Medical College of Wisconsin, HL077867University of Washington, HL077871-University of Pittsburgh, HL077872-St. Michael’s Hospital, HL077873-Oregon Health and Science University, HL077881-University of Alabama at Birmingham, HL077885-Ottawa Hospital Research Institute, HL077887-University of Texas SW Medical Ctr/Dallas, HL077908-University of California San Diego) from the National Heart, Lung and Blood Institute in partnership with the National Institute of Neurological Disorders and Stroke, U.S. Army Medical Research & Material Command, The Canadian Institutes of Health Research (CIHR) - Institute of Circulatory and Respiratory Health, Defense Research and Development Canada, the Heart, Stroke Foundation of Canada, and the American Heart Association. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Heart, Lung and Blood Institute or the National Institutes of Health.
J.E.B. was a worksheet author and evidence reviewer for the ILCOR 2015 CPR and ECC guidelines. A.I. has a research grant from and is a volunteer member of clinical advisory board for HeartSine, Inc.
Footnotes
COI Disclosure
The following authors wish to disclose potential conflicts of interest. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.
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