Delayed versus immediate defibrillation for out-of-hospital cardiac arrest due to ventricular fibrillation: A systematic review and meta-analysis of randomised controlled trials

The impact of time to defibrillation on return of spontaneous circulation in out-of-hospital cardiac arrest patients with recurrent shockable rhythms

OBJECTIVE

Optimal timing for subsequent defibrillation attempts for Out-of-hospital cardiac arrest (OHCA) patients with recurrent VF/pVT is uncertain. We investigated the relationship between VF/pVT duration and return of spontaneous circulation (ROSC) in OHCA patients with recurrent shockable rhythms.

METHODS

We analyzed data from the Salt Lake City Fire Department (SLCFD) spanning from 2012 to 2023. The implementation of rhythm-filtering technology since 2011 enabled real-time rhythm interpretation during CPR, with local protocols allowing early defibrillation for recurrent/refractory VF/pVT cases. We included patients experiencing four or five episodes of VF and pVT rhythms and employed generalized estimating equation (GEE) regression analysis to examine the association between VF/pVT durations preceding recurrent defibrillation and return of spontaneous circulation (ROSC).

RESULTS

Analysis of 622 appropriate shocks showed that patients achieving ROSC had significantly shorter median VF/pVT duration than those who did not achieve ROSC (0.83 minutes vs. 1.2 minutes, p = 0.004). Adjusted analysis of those with 4 VF/pVT episodes (N = 142) revealed that longer VF/pVT durations were associated with lower odds of achieving ROSC (odds ratio: 0.81, 95% CI: 0.72-0.93, p = 0.005). Every one-minute delay in intra-arrest defibrillation is predicted to decrease the likelihood of achieving ROSC by 19%.

CONCLUSION

Every one-minute increase in intra-arrest VF/pVT duration was associated with a statistically significant 19% decrease in the chance of achieving ROSC. This highlights the importance of reducing time to shock in managing recurrent VF/pVT. The findings suggest reevaluating the current recommendations of two minutes intervals for rhythm check and shock delivery.

Predefibrillation end-tidal CO2 and defibrillation success in out-of-hospital cardiac arrest: an observational cohort study

BACKGROUND

Predefibrillation end-tidal CO₂ (ETCO₂) may predict defibrillation success and could guide defibrillation timing in ventricular fibrillation (VF) cardiac arrest. This relationship has only been studied using advanced airways. Our aim was to evaluate this relationship using both basic (bag-valve-mask (BVM)) and advanced airways (supraglottic airways and endotracheal tubes).

METHODS

Prehospital patient records and defibrillator files were abstracted for patients with out-of-hospital cardiac arrest in Ontario, Canada, with initial VF cardiac rhythms between 1 January 2018, and 31 December 2019. Analyses assessed the relationship between each predefibrillation ETCO₂ reading and defibrillation outcomes at the subsequent 2 min pulse check (ie, VF, asystole, pulseless electrical activity (PEA) or return of spontaneous circulation (ROSC)), accounting for airway types used during resuscitation. Multivariable logistic regression evaluated the association between the first documented predefibrillation ETCO₂ and postshock VF termination or ROSC.

RESULTS

Of 269 cases abstracted, 153 had predefibrillation ETCO₂ measurements and were included in the study. Among these cases, 904 shocks were delivered and 44.4% (n=401) had predefibrillation ETCO₂ measured. The first ETCO₂ reading was more often from BVM (n=134) than advanced airways (n=19). ETCO₂ readings were lower when measured through BVM versus advanced airways (30.5 mm Hg (4.06 kPa) (±14.4 mm Hg (1.92 kPa)) vs 42.1 mm Hg (5.61 kPa) (±22.5 mm Hg (3.00 kPa)), _adjANOVA p<0.01). Of all shocks with ETCO₂ reading (n=401), no difference in preshock ETCO₂ was found for subsequent shocks that resulted in persistent VF (32.2 mm Hg (4.29 kPa) (±15.8 mm Hg (2.11 kPa))), PEA (32.8 mm Hg (4.37 kPa) (±17.1 mm Hg (2.30 kPa))), asystole (32.4 mm Hg (4.32 kPa) (±20.6 mm Hg (2.75 kPa))) or ROSC (32.5 mm Hg (4.33 kPa) (±15.3 mm Hg (2.04 kPa))), analysis of variance p=0.99. In the multivariate analysis using the initial predefibrillation ETCO₂, there was no association with VF termination on the subsequent shock (adjusted OR (_adjOR) 0.99, 95% CI 0.97 to 1.02, p=0.57) or ROSC (_adjOR 1.00, 95% CI 0.97 to 1.03, p=0.94) when evaluated as a continuous or categorical variable.

CONCLUSION

Predefibrillation ETCO₂ measurement is not associated with VF termination or ROSC when basic and advanced airways are included in the analysis. The role of predefibrillation ETCO₂ requires careful consideration of the type of airway used during resuscitation.

Predictive Utility of End-Tidal Carbon Dioxide on Defibrillation Success in Out-of-Hospital Cardiac Arrest

INTRODUCTION

The likelihood of survival from ventricular fibrillation (VF) declines 7%-10% per minute until successful defibrillation. When VF duration is prolonged, immediate defibrillation of the ischemic myocardium is less likely to result in ROSC, and repeated unsuccessful defibrillations are associated with post-resuscitation myocardial dysfunction. Thus, the timing of defibrillation should be based upon the probability of shock success-a function of VF duration. Unfortunately, VF duration is often unknown in out-of-hospital cardiac arrest (OHCA) and a better predictor of shock success is needed.

OBJECTIVE

To assess the ability of end-tidal carbon dioxide (EtCO₂) to predict successful defibrillation in OHCA.

METHODS

This retrospective study included adult patients among four EMS systems who experienced non-traumatic OHCA from August, 2015-July, 2017 and received one or more defibrillations. First and succedent shocks were analyzed separately. First shocks represented EMS-attempted defibrillation of patients who had not received a prior AED shock, whereas succedent shocks included all shocks subsequent to the first. Logistic regression provided odds ratios (OR) for first shocks resulting in ROSC, while a generalized estimating equation was used to analyze succedent shocks.

RESULTS

Among 324 patients, 869 shocks were delivered by EMS (153 first and 716 succedent shocks). Layperson CPR was performed in 48.1% of cases and 21.6% received an AED shock before EMS arrival. First defibrillation ROSC was more likely with layperson CPR (OR = 4.41;p = 0.01) and increasing EtCO₂ (OR = 1.03/mmHg;p = 0.01). No other variables were statistically significant. Notably, only one patient with EtCO₂ < 20 mmHg was successfully defibrillated on the first shock. The probability of ROSC was higher with increasing values of EtCO₂ when layperson CPR was provided, yet remained relatively unchanged across all values of EtCO₂ ≥ 20 mmHg without layperson CPR. The optimal threshold first shock EtCO₂ was 27 and 32 mmHg for those with/without layperson CPR, respectively. EtCO₂ was not a predictor of ROSC for succedent shocks.

CONCLUSIONS

An optimal defibrillation threshold EtCO2 of 27 and 32 mmHg was observed for patients with and without layperson CPR, respectively. Further studies are warranted to verify these results and to evaluate the clinical effect of delaying defibrillation in favor of chest compressions until these values are attained.

Selective distant electrostimulation by synchronized bipolar nanosecond pulses

A unique aspect of electrostimulation (ES) with nanosecond electric pulses (nsEP) is the inhibition of effects when the polarity is reversed. This bipolar cancellation feature makes bipolar nsEP less efficient at biostimulation than unipolar nsEP. We propose to minimize stimulation near pulse-delivering electrodes by applying bipolar nsEP, whereas the superposition of two phase-shifted bipolar nsEP from two independent sources yields a biologically-effective unipolar pulse remotely. This is accomplished by electrical compensation of all nsEP phases except the first one, resulting in the restoration of stimulation efficiency due to cancellation of bipolar cancellation (CANCAN-ES). We experimentally proved the CANCAN-ES paradigm by measuring YO-PRO-1 dye uptake in CHO-K1 cells which were permeabilized by multiphasic nsEP (600 ns per phase) from two generators; these nsEP were synchronized either to overlap into a unipolar pulse remotely from electrodes (CANCAN), or not to overlap (control). Enhancement of YO-PRO-1 entry due to CANCAN was observed in all sets of experiments and reached ~3-fold in the center of the gap between electrodes, exactly where the unipolar pulse was formed, and equaled the degree of bipolar cancellation. CANCAN-ES is promising for non-invasive deep tissue stimulation, either alone or combined with other remote stimulation techniques to improve targeting.

Excitation and injury of adult ventricular cardiomyocytes by nano- to millisecond electric shocks

Intense electric shocks of nanosecond (ns) duration can become a new modality for more efficient but safer defibrillation. We extended strength-duration curves for excitation of cardiomyocytes down to 200 ns, and compared electroporative damage by proportionally more intense shocks of different duration. Enzymatically isolated murine, rabbit, and swine adult ventricular cardiomyocytes (VCM) were loaded with a Ca²⁺ indicator Fluo-4 or Fluo-5N and subjected to shocks of increasing amplitude until a Ca²⁺ transient was optically detected. Then, the voltage was increased 5-fold, and the electric cell injury was quantified by the uptake of a membrane permeability marker dye, propidium iodide. We established that: (1) Stimuli down to 200-ns duration can elicit Ca²⁺ transients, although repeated ns shocks often evoke abnormal responses, (2) Stimulation thresholds expectedly increase as the shock duration decreases, similarly for VCMs from different species, (3) Stimulation threshold energy is minimal for the shortest shocks, (4) VCM orientation with respect to the electric field does not affect the threshold for ns shocks, and (5) The shortest shocks cause the least electroporation injury. These findings support further exploration of ns defibrillation, although abnormal response patterns to repetitive ns stimuli are of a concern and require mechanistic analysis.

Part 3: Adult Basic Life Support and Automated External Defibrillation: 2015 International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science With Treatment Recommendations

This review comprises the most extensive literature search and evidence evaluation to date on the most important international BLS interventions, diagnostics, and prognostic factors for cardiac arrest victims. It reemphasizes that the critical lifesaving steps of BLS are (1) prevention, (2) immediate recognition and activation of the emergency response system, (3) early high-quality CPR, and (4) rapid defibrillation for shockable rhythms. Highlights in prevention indicate the rational and judicious deployment of search-and-rescue operations in drowning victims and the importance of education on opioid-associated emergencies. Other 2015 highlights in recognition and activation include the critical role of dispatcher recognition and dispatch-assisted chest compressions, which has been demonstrated in multiple international jurisdictions with consistent improvements in cardiac arrest survival. Similar to the 2010 ILCOR BLS treatment recommendations, the importance of high quality was reemphasized across all measures of CPR quality: rate, depth, recoil, and minimal chest compression pauses, with a universal understanding that we all should be providing chest compressions to all victims of cardiac arrest. This review continued to focus on the interface of BLS sequencing and ensuring high-quality CPR with other important BLS interventions, such as ventilation and defibrillation. In addition, this consensus statement highlights the importance of EMS systems, which employ bundles of care focusing on providing high-quality chest compressions while extricating the patient from the scene to the next level of care. Highlights in defibrillation indicate the global importance of increasing the number of sites with public-access defibrillation programs. Whereas the 2010 ILCOR Consensus on Science provided important direction for the “what” in resuscitation (ie, what to do), the 2015 consensus has begun with the GRADE methodology to provide direction for the quality of resuscitation. We hope that resuscitation councils and other stakeholders will be able to translate this body of knowledge of international consensus statements to build their own effective resuscitation guidelines.

Standards for Resuscitation After Cardiac Surgery

Of the 250 000 patients who undergo major cardiac operations in the United States annually, 0.7% to 2.9% will experience a postoperative cardiac arrest. Although Advanced Cardiac Life Support (ACLS) is the standard approach to management of cardiac arrest in the United States, it has significant limitations in these patients. The European Resuscitation Council (ERC) has endorsed a new guideline specific to resuscitation after cardiac surgery that advises important, evidence-based deviations from ACLS and is under consideration in the United States. The ACLS and ERC recommendations for resuscitation of these patients are contrasted on the basis of the essential components of care. Key to this approach is the rapid elimination of reversible causes of arrest, followed by either defibrillation or pacing (as appropriate) before external cardiac compressions that can damage the sternotomy, cautious use of epinephrine owing to potential rebound hypertension, and prompt resternotomy (within 5 minutes) to promote optimal cerebral perfusion with internal massage, if prior interventions are unsuccessful. These techniques are relatively simple, reproducible, and easily mastered in Cardiac Surgical Unit–Advanced Life Support courses. Resuscitation of patients after heart surgery presents a unique opportunity to achieve high survival rates with key modifications to ACLS that warrant adoption in the United States.

Cardiopulmonary resuscitation (CPR) plus delayed defibrillation versus immediate defibrillation for out-of-hospital cardiac arrest

BACKGROUND

Sudden cardiac arrest (SCA) is a common health problem associated with high levels of mortality. Cardiac arrest is caused by three groups of dysrhythmias: ventricular fibrillation (VF) or pulseless ventricular tachycardia (VT), pulseless electric activity (PEA) and asystole. The most common dysrhythmia found in out-of-hospital cardiac arrest (OHCA) is VF. During VF or VT, cardiopulmonary resuscitation (CPR) provides perfusion and oxygenation to the tissues, whilst defibrillation restores a viable cardiac rhythm. Early successful defibrillation is known to improve outcomes in VF/VT. However, it has been hypothesized that a period of CPR before defibrillation creates a more conducive physiological environment, increasing the likelihood of successful defibrillation. The order of priority of CPR versus defibrillation therefore remains in contention. As previous studies have remained inconclusive, we conducted a systematic review of available evidence in an attempt to draw conclusions on whether CPR plus delayed defibrillation or immediate defibrillation resulted in better outcomes in OHCA.

OBJECTIVES

To examine whether an initial one and one-half to three minutes of CPR administered by paramedics before defibrillation versus immediate defibrillation on arrival influenced survival rates, neurological outcomes or rates of return of spontaneous circulation (ROSC) in OHCA.

SEARCH METHODS

We searched the following databases: the Cochrane Central Register of Controlled trials (CENTRAL) (2013, Issue 6); MEDLINE (Ovid) (1948 to May 2013); EMBASE (1980 to May 2013); the Institute for Scientific Information (ISI) Web of Science (1980 to May 2013) and the China Academic Journal Network Publishing Database (China National Knowledge Infrastructure (CNKI), 1980 to May 2013). We included studies published in all languages. We also searched the Current Controlled Trials and Clinical Trials databases for ongoing trials. We screened the references lists of studies included in our review against the reference lists of relevant International Liaison Committee on Resuscitation (ILCOR) evidence worksheets.

SELECTION CRITERIA

Our participant group consisted of adults over 18 years of age presenting with OHCA who were in VF or pulseless VT at the time of emergency medical service (EMS) paramedic arrival. We included randomized controlled trials (RCTs) and quasi-randomized controlled trials that evaluated the effects of one and one-half to three minutes of CPR versus defibrillation as initial therapy on survival and neurological outcomes of these participants. We excluded observational and cross-over design studies.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted the data. We contacted study authors to ask for additional data when required. The risk ratio (RR) for each outcome was calculated and summarized in the meta-analysis after heterogeneity was considered. We used Review Manager software for all analyses.

MAIN RESULTS

We included four RCTs with a total of 3090 enrolled participants (one study used a cluster-randomized design). Three trials were considered to have a relatively low risk of bias, and one trial was considered to have a relatively high risk. When survival to hospital discharge was compared, 38 of 320 (11.88%) participants survived to discharge in the initial CPR plus delayed defibrillation group compared with 39 of 338 participants (11.54%) in the immediate defibrillation group (RR 1.09, 95% CI 0.54 to 2.20, Chi(2) = 10.78, degrees of freedom (df) = 5, P value 0.06, I(2) = 54%, low-quality evidence).When we compared the neurological outcome at hospital discharge (RR 1.12, 95% CI 0.65 to 1.93, low-quality evidence), the rate of return of spontaneous circulation (ROSC) (RR 0.94, 95% CI 0.77 to 1.15,low-quality evidence) and survival at one year (RR 0.77, 95% CI 0.24 to 2.49, low-quality evidence), we could not rule out the superiority of either treatment.Adverse effects were not associated with either treatment.

AUTHORS' CONCLUSIONS

Owing to the low quality of available evidence, we have been unable to determine conclusively whether immediate defibrillation and one and one-half to three minutes of CPR as initial therapy before defibrillation have similar effects on rates of return of spontaneous circulation, survival to discharge or neurological insult.We have also been unable to conclude whether either treatment approach provides a degree of superiority in OHCA.We propose that this is an area that needs further rigorous research through additional high-quality RCTs, including larger sample sizes and proper subgroup analysis.

The potential mechanism of the detrimental effect of defibrillation prior to cardiopulmonary resuscitation in prolonged cardiac arrest model

Defibrillation is no longer universally recommended as initial intervention for the reversal of ventricular fibrillation (VF) after a prolonged and untreated cardiac arrest. We sought to examine this issue in an animal model where a prolonged untreated VF was induced. The aim of this study was to investigate the potential mechanism of the detrimental effect of defibrillation prior to cardiopulmonary resuscitation (CPR) in prolonged cardiac arrest model. VF was electrically induced in 32 domestic male swine weighing 40±3 kg and remained untreated for 15 minutes. The animals were then randomly allocated to either the initial defibrillation group or the chest compression group. Mean aortic pressure, right atrial pressure and coronary perfusion pressure (CPP) were continuously measured during the performance. The dimensions of the left ventricle (LV) were assessed by echocardiographic methods. The CPP induced by CPR after defibrillation was significantly lower in the initial defibrillation group than in the chest compression group; 1 minute after defibrillation (9±3 mmHg vs. 14.8±7 mmHg (P<0.05)), and after 5 minutes 16±5 mmHg vs. 21.7±1 mmHg (P<0.05). The LV volumes were reduced from 18±2 mmHg to 14±1 mmHg after defibrillation (P<0.05). In brief, this study showed that the conducting defibrillation prior to chest compression may cause a contracture of the LV, resulting in lowering CPP, thus dropping the efficiency of chest compression in a prolonged cardiac arrest model.

Cardiac Advanced Life Support–Surgical Guideline

Cardiac arrest in the immediate postoperative recovery period in a patient who underwent cardiac surgery is typically related to reversible causes—tamponade, bleeding, ventricular arrhythmias, or heart blocks associated with conduction problems. When treated promptly, 17% to 79% of patients who experience cardiac arrest after cardiac surgery survive to discharge. The Cardiac Advanced Life Support–Surgical (CALS-S) guideline provides a standardized algorithm approach to resuscitation of patients who experience cardiac arrest after cardiac surgery. The purpose of this article is to discuss the CALS-S guideline and how to implement it.

Comparison of shock-first strategy and cardiopulmonary resuscitation-first strategy in a porcine model of prolonged cardiac arrest

OBJECTIVE

The choice of a shock-first or a cardiopulmonary resuscitation (CPR)-first strategy in the treatment of prolonged cardiac arrest (CA) is still controversial. The purpose of this study was to compare the effects of these strategies on oxygen metabolism and resuscitation outcomes in a porcine model of 8min CA.

METHODS

Ventricular fibrillation (VF) was electrically induced. After 8min of untreated VF, 24 male inbred Wu-Zhi-Shan miniature pigs were randomized to receive either defibrillation first (ID group) or chest compression first (IC group). In the ID group, a shock was delivered immediately. If the defibrillation attempt failed to attain restoration of spontaneous circulation (ROSC), manual chest compressions were rapidly initiated at a rate of 100compressionsmin(-1), and the compression-to-ventilation ratio was 30:2. If VF persisted after five cycles of CPR, a second defibrillation attempt was made. In the IC group, chest compressions were delivered first, followed by a shock.

RESULTS

Hemodynamic variables, the VF waveform and blood gas analysis outcomes were recorded. Oxygen metabolism parameters and the amplitude spectrum area (AMSA) of the VF waveform were computed. There were no significant differences in the rate of ROSC and 24h survival between two groups. The ID group had lower lactic acid levels, higher cardiac output, better oxygen consumption and better oxygen extraction ratio at 4 and 6h after ROSC than the IC group.

CONCLUSIONS

In a porcine model of prolonged CA, the choice of a shock-first or CPR-first strategy did not affect the rate of ROSC and 24h survival, but the shock-first strategy might result in better hemodynamic status and better oxygen metabolism than the CPR-first strategy at the first 6h after ROSC.

Effect of cardiopulmonary resuscitation on restoration of myocardial ATP in prolonged ventricular fibrillation

BACKGROUND

There has been controversy over whether a short period of cardiopulmonary resuscitation (CPR) prior to defibrillation improves survival in patients who experienced a sudden cardiac arrest. However, there have been no reports about whether CPR restores the myocardial energy source during prolonged ventricular fibrillation (VF). The aim of this study is to investigate the effect of CPR in restoring myocardial high energy phosphates during prolonged VF.

METHODS AND RESULTS

Seventy-two adult male Sprague-Dawley rats were used in this study. Baseline adenosine triphosphate (ATP) and adenosine diphosphate (ADP) prior to induction of VF were measured in nine rats, the No-VF group. Sixty-three rats were subjected to 4 min of untreated VF. Animals were then randomized into two groups: No-CPR (n=37) and CPR (n=26). In the No-CPR group, ATPs and ADPs were measured at 4 min (No-CPR4), 6 min (No-CPR6), 8 min (No-CPR8) or 10 min (No-CPR10) after the induction of VF. The CPR group received 2 min (CPR2), 4 min (CPR4) or 6 min (CPR6) of mechanical chest compressions before ATP was measured. Myocardial ATP (nmol/mg protein) was decreased as VF duration was prolonged (No-VF: 5.49±1.71, No-CPR4: 4.27±1.58, No-CPR6: 4.13±1.31, No-CPR8: 3.77±1.42, No-CPR10: 3.52±0.90, p<0.05 between each of No-CPRs vs. No-VF). Two minutes of CPR restored myocardial ATP to the level of No-VF group (5.27±1.67 nmol/mg protein in CPR2, p>0.05 vs. No-VF group). However, myocardial ATP (nmol/mg protein) decreased if the duration of CPR was longer than 2 min (CPR4: 3.77±1.05, CPR6: 3.49±1.08, p<0.05 between CPR4 and CPR6 vs. No-VF).

CONCLUSIONS

CPR for 2 min helps to maintain myocardial ATP after prolonged VF.