Double sequential external defibrillation for refractory ventricular fibrillation out-of-hospital cardiac arrest: A systematic review and meta-analysis

Defibrillation strategies for patients with refractory ventricular fibrillation: A systematic review and meta-analysis

AIM

The aim of this study was to summarize the existing evidence about the effectiveness of double defibrillation (DD) in comparison to standard defibrillation for patients with refractory ventricular fibrillation (RVF). DD encompasses double "sequential" external defibrillation (DSeq-D) and double "simultaneous" defibrillation (DSim-D), with the study also shedding light on the respective effects of DSeq-D and DSim-D.

METHODS

Investigators systematically searched PubMed, EMBASE and Cochrane Central databases for randomized controlled trials (RCTs) and cohort studies from their inception until June 06, 2024. The rate of survival to hospital discharge was the primary outcome, while the incidence of return of spontaneous circulation (ROSC), termination of ventricular fibrillation (VF), survival to hospital admission and good neurologic outcome were secondary outcomes. Relative ratios (RR) and 95% confidence intervals (CIs) were calculated for each outcome. Heterogeneity was assessed using I square value.

RESULTS

A total of 6 trials, comprising 1360 patients, were included. One was an RCT, and five were observational cohort studies. The RCT showed that, compared to standard defibrillation, DSeq-D was associated with higher incidences of survival to hospital discharge, termination of VF, ROSC and good neurologic outcome. However, the pooled results of cohort studies found no benefit of DD over standard defibrillation in survival to hospital discharge (RR, 0.91; 95% CI, 0.46-1.78), nor in secondary outcomes. Furthermore, subgroup analysis suggested DSim-D was linked with lower ROSC rate compared to standard defibrillation (RR, 0.65; 95% CI, 0.49-0.86), while there was no significance between DSeq-D and standard defibrillation (RR, 1.00; 95% CI, 0.70-1.42).

CONCLUSIONS

The benefit of DSeq-D in survival to hospital discharge for RVF patients was found in the RCT, but not in cohort studies. Additionally, DSim-D should be applied with greater caution for RVF patients. Further validation is needed through larger-scale and higher-quality trials.

TRIAL REGISTRY

INPLASY; Registration number: INPLASY202340015; URL: https://inplasy.com/.

Temporal trends in the incidence and outcomes of shock-refractory ventricular fibrillation out-of-hospital cardiac arrest

Aim

We aimed to describe trends in the incidence and outcomes of refractory ventricular fibrillation (RVF) compared to non-refractory ventricular fibrillation (non-RVF) in out-of-hospital cardiac arrest (OHCA).

Methods

Between 2010 and 2019, we included all OHCA cases involving adults ≥ 16 years old with an initial shockable rhythm and who received an attempted resuscitation by Emergency Medical Services (EMS) or a bystander shock prior to EMS arrival in Victoria, Australia. Trends in incidence and survival outcomes over the study period were examined. Adjusted logistic regression analyses were conducted to examine factors associated with RVF, as well as the association of RVF on survival to hospital discharge. RVF refers to patients receiving three or more consecutive shocks without a return of spontaneous circulation (ROSC).

Results

Of the 57,749 OHCA attended by EMS, 7,267 met the inclusion criteria. Of these, 4,168 (57.4%) were non-RVF and 3,099 (42.6%) were RVF. The incidence of RVF decreased significantly from 7.7 per 100,000 population in 2010 to 5.6 per 100,000 population in 2019 (p-trend = 0.01). Survival to hospital discharge increased significantly for both the RVF and non-RVF groups (26% vs 41% in 2010 to 31% vs 53% in 2019, p-trend = 0.004 for RVF; and p-trend = 0.01 for non-RVF). Compared to non-RVF, RVF was associated with reduced odds of survival to hospital discharge (Odds Ratio = 0.503 [95% confidence interval 0.448 - 0.565]). Factors associated with a lower likelihood of RVF and improved survival to hospital discharge included being witnessed to arrest by EMS, receiving bystander defibrillation and bystander cardiopulmonary resuscitation (CPR).

Conclusion

The incidence of RVF is declining, and survival rates are improving. Early treatment of VF patients with bystander CPR and defibrillation is likely to reduce RVF incidence.

Association of coronary angiography with ST-elevation and no ST-elevation in patients with refractory ventricular fibrillation - A substudy of the DOuble SEquential External Defibrillation for Refractory Ventricular Fibrillation (DOSE-VF randomized control trial)

BACKGROUND

Refractory ventricular fibrillation or pulseless ventricular tachycardia (rVF/pVT) during out-of-hospital cardiac arrest (OHCA) is associated with poor survival. Double sequential defibrillation (DSED) and vector change (VC) improved survival for rVF/pVT in the DOSE-VF RCT. However, the role of angiography and percutaneous coronary intervention (angiography/PCI) during the trial is unknown.

OBJECTIVES

To determine the incidence of ST-elevation (STE) and no ST-elevation (NO-STE) on post-arrest ECG and the use of angiography/PCI in patients with rVF/pVT during the DOSE-VF RCT.

METHOD

Adults (≥18-years) with rVF/pVT OHCA randomized in the DOSE-VF RCT who survived to hospital admission were included. The primary analysis compared the proportion of angiography in STE and NO-STE. We performed regression modelling to examine association between STE, the interaction with defibrillation strategy, and survival to discharge controlling for known covariates.

RESULTS

We included 151 patients, 74 (49%) with STE and 77 (51%) with NO-STE. The proportion of angiography was higher in the STE cohort than NO-STE (87.8% vs 44.2%, p < 0.001); similarly the proportion of PCI was also higher (75.7% vs 9.1%, p < 0.001). Survival to discharge was similar between STE and NO-STE (63.5% vs 51.9%, p = 0.15). Use of angiography/PCI did not differ between defibrillation strategies. Decreased age (OR 0.95, 95% CI 0.92-0.98; p = 0.001) and angiography (OR 9.33, 95% CI 3.60-26.94; p < 0.001) were predictors of survival; however, STE was not.

CONCLUSION

We found high rates of angiography/PCI in patients with STE compared to NO-STE, however similar rates of survival. Angiography was an independent predictor of survival. Improved rates of survival employing DSED and VC were independent of angiography/PCI.

Defibrillation strategies for refractory ventricular fibrillation out-of-hospital cardiac arrest: A systematic review and network meta-analysis

BACKGROUND AND OBJECTIVE

Double sequential external defibrillation (DSED) and vector-change defibrillation (VCD) have been suggested to enhance clinical outcomes for patients with ventricular fibrillation (VF) refractory of standard defibrillation (SD). Therefore, this network meta-analysis aims to evaluate the comparative efficacy of DSED, VCD, and SD for refractory VF.

METHODS

A systematic review and network meta-analysis synthesizing randomized controlled trials (RCTs) and comparative observational studies retrieved from PubMed, EMBASE, WOS, SCOPUS, and Cochrane through November 15th, 2022. R software netmeta and netrank package (R version 4.2.0) and meta-insight software were used to pool dichotomous outcomes using odds ratio (OR) presented with the corresponding confidence interval (CI). Our protocol was prospectively published in PROSPERO with ID: CRD42022378533.

RESULTS

We included seven studies with a total of 1632 participants. DSED was similar to SD in survival to hospital discharge (OR: 1.14 with 95% CI [0.55, 2.83]), favorable neurological outcome (modified Rankin scale ≤2 or cerebral performance category ≤2) (OR: 1.35 with 95% CI [0.46, 3.99]), and return of spontaneous circulation (ROSC) (OR: 0.81 with 95% CI [0.43; 1.5]). In addition, VCD was similar to SD in survival to hospital discharge (OR: 1.12 with 95% CI [0.27, 4.57]), favorable neurological outcome (OR: 1.01 with 95% CI [0.18, 5.75]), and ROSC (OR: 0.88 with 95% CI [0.24; 3.15]).

CONCLUSION

Double sequential external defibrillation and VCD were not associated with enhanced outcomes in patients with refractory VF out-of-hospital cardiac arrest, compared to SD. However, the current evidence is still inconclusive, warranting further large-scale RCTs.

Cardiopulmonary Resuscitation: The Importance of the Basics

Cardiac arrest is the loss of organized cardiac activity. Unfortunately, survival to hospital discharge is poor, despite recent scientific advances. The goals of cardiopulmonary resuscitation (CPR) are to restore circulation and identify and correct an underlying etiology. High-quality compressions remain the foundation of CPR, optimizing coronary and cerebral perfusion pressure. High-quality compressions must be performed at the appropriate rate and depth. Interruptions in compressions are detrimental to management. Mechanical compression devices are not associated with improved outcomes but can assist in several situations.

Esmolol, vector change, and dose-capped epinephrine for prehospital ventricular fibrillation or pulseless ventricular tachycardia

BACKGROUND

Refractory ventricular fibrillation (VF) and pulseless ventricular tachycardia (pVT) cardiac arrest describes a subset of patients who do not respond to standard Advanced Cardiac Life Support (ACLS) interventions and are associated with poor outcomes. Esmolol administration and vector change defibrillation have shown promise in improving outcomes in these patients, however evidence is limited.

OBJECTIVES

This study compares clinical outcomes between patients with prehospital refractory VF/pVT who received an Emergency Medical Service (EMS) bundle, comprised of esmolol administration, vector change defibrillation, and dose-capped epinephrine at 3 mg, to patients who received standard ACLS interventions.

METHODS

This multicenter, retrospective, cohort study evaluated medical records between October 18, 2017 and March 15, 2022. Patients were enrolled if they experienced a prehospital cardiac arrest with the rhythm VF or pVT, had received at least three standard defibrillations, at least 3 mg of epinephrine, and 300 mg of amiodarone. Patients who received the EMS bundle after its implementation were compared to patients who received standard ACLS interventions prior to its implementation. The primary outcome was sustained return of spontaneous circulation (ROSC), defined as ROSC lasting 20 min without recurrence of cardiac arrest. Secondary outcomes included the incidence of any ROSC, survival to hospital arrival, survival at hospital discharge, and neurologically intact survival at hospital discharge.

RESULTS

Eighty-three patients were included in the study. Thirty-six were included in the pre-EMS bundle group and 47 patients were included in the post-EMS bundle group. Patients in the pre-EMS bundle group achieved significantly higher rates of sustained ROSC (58.3% vs 17%, p < 0.001), any ROSC (66.7% vs 19.1%, p < 0.001), and survival to hospital arrival (55.6% vs 17%, p < 0.001). The rates of survival to hospital discharge (16.7% vs 6.4%, p = 0.17) and neurologically intact survival at hospital discharge (5.9% vs 4.3%, p = 1.00) were not significantly different between groups.

CONCLUSIONS

Patients who received the EMS bundle achieved sustained ROSC significantly less often and were less likely to have pulses at hospital arrival. The incidence of neurologically intact survival was low and similar between groups.

Defibrillation Strategies for Refractory Ventricular Fibrillation

BACKGROUND

Despite advances in defibrillation technology, shock-refractory ventricular fibrillation remains common during out-of-hospital cardiac arrest. Double sequential external defibrillation (DSED; rapid sequential shocks from two defibrillators) and vector-change (VC) defibrillation (switching defibrillation pads to an anterior-posterior position) have been proposed as defibrillation strategies to improve outcomes in patients with refractory ventricular fibrillation.

METHODS

We conducted a cluster-randomized trial with crossover among six Canadian paramedic services to evaluate DSED and VC defibrillation as compared with standard defibrillation in adult patients with refractory ventricular fibrillation during out-of-hospital cardiac arrest. Patients were treated with one of these three techniques according to the strategy that was randomly assigned to the paramedic service. The primary outcome was survival to hospital discharge. Secondary outcomes included termination of ventricular fibrillation, return of spontaneous circulation, and a good neurologic outcome, defined as a modified Rankin scale score of 2 or lower (indicating no symptoms to slight disability) at hospital discharge.

RESULTS

A total of 405 patients were enrolled before the data and safety monitoring board stopped the trial because of the coronavirus disease 2019 pandemic. A total of 136 patients (33.6%) were assigned to receive standard defibrillation, 144 (35.6%) to receive VC defibrillation, and 125 (30.9%) to receive DSED. Survival to hospital discharge was more common in the DSED group than in the standard group (30.4% vs. 13.3%; relative risk, 2.21; 95% confidence interval [CI], 1.33 to 3.67) and more common in the VC group than in the standard group (21.7% vs. 13.3%; relative risk, 1.71; 95% CI, 1.01 to 2.88). DSED but not VC defibrillation was associated with a higher percentage of patients having a good neurologic outcome than standard defibrillation (relative risk, 2.21 [95% CI, 1.26 to 3.88] and 1.48 [95% CI, 0.81 to 2.71], respectively).

CONCLUSIONS

Among patients with refractory ventricular fibrillation, survival to hospital discharge occurred more frequently among those who received DSED or VC defibrillation than among those who received standard defibrillation. (Funded by the Heart and Stroke Foundation of Canada; DOSE VF ClinicalTrials.gov number, NCT04080986.).

Double sequential external defibrillation versus standard defibrillation in refractory ventricular fibrillation: A systematic review and meta-analysis

Introduction

Double sequential external defibrillation (DSED) in cardiopulmonary resuscitation has shown different results in comparison with standard defibrillation in the treatment of refractory ventricular fibrillation (RVF). This review aims to compare the advantages of DSED with standard defibrillation in the treatment of refractory ventricular fibrillation.

Materials and methods

PubMed, Embase, Web of Science, and Cochrane Library were searched from inception to May 1, 2022. Studies included adult patients who developed RVF. The study used random-effects and fixed-effects models for meta-analysis, which was reported by risk ratio (RR) with 95% confidence interval (CI), mean difference (MD), or standardized mean difference (SMD). The risk of bias in individual studies was assessed using the Robins-I tool for observational studies and the Cochrane Risk of Bias 2 (ROB-2) tool for clinical trials. Primary outcomes included the termination of RVF, prehospital return of spontaneous circulation (ROSC), survival to hospital admission, survival to hospital discharge, and good neurological recovery. Secondary outcomes included age, total defibrillation attempts, emergency medical system arrival time, and dose of epinephrine and amiodarone used.

Results

In this systematic review and meta-analysis, 10 studies containing 1347 patients with available data on treatment outcomes were included. The pooled estimate was (RR 1.03, 95% CI, 0.89 to 1.19; Z = 0.42, P = 0.678 > 0.05) for Termination of RVF, (RR 0.84, 95% CI, 0.63 to 1.11; Z = 1.23, P = 0.219 > 0.05) for ROSC, (RR 0.86, 95% CI, 0.69 to 1.06; Z = 1.4, P = 0.162 > 0.05) for survival to hospital admission, (RR 0.77, 95%CI, 0.52 to 1.15; Z = 1.26, P = 0.206 > 0.05) for survival to hospital discharge, (RR 0.65, 95%CI, 0.35 to 1.22; Z = 1.33, P = 0.184 > 0.05) for good neurologic recovery, (MD -1.01, 95%CI, -3.07 to 1.06; Z = 0.96, P = 0.34 > 0.05) for age, (MD 2.27, 95%CI, 1.80 to 2.73; Z = 9.50, P = 0.001 < 0.05) for total defibrillation attempts, (MD 1.10, 95%CI, -0.45 to 66; Z = 1.39, P = 0.16 > 0.05) for emergency medical system arrival time, (SMD 0.34, 95%CI, 0.17 to 0.50; Z = 4.04, P = 0.001 < 0.05) for epinephrine, and (SMD -0.30, 95%CI, -0.65 to -0.05; Z = 1.66, P = 0.1 > 0.05) for amiodarone.

Conclusion

We discovered no differences between DSED and standard defibrillation in termination of RVF, prehospital return of spontaneous circulation, survival to hospital admission, survival to hospital discharge, good neurological outcome, emergency medical system arrival time, and amiodarone doses in patients with RVF. There were some differences in the number of defibrillations and epinephrine doses utilized during resuscitation.

Systematic review registration

[https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=329354], identifier [CRD42022329354].

Coronary angiography findings in patients with shock-resistant ventricular fibrillation cardiac arrest

INTRODUCTION

Shock-resistant ventricular fibrillation (VF) poses a therapeutic challenge during out-of-hospital cardiac arrest (OHCA). For these patients, new treatment strategies are under active investigation, yet underlying trigger(s) and substrate(s) have been poorly characterised, and evidence on coronary angiography (CAG) data is often limited to studies without a control group.

METHODS

In our OHCA-registry, we studied CAG-findings in OHCA-patients with VF who underwent CAG after hospital arrival. We compared baseline demographics, arrest characteristics, CAG-findings and outcomes between patients with VF that was shock-resistant (defined as >3 shocks) or not shock-resistant (≤3 shocks).

RESULTS

Baseline demographics, arrest location, bystander resuscitation and AED-use did not differ between 105 patients with and 196 patients without shock-resistant VF. Shock-resistant VF-patients required more shocks, with higher proportions endotracheal intubation, mechanical CPR, amiodaron and epinephrine. In both groups, significant coronary artery disease (≥1 stenosis >70%) was highly prevalent (78% vs. 77%, p = 0.76). Acute coronary occlusions (ACOs) were more prevalent in shock-resistant VF-patients (41% vs. 26%, p = 0.006). Chronic total occlusions did not differ between groups (29% vs. 33%, p = 0.47). There was an association between increasing numbers of shocks and a higher likelihood of ACO. Shock-resistant VF-patients had lower proportions 24-h survival (75% vs. 93%, p < 0.001) and survival to discharge (61% vs. 78%, p = 0.002).

CONCLUSION

In this cohort of OHCA-patients with VF and CAG after transport, acute coronary occlusions were more prevalent in patients with shock-resistant VF compared to VF that was not shock-resistant, and their clinical outcome was worse. Confirmative studies are warranted for this potentially reversible therapeutic target.

A review of pre-hospital case series among those with time to double external defibrillation and neurologic outcomes

BACKGROUND

Double external defibrillation (DED) has been used as a final effort to terminate refractory ventricular fibrillation/pulseless ventricular tachycardiac (rVF/pVT). Data surrounding time to DED and patient-centered outcomes remains limited.

OBJECTIVES

This study summarizes patient-level data from case-series of observed survival and neurologic outcomes following the use of DED for rVF/pVT among those with data regarding time to DED.

METHODS

We conducted a literature search of PubMed, MEDLINE (OVID interface), and Scopus from January 1, 2000, through January 5, 2020. The literature was screened according to inclusion and exclusion criteria. Two investigators independently conducted the literature search, study selection, and data extraction.

RESULTS

Our database search identified 3139 records. Of these, 1660 studies were eliminated following inspection of the titles and 22 studies underwent full-text screening, three included in the final analysis, describing a total of 29 cases. All studies were considered to have critical risk of bias. For the critical outcomes of survival to discharge and neurologically intact survival we identified that patients who received DED before 30 min from collapse compared to those who received DED after 30 min had better survival to discharge (33.3% [5/15] vs. 7.1% [1/14]) and neurologically intact survival (20.0% [3/15] vs. 7.1% [1/14]). Overall, 20.6% of patients survived to discharge, 13.8% with neurologically intact survival. It is noteworthy that the patients who were discharged with a CPC of 1 received two, four, five, and three standard shocks before receiving DED, and the time between their onset of cardiac arrest to their first DED attempt was recorded to be 15, 26, 26, and 32 min, respectively.

CONCLUSION

We would like to indicate that there is not enough evidence to suggest that early use of pre-hospital DED is associated with improved outcomes. Further research should strive to address these issues before conclusions can be drawn.

Updates in Cardiac Arrest Resuscitation

There are approximately 350,000 out-of-hospital cardiac arrests and 200,000 in-hospital cardiac arrests annually in the United States, with survival rates of approximately 5% to 10% and 24%, respectively. The critical factors that have an impact on cardiac arrest survival include prompt recognition and activation of prehospital care, early cardiopulmonary resuscitation, and rapid defibrillation. Advanced life support protocols are continually refined to optimize intracardiac arrest management and improve survival with favorable neurologic outcome. This article focuses on current treatment recommendations for adult nontraumatic cardiac arrest, with emphasis on the latest evidence and controversies regarding intracardiac arrest management.

Double (dual) sequential defibrillation for refractory ventricular fibrillation cardiac arrest: A systematic review

INTRODUCTION

Cardiac arrests associated with shockable rhythms such as ventricular fibrillation or pulseless VT (VF/pVT) are associated with improved outcomes from cardiac arrest. The more defibrillation attempts required to terminate VF/pVT, the lower the survival. Double sequential defibrillation (DSD) has been used for refractory VF/pVT cardiac arrest despite limited evidence examining this practice. We performed a systematic review to summarize the evidence related to the use of DSD during cardiac arrest.

METHODS

This review was performed according to PRISMA and registered on PROSPERO (ID: CRD42020152575). We searched Embase, Pubmed, and the Cochrane library from inception to 28 February 2020. We included adult patients with VF/pVT in any setting. We excluded case studies, case series with less than five patients, conference abstracts, simulation studies, and protocols for clinical trials. We predefined our outcomes of interest as neurological outcome, survival to hospital discharge, survival to hospital admission, return of spontaneous circulation (ROSC), and termination of VF/pVT. Risk of bias was examined using ROBINS-I or ROB-2 and certainty of studies were reported according to GRADE methodology.

RESULTS

Overall, 314 studies were identified during the initial search. One hundred and thirty studies were screened during title and abstract stage and 10 studies underwent full manuscript screening, nine included in the final analysis. Included studies were cohort studies (n = 4), case series (n = 3), case-control study (n = 1) and a prospective pilot clinical trial (n-1). All studies were considered to have serious or critical risk of bias and no meta-analysis was performed. Overall, we did not find any differences in terms of neurological outcome, survival to hospital discharge, survival to hospital admission, ROSC, or termination of VF/pVT between DSD and a standard defibrillation strategy.

CONCLUSION

The use of double sequential defibrillation was not associated with improved outcomes from out-of-hospital cardiac arrest, however the current literature has a number of limitations to interpretation. Further high-quality evidence is needed to answer this important question.

Electrical storm: A focused review for the emergency physician

BACKGROUND

Electrical storm is a dangerous condition presenting to the Emergency Department that requires rapid diagnosis and management.

OBJECTIVE

This article provides a review of the diagnosis and management of electrical storm for the emergency clinician.

DISCUSSION

Electrical storm is defined as ≥3 episodes of sustained ventricular tachycardia, ventricular fibrillation, or shocks from an implantable cardioverter defibrillator within 24 h. Patients may present with a wide array of symptoms. Initial evaluation should include an electrocardiogram with a rhythm strip and continuous cardiac monitoring, a medication history, assessment of hemodynamic stability, and identification of potential triggers. Management includes an antiarrhythmic and a beta blocker. Refractory patients may benefit from double-sequential defibrillation or more invasive procedures such as intra-aortic balloon pumps, catheter ablation and extracorporeal membrane oxygenation for critically ill patients. These patients will typically require admission to an intensive care unit.

CONCLUSION

Electrical storm is a condition associated with significant morbidity and mortality. It is important for clinicians to be aware of the current evidence regarding the evaluation and management of these patients.

The Potential Impact of Intrathoracic Impedance on Defibrillation Threshold Testing in S-ICDs

A man with an ischemic cardiomyopathy and chronic obstructive pulmonary disease underwent subcutaneous implantable cardioverter-defibrillator (S-ICD) placement under general anesthesia. Following induction of ventricular fibrillation (VF), defibrillation testing (65J) failed, requiring external rescue. Repeat shock testing with reversed polarity (65J) failed. A third shock and external defibrillation failed (80J and 200J), followed by a second external defibrillation (200J), which did not immediately terminate VF, and a device shock 2 seconds later (80J, successful). Repeat shock testing (80J) under conscious sedation without mechanical ventilation was successful. We discuss this case of failed defibrillation testing during S-ICD placement, potentially due to lung hyperinflation, requiring double sequential defibrillation.

An investigation of inter-shock timing and electrode placement for double-sequential defibrillation

BACKGROUND

Double-Sequential Defibrillation (DSD) is the near-simultaneous use of two defibrillators to treat refractory VF. We hypothesized that (1) risk of DSD-associated defibrillator damage depends on shock vector and (2) the efficacy of DSD depends on inter-shock time.

METHODS

Part 1: risk of defibrillator damage was assessed in three anaesthetized pigs by applying two sets of defibrillation electrodes in six different configurations (near-orthogonal or near-parallel vectors). Ten 360J shocks were delivered from one set of pads and peak voltage was measured across the second set. Part 2: the dependence of DSD efficacy on inter-shock time was assessed in ten anaesthetized pigs. Electrodes were applied in lateral-lateral (LL) and anterior-posterior positions. Control (LL Stacked Shocks; one vector, two shocks ∼10 s apart) and DSD therapies (Overlapping, 10 ms, 50 ms, 100 ms, 200 ms, 500 ms, 1000 ms apart) were tested in a block randomized design treating electrically-induced VF (n = ∼89 VF episodes/therapy). Shock energies were selected to achieve 25% shock success for a single LL shock.

RESULTS

Part 1: peak voltage delivered was 1833 ± 48 V (mean ± 95%CI). Peak voltage exposure was, on average, 10-fold higher for parallel than orthogonal vectors (p < 0.0001). Part 2: DSD efficacy compared to Stacked LL shocks was higher for Overlapping, 10 ms, and 100 ms (p < 0.05); lower at 50 ms (p < 0.05); and not different at 200 ms or longer inter-shock times.

CONCLUSION

Risk of DSD-associated defibrillator damage can be mitigated by using near-orthogonal shock vectors. DSD efficacy is highly dependent on the inter-shock time and can be better, worse, or no different than stacked shocks from a single vector.

INSTITUTIONAL PROTOCOL NUMBER

University of Alabama at Birmingham Institutional Animal Care and Use Committee (IACUC) Protocol Number 06860.