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Ventricular fibrillation (VF) waveform measures reflect myocardial physiologic status. Continuous assessment of VF prognosis using such measures could guide resuscitation, but has not been possible due to CPR artifact in the ECG. A recently-validated VF measure (termed VitalityScore), which estimates the probability (0-100%) of return-of-rhythm (ROR) after shock, can assess VF during CPR, suggesting potential for continuous application during resuscitation.We evaluated VF using VitalityScore to characterize VF prognostic status continuously during resuscitation.We characterized VF using VitalityScore during 60 seconds of CPR and 10 seconds of subsequent pre-shock CPR interruption in patients with out-of-hospital VF arrest. VitalityScore utility was quantified using area under the receiver operating characteristic curve (AUC). VitalityScore trends over time were estimated using mixed-effects models, and associations between trends and ROR were evaluated using logistic models. A sensitivity analysis characterized VF during protracted (100-second) periods of CPR.We evaluated 724 VF episodes among 434 patients. After an initial decline from 0-8 seconds following VF onset, VitalityScore increased slightly during CPR from 8-60 seconds (slope: 0.18%/min). During the first 10 seconds of subsequent pre-shock CPR interruption, VitalityScore declined (slope: -14%/min). VitalityScore predicted ROR throughout CPR with AUCs 0.73-0.75. Individual VitalityScore trends during 8-60 seconds of CPR were marginally associated with subsequent ROR (adjusted odds ratio for interquartile slope change (OR) = 1.10, p = 0.21), and became significant with protracted (100 seconds) CPR duration (OR = 1.28, p = 0.006).VF prognostic status can be continuously evaluated during resuscitation, a development that could translate to patient-specific resuscitation strategies.

Background: Women with congenital long QT syndrome (LQTS) experience increased cardiac event risk after the onset of adolescence, perhaps stemming from the known modulating effects of sex hormones on the cardiac potassium channels. Objective: We hypothesized that the effect of sex hormones on cardiac ion channel function may modify electrocardiographic (ECG) parameters associated with the propensity for ventricular tachyarrhythmias during the menstrual cycle in women with LQTS. Methods: We prospectively enrolled 65 women with congenital LQTS (type 1 LQTS [LQT1], n = 24 [36.9%]; type 2 LQTS [LQT2], n = 20 [30.8%]) and unaffected female relatives (n = 21 [32.3%]). Patients underwent three 7-day ECG recordings during their menstrual cycles. Simultaneous saliva testing of sex hormone levels was conducted on the first day of each 7-day ECG recording cycle. Results: The mean age was 35 ± 8 years, without a significant difference among the groups. In women with LQT2, linear mixed effects models showed significant inverse correlations of the corrected QT interval with progesterone levels (P < .001) and with the progesterone to estradiol ratio (P < .001). Inverse relationships of the R-R interval with estradiol levels (P = .003) and of the T-wave duration with testosterone levels (P = .014) were also observed in women with LQT2. In contrast, no significant associations were observed between ECG parameters and sex hormone levels in women with LQT1 or unaffected relatives. Conclusion: This is the first study to prospectively assess correlations between repolarization dynamics and sex hormone levels during the menstrual cycle in women with congenital LQTS. Our findings show genotype-specific unique corrected QT dynamics during the menstrual cycle that may affect the propensity for ventricular tachyarrhythmia in women with LQTS, particularly women with LQT2.

Background Use of oral contraceptives (OCs) may modulate the clinical course of women with congenital long QT syndrome (LQTS). The safety of OC use by sex hormone content has not been assessed in women with LQTS. Objective We aimed to evaluate the association of OCs with the risk of cardiac events (CEs) in women with LQTS. Methods Beginning in 2010, information on menarche onset, OC use, pregnancy, and menopause were obtained from women enrolled in the Rochester LQTS Registry. Type of OC was categorized as progestin-only, estrogen-only, or combined (estrogen/progestin). Andersen-Gill multivariate modeling was used to evaluate the association of time-dependent OC use with the burden of CE (total number of syncope, aborted cardiac arrest, and LQTS-related sudden cardiac death) from menarche onset through 40 years. Findings were adjusted for genotype, corrected QT duration, and time-dependent β-blocker therapy. Results A total of 1659 women with LQTS followed through March 2021, of whom 370 (22%) were treated with an OC. During a cumulative follow-up of 35,797 years, there were a total of 2027 CE. Multivariate analysis showed that progestin-only OC was associated with a pronounced 2.8-fold (P = .01) increased risk of CEs in women who did not receive β-blocker therapy, while β-blockers were highly protective during progestin-only OC treatment (hazard ratio 0.22; P = .01; P = .006 for β-blocker-by-OC interaction). The risk associated with OC use without concomitant β-blocker treatment was pronounced in women with LQTS type 2. Conclusion Our findings suggest that progestin-only OC should not be administered in women with LQTS without concomitant β-blocker therapy. OCs should be used with caution in women with LQTS type 2.

Importance Emergency research is challenging to do well as it involves time sensitive interventions in unstable patients. There is limited time to obtain informed consent from the patient or their legally authorized representative (LAR). Such research is permitted under exception from informed consent (EFIC) if specific criteria are met, including notification after enrollment. Some question whether the risks of EFIC outweighs its benefits. To date, there is limited empiric information about time to notification (TTN) and rates of withdrawal in such trials. Objective To describe variation in TTN and rates of withdrawal among that patients enrolled in EFIC trials over a twelve-year period. Design We performed post hoc descriptive analyses of data from five trials conducted under EFIC. Setting Emergency medical services and receiving hospitals participating in the Resuscitation Outcomes Consortium in the United States and Canada. Participants Patients with out-of-hospital cardiac arrest or life-threatening traumatic injury. Exposures Notification strategies were specified at each site before initiation of enrollment by a local institutional review board. We monitored TTN within each site centrally throughout each study’s enrollment period. Outcomes TTN was defined as time from randomization to first-reported notification of patient or LAR of enrollment. Withdrawal was defined as patient or LAR opt out of ongoing participation at the time of notification. Results Of 35,442 patients enrolled in five trials, 33,805 had cardiac arrest; and 1636 had traumatic injury. TTN varied overall and by patient outcome. Among those with cardiac arrest, TTN ranged from median (5%ile, 95%ile) of 6 (1,27) days to 28 (2, 53) days across sites. 0.3% of notified patients with cardiac arrest withdrew. Among those with traumatic injury, TTN ranged from 0 (0, 5) days to 36 (5, 68) days across sites. 7.7% of notified patients with traumatic injury withdrew. Conclusions and Relevance There is large variation in TTN in trials conducted under EFIC for emergency research. This may be due to several factors. It may or may not be modifiable. Overall rates of withdrawal are low, which suggests current practices related to EFIC are acceptable to those who have participated in emergency research.

his is the sixth annual summary of the International Liaison Committee on Resuscitation International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science With Treatment Recommendations. This summary addresses the most recently published resuscitation evidence reviewed by International Liaison Committee on Resuscitation Task Force science experts. Topics covered by systematic reviews include cardiopulmonary resuscitation during transport; approach to resuscitation after drowning; passive ventilation; minimizing pauses during cardiopulmonary resuscitation; temperature management after cardiac arrest; use of diagnostic point-of-care ultrasound during cardiac arrest; use of vasopressin and corticosteroids during cardiac arrest; coronary angiography after cardiac arrest; public-access defibrillation devices for children; pediatric early warning systems; maintaining normal temperature immediately after birth; suctioning of amniotic fluid at birth; tactile stimulation for resuscitation immediately after birth; use of continuous positive airway pressure for respiratory distress at term birth; respiratory and heart rate monitoring in the delivery room; supraglottic airway use in neonates; prearrest prediction of in-hospital cardiac arrest mortality; basic life support training for likely rescuers of high-risk populations; effect of resuscitation team training; blended learning for life support training; training and recertification for resuscitation instructors; and recovery position for maintenance of breathing and prevention of cardiac arrest. Members from 6 task forces have assessed, discussed, and debated the quality of the evidence using Grading of Recommendations Assessment, Development, and Evaluation criteria and generated consensus treatment recommendations. Insights into the deliberations of the task forces are provided in the Justification and Evidence-to-Decision Framework Highlights sections, and priority knowledge gaps for future research are listed. This is the sixth annual summary of the International Liaison Committee on Resuscitation International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science With Treatment Recommendations. This summary addresses the most recently published resuscitation evidence reviewed by International Liaison Committee on Resuscitation Task Force science experts. Topics covered by systematic reviews include cardiopulmonary resuscitation during transport; approach to resuscitation after drowning; passive ventilation; minimizing pauses during cardiopulmonary resuscitation; temperature management after cardiac arrest; use of diagnostic point-of-care ultrasound during cardiac arrest; use of vasopressin and corticosteroids during cardiac arrest; coronary angiography after cardiac arrest; public-access defibrillation devices for children; pediatric early warning systems; maintaining normal temperature immediately after birth; suctioning of amniotic fluid at birth; tactile stimulation for resuscitation immediately after birth; use of continuous positive airway pressure for respiratory distress at term birth; respiratory and heart rate monitoring in the delivery room; supraglottic airway use in neonates; prearrest prediction of in-hospital cardiac arrest mortality; basic life support training for likely rescuers of high-risk populations; effect of resuscitation team training; blended learning for life support training; training and recertification for resuscitation instructors; and recovery position for maintenance of breathing and prevention of cardiac arrest. Members from 6 task forces have assessed, discussed, and debated the quality of the evidence using Grading of Recommendations Assessment, Development, and Evaluation criteria and generated consensus treatment recommendations. Insights into the deliberations of the task forces are provided in the Justification and Evidence-to-Decision Framework Highlights sections, and priority knowledge gaps for future research are listed.

BACKGROUND: A large, randomized trial showed no significant difference in survival to discharge between cardiopulmonary resuscitation (CPR) strategies of 30 compressions with pause for 2 ventilations per cycle (30:2) and continuous chest compression with asynchronous ventilations (CCC). Data from the same trial suggested that adherence to the intended CPR strategy was associated with significantly greater survival. We sought to determine the adherence rate with intended strategy and then explore the association of adherence with survival to discharge in the Resuscitation Outcomes Consortium (ROC). METHODS: This secondary analysis of data from the ROC included three interventional trials and a prospective registry. We modified an automated software algorithm that classified care as 30:2 or CCC before intubation based on compression segment length (defined as the elapsed time from start of compressions to subsequent pause of ≥2 seconds), number of pauses per minute ≥2 seconds in length and chest compression fraction. Intended CPR strategy for individual agencies was based on study randomization (during trial phase) or local standard of care (during registry phase). We defined CPR delivered as adherent when its classification matched the intended strategy. We characterized adherence with intended strategy across trial and registry periods. We examined its association with survival to hospital discharge using multivariate logistic regression after adjustment for Utstein and other potential confounders. Effect modification with intended strategy was assessed through a multiplicative interaction term. RESULTS: Included were 26,810 adults with out of hospital cardiac arrest, of which 10,942 had an intended strategy of 30:2 and 15,868 an intended strategy of CCC. The automated algorithm classified 12,276 cases as CCC, 7,037 as 30:2 and left 7,497 as unclassified. Adherence to intended strategy was 54.4%; this differed by intended strategy (58.6% for CCC vs 48.3% for 30:2). Overall adherence was less during the registry phase as compared to during the trial phase(s). The association between adherence and survival was modified by treatment arm (CCC OR: 0.72, 95% CI: 0.64–0.81 vs 30:2 OR: 1.05, 95% CI: 0.90–1.22; interaction p-value

ImportanceEpinephrine improves return of spontaneous circulation after out-of-hospital cardiac arrest (OHCA). These beneficial cardiac effects do not directly translate to better neurologic outcomes, possibly because of epinephrine-induced microvascular effects that produce critical brain ischemia.ObjectiveTo examine whether targeted temperature management (TTM) modifies the adverse association between increasing prehospital epinephrine dose and neurologically favorable survival.Design, Setting, and ParticipantsThis retrospective cohort study assessed 14 612 adults from Seattle and King County, Washington, with nontraumatic OHCA between January 1, 2008, and December 31, 2018, and included those who achieved return of spontaneous circulation and were unconscious at hospital admission. Data analysis was performed from April 2021 to May 2022.ExposuresEpinephrine dose and TTM during prehospital resuscitation.Main Outcomes and MeasuresFavorable neurologic survival (Cerebral Performance Category [CPC] 1 or 2) and survival to hospital discharge.ResultsOf the 14 612 assessed adults, 5253 (median age, 63 years; IQR, 51-74 years; 3460 [65.8%] male) were eligible for the study. The median epinephrine dose was 2.0 mg (IQR, 1.0-3.0 mg); 3052 patients (58.1%) received TTM. In all, 1889 patients (36.0%) survived with CPC 1 to 2, and 2177 (41.4%) survived to discharge. Increasing doses of epinephrine were associated with a decreasing likelihood of CPC 1 to 2 (odds ratio [OR], 0.46; 95% CI 0.42-0.50 for each additional milligram of epinephrine) and survival (OR, 0.47; 95% CI, 0.43-0.51). The dose-dependent epinephrine association was modified by TTM. After adjusting for Utstein covariates, TTM was associated with a relative stepwise improvement in odds of CPC 1 to 2 (interaction OR, 1.36; 95% CI, 1.22-1.51) and survival (interaction OR, 1.37; 95% CI, 1.24-1.51). A significant interaction was also observed when the analysis was stratified according to initial rhythm among shockable OHCA and nonshockable OHCA (shockable interaction OR, 1.20; 95% CI, 1.04-1.39; and nonshockable interaction OR, 1.24, 95% CI, 1.07-1.45).Conclusions and RelevanceThis cohort study found an interaction between TTM and epinephrine dose such that the beneficial association of TTM increased with increasing epinephrine dose, suggesting that TTM may attenuate the adverse effects of higher-dose epinephrine.

Objectives Patients resuscitated from an out-of-hospital circulatory arrest (OHCA) commonly present without an obvious etiology. We assessed the diagnostic capability and safety of early head-to-pelvis computed tomography (CT) imaging in such patients. Methods From November 2015 to February 2018, we enrolled 104 patients resuscitated from OHCA without obvious cause (idiopathic OHCA) to an early sudden-death CT (SDCT) scan protocol within 6 h of hospital arrival. The SDCT protocol included a noncontrast CT head, an electrocardiogram-gated cardiac and thoracic CT angiogram, and a nongated venous-phase abdominopelvic CT angiogram. Patients needing urgent cardiac catheterization or hemodynamically unable to tolerate SDCT were excluded. Cardiac CT analyses were blinded, but other SDCT findings were clinically available. Primary endpoints were the number of OHCA causes identified by SDCT compared to the adjudicated cause and critical diagnoses identified by SDCT, including resuscitation complications. Safety endpoints were acute kidney injury (AKI) and inappropriate treatments based on SDCT findings. Acute coronary syndrome was the presumed etiology if any major coronary artery had a >50% stenosis without another OHCA cause. Results SDCT scans occurred within 1.9 ± 1.0 h of hospital arrival and identified 39% (41/104) of all OHCA causes and 95% (39/41) of causes potentially identifiable by SDCT. Critical findings were identified by SDCT in 98% (43/44) of patients that included potentially life-threatening resuscitation complications of liver or spleen laceration (n = 6); pneumothorax or thoracic organ laceration (n = 8); and mediastinal, pericardial, or vascular hemorrhage (n = 3). SDCT exclusively identified 13 (13%) OHCA causes that would otherwise not be identified without SDCT imaging. No inappropriate treatments resulted from SDCT findings. AKI was common (28%) but only one (1%) patient required new dialysis. Conclusions This observational cohort study suggests that early SDCT scanning is safe, can expedite the diagnosis of potential causes, and can meaningfully change clinical management after idiopathic OHCA.

We investigated the risk of coronavirus disease (COVID-19)­ patients transmitting severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to emergency medical service (EMS) providers, stratified by aerosol-generating procedures (AGP), in King County, Washington, USA, during February 16–July 31, 2020. We conducted a retrospective cohort investigation using a statewide COVID-19 registry and identified 1,115 encounters, 182 with ≥1 AGP. Overall, COVID-19 incidence among EMS personnel was 0.57 infections/10,000 person-days. Incidence per 10,000 person-days did not differ whether or not infection was attributed to a COVID-19 patient encounter (0.28 vs. 0.59; p>0.05). The 1 case attributed to a COVID-19 patient encounter occurred within an at-risk period and involved an AGP. We observed a very low risk for COVID-19 infection attributable to patient encounters among EMS first responders, supporting clinical strategies that maintain established practices for treating patients in emergency conditions.

Background Emergency Medical Services (EMS) are often involved in end-of-life circumstances, yet little is known about how EMS interfaces with advance directives to forego unwanted resuscitation (Do Not Attempt Resuscitation (DNAR)). We evaluated the frequency of these directives involved in out-of-hospital cardiac arrest (OHCA) and how they impact care. Methods We conducted a cohort investigation of adult, EMS-attended OHCA from January 1 to December 31, 2018 in King County, WA. DNAR status was ascertained from dispatch, EMS, and hospital records. Resuscitation was classified according to DNAR status: not initiated, initiated but ceased due to the DNAR, or full efforts. Results Of 3152 EMS-attended OHCA, 314 (9.9%) had a DNAR directive. DNAR was present more often among those for whom EMS did not attempt resuscitation compared to when EMS provided some resuscitation (13.2% [212/1611] vs 6.6% [101/1541], (p Of those receiving resuscitation with a DNAR directive (n = 101), the DNAR was presented on average 6 min following EMS arrival. A total of 82% (n = 83) had EMS efforts ceased as a consequence of the DNAR while 18% (n = 18) received full efforts. Full-efforts compared to ceased-efforts were more likely to have a witnessed arrest (67% vs 36%), present with shockable rhythm (22% vs 6%), achieve spontaneous circulation by time of DNAR presentation (50% vs 4%), and have family contradict the DNAR (33% vs 0%) (p Conclusions Approximately 10% of EMS-attended OHCA involved DNAR. EMS typically fulfilled this end-of-life preference, though wishes were challenged by delayed directive presentation or contradictory family wishes.

Background The Utstein population is defined by non-traumatic, bystander-witnessed out-of-hospital cardiac arrest (OHCA) presenting with ventricular fibrillation (VF). It is used to compare resuscitation performance across emergency medical services (EMS) systems. We hypothesized a system-specific survival correlation between the current Utstein population and other VF populations defined by unwitnessed VF OHCA and VF OHCA after EMS arrival (EMS-witnessed). Expanding performance metrics to this more comprehensive population would make the Utstein definition more representative of the actual community burden and response to VF OHCA. Methods We performed a cohort investigation of all non-traumatic, VF OHCA in the Cardiac Arrest Registry to Enhance Survival from 1/1/2013-12/31/2018 among EMS agencies that treated > = 100 VF OHCA. We evaluated sample size and survival with the addition of the new VF populations. We used Pearson coefficient to assess whether there was a correlation of agency-specific survival outcomes between the current Utstein population and unwitnessed and EMS-witnessed VF OHCA. Results A total of 107 EMS agencies treated 38,836 VF arrests: 22,918 current Utstein, 11,297 unwitnessed VF, and 4621 EMS-witnessed VF OHCA. Overall, survival was 29.8% (11,567/38,836): 33.9% (7774/22,918) among current Utstein, 17.2% (1942/11,297) among unwitnessed VF, and 40.1% (1851/4621) among EMS-witnessed VF. For agency-specific survival outcome, the Pearson correlation was 0.52 between the current Utstein population versus combined unwitnessed and EMS-witnessed groups. For survival with Cerebral Performance Category 1–2, the Pearson correlation was 0.61. Conclusion Expanding the Utstein population to include unwitnessed and EMS-witnessed VF OHCA achieves a simpler, more inclusive case definition that minimizes variability in case determination and increases the number of survivors and eligible population by ∼50%, while still achieving a distinguishing metric of system-specific performance.

To test the diagnostic accuracy of ECG-gated coronary computed tomography angiography (CCTA) to detect coronary artery disease (CAD) among survivors of out-of-hospital circulatory arrest (OHCA).We prospectively studied head-to-pelvis computed tomography (CT) scanning (6 h from hospital arrival) in OHCA survivors. This sub-study tested the primary outcome of CCTA diagnostic accuracy to identify obstructive CAD (≥50% stenosis) compared to clinically-ordered invasive coronary angiography. Patients were not optimized with beta receptor blockade or nitroglycerin. Secondary analyses included CCTA accuracy for CAD in major coronary arteries, obstructive disease at ≥70% stenosis threshold, and where non-evaluable CCTA segments were considered either obstructive or non-obstructive.Of the 104 enrolled OHCA survivors, 28 (27%) received both CT and invasive angiography in this sub study. All CCTA studies were evaluable although 49/346 (14%) individual coronary segments were unevaluable, primarily due to being too small to evaluate (65%). Patient-level diagnostic accuracy for the ≥50% stenosis threshold was high at 0.93 (95% CI 0.77-0.98) with a specificity of 1.0 (95% CI 0.8-1.0), sensitivity of 0.85 (95%CI 0.58-0.96), negative predictive value of 0.88 (95% CI 0.66-0.97) and positive predictive value of 1.0 (0.74-1.0). When non-evaluable segments were considered obstructive, the sensitivity rose to 0.92 (95% CI 0.67-0.99) with lower specificity of 0.27 (95% CI 0.11-0.52).Early CCTA of OHCA survivors has high diagnostic accuracy to detect obstructive coronary artery disease. However, the number of non-diagnostic coronary segments is high suggesting further CCTA refinement is needed, such as the pre-CCTA use of nitroglycerin.NCT03111043 https://clinicaltrials.gov/ct2/show/record/NCT03111043.

Resuscitation requires CPR interruptions every 2 min to assess rhythm and pulse status. We developed a method to predict real-time pulse status in organized rhythm ECG segments with and without CPR artifact.The study cohort included patients who received attempted resuscitation following ventricular fibrillation arrest. Using audio-supplemented defibrillator recordings, we annotated CPR, rhythm, and pulse status at each two-minute rhythm/pulse check. Paired ECG segments with and without CPR were extracted at each rhythm/pulse check. Using one-third of cases for training and two-thirds for validation, we developed three wavelet-based ECG features and combined them with a logistic model to predict pulse status. Predictive performances of each individual ECG feature and the combined logistic model were measured by the area under the receiver operator characteristic curve (AUC) in the validation cases with and without CPR.There were 238 cases and 911 ECG segment pairs. Among 319 organized rhythm segments in the validation set, AUC for pulse prediction during CPR ranged from 0.67 to 0.79 for the individual ECG features. The logistic model was more predictive than any individual feature (AUC 0.84, 95% CI 0.80-0.89, p 0.05 for each comparison) and performed similarly regardless of CPR (p = 0.2 for difference).ECG features extracted by wavelet analysis predicted pulse status with moderate accuracy among organized rhythm segments with and without CPR. Further study is required to understand how real-time pulse prediction during CPR could help direct care while limiting CPR interruption.

Background: Antiarrhythmic drugs have not proven to significantly improve overall survival after out-of-hospital cardiac arrest from shock-refractory ventricular fibrillation/pulseless ventricular tachycardia. How this might be influenced by the route of drug administration is not known. Methods: In this prespecified analysis of a randomized, placebo-controlled clinical trial, we compared the differences in survival to hospital discharge in adults with shock-refractory ventricular fibrillation/pulseless ventricular tachycardia out-of-hospital cardiac arrest who were randomly assigned by emergency medical services personnel to an antiarrhythmic drug versus placebo in the ALPS trial (Resuscitation Outcomes Consortium Amiodarone, Lidocaine or Placebo Study), when stratified by the intravenous versus intraosseous route of administration. Results: Of 3019 randomly assigned patients with a known vascular access site, 2358 received ALPS drugs intravenously and 661 patients by the intraosseous route. Intraosseous and intravenous groups differed in sex, time-to-emergency medical services arrival, and some cardiopulmonary resuscitation characteristics, but were similar in others, including time-to-intravenous/intrasosseous drug receipt. Overall hospital discharge survival was 23%. In comparison with placebo, discharge survival was significantly higher in recipients of intravenous amiodarone (adjusted risk ratio, 1.26 [95% CI, 1.06–1.50]; adjusted absolute survival difference, 5.5% [95% CI, 1.5–9.5]) and intravenous lidocaine (adjusted risk ratio, 1.21 [95% CI, 1.02–1.45]; adjusted absolute survival difference, 4.7% [95% CI, 0.7–8.8]); but not in recipients of intraosseous amiodarone (adjusted risk ratio, 0.94 [95% CI, 0.66–1.32]) or intraosseous lidocaine (adjusted risk ratio, 1.03 [95% CI, 0.74–1.44]). Survival to hospital admission also increased significantly when drugs were given intravenously but not intraosseously, and favored improved neurological outcome at discharge. There were no outcome differences between intravenous and intraosseous placebo, indicating that the access route itself did not demarcate patients with poor prognosis. The study was underpowered to assess intravenous/intraosseous drug interactions, which were not statistically significant. Conclusions: We found no significant effect modification by drug administration route for amiodarone or lidocaine in comparison with placebo during out-of-hospital cardiac arrest. However, point estimates for the effects of both drugs in comparison with placebo were significantly greater for the intravenous than for the intraosseous route across virtually all outcomes and beneficial only for the intravenous route. Given that the study was underpowered to statistically assess interactions, these findings signal the potential importance of the drug administration route during resuscitation that merits further investigation.

Large animal studies are an important step in the translation pathway, but single laboratory experiments do not replicate the variability in patient populations. Our objective was to demonstrate the feasibility of performing a multicenter, preclinical, randomized, double-blinded, placebo-controlled cardiac arrest trial. We evaluated the effect of epinephrine on coronary perfusion pressure (CPP) as previous single laboratory studies have reported mixed results.Forty-five swine from 5 different laboratories (Ann Arbor, MI; Baltimore, MD; Los Angeles, CA; Pittsburgh, PA; Toronto, ON) using a standard treatment protocol. Ventricular fibrillation was induced and left untreated for 6 min before starting continuous cardiopulmonary resuscitation (CPR). After 2 min of CPR, 9 animals from each lab were randomized to 1 of 3 interventions given over 12 minutes: (1) Continuous IV epinephrine infusion (0.00375 mg/kg/min) with placebo IV normal saline (NS) boluses every 4 min, (2) Continuous placebo IV NS infusion with IV epinephrine boluses (0.015 mg/kg) every 4 min or (3) Placebo IV NS for both infusion and boluses. The primary outcome was mean CPP during the 12 mins of drug therapy.There were no significant differences in mean CPP between the three groups: 14.4 ± 6.8 mmHg (epinephrine Infusion), 16.9 ± 5.9 mmHg (epinephrine bolus), and 14.4 ± 5.5 mmHg (placebo) (p = NS). Sensitivity analysis demonstrated inter-laboratory variability in the magnitude of the treatment effect (p = 0.004).This study demonstrated the feasibility of performing a multicenter, preclinical, randomized, double-blinded cardiac arrest trials. Standard dose epinephrine by bolus or continuous infusion did not increase coronary perfusion pressure during CPR when compared to placebo.

Respiratory mechanics, such as tidal volume (VIn this prospective, pilot investigation of patients receiving prehospital advanced airway placement, paramedics applied a device to measure respiratory mechanics. We evaluated tidal volume (VOver 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 VWe 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 V

Introduction: Patients resuscitated from out-of-hospital cardiac arrest (OHCA) frequently have skeletal and visceral injuries identifiable by computed tomography, although the prevalence, types of injury, and potential effects on clinical outcomes are poorly characterized. Methods: We assessed the prevalence of resuscitation-attributable injury in a prospective, observational diagnostic utility study of a head-to-pelvis sudden death computed tomography (SDCT) protocol after successful resuscitation from OHCA. SDCT was performed within six hours of arrival at two academic medical centers. CT data were independently analyzed by two blinded radiologists. Primary outcomes included total injuries and time-critical injuries (such as organ laceration). Exploratory outcomes were clinical associations with injury and survival to discharge. Results: Among 104 patients with OHCA (mean age 56 ± 15 years, 31% female), 59% of events were witnessed and 60% had bystander CPR. Initial rhythms were pulseless electrical activity (38%), ventricular tachycardia/fibrillation (29%), and asystole/unknown (33%). Mean CPR time was 15.4 ± 10.6 minutes; mechanical chest compression systems were used in 27% of cases. The prevalence of injury was high (80%; Table), including 19 patients (18%) with time-critical findings. Compared to patients without injury, patients with injury had numerically lower BMI (24.2 ± 7.7 vs. 26.7 ± 8.0), higher use of mechanical CPR (29% vs. 19%), longer CPR time (16.1 ± 11.0 vs. 12.3 ± 8.5 min), and lower survival to discharge (40% vs. 52%), although none were significant (p= NS for all). Conclusion: In patients resuscitated from OHCA, head-to-pelvis SDCT identified injury in most patients, with nearly one in five with time-critical findings and nearly one half with extensive ribcage injuries that may affect ventilation. These data suggest that SDCT has additional diagnostic utility and treatment implications beyond evaluating causes of OHCA.

Introduction: Transthoracic echocardiography (TTE) is commonly performed early after resuscitation from cardiac arrest (CA). The ability of early TTE to differentiate cardiac from non-cardiac causes of CA or to inform patient outcomes has not been systematically reviewed. Methods: We reviewed MEDLINE, EMBASE, and CENTRAL databases from inception to December 2020 for studies that assessed adult recipients of TTE after resuscitation from non-traumatic CA. Studies were included if TTE was obtained early ( Results: Of 2518 articles screened, 12 (0.5%) studies met inclusion criteria, representing 1570 unique patients. Meta-analysis was not possible due to missing data and study heterogeneity. Five studies were included in diagnosis review and nine in the prognosis review. No studies reported the diagnostic accuracy of TTE for AMI, although in 3 of 5 studies RWMA were associated with AMI in 53-83% of patients. Reduced left ventricular ejection fraction was reported in 8 studies but was not associated with survival (Figure) or neurologic outcomes (n=4). Only high mitral inflow E/e’ ratio (n=1) and decreased right ventricular function (RVD; n=2) were associated with worse survival. Conclusion: This scoping review highlights the limited available data on the utility of early TTE after CA. Assessment of left and right ventricular function and other parameters by TTE is feasible, but further research is necessary to determine their diagnostic and prognostic value after CA.

Current resuscitation protocols require pausing chest compressions during cardiopulmonary resuscitation (CPR) to check for a pulse. However, pausing CPR when a patient is pulseless can worsen patient outcomes. Our objective was to design and evaluate an ECG-based algorithm that predicts pulse presence with or without CPR. We evaluated 383 patients being treated for out-of-hospital cardiac arrest with real-time ECG, impedance and audio recordings. Paired ECG segments having an organized rhythm immediately preceding a pulse check (during CPR) and during the pulse check (without CPR) were extracted. Patients were randomly divided into 60% training and 40% test groups. From training data, we developed an algorithm to predict the clinical pulse presence based on the wavelet transform of the bandpass-filtered ECG. Principal component analysis was used to reduce dimensionality, and we then trained a linear discriminant model using three principal component modes as input features. Overall, 38% (351/912) of checks had a spontaneous pulse. AUCs for predicting pulse presence with and without CPR on test data were 0.84 (95% CI (0.80, 0.88)) and 0.89 (95% CI (0.86, 0.92)), respectively. This ECG-based algorithm demonstrates potential to improve resuscitation by predicting the presence of a spontaneous pulse without pausing CPR with moderate accuracy.

Background Air travel affords an opportunity to evaluate resuscitation performance and outcome in a setting where automated external defibrillators (AEDs) are readily available. Methods and Results The study cohort included people aged ≥18 years with out of hospital cardiac arrest (OHCA) traveling through Seattle‐Tacoma International Airport between January 1, 2004 and December 31, 2019 treated by emergency medical services (EMS). The primary outcomes were pre‐EMS therapies (cardiopulmonary resuscitation, application of AED), return of spontaneous circulation, and survival to hospital discharge. Over the 16‐year study period, there were 143 OHCA occurring before EMS arrival, 34 (24%) on‐plane and 109 (76%) off‐plane. Cardiac etiology (81%) was the most common mechanism of arrest. The majority of arrests were bystander‐witnessed and presented with a shockable rhythm; these characteristics were more common in off‐plane OHCA compared with on‐plane (witnessed: 89% versus 74% and shockable: 72% versus 50%). Pre‐EMS therapies including cardiopulmonary resuscitation and AED application were common regardless of arrest location. Compared with on‐plane OHCA, off‐plane OHCA was associated with greater rates of return of spontaneous circulation (68% versus 44%) and 3‐fold higher rate of survival to hospital discharge (44% versus 15%). All survivors of on‐plane OHCA had AED application with defibrillation before EMS arrival. Conclusions When applied to air travel volumes, we estimate 350 air travel‐associated OHCA occur in the United States and 2000 OHCA worldwide each year, nearly a quarter of which happen on‐plane. These events are survivable when early arrest interventions including rapid arrest recognition, AED application, and CPR are deployed.

Background We aimed to provide personalized risk estimates for cardiac events (CEs) and life‐threatening events in women with either type 1 or type 2 long QT. Methods and Results The prognostic model was derived from the Rochester Long QT Syndrome Registry, comprising 767 women with type 1 long QT (n=404) and type 2 long QT (n=363) from age 15 through 60 years. The risk prediction model included the following variables: genotype/mutation location, QTc‐specific thresholds, history of syncope, and β‐blocker therapy. A model was developed with the end point of CEs (syncope, aborted cardiac arrest, or long QT syndrome–related sudden cardiac death), and was applied with the end point of life‐threatening events (aborted cardiac arrest, sudden cardiac death, or appropriate defibrillator shocks). External validation was performed with data from the Mayo Clinic Genetic Heart Rhythm Clinic (N=467; type 1 long QT [n=286] and type 2 long QT [n=181]). The cumulative follow‐up duration among the 767 enrolled women was 22 243 patient‐years, during which 323 patients (42%) experienced ≥1 CE. Based on genotype‐phenotype data, we identified 3 risk groups with 10‐year projected rates of CEs ranging from 15%, 29%, to 51%. The corresponding 10‐year projected rates of life‐threatening events were 2%, 5%, and 14%. C statistics for the prediction model for the 2 respective end points were 0.68 (95% CI 0.65–0.71) and 0.71 (95% CI 0.66–0.76). Corresponding C statistics for the model in the external validation Mayo Clinic cohort were 0.65 (95% CI 0.60–0.70) and 0.77 (95% CI 0.70–0.84). Conclusions This is the first risk prediction model that provides absolute risk estimates for CEs and life‐threatening events in women with type 1 or type 2 long QT based on personalized genotype‐phenotype data. The projected risk estimates can be used to guide female‐specific management in long QT syndrome.

Background: Anoxic brain injury is a common mode of death following out-of-hospital cardiac arrest (OHCA). We assessed the course of regional cerebral oxygen saturation (rSO2) at the outset and during first responder resuscitation to understand its relationship with return of spontaneous circulation (ROSC) and functional survival. Methods: We undertook a prospective observational investigation of adult OHCA patients treated by a first-responder EMS agency in King County, WA. Cerebral oximetry was performed using the SenSmart® Model X-100 Universal Oximetry System (Nonin Medical, Inc). We determined cerebral oximetry rSO2 overall and stratified according to ROSC and favorable survival status defined by Cerebral Performance Category (CPC) of 1-2. Results: Among the 59 OHCA cases enrolled, 47% (n = 28) achieved ROSC and 14% (n = 8) survived with CPC 1-2. On average, initial rSO2 cerebral oximetry was 41% and was not different at the outset according to return of spontaneous circulation (ROSC) or survival status. Within 5 minutes of first responder resuscitation, those who would subsequently achieve ROSC had a higher rSO2 than those who would not achieve ROSC (51% vs. 43%, p = 0.03). Among patients who achieved ROSC, those who would survive with CPC 1-2 had a higher rSO2 cerebral oximetry following ROSC than nonsurvivors (74% vs. 60%, p = 0.04 at 5 minutes post ROSC), a difference that was not evident in the minutes prior to ROSC (55% vs. 51% at 3 minutes prior to ROSC, p = 0.5). Conclusion: In this observational study, where first responders applied cerebral oximetry, higher rSO2 during the course of care predicted ROSC among all patients and predicted favorable survival among those who achieved ROSC. Future investigation should evaluate whether and how treatments might modify rSO2 and in turn may influence prognosis.

Advances in resuscitation following out-of-hospital cardiac arrest (OHCA) provide an opportunity to improve public health. This review reflects on past developments, present status, and future possibilities using the science-education-implementation framework of the Utstein Formula and the clinical framework of the links in the chain of survival. With the discovery of CPR and defibrillation in the mid 20th century, resuscitation developed a scientific construct for progress. Systems of emergency community response provided operational efficiency to treat OHCA. Contemporary resuscitation involves integrated interventions in the chain of survival: early recognition, early CPR, early defibrillation, expert and timely advanced life support and hospital care, and multidimensional rehabilitation. Implementation of scientific advances is especially challenging given the unexpected nature of OHCA, the need for time-sensitive interventions, and the substantial collective of stakeholders involved in the chain of survival. Systematic measurement provides the foundation to evaluate performance and guide implementation initiatives. For many systems, telecommunicator CPR and high-performance CPR by emergency professionals are accessible, near-term programs to improve OHCA outcome. Smart technologies that activate, coordinate, and/or coach community "volunteers" to accelerate early CPR and defibrillation have conceptual promise, though robust implementation has been achieved by only a handful of systems. Longer-term strategies may leverage technology to develop a high-fidelity "life-detector" or engineer and disseminate a specialized consumer defibrillator designed to bridge care until arrival of professional response.

Thyroid hormones have long been known to have a range of effects on the cardiovascular system. However, significant knowledge gaps exist concerning the precise molecular and biochemical mechanisms governing these effects and the optimal strategies for management of abnormalities in thyroid function in patients with and without preexisting cardiovascular disease. In September 2017, the National Heart, Lung, and Blood Institute convened a Working Group with the goal of developing priorities for future scientific research relating thyroid dysfunction to the progression of cardiovascular disease. The Working Group reviewed and discussed the roles of normal thyroid physiology, the consequences of thyroid dysfunction, and the effects of therapy in 3 cardiovascular areas: cardiac electrophysiology and arrhythmias, the vasculature and atherosclerosis, and the myocardium and heart failure. This report describes the current state of the field, outlines barriers and challenges to progress, and proposes research opportunities to advance the field, including strategies for leveraging novel approaches using omics and big data. The Working Group recommended research in 3 broad areas: (1) investigation into the fundamental biology relating thyroid dysfunction to the development of cardiovascular disease and into the identification of novel biomarkers of thyroid hormone action in cardiovascular tissues; (2) studies that define subgroups of patients with thyroid dysfunction amenable to specific preventive strategies and interventional therapies related to cardiovascular disease; and (3) clinical trials focused on improvement in cardiovascular performance and cardiovascular outcomes through treatment with thyroid hormone or thyromimetic drugs.

Background\ud \ud Dispatcher-assisted cardiopulmonary resuscitation (DA-CPR) has been reported in individual studies to significantly increase the rate of bystander CPR and survival from cardiac arrest.\ud \ud Methods \ud \ud We undertook a systematic review and meta-analysis to evaluate the impact of DA-CPR programs on key clinical outcomes following out-of-hospital cardiac arrest. We searched the PubMED, EMBASE, CINAHL, ERIC and Cochrane Central Register of Controlled Trials databases from inception until July 2018. Eligible studies compared systems with and without dispatcher-assisted CPR programs. Included studies were divided into three groups: comparison of outcomes in systems providing DA-CPR; comparison of cases where DA-CPR was provided to cases where bystander CPR was ongoing, and DA-CPR was not provided; and comparison of cases where DA-CPR was provided to cases where no bystander CPR was provided (patient level comparisons). The GRADE system was used to assess certainty of evidence at an outcome level. We used random-effects models to produce summary effect sizes across all outcomes.\ud \ud Results \ud \ud Of 5,531 citations screened, 33 studies were eligible for inclusion. All included studies were observational. Evidence certainty across all outcomes was assessed as low or very low. In system-level and patient-level comparisons, the provision of DA-CPR compared with no DA-CPR was consistently associated with improved outcome across all analyses. Comparison of DA-CPR to bystander CPR produced conflicting results. Findings were consistent across sensitivity analyses and the pediatric sub-group.\ud \ud Conclusion \ud \ud These results support the recommendation that dispatchers provide CPR instructions to callers for adults and children with suspected OHCA.\ud

An increasing proportion of patients with OHCA present with non-shockable rhythms, among whom the benefit from AED application is not known.We performed a retrospective analysis of adults with non-traumatic, public, bystander-witnessed, non-shockable OHCA occurring between 2005-2015 at 9 locations participating in the Resuscitation Outcomes Consortium. Non-shockable arrest was defined as when no shock was administered by a bystander applied AED and confirmed by the initial rhythm on EMS arrival. Outcomes were compared between patients with non-shockable OHCA in whom a bystander AED was or was not applied.Among 2809 patients with non-shockable public, witnessed OHCA, 8.4% had an AED applied. CPR was more often performed in the AED-applied group (99% vs. 51% of patients, p 0.001). Among patients in whom an AED was not applied, 39.8% had any pre-hospital ROSC, 29.6% had a pulse at ED arrival and 11.1% survived to hospital discharge compared to 44.1%, 29.6% and 9.7%, respectively with AED application. After adjustment for the Utstein variables excluding bystander CPR, the OR for survival to hospital discharge for AED application was 0.90 (95% CI:0.57-1.42); when adjusted for the higher frequency of CPR in the AED group the OR was 0.92 (95% CI:0.57-1.47).The application of an AED in non-shockable public witnessed OHCA was associated with a higher frequency of bystander CPR. The probabilities of pre-hospital ROSC, pulse at ED arrival, and survival to hospital discharge were not altered by the application of an AED.

Aim To review data for non-invasive imaging in the diagnosis of non-traumatic out-of-hospital cardiac arrest (OHCA). Data sources We searched MEDLINE, EMBASE, Cochrane library, and clinicaltrials.gov databases from inception to January 2017 for studies utilizing non-invasive imaging to identify potential causes of OHCA [computed tomography (CT), ultrasound including echocardiography, and magnetic resonance (MRI)]. Study selection Inclusion criteria were the following: (1) randomized control trials, cohort studies or observational studies; (2) contained a population ≥18 years old with non-traumatic OHCA who underwent diagnostic imaging with CT, MRI, echocardiography, or abdominal ultrasound; (3) imaging was obtained for diagnostic purposes; (4) patients were alive or were undergoing cardiopulmonary resuscitation at the time of imaging; (5) contained potential causes of OHCA. Endpoints studied were the number of potential OHCA causes identified, diagnostic accuracy measures (sensitivity, specificity, positive and negative predictive values), and diagnostic utility (number of imaging findings with reported changes in clinical management). Results Of the total 5722 studies identified, 17 (0.3%) met inclusion criteria. The majority of studies assessed the utility of CT in OHCA (n = 10), and potential causes of OHCA were found in 8–54% of patients following head, abdominal and/or chest CT. Only 1/17 (6%) studies reported diagnostic accuracy measures, and 9/17 (53%) studies included a time to imaging criteria within 24 h. Conclusion Although non-invasive imaging is commonly performed in patients after OHCA, its diagnostic utility remains poorly characterized. Prospective studies are needed for appropriate imaging selection and their potential impact on treatment and outcome.

Out-of-hospital cardiac arrest (OHCA) causes brain injury. Functional status of survivors at hospital discharge is a core resuscitation measure, frequently using the Cerebral Performance Category (CPC) or modified Rankin Scale (mRS). Which scale better predicts long-term survival following OHCA is not known.We evaluated long-term survival after hospital discharge in a retrospective cohort of persons resuscitated from OHCA in King County, WA from 2007 to 2015. Patients were independently assessed at discharge using both scales, leveraging the regional quality improvement registry, which records the 5-level CPC, and concurrent research studies involving the Resuscitation Outcomes Consortium, which used the 7-level mRS, taken from information in the hospital record. The risk of mortality associated with CPC and mRS categories was estimated using Kaplan-Meier survival analysis and Cox proportional hazards regression.Among 878 eligible patients discharged alive, there were 358 deaths during 9118.5 person-years of follow-up. Overall 1, 5 and 10-year survival was 84.4%, 68.5%, and 53.7% and varied according to CPC and mRS (p0.01 per Kaplan-Meier). Compared to CPC-1, hazard ratio (HR) increased incrementally for CPC-2 = 1.33 (1.03-1.73), CPC-3 = 1.90 (1.37-2.65), and CPC-4 = 8.25 (5.63-12.10). Compared to mRS = 0, HR for mRS-1 = 1.02 (0.66-1.58), mRS-2 = 1.52 (1.00-2.32), mRS-3 = 1.41 (0.92-2.14), mRS-4 = 2.00 (1.37-2.97), and mRS-5 = 4.90 (3.23-7.44).In OHCA survivors, CPC and mRS scales both predicted long-term survival. However mRS 0-1 and 2-3 groups did not have distinct prognoses, suggesting that a consolidated mRS score may simplify capture of relevant prognostic information for survival predictions.

Importance Therapeutic delivery of sodium nitrite during resuscitation improved survival in animal models of cardiac arrest, but efficacy has not been evaluated in clinical trials in humans. Objective To determine whether parenteral administration of sodium nitrite given by paramedics during resuscitation for out-of-hospital cardiac arrest improved survival to hospital admission. Design, setting, and participants Double-blind, placebo-controlled, phase 2 randomized clinical trial including 1502 adults in King County, Washington, with out-of-hospital cardiac arrest from ventricular fibrillation or nonventricular fibrillation. Patients underwent resuscitation by paramedics and were enrolled between February 8, 2018, and August 19, 2019; follow-up and data abstraction were completed by December 31, 2019. Interventions Eligible patients with out-of-hospital cardiac arrest were randomized (1:1:1) to receive 45 mg of sodium nitrite (n = 500), 60 mg of sodium nitrite (n = 498), or placebo (n = 499), which was given via bolus injection by the paramedics as soon as possible during active resuscitation. Main outcomes and measures The primary outcome was survival to hospital admission and was evaluated with 1-sided hypothesis testing. The secondary outcomes included out-of-hospital variables (rate of return of spontaneous circulation, rate of rearrest, and use of norepinephrine to support blood pressure) and in-hospital variables (survival to hospital discharge; neurological outcomes at hospital discharge; cumulative survival to 24 hours, 48 hours, and 72 hours; and number of days in the intensive care unit). Results Among 1502 patients with out-of-hospital cardiac arrest who were randomized (mean age, 64 years [SD, 17 years]; 34% were women), 99% completed the trial. Overall, 205 patients (41%) in the 45 mg of sodium nitrite group and 212 patients (43%) in the 60 mg of sodium nitrite group compared with 218 patients (44%) in the placebo group survived to hospital admission; the mean difference for the 45-mg dose vs placebo was -2.9% (1-sided 95% CI, -8.0% to ∞; P = .82) and the mean difference for the 60-mg dose vs placebo was -1.3% (1-sided 95% CI, -6.5% to ∞; P = .66). None of the 7 prespecified secondary outcomes were significantly different, including survival to hospital discharge for 66 patients (13.2%) in the 45 mg of sodium nitrite group and 72 patients (14.5%) in the 60 mg of sodium nitrite group compared with 74 patients (14.9%) in the placebo group; the mean difference for the 45-mg dose vs placebo was -1.7% (2-sided 95% CI, -6.0% to 2.6%; P = .44) and the mean difference for the 60-mg dose vs placebo was -0.4% (2-sided 95% CI, -4.9% to 4.0%; P = .85). Conclusions and relevance Among patients with out-of-hospital cardiac arrest, administration of sodium nitrite, compared with placebo, did not significantly improve survival to hospital admission. These findings do not support the use of sodium nitrite during resuscitation from out-of-hospital cardiac arrest. Trial registration ClinicalTrials.gov Identifier: NCT03452917.

Key Points Question Can a machine learning model help medical dispatchers improve recognition of out-of-hospital cardiac arrest? Findings In this randomized clinical trial of 5242 emergency calls, a machine learning model listening to calls could alert the medical dispatchers in cases of suspected cardiac arrest. There was no significant improvement in recognition of out-of-hospital cardiac arrest during calls on which the model alerted dispatchers vs those on which it did not; however, the machine learning model had higher sensitivity that dispatchers alone. Meaning These findings suggest that while a machine learning model recognized a significantly greater number of out-of-hospital cardiac arrests than dispatchers alone, this did not translate into improved cardiac arrest recognition by dispatchers., This randomized clinical trial examines how a machine learning model trained to identify out-of-hospital cardiac arrest and alert dispatchers during emergency calls affected the recognition of and response to out-of-hospital cardiac arrests., Importance Emergency medical dispatchers fail to identify approximately 25% of cases of out-of-hospital cardiac arrest (OHCA), resulting in lost opportunities to save lives by initiating cardiopulmonary resuscitation. Objective To examine how a machine learning model trained to identify OHCA and alert dispatchers during emergency calls affected OHCA recognition and response. Design, Setting, and Participants This double-masked, 2-group, randomized clinical trial analyzed all calls to emergency number 112 (equivalent to 911) in Denmark. Calls were processed by a machine learning model using speech recognition software. The machine learning model assessed ongoing calls, and calls in which the model identified OHCA were randomized. The trial was performed at Copenhagen Emergency Medical Services, Denmark, between September 1, 2018, and December 31, 2019. Intervention Dispatchers in the intervention group were alerted when the machine learning model identified out-of-hospital cardiac arrest, and those in the control group followed normal protocols without alert. Main Outcomes and Measures The primary end point was the rate of dispatcher recognition of subsequently confirmed OHCA. Results A total of 169 049 emergency calls were examined, of which the machine learning model identified 5242 as suspected OHCA. Calls were randomized to control (2661 [50.8%]) or intervention (2581 [49.2%]) groups. Of these, 336 (12.6%) and 318 (12.3%), respectively, had confirmed OHCA. The mean (SD) age among of these 654 patients was 70 (16.1) years, and 419 of 627 patients (67.8%) with known gender were men. Dispatchers in the intervention group recognized 296 confirmed OHCA cases (93.1%) with machine learning assistance compared with 304 confirmed OHCA cases (90.5%) using standard protocols without machine learning assistance (P = .15). Machine learning alerts alone had a significantly higher sensitivity than dispatchers without alerts for confirmed OHCA (85.0% vs 77.5%; P