Termination Of Ventricular Fibrillation Research Articles

Abstract Su503: Relationships Between Quantitative ECG Measures and Defibrillation Success in Early Ventricular Fibrillation

Introduction: Rapid termination of ventricular fibrillation (VF) has long been recognized as the cornerstone of effective cardiac arrest resuscitation. In recent years, amplitude spectral area (AMSA) has been shown to be highly associated with defibrillation success, and AMSA has been experimentally used to personalize defibrillation timing and strategy. However, questions remain about whether the interpretation of AMSA holds uniformly in varied conditions, such as ultra-early or prolonged cardiac arrest or after anti-arrhythmic administration. Hypothesis: AMSA is greater after 20 seconds of untreated VF compared to 50 seconds of untreated VF; a higher AMSA predicts greater first-defibrillation success. Methods: VF was induced in adult swine (n = 3) with a bipolar pacing catheter placed in the right ventricle. Animals were randomized to 20- or 50-second-long episodes of VF (n = 123), followed by standard 150 J biphasic defibrillation. In MATLAB, AMSA was calculated as the summed product of frequency and square root of power after Fast Fourier Transform for the four second period of VF immediately prior to defibrillation. Results were analyzed by a two-sided Chi-squared test or ANOVA with Tukey’s HSD in R; a p-value < 0.05 was considered significant. Results: First shock success was lower in the 20-second-VF group compared to the 50 second group (31/78 (39.7%) vs 31/45 (68.8%), p = 0.003). The AMSA at 20 seconds was significantly higher for successful compared to unsuccessful first defibrillation (8.20 vs. 7.31 mV-Hz, p = 0.034). The AMSA at 50 seconds was not statistically different between successful and unsuccessful defibrillations (6.32 vs. 5.67 mV-Hz, p = 0.470). Evaluating the AMSA after a duration of VF irrespective of shock success, AMSA was higher at 20 seconds compared to 50 seconds (7.66 vs 6.12 mV-Hz, p < 0.001). Conclusion(s): AMSA decreases from 20 to 50 seconds of untreated VF, and higher AMSA at a given time point is associated with greater first defibrillation success. However, first defibrillation success was higher after 50 seconds of untreated VF compared to 20 seconds, raising questions about special cases, such as edge effects, that may influence AMSA interpretation.

Defibrillation success with a second generation intercostal extravascular ICD lead and commercially available left pectoral pulse generator

Abstract Background/Introduction An investigational intercostal extravascular ICD lead has been developed for compatibility with commercially available pulse generators (PGs) that are placed in a left pectoral position in appropriate patients. This is substantially different from currently available extravascular ICD systems that require a custom PG placed in a left lateral position. Purpose The purpose of this analysis was to evaluate sensing and defibrillation of a second-generation intercostal, extravascular defibrillation lead (EV-ICD Lead) when used with currently available ICD PGs in a traditional left pectoral location. Methods Patients (n=20) undergoing an ICD implant or replacement underwent acute VF EV-ICD Lead connected to a left pectoral pulse generator. Induced VF was sensed and shocked using a 10 J safety margin, with subsequent higher-energy shocks delivered if required. Testing was also conducted in the left lateral pocket for a paired analysis with patients serving as their own control. Results Automatic sensing of acute, induced VF episodes from the left pectoral PG was successful in 19 of 20 patients (95%) whose pre-induction R-waves were greater than 1.0 mV and unsuccessful in one subject with a pre-induction R-wave of 0.3 mV. VF was successfully terminated with a 10 J safety margin in 17 of 20 (83%) patients, a 5 J safety margin in 2 of 20 (10%) patients and failed to convert one patient (BMI 32.9) from the pectoral pocket (however, conversion was successful from a lateral pocket with a 10 J shock, which provides a 30 J safety margin. With a left lateral ICD, 100% of patients demonstrated successful VF termination with ≥10 J safety margin. Conclusion(s) Sensing and defibrillation using a left pectoral PG location is feasible with a new intercostal, extravascular defibrillation lead.

Association Between Delay to First Shock and Successful First-Shock Ventricular Fibrillation Termination in Patients With Witnessed Out-of-Hospital Cardiac Arrest.

In patients with out-of-hospital cardiac arrest who present with an initial shockable rhythm, a longer delay to the first shock decreases the probability of survival, often attributed to cerebral damage. The mechanisms of this decreased survival have not yet been elucidated. Estimating the probability of successful defibrillation and other factors in relation to the time to first shock may guide prehospital care systems to implement policies that improve patient survival by decreasing time to first shock. Patients with a witnessed out-of-hospital cardiac arrest and ventricular fibrillation (VF) as an initial rhythm were included using the prospective ARREST registry (Amsterdam Resuscitation Studies). Patient and resuscitation data, including time-synchronized automated external defibrillator and manual defibrillator data, were analyzed to determine VF termination at 5 seconds after the first shock. Delay to first shock was defined as the time from initial emergency call until the first shock by any defibrillator. Outcomes were the proportion of VF termination, return of organized rhythm, transportation with return of spontaneous circulation, and survival to discharge, all in relation to the delay to first shock. A Poisson regression model with robust standard errors was used to estimate the association between delay to first shock and outcomes. Among 3723 patients, the proportion of VF termination declined from 93% when the delay to first shock was <6 minutes to 75% when that delay was >16 minutes (Ptrend<0.001). Every additional minute in VF from emergency call was associated with 6% higher probability of failure to terminate VF (adjusted relative risk, 1.06 [95% CI, 1.04-1.07]), 4% lower probability of return of organized rhythm (adjusted relative risk, 0.96 [95% CI, 0.95-0.98]), and 6% lower probability of surviving to discharge (adjusted relative risk, 0.94 [95% CI, 0.93-0.95]). Every minute of delay to first shock was associated with a significantly lower proportion of VF termination and return of organized rhythm. This may explain the worse outcomes in patients with a long delay to defibrillation. Reducing the time interval from emergency call to first shock to ≤6 minutes could be considered a key performance indicator of the chain of survival.

Electrophysiological Characteristics Associated With Spontaneous Termination of Ventricular Fibrillation.

Electrophysiological Characteristics Associated With Spontaneous Termination of Ventricular Fibrillation.

Abstract Mo035: Double (Dual) Sequential Defibrillation Versus Standard Defibrillation for Refractory Ventricular Fibrillation: A Systematic Review and Meta-Analysis

Background: Refractory ventricular fibrillation (RVF) is VF that persists despite 3 or more single defibrillation attempts. Double sequential defibrillation (DSD) is a proposed defibrillation strategy for RVF that employs delivering 2 rapid sequential, transthoracic electric shocks from 2 separate defibrillators. This meta-analysis aims to identify evidence in the literature surrounding the use of DSD and compare its efficacy with standard defibrillation (SD) in patients with RVF. Methods: We conducted our meta-analysis in compliance with the PRISMA guidelines. PubMed, Embase, and Cochrane databases were used to retrieve articles. We included studies that evaluated and compared the utility of DSD versus SD in cardiac arrest adult patients who received 3 or more standard defibrillatory shocks for RVF. Our predefined outcomes of interest were VF termination (VFT), return of spontaneous circulation (ROSC), survival to hospital admission (SHA), and survival to hospital discharge (SHD). Odds ratio (OR) and 95% confidence intervals (CIs) were calculated using the random-effects model. Heterogeneity was assessed by I 2 statistic. Results: A total of 8 studies (2 randomized controlled trials and 6 observational studies) involving 1,579 patients were included in the meta-analysis. No statistically significant difference existed between DSD and SD in terms of VFT (OR, 1.58; 95% CI, 0.84-2.99; p= 0.15; I 2 =0.54), ROSC (OR, 0.91; 95% CI, 0.53-1.55; p= 0.72; I 2 =0.76), SHA (OR, 1.18; 95% CI, 0.54-2.55; p= 0.68; I 2 =0.79), and SHD (OR, 1.03; 95% CI, 0.49-2.17; p= 0.94; I 2 =0.69). Substantial heterogeneity was noticed across the analysed studies. Conclusion: Despite the growing use of DSD for the management of RVF, there remains insufficient evidence to support its widespread implementation. This meta-analysis demonstrated that DSD had no statistically significant advantage over SD. However , due to limited data in the literature further clinical trials with large sample sizes are warranted to assess the efficacy and clinical impact of DSD, and whether it can potentially be integrated into resuscitation protocols.

The impact of alternate defibrillation strategies on shock-refractory and recurrent ventricular fibrillation: A secondary analysis of the DOSE VF cluster randomized controlled trial

BackgroundThe DOSE VF randomized controlled trial (RCT) employed a pragmatic definition of refractory ventricular fibrillation (VF after three successive shocks). However, it remains unclear whether the underlying rhythm during the first three shocks was shock-refractory or recurrent VF. ObjectiveTo explore the relationship between alternate defibrillation strategies employed during the DOSE VF RCT and the type of VF, either shock-refractory VF or recurrent VF, on patient outcomes. MethodsWe performed a secondary analysis of the DOSE VF RCT. We categorized cases as shock-refractory or recurrent VF based on pre-randomization shocks (shocks 1–3). We then analyzed all subsequent (post-randomization) shocks to assess the impact of standard, vector change (VC) or double sequential external defibrillation (DSED) shocks on clinical outcomes employing logistic regression adjusted for Utstein variables, antiarrhythmics, and epinephrine. ResultsWe included 345 patients; 60 (17%) shock-refractory VF, and 285 (83%) recurrent VF. Patients in recurrent VF had greater survival than shock-refractory VF (OR: 2.76 95% CI [1.04, 7.27]). DSED was superior to standard defibrillation for survival overall, and for patients with shock-refractory VF (28.6% vs 0%, p = 0.041) but not for those in recurrent VF. DSED was superior to standard defibrillation for return of spontaneous circulation (ROSC) and neurologic survival for shock-refractory and recurrent VF. VC defibrillation was not superior for survival or ROSC overall, for shock-refractory, or recurrent VF groups, but was superior for VF termination across all groups. ConclusionDSED appears to be the superior defibrillation strategy in the DOSE VF trial, irrespective of whether the preceding VF is shock-refractory or recurrent.

The impact of double sequential shock timing on outcomes during refractory out-of-hospital cardiac arrest

BackgroundAnimal studies suggest the efficacy of double sequential external defibrillation (DSED) may depend on the interval between the two shocks, or “DSED interval”. No human studies have examined this concept. ObjectivesTo determine the relationship between DSED interval and termination of ventricular fibrillation (VFT), return of spontaneous circulation (ROSC), survival to hospital discharge, and favourable neurological status (MRS ≤ 2) for patients in refractory VF. MethodsWe performed a retrospective review of adult (≥18 years) out-of-hospital cardiac arrest between January 2015 and May 2022 with refractory VF who received ≥1 DSED shock. DSED interval was divided into four pre-defined categories. We examined the association between DSED interval and patient outcomes using general estimated equation logistic regression or Fisher's exact test. ResultsAmong 106 included patients, 303 DSED shocks were delivered (median 2, IQR 1–3). DSED intervals of 75–125 ms (OR 0.39, 95% CI 0.16–0.98), 125–500 ms (OR 0.36, 95% CI 0.16–0.82), and >500 ms (OR 0.27, 95% CI 0.11–0.63) were associated with lower probability of VF termination compared to <75 ms interval. DSED interval of >75 ms was associated with lower probability of ROSC compared to <75 ms interval (OR 0.37, 95% CI 0.14–0.98). No association was noted between DSED interval and survival to hospital discharge or neurologic outcome. ConclusionsAmong patients in refractory VF a DSED interval of less than 75 ms was associated with improved rates of VF termination and ROSC. No association was noted between DSED interval and survival to hospital discharge or neurologic outcome.

Abstract 420: The Association Between Ventricular Fibrillation Duration and Successful Termination After the First Shock in Witnessed Out-of-Hospital Cardiac Arrest Patients

Introduction: In OHCA patients with an initial shockable rhythm, a longer time interval between onset of VF and the first shock decreases the likelihood of survival. The exact mechanism to explain this decrease is not clear. We investigated the time interval between delay to the first shock and outcomes VF termination, return of organized rhythm (ROOR), ROSC and survival. Methods: We studied witnessed OHCA patients with VF as an initial rhythm using the prospective ARREST registry. Patient- and resuscitation data, including time-synchronized AED and manual defibrillator data, were analysed to determine VF termination at 5 seconds after the first shock. Shock delay was defined as the time from initial emergency call till first shock by any defibrillator. Outcomes were rates of termination of VF, ROOR 5 seconds after the first shock, ROSC before transport, and survival to discharge, all in relation to the delay to the first shock. A logistic regression corrected for age, sex and basic life support before EMS arrival was used to analyse the association between VF duration and outcomes. Results: A total of 3676 cases were analysed. VF termination rates declined from 95% when the first shock was delivered &lt;2 minutes after the call to 75% when delivered after &gt;16 minutes (Figure 1). Rates of ROOR (49% to 23%), ROSC before transport (86% to 33%), and survival to discharge (79% to 23%) all declined significantly. Every additional minute in VF was associated with a 9% increased odds of failure to terminate VF (OR 1.09 [95% CI 1.07-1.12]), a 7% reduced odds of ROOR (OR 0.93 [95% CI 0.91-0.95]), a 12% reduced odds of acquiring ROSC before transport (OR 0.88 [95% CI 0.86-0.90]), and a 15% reduced odds of surviving to discharge (OR 0.85 [95% CI 0.83-0.87]). Conclusions: Every additional minute of delay to the first shock was associated with significant decreases in rates of VF termination, ROOR, and ROSC during transportation. This may explain the worse outcomes in patients with a long delay to defibrillation.

Abstract 419: Incidence of True Refractory Ventricular Fibrillation in Patients Meeting a Pragmatic Definition of Refractory Ventricular Fibrillation

Introduction: Refractory VF, pragmatically defined as a shockable presenting rhythm that is still observed after three shocks and associated 2-minute CPR cycles, is often encountered in out-of-hospital cardiac arrest (OHCA) and is associated with worse outcomes. A recent clinical trial tested alternative strategies for treating patients meeting this definition of refractory VF. It is unknown how often standard defibrillation truly fails to terminate VF in these patients. Methods: Using the prospective AmsteRdam REsuscitation STudies (ARREST) registry of OHCA patients, we examined termination of VF in patients meeting the pragmatic definition of refractory VF between 2016 and 2019. All patients received standard defibrillation. We reviewed ECG waveforms from all AEDs and manual defibrillators to analyze termination of VF to a non-shockable rhythm at five seconds after each of the first 3 shocks. Refibrillation was defined as recurrence of VF after a shock terminated VF. Results: Out of 1573 OHCAs with an initial shockable rhythm, we analyzed the 453 cases (29%) that met the pragmatic definition of refractory VF. Median time to first shock was 8.0 (IQR 6.3-9.7) minutes; in 65% an AED was used. The first three shocks terminated VF at least once in 96% of the patients, at least twice in 81%, and all three times in 57%. Altogether, VF was terminated by 78% of all individual shocks. In 4% of patients all three shocks failed to terminate VF (Figure). Median time to refibrillation was 32 (IQR 12-61) seconds. ROSC at any time occurred in 59% of patients; 27% survived to discharge. Conclusions: In patients meeting a pragmatic definition of refractory VF, true refractory VF without termination of the shockable rhythm by any of the first three shocks was rare. Instead, VF was successfully terminated by most shocks and recurred during the ensuing CPR cycle. Therefore, the mechanism of benefit from alternative defibrillation strategies in these patients is unclear.

Optimising low-energy defibrillation in 2D cardiac tissue with a genetic algorithm.

Sequences of low-energy electrical pulses can effectively terminate ventricular fibrillation (VF) and avoid the side effects of conventional high-energy electrical defibrillation shocks, including tissue damage, traumatic pain, and worsening of prognosis. However, the systematic optimisation of sequences of low-energy pulses remains a major challenge. Using 2D simulations of homogeneous cardiac tissue and a genetic algorithm, we demonstrate the optimisation of sequences with non-uniform pulse energies and time intervals between consecutive pulses for efficient VF termination. We further identify model-dependent reductions of total pacing energy ranging from ∼4% to ∼80% compared to reference adaptive-deceleration pacing (ADP) protocols of equal success rate (100%).

PO-05-008 NETWORK META-ANALYSIS OF THE COMPARATIVE EFFICACY OF DOUBLE SEQUENTIAL EXTERNAL, VECTOR-CHANGE, AND STANDARD DEFIBRILLATION FOR REFRACTORY VENTRICULAR FIBRILLATION OUT-OF-HOSPITAL CARDIAC ARREST

Double sequential external defibrillation (DSED; rapid successive shocks from two defibrillators) and vector-change defibrillation (VCD; relocating defibrillation pads anteriorly-posteriorly) have been suggested to enhance clinical outcomes for patients with ventricular fibrillation (VF) refractory of standard defibrillation (SD). This systematic review and network meta-analysis aims to evaluate the comparative efficacy of DSED, VCD, and SD for refractory VF. We conducted a systematic review and network meta-analysis synthesizing randomized controlled trials (RCTs) and comparative observational studies, which were retrieved by systematically searching: PubMed, EMBASE, Web of Science, 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. Five retrospective cohorts, one RCT, one pilot RCT, and one case-control study with a total of 1,784 patients were included in our analysis. A total of 439 patients (24.6%) received DSED, 205 patients (11.5%) received VCD, and 1140 patients (n= 63.9%) received SD. In the network meta-analysis, DSED was similar to SD in survival to hospital discharge (OR: 1.14 with 95% CI [0.55, 2.83]), favorable neurological outcome (defined as modified Rankin scale (mRS) or cerebral performance category (CPC) ≤2) (OR: 1.35 with 95% CI [0.46, 3.99]), return of spontaneous circulation (ROSC) (OR: 0.90 with 95% CI [0.53;1.54]), and VF termination (OR: 1.59 with 95% CI [0.92, 2.75]). Also, 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]), ROSC (OR: 1.06 with 95% CI [0.44, 2.55]), and VF termination (OR: 1.78 with 95% CI [0.95, 3.3]). In the pairwise meta-analysis, there was no difference between DSED and SD in survival to hospital admission (OR: 1.12 with 95% CI [0.58, 2.16]). There was no difference between the use of DSED and VCD compared to SD in patients with out-of-hospital cardiac arrest secondary to refractory VF. However, the current evidence is still not conclusive, warranting further large-scale RCTs.

Automated external defibrillator electrode size and termination of ventricular fibrillation in out-of-hospital cardiac arrest

Smaller electrodes allow more options for design of automated external defibrillator (AED) user interfaces. However, previous studies employing monophasic-waveform defibrillators found that smaller electrode sizes have lower defibrillation shock success rates. We hypothesize that, for impedance-compensated, biphasic truncated exponential (BTE) shocks, smaller electrodes increase transthoracic impedance (TTI) but do not adversely affect defibrillation success rates. Methods and ResultsIn this prospective before-and-after clinical study, Amsterdam police and firefighters used AEDs with BTE waveforms: an AED with larger electrodes in 2016–2017 (113 cm2), and an AED with smaller electrodes in 2017–2020 (65 cm2). We analyzed 157 and 178 patient cases with an initial shockable rhythm where the larger and smaller electrodes were used, respectively. A single 200-J shock terminated ventricular fibrillation (VF) in 86% of patients treated with large electrodes and 89% of patients treated with smaller electrodes. Small electrodes had a non-inferior first shock defibrillation success rate compared to large electrodes, with a difference of 3% (95% CI: –3% −9%) with the lower confidence limit remaining above the defined non-inferiority threshold. TTI was significantly higher for the smaller electrodes (median: 100 Ω) compared to the larger electrodes (median: 88 Ω) (p < 0.001). ConclusionsFor AEDs with impedance-compensating BTE waveforms, TTI was higher for smaller electrodes than the large electrode electrodes. Overall defibrillation shock success for AEDs with smaller electrodes was non-inferior to the AEDs with larger electrodes.

Defibrillation Strategies for Refractory Ventricular Fibrillation

BackgroundDespite 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.MethodsWe 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.ResultsA 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).ConclusionsAmong 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.)

Abstract 240: High First Shock Success With Reduction In Refractory Ventricular Fibrillation In A Real-world Public Access Defibrillator Registry Of Out-of-hospital Cardiac Arrests

Introduction: Refractory VF, which is defined as fibrillation that persists after three or more shocks, has been reported to occur in 20% of VF presenting cardiac arrest patients. This analysis was conducted to assess the frequency of shock resistant VF, during OHCA treated with a public access defibrillator (PAD). Methods: Heartsine Samaritan PAD post-market data collected between October 2012 to January 2021 were analyzed; electrocardiography (ECG) is recorded by the PAD and is assessed for shockability immediately after detecting patient impedance and then following each 2-minute period of CPR. Shock success (SS) was determined for each shock. SS was defined as one in which the initial shockable arrhythmia was terminated for at least five seconds. A consecutive shock was defined as a shock delivered after the first analysis mode following a previous shock. Results: Data was analyzed for 1082 patients who received at least one shock during OHCA. First shock success (FSS) was 88.2% (862/977 assessable shocks). At least three consecutive shocks were delivered in 207/1082 (19.1%) patients. Three patients (3/207, 1.4%) had two unsuccessful shocks followed by termination of VF on the third shock. A further thirteen (13/204, 6.4%) patients had VF which was resistant to defibrillation (i.e., three or more consecutive failed shocks with no observed successful shock). In the remaining 191 patients at least one of the three consecutive shocks was successful, or shock success could not be determined. Conclusion: The prevalence of shock resistant VF for OHCA treated with a PAD is much lower (6.4%) than published data. This low prevalence is in part due to the high FSS observed resulting in reduction in the number of possible shock resistant cases.

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

BackgroundPredefibrillation 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...

B-PO03-206 TERMINATION OF VENTRICULAR FIBRILLATION DURING CATHETER ABLATION

Catheter ablation (CA) targeting Purkinje triggers is an established technique for treating ventricular fibrillation (VF). However, the mechanism of human VF maintenance is not well understood. While 2 previous cases of spontaneous termination of VF after CA have been reported, none have occurred during radiofrequency (RF) application. N/A N/A A 50 year-old man presented to an outside hospital with a STEMI and underwent PCI to the RCA. He developed VF refractory to IV amiodarone, lidocaine and over 10 defibrillation attempts. He was placed on full circulatory support and transferred to our institution. Procainamide and then PO quinidine were also ineffective with persistent VF storm. The VF appeared to be initiated by a PVC with indeterminate V1 morphology with superior axis and dominant S wave, suggestive of moderator band (MB) or left posterior fascicle PVC (Panel A). He was brought to the EP lab, where the same PVC initiated VF, requiring defibrillation. An ablation catheter was positioned at the MB (Panels B, C). 85 s into an episode of VF, RF energy was delivered and in 3.8 s terminated VF to monomorphic VT (MMVT) (Panel D). The MMVT was then mapped to an exit site lateral to the posteromedial papillary muscle. The signal was 65 ms pre-QRS at this site and ablation terminated VT to SR. VF and VT did not recur and circulatory support was weaned. To our knowledge, this case is the first reporting direct termination of VF during delivery of RF energy. Though it is well known that abnormal Purkinje potentials and resultant PVCs may serve as initiators of VF, this case presents direct evidence that the triggering focus may in fact be critical to VF maintenance.

B-YIA2-03 A GOVERNING EQUATION TO EXPLAIN THE NUMBER OF WAVELETS AND ROTORS OBSERVED IN HUMAN VENTRICULAR FIBRILLATION

VF is commonly characterised by two mechanisms, multi wavelet reentry and rotors, but no governing equation exists to explain and predict their population dynamics. We hypothesized a single equation derived from an M/G/∞ renewal process could explain rotor and wavelet numbers in VF. Phase singularity (PS) and wavefront (WF) tracking was used to identify wavelets and rotors in epicardial recordings of induced VF during cardiac surgery (n=13 patients). Autocorrelation and distributions of PS and WF lifetimes and inter-formation times were assessed to verify an underlying renewal process. Distributions were fitted using maximum likelihood to calculate formation (λf) and destruction (λd) rates, and combined in an M/G/∞ process to develop a potential governing equation of VF dynamics. PS and WF inter-event-time distributions were consistent with the Weibull in all 210 epochs (PS: mean Χ2 P=0.23(95%CI,0.18,0.28); WF: mean Χ2 P=0.19(95%CI,0.13,0.27)), with zero autocorrelation at non-zero lags, indicative of an underlying renewal process over all stages (perfusion, ischemia and reflow). The M/G/∞ equation accurately predicted average PS and WF number (R>0.90) and population distribution (Χ2 P>0.05) in all epochs. Differences in λf (term: 0.015/ms (95%CI,0.010,0.020), non-term 0.023/ms (95%CI,0.019,0.027)), and average PS number (term: 1.68 (95%CI, 1.36, 2.00), non-term: (2.00 (95%CI, 1.86, 2.15)) was observed in spontaneous VF termination. M/G/∞ renewal process provides a governing equation to explain the number of wavelets and rotors in VF, which could be used in mechanistic studies to guide development of new therapies.

Effect of Amplitude Spectral Area on Termination of Fibrillation and Outcomes in Pediatric Cardiac Arrest

BackgroundAmplitude spectral area (AMSA) predicts termination of fibrillation (TOF) with return of spontaneous circulation (ROSC) and survival in adults but has not been studied in pediatric cardiac arrest. We characterized AMSA during pediatric cardiac arrest from a Pediatric Resuscitation Quality Collaborative and hypothesized that AMSA would be associated with TOF and ROSC.Methods and ResultsChildren aged <18 years with cardiac arrest and ventricular fibrillation were studied. AMSA was calculated for 2 seconds before shock and averaged for each subject (AMSA‐avg). TOF was defined as termination of ventricular fibrillation 10 seconds after defibrillation to any non‐ventricular fibrillation rhythm. ROSC was defined as >20 minutes without chest compressions. Univariate and multivariable logistic regression analyses controlling for weight, current, and illness category were performed. Primary end points were TOF and ROSC. Secondary end points were 24‐hour survival and survival to discharge. Between 2015 and 2019, 50 children from 14 hospitals with 111 shocks were identified. In univariate analyses AMSA was not associated with TOF and AMS‐Aavg was not associated with ROSC. Multivariable logistic regression showed no association between AMSA and TOF but controlling for defibrillation average current and illness category, there was a trend to significant association between AMSA‐avg and ROSC (odds ratio, 1.10 [1.00‒1.22] P=0.058). There was no significant association between AMSA‐avg and 24‐hour survival or survival to hospital discharge.ConclusionsIn pediatric patients, AMSA was not associated with TOF, whereas AMSA‐avg had a trend to significance for association in ROSC, but not 24‐hour survival or survival to hospital discharge.RegistrationURL: https://www.clinicaltrials.gov; Unique identifier: NCT02708134.

Esmolol during cardiopulmonary resuscitation reduces neurological injury in a porcine model of cardiac arrest

Primary vasopressor efficacy of epinephrine during cardiopulmonary resuscitation (CPR) is due to its α-adrenergic effects. However, epinephrine plays β1-adrenergic actions, which increasing myocardial oxygen consumption may lead to refractory ventricular fibrillation (VF) and poor outcome. Effects of a single dose of esmolol in addition to epinephrine during CPR were investigated in a porcine model of VF with an underlying acute myocardial infarction. VF was ischemically induced in 16 pigs and left untreated for 12 min. During CPR, animals were randomized to receive epinephrine (30 µg/kg) with either esmolol (0.5 mg/kg) or saline (control). Pigs were then observed up to 96 h. Coronary perfusion pressure increased during CPR in the esmolol group compared to control (47 ± 21 vs. 24 ± 10 mmHg at min 5, p < 0.05). In both groups, 7 animals were successfully resuscitated and 4 survived up to 96 h. No significant differences were observed between groups in the total number of defibrillations delivered prior to final resuscitation. Brain histology demonstrated reductions in cortical neuronal degeneration/necrosis (score 0.3 ± 0.5 vs. 1.3 ± 0.5, p < 0.05) and hippocampal microglial activation (6 ± 3 vs. 22 ± 4%, p < 0.01) in the esmolol group compared to control. Lower circulating levels of neuron specific enolase were measured in esmolol animals compared to controls (2[1–3] vs. 21[16–52] ng/mL, p < 0.01). In this preclinical model, β1-blockade during CPR did not facilitate VF termination but provided neuroprotection.

Optimizing defibrillation during cardiac arrest

Current cardiac arrest guidelines are based on a fixed, time-based defibrillation strategy. Rhythm analysis and shock delivery (if indicated) are repeated every 2 min requiring cyclical interruptions of chest compressions. This approach has several downsides, such as the need to temporarily stop cardiopulmonary resuscitation (CPR) for a variable amount of time, thus reducing myocardial perfusion and decreasing the chance of successful defibrillation. A tailored defibrillation strategy should identify treatment priority for each patient, that is chest compressions (CCS) or defibrillation, minimize CCs interruptions, speed up the delivery of early effective defibrillation and reduce the number of ineffective shocks. Real-time ECG analysis (using adaptive filters, new algorithms robust to chest compressions artifacts and shock-advisory algorithms) is an effective strategy to correctly identify heart rhythm during CPR and reduce the hands-off time preceding a shock. Similarly, ventricular fibrillation waveform analysis, that is amplitude spectrum area (AMSA) represents a well established approach to reserve defibrillation in patients with high chance of shock success and postpone it when ventricular fibrillation termination is unlikely. Both approaches demonstrated valuable results in improving cardiac arrest outcomes in experimental and observational study. Real-time ECG analysis and AMSA have the potential to predict ventricular fibrillation termination, return of spontaneous circulation and even survival, with discretely high confidence. Prospective studies are now necessary to validate these new approaches in the clinical scenario.