Shock Success Rate Research Articles

Recurrence of ventricular fibrillation in out-of-hospital cardiac arrest: Clinical evidence and underlying ionic mechanisms.

Defibrillation remains the optimal therapy for terminating ventricular fibrillation (VF) in out-of-hospital cardiac arrest (OHCA) patients, with reported shock success rates of ∼90%. A key persistent challenge, however, is the high rate of VF recurrence (∼50-80%) seen during post-shock cardiopulmonary resuscitation (CPR). Studies have shown that the incidence and time spent in recurrent VF are negatively associated with neurologically-intact survival. Recurrent VF also results in the administration of extra shocks at escalating energy levels, which can cause cardiac dysfunction. Unfortunately, the mechanisms underlying recurrent VF remain poorly understood. In particular, the role of chest-compressions (CC) administered during CPR in mediating recurrent VF remains controversial. In this review, we first summarize the available clinical evidence for refibrillation occurring during CPR in OHCA patients, including the postulated contribution of CC and non-CC related pathways. Next, we examine experimental studies highlighting how CC can re-induce VF via direct mechano-electric feedback. We postulate the ionic mechanisms involved by comparison with similar phenomena seen in commotio cordis. Subsequently, the hypothesized contribution of partial cardiac reperfusion (either as a result of CC or CC independent organized rhythm) in re-initiating VF in a globally ischaemic heart is examined. An overview of the proposed ionic mechanisms contributing to VF recurrence in OHCA during CPR from a cellular level to the whole heart is outlined. Possible therapeutic implications of the proposed mechanistic theories for VF recurrence in OHCA are briefly discussed.

Acute human defibrillation performance of a subcutaneous implantable cardioverter-defibrillator with an additional coil electrode

The subcutaneous implantable cardioverter-defibrillator (S-ICD) delivers 80 J shocks from an 8 cm left-parasternal coil to a 59 cm3 left lateral pulse generator (PG). A system that defibrillates with lower energy could significantly reduce PG size. Computer modeling and animal studies suggested that a second shock coil either parallel to the left-parasternal coil or transverse from the xiphoid to the PG pocket would significantly reduce the defibrillation threshold. The purpose of this study was to acutely assess the defibrillation efficacy of parallel and transverse configurations in patients receiving an S-ICD. Testing was performed in patients receiving a conventional S-ICD system. Success at 65 J was required before investigational testing. A second electrode was temporarily inserted from the xiphoid incision connected to the PG with an investigational Y-adapter. Phase 1 (n = 11) tested the parallel configuration. Phase 2 (n = 21) tested both parallel and transverse configurations in random order. This study enrolled 35 patients (28 males (80%); mean age 51 ± 17 years; left ventricular ejection fraction 40% ± 15%; body mass index 26 ± 4 kg/m2; prior myocardial infarction 46%; congestive heart failure 49%; cardiomyopathy 63%). Compared to the conventional S-ICD system, mean shock impedance decreased for both parallel (69 ± 15 Ω vs 86 ± 20 Ω; n = 33; P < .001) and transverse (56 ± 14 Ω vs 81 ± 21 Ω; n = 20; P < .001) configurations. Shock success rates at 20, 30, and 40 J were 55%, 79%, 97%, and 25%, 70%, 90% for parallel and transverse configurations, respectively. Defibrillation threshold testing was well tolerated with no serious adverse events. Adding a second shock coil, particularly in the parallel configuration, significantly reduced the impedance and had a high likelihood of defibrillation success at energies ≤40 J. This may enable the development of a smaller S-ICD.

Defibrillation effectiveness and safety of the shock waveform used in a contemporary wearable cardioverter defibrillator: Results from animal and human studies.

The wearable cardioverter defibrillator (WCD) is used to protect patients at risk for sudden cardiac arrest. We examined defibrillation efficacy and safety of a biphasic truncated exponential waveform designed for use in a contemporary WCD in three animal studies and a human study. Animal (swine) studies: #1: Efficacy comparison of a 170J BTE waveform (SHOCK A) to a 150J BTE waveform (SHOCK B) that approximates another commercially available waveform. Primary endpoint first shock success rate. #2: Efficacy comparison of the two waveforms at attenuated charge voltages in swine at three prespecified impedances. Primary endpoint first shock success rate. #3: Safety comparison of SHOCK A and SHOCK B in swine. Primary endpoint cardiac biomarker level changes baseline to 6 and 24 hours post-shock. Human Study: Efficacy comparison of SHOCK A to prespecified goal and safety evaluation. Primary endpoint cumulative first and second shock success rate. Safety endpoint adverse events. Animal Studies #1: 120 VF episodes in six swine. First shock success rates for SHOCK A and SHOCK B were 100%; SHOCK A non-inferior to SHOCK B (entire 95% CI of rate difference above -10% margin, p < .001). #2: 2,160 VF episodes in thirty-six swine. Attenuated SHOCK A was non-inferior to attenuated SHOCK B at each impedance (entire 95% CI of rate difference above -10% margin, p < .001). #3: Ten swine, five shocked five times each with SHOCK A, five shocked five times each with SHOCK B. No significant difference in troponin I (p = 0.658) or creatine phosphokinase (p = 0.855) changes from baseline between SHOCK A and SHOCK B. Human Study: Thirteen patients, 100% VF conversion rate. Mild skin irritation from adhesive defibrillation pads in three patients. The BTE waveform effectively and safely terminated induced VF in swine and a small sample in humans. Human study clinical trial registration: URL: https://clinicaltrials.gov; Unique identifier: NCT04132466.

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.

Amiodarone and ventricular fibrillation amplitude of spectral area in patients with out-of-hospital cardiac arrest. Is there an effect?

Abstract Background The use of antiarrhythmic drug therapy is usually recommended in addition to defibrillation in shockable cardiac arrest. The role of the amplitude spectral area (AMSA) of ventricular fibrillation as a predictor of defibrillation efficacy has been established, but little is known about how amiodarone could affect AMSA values. Purpose The aim of our study was to evaluate whether the administration of amiodarone during resuscitation could affect AMSA and to verify if AMSA preserves its predictive role of shock success in OHCA patients treated with amiodarone. Material All the OHCAs with an attempted resuscitation and at least one shockable rhythm which occurred from January 2015 to December 2020 in the province of Pavia were considered. AMSA values were calculated by retrospectively analyzing the data collected by the Corpuls 3 monitors/defibrillators (Corpuls, Kaufering, Germany) used in the field and by considering a pre-shock interval of 2 seconds. Results Of 4619 OHCAs, 697 underwent attempted CPR with at least one shock delivered. Of these, AMSA was available on 250 patients (male 84%, median age 67 years), for a total of 830 shocks, of which 534 (64%) shocks were in patients receiving amiodarone. The success rate of each single shock was similar in the two groups (amiodarone 42% vs no amiodarone 41%, p=0.68). The AMSA median values were significantly lower in the amiodarone group as compared to the non-amiodarone group when shocks were delivered to patients older than 67 years old [median difference: 1.55 mV Hz (95% CI 0.6–2.5), p=0.0013] or receiving bystander CPR [median difference 0.9 mV Hz (95% CI 0.1–1.8), p=0.03] or after more than 33 minutes from the emergency call to each single shock [median difference: 0.91 mV Hz (95% CI 1.9–0.01), p=0.047]. AMSA value lower than the median (8.3 Hz mV) was associated with a lower probability of shock success (19% vs 64%, p&amp;lt;0.001). According to a multivariate analysis corrected for age, sex, witnessed status, call to shock time and bystander CPR, the probability of having AMSA lower than the median was independently associated with the administration of amiodarone [OR 1.5 (95% CI 1.1–2.1) p=0.009]. At ROC curves analysis, amongst patients receiving amiodarone, AMSA was confirmed to be a predictor of both shock success and ROSC [AUC 0.755 (95% CI 0.72–0.79), p&amp;lt;0.001 and AUC 0.826 (95% CI 0.79–0.86), p&amp;lt;0.001 respectively], similarly to the general population [AUC 0.778 (95% CI0.75–0.81), p&amp;lt;0.001; AUC 0.817 (95% CI 0.79–0.84), p&amp;lt;0.001]. Conclusions Amiodarone administration is independently associated with lower values of AMSA. This could justify the lack of benefit from amiodarone administration in term of defibrillation success which would be expected by the administration of an antiarrhythmic drug during the resuscitation. Moreover, AMSA maintains its predictive value for shock success and ROSC rate in patients receiving amiodarone as well as in the general population. Funding Acknowledgement Type of funding sources: None.

Defibrillation success after subcutaneous implantable cardioverter-defibrillator generator replacement is not affected by impedance increase

Abstract Funding Acknowledgements Type of funding sources: None. Background Routine defibrillation testing during implant and replacement of the subcutaneous implantable cardioverter-defibrillator (S-ICD) is recommended per current guidelines. Recently, concerns have been raised about an increase in shock impedance and consequent shock failure during defibrillation testing in S-ICD patients undergoing a generator replacement. Purpose We aim to describe the defibrillation success rate in relation to the shock impedance in patients undergoing S-ICD generator replacement in our large tertiary center. Methods In this retrospective analysis, data from replacement procedures were collected from all patients who underwent an S-ICD generator replacement in our center from June 2014 to December 2020. Defibrillation testing was performed with at least one shock of ≤65J, and a successful shock was defined as terminating the ventricular arrhythmia within 5 seconds after the shock. Results A total of 133 patients underwent an S-ICD generator replacement, 5.8 ± 0.9 years after initial implant. Reasons for replacement were: reaching of elective replacement indicator (n = 119), early battery depletion (n = 9), complaints of generator pocket (n = 3) and device malfunction (n = 2). Defibrillation testing was performed in 111 patients (86.5%) undergoing a replacement procedure. Shock impedance data from both the implant and replacement procedure were available in 101 patients. The median shock impedance of these patients during their replacement procedure was significantly higher than during their implant, 79Ω (IQR 66-94) and 66Ω (IQR 57.5-81) respectively (Z = -5.552, p &amp;lt; 0.001). Despite the higher shock impedance, first shock during defibrillation testing was successful in 105/111 patients (94.6%), with a success rate of 97.3% after two attempts. In the remaining three patients, the ventricular arrhythmia could only be terminated with a 80J shock. This was the case during both their initial implant and their replacement procedure. Shock impedance increase between implant and replacement was not significantly higher in patients with a successful first shock compared to patients with an unsuccessful first shock (Δ+11.1 ± 20.0Ω versus Δ+12.7 ± 27.6Ω, p = 0.86). Conclusion In this large retrospective analysis, we have shown a first shock success rate during S-ICD generator replacement of 94.6%, which is similar to the success rate of defibrillation testing after initial implant. After multiple attempts, defibrillation testing success rate was 100%. Even though the median shock impedance during replacement was significantly higher than during the initial implant, there was no difference in impedance increase in patients with a successful shock compared to patients with an unsuccessful shock. Abstract Figure. Defibrillation success

Abstract 130: Pediatric Cardiac Arrest: Adult Defibrillation Energies are Safe and Effective When Treating a Pediatric Porcine Model

Objective: When attempting defibrillation in an out-of-hospital pediatric patient, the use of a reduced energy is recommended by the resuscitation guidelines due to concerns surrounding potential myocardial damage. This study investigated the effectiveness (first shock success) and safety (myocardial damage) of using adult defibrillation energies in a pediatric model of cardiac arrest. Methods: Twelve piglets (9.5-25.5 kg; typical weight range of 1 to 8 year old children) were anaesthetized and VF was electrically induced. After 15 seconds of untreated VF, defibrillation was delivered using either Protocol A (adult energies; 150J) or Protocol B (pediatric energies; 75J). Following successful defibrillation, a 3 minute rest period was allowed for the heart to recover before VF was again induced. Blood samples were collected and analyzed for cardiac troponin I (cTnI). After 20 shocks were delivered, each animal remained anaesthetized and monitored for 6 hours. Results: A total of 240 shocks were delivered across both protocols with adult and pediatric energies providing comparable first shock success rates of 98.3% (116/118) and 96.6% (112/116). Prior to the induction of VF, Protocols A and B presented with equivalent median (IQR) levels of cardiac damage marker cTnI; 0.04 (0.02, 0.07) ng/ml ( n =6) and 0.05 (0.03, 0.08) ng/ml ( n =6), respectively. Comparable cTnI results were also observed upon completion of the defibrillation phase: Protocol A – 0.23 (0.12, 0.32) ng/ml; Protocol B – 0.20 (0.12, 0.27) ng/ml. There was 100% (12/12) survival after the 6 hour monitoring period with both protocols presenting similar cTnI: Protocol A – 0.32 (0.27, 0.55) ng/ml; Protocol B – 0.28 (0.20, 0.46) ng/ml. There were no clinically significant differences observed between the adult and pediatric defibrillation energy groups. Furthermore, histopathological evaluation revealed no discernible difference in cardiac damage between energy protocols. Conclusion: This study demonstrates that adult defibrillation energies are as effective in terminating VF and do not produce statistically higher levels of cTnI than pediatric defibrillation energies. These results suggest that adult defibrillation energies are appropriate for the treatment of pediatric cardiac arrest.

Short period of mild hypothermia improves resuscitation outcome in a porcine model of prolonged ventricular fibrillation

Objective To investigate the resuscitation outcome after a short period of mild hypothermia in porcine model of prolonged ventricular fibrillation (VF). Methods Fourteen male healthy domestic swine weighting 34 to 36 kg were used. VF was induced electrically and maintained untreated for 11 mins, followed by manual cardiopulmonary resuscitation (CPR) procedure. Two investigators initiated chest compression and bag-valve mask ventilation in pattern of 2 min rotation. A biphasic wave of 120 J electric defibrillation (ED) was attempted 6 mins after CPR. If there was no return of spontaneous circulation (ROSC), CPR was restored and ED was delivered when necessarily. Resuscitation was considered unsuccessful if absence of ROSC for 12 mins. However, if ROSC occurred, animals were randomly(random number) diveded into normothermia (NT) group and hypothermia treatment (CH) group. Animals in CH group were immediately cooled by using intravenous infusion of ice-cold saline and surface cooling. Core temperature was reduced to 32-34 degrees centigrade within 120 mins and maintained at this level for 2 h. Active rewarming was completed within 2 h until baseline body temperature was reached. Data of hemodynamic variables, blood-gas analysis and blood lactate before VF of two groups were recorded. Meawhile, cardiac output (CO), heart rate and Tc after ROSC were recorded. Neurological defect scores (NDS) were evaluated every 24 h until 96 h after ROSC. Variables were compared using either Fisher test or repeated measures analysis of variance, followed by Bonferroni for multiple comparisons. A two-sided P value<0.05 was regarded statistically significant. Results There was no significant difference in body weight, mean arterial pressure, CO, pH, pressure of end-tidal carbon dioxide (ETCO2) and lactate between groups before VF. In the period of CPR, there were also no significant difference in total resuscitation time, first shock success rate, ROSC rate, shock ROSC rate, total number of shock and doses of epinephrine. However, animals in CH group survived longer time than that in NT groups [（96.00±0.00)h vs (49.71±43.65)h,P=0.031]. Meanwhile, the survival rate of 96 h was significantly higher in CH than that in NT (P<0.05). For neurological function, there was a obviously better NDS in CH group than that in NT group within ROSC 96 h (P<0.05). Conclusion Even a short duration of 2 hour mild hypothermia could improve resuscitation outcome in porcine model of 11 minute VF. Key words: Cardiopulmonary resuscitation; Mild hypothermia; Short duration; Resuscitation outcome

The use of wearable cardioverter-defibrillators in Europe: results of the European Heart Rhythm Association survey

The aim of this European Heart Rhythm Association (EHRA) survey was to collect data on the use of wearable cardioverter-defibrillators (WCDs) among members of the EHRA electrophysiology research network. Of the 50 responding centres, 23 (47%) reported WCD use. Devices were fully reimbursed in 17 (43.6%) of 39 respondents, and partially reimbursed in 3 centres (7.7%). Eleven out of 20 centres (55%) reported acceptable patients' compliance (WCD worn for >90% of time). The most common indications for WCD (8 out of 10 centres; 80%) were covering the period until re-implantation of ICD explanted due to infection, in patients with left ventricular impairment due to myocarditis or recent myocardial infarction and those awaiting heart transplantation. Patient life expectancy of <12 months and poor compliance were the most commonly reported contraindications for WCD (24 of 46 centres, 52.2%). The major problems encountered by physicians managing patients with WCD were costs (8 of 18 centres, 44.4%), non-compliance, and incorrect use of WCD. Four of 17 centres (23.5%) reported inappropriate WCD activations in <5% of patients. The first shock success rate in terminating ventricular arrhythmias was 95-100% in 6 of 15 centres (40%), 85-95% in 4 (26.7%), 75-85% in 2 (13.3%), and <75% in 3 centres (20%). The survey has shown that the use of WCD in Europe is still restricted and depends on reimbursement. Patients' compliance remains low. Heterogeneity of indications for WCD among centres underscores the need for further research and a better definition of indications for WCD in specific patient groups.

Abstract 16924: Initial AMSA and Increased AMSA After CPR Predict Second Shock Success in Initially Shock-resistant VF During Out-of-hospital Cardiac Arrest

Purpose: Amplitude spectrum area (AMSA), which is calculated from the ventricular fibrillation (VF) waveform using fast Fourier transformation, has been recognized as a predictor of successful defibrillation (DF) and as an index of myocardial perfusion and viability during resuscitation. In this study, we investigated whether a change in AMSA occurring during CPR would predict DF outcome for subsequent DF attempts after a failed DF. We hypothesized that a patient responding to CPR with an increase in AMSA would have an increased likelihood of DF success. Methods: This was a retrospective analysis of out-of-hospital cardiac arrest patients who received a second DF due to initially shock-resistant VF. A total of 193 patients with an unsuccessful first DF were identified in a manufacturer database of electrocardiographic defibrillator records. AMSA was calculated for the first DF (AMSA1) and the second DF (AMSA2) during a 2.1 sec window ending 0.5 sec prior to DF. A successful DF attempt was defined as the presence of an organized rhythm with a rate ≥ 40 / min starting within 60 sec from the DF and lasting for &gt; 30 sec. After the failed first DF, all patients received CPR for 2 to 3 minutes before delivery of the second DF. Change in AMSA (dAMSA) was calculated as dAMSA = AMSA2 - AMSA1. Results: The overall second DF success rate was 14.5%. Multivariable logistic regression showed that both AMSA1 and dAMSA were independent predictors of second DF success with odds ratios of 1.24 (95% CI 1.12 - 1.38, p&lt;0.001) and 1.27 (95% CI 1.16 - 1.41, p&lt;0.001) for each mVHz change in AMSA or dAMSA, respectively. Conclusions: In initially DF-resistant VF, a high initial AMSA value predicted an increased likelihood of second shock success. An increase of AMSA in response to CPR also predicted a higher second shock success rate. Monitoring of AMSA during resuscitation therefore may be useful to guide CPR efforts, possibly including timing of second shock delivery. These findings also further support the value of AMSA as indicator of myocardial viability.

An increase in AMSA value after CPR predicts higher second shock success rates in defibrillation-resistant VF

An increase in AMSA value after CPR predicts higher second shock success rates in defibrillation-resistant VF

Abstract 151: AMSA-Dependent Association Between Shock Energy and Shock Success

Purpose: Previous studies have demonstrated that quantitative analysis of ventricular fibrillation (VF) waveform has the potential to optimize the timing of defibrillation. However, the interaction between energy and the predictability of quantitative VF analysis is unknown. In the present study, we investigated the relationship between shock success and shock energy in the different amplitude spectrum area (AMSA) ranges and the possibility of using AMSA to guide the shock energy selection. Materials and Methods: Digitized ECG recordings were analyzed from a registry data of out-of-hospital cardiac arrests. Current-based impedance compensation automated external defibrillators with an escalating defibrillation energy protocol from 120J to 150 and 200 J were used in this study. A waveform episode of 2.05 seconds (512 data points) ending at 0.5 second before each shock attempt was selected for analysis. Shock success was defined as an organized rhythm that was present for a minimum of 30 seconds, started within 60 seconds after the shock, and had a rate of 40 beats per minute or greater. Results: A total of 1219 shocks from 536 patients with VF were analyzed. The shock success rate was increased with escalated energies when AMSA was greater than 12 mvHz (50.0% for 120J, 64.6% for 150J and 82.5% for 200J, p&lt;0.05). When AMSA was low (&lt;12 mvHz), escalated energies did not increase the shock success rate (9.3% for 120J, 12.4% for 150J and 10.4% for 200J, p:NS). Multivariable logistic regression demonstrated that the only independent predictor of shock success for low AMSA values was the AMSA (OR=1.494, 95% CI:1.362-1.638, p&lt;0.001), while for high AMSA values, it was the shock energy (OR=1.011, 95% CI=1.004-1.018, p=0.003) Conclusions: In this patient population, escalating energy protocol improved defibrillation success when AMSA was high. When AMSA was low the escalating energy protocol did not improve defibrillation success and a fixed low energy protocol may perform equally well as the escalating energy protocol. This may help to reduce myocardial damage associated with higher cumulative energy delivery. Real-time AMSA analysis during CPR could optimize not only the timing of defibrillation, but also provide robust energy selection for defibrillation.

Abstract 287: Shock Success Rates with Sternal-apical vs. Anterior-posterior Pad Positioning During Out-of-hospital Cardiac Arrest

Background: Shock success rates for sternal-apical (SA) and anterior-posterior (AP) defibrillator pad positions have not been compared clinically. Houston Fire EMS historically used AP, but changed to SA position, enabling shock success rate comparisons in out-of-hospital cardiac arrest (OHCA) patients. Methods: Patients treated with manual CPR and biphasic LifePak 500/12 defibrillators (Physio-Control, Redmond, US) were included from January 2006 to April 2007 for AP and from March 2009 to January 2011 for SA, this excluded the transition period when either position may have been used. ECG files were reviewed and initial rhythm, immediate pre-shock and five seconds post-shock rhythms were recorded as shockable or non-shockable. Only indicated shocks were included in analysis of shock success defined as termination of ventricular arrhythmias for at least five seconds. Data were analyzed using SPSS, and differences between the SA and AP groups were calculated using chi-square test and odds ratios (OR). Results: Of 989 shocked patients, 917 (93%) received 3074 indicated shocks. Of these indicated shocks 1163 of 1436 (81.0%) were successful in 476 SA patients vs. 1303 of 1638 (79.5%) in 441 AP patients (OR 1.10, 95% CI: 0.92-1.31, p=0.32). Median number of indicated shocks was 3 (IQR 1-4) in SA group and 3 (IQR 1-5) in AP group. Initial rhythm was shockable in 269 (57%) SA patients and in 277 (63%) AP patients (p=0.05) with 797 of 993 shocks (80.3%) being successful in this subgroup of SA patients vs. 859 of 1069 (80.4%) in the AP patients (OR 0.99, 95% CI: 0.80-1.24, p=0.96). Conclusion: There was no significant difference in shock success rate between sternal-apical and anterior-posterior defibrillator pads positioning during manual CPR of OHCA patients.

The impact of body mass index on wearable cardioverter defibrillator efficacy

Introduction: The effect of BMI on defibrillation in patients treated with a wearable cardioverter defibrillation (WCD) is unknown. We examined shock efficacy, event survival and compliance among different BMI groups. Methods: Patients prescribed a WCD from 1/1/2008 until 10/25/2012 and treated by the WCD for sudden cardiac arrest (SCA) were screened for this study. An SCA event was defined as sustained ventricular tachycardia (VT) and/or ventricular fibrillation (VF) within a single 24-hour period from the index episode. Charts were reviewed for height, weight, demographics and clinical background. BMI was used to categorize subjects as normal (18 Results: Height and weight were available for 366 patients. Patient characteristics were similar across all groups. Mean length of use for normal, overweight and obese was 77.0±103.8, 65.6±90.7 and 49.2±92.7 days (p=NS); the average daily wear time was 19.4±4.5, 18.8±4.7 and 18.3±4.8 hours (p=NS), respectively. WCD delivered 816 treatments during 418 SCA events. The characteristics of SCA events are summarized in table 1. Characteristics of SCA events (N=418) Conclusion: The WCD first shock success rate and event survival were high regardless of BMI. Mean TTI was positively correlated with BMI but did not impact clinical outcomes.

Impact of shock energy and ventricular rhythm on the success of first shock therapy: The ALTITUDE first shock study

The efficacy of shock in converting different ventricular tachyarrhythmias has not been well characterized in a large natural-practice setting. To determine shock success rate by energy and ventricular rhythm in a large cohort of patients with implantable cardioverter-defibrillators. Two thousand patients with 5279 shock episodes were randomly sampled for analysis from the LATITUDE remote monitoring system. Within an episode, the rhythm preceding therapy (shock or antitachycardia pacing [ATP]) was adjudicated. Patients who died after unsuccessful implantable cardioverter-defibrillator shocks did not transmit final remote monitoring data and were not included in the study. Of 3677 shock episodes for ventricular tachyarrhythmia, 2679 were treated with shock initially and were classified as monomorphic ventricular tachycardia ( n = 1544), polymorphic/monomorphic ventricular tachycardia (n = 371), or ventricular fibrillation (n = 764). The success rate after the first, second, and final shock averaged 90.3%, 96.4%, and 99.8%, respectively. After unsuccessful initial ATP (n = 998), the first, second, and final shock was successful in 84.8%, 92.9%, and 100% of the episodes. The success rate after the first or second shock was significantly lower after failed ATP compared to shock as first therapy (both P<.001). Among episodes treated initially with shock, the success rate for monomorphic ventricular tachycardia (89.2%) when treated with energy level ≤ 20 J was significantly higher than that for ventricular fibrillation (80.8%) (P = .04). The level of shock energy was a significant predictor of the success of the first shock (odds ratio 1.16; 95% confidence interval 1.03-1.30; P = .013). The success rate of first shock as first therapy is approximately 90%, but was lower after failed ATP. Programming a higher level of energy after ATP is suggested.

Beyond the pre-shock pause: the effect of prehospital defibrillation mode on CPR interruptions and return of spontaneous circulation

AimsThe pattern of interruptions to chest compressions in pre-hospital cardiac arrests in Wellington, New Zealand, was examined prospectively to determine whether the mode of defibrillation chosen by paramedics influenced interruptions, shock success and the return of spontaneous circulation (ROSC). MethodsA prospective observational cohort study of 44 adult cardiac arrests in which 203 shocks were administered by Wellington Free Ambulance (WFA) paramedics was undertaken to compare Code-stat® electronic records from Medtronic® Lifepak 12 and Lifepak 15 defibrillators used in semi-automated (AED) or manual mode. Interruptions during the 30s prior to shock delivery as well as pre-shock and post-shock pauses were calculated. Shock success and ROSC were the outcome measures. ResultsPre-shock pauses were shorter in manual mode (median 3s, IQR 2–5) versus AED mode (median 4s, IQR 3–6; p=0.003). Interruptions of CPR in the 30s prior to shock delivery were also shorter in manual mode (median 7s, IQR 4–11) versus AED mode (median 14s, IQR 12–16; p=<0.001). Shock success rates and post-shock pauses were not statistically different between modes. ROSC was significantly higher in manual mode (18.49%) versus AED mode (8.33%, p=0.042). ConclusionWhen paramedics used the defibrillator in manual mode as compared to AED mode, interruptions to CPR during the 30s prior to shock delivery were significantly reduced and pre-shock pauses were also shorter. This was associated with increased ROSC. Manual defibrillation should be the preferred option for appropriately trained paramedics. Training in this locality has been changed accordingly.

Abstract 215: First Shock Success Rates Across Waveforms and Energy Levels in Adult Cardiac Arrest: A Systematic Review and Meta-analysis

Objectives: Current guidelines advise a single biphasic shock followed by chest compressions; however, it is unclear if this applies to all waveforms and energy levels. We conducted a systematic review and meta-analysis of the literature to determine the comparative success rates for single-shock defibrillation across waveforms evaluated in out-of-hospital cardiac arrest patients presenting in Ventricular Fibrillation. Methods: A comprehensive search strategy was used across Embase, Medline, Cochrane libraries, dissertation abstracts and clinicaltrials.gov, and unpublished data was sought. Two investigators independently reviewed titles, abstracts and full texts in a hierarchical manner for study eligibility with a quadratic kappa score at each level. Two authors abstracted data independently, and the quality of the articles was assessed using the Jadad scale. Outcomes were termination of fibrillation to any rhythm (TOF), return of organized rhythm (ROOR) and return of spontaneous circulation (ROSC). Results: A total of 3,281 potentially relevant citations were identified and of these 7 RCTs were selected with Kappa values of titles 0.53, abstract 0.71, and article 0.94. Mean quality scores varied from 1-2.5/3. First-biphasic shock success (pooled mean) for TOF were similar: Biphasic Truncated Exponential (BTE) 200J 90.5%, BTE 150J 89.9%, Rectilinear Biphasic (RLB) 120J 84.9% but were lower and divergent for both ROOR BTE 200J 43%, BTE 150J 38%, RLB 23% and ROSC; BTE 200J 39%, BTE 150J 78%, RLB 46%. Median time to first shock (min) varied across trials (5.1 BTE 200/150J, 10.4 RLB) and may contribute to observed differences. Conclusion: First shock success rates as measured by the industry standard of TOF do not significantly differ across biphasic waveforms and energy levels.

Abstract 224: Amplitude Spectrum Area Based Defibrillation Decision Greatly Improves Shock Success Rate and Accuracy During Prehospital Cardiopulmonary Resuscitation

Background. We retrospectively evaluated the capability of “amplitude spectrum area” (AMSA) to predict the likelihood that a defibrillation (DF) would restore a perfusing rhythm during CPR in human victims of out-of-hospital cardiac arrest. We hypothesized that threshold values of AMSA could be identified and would increase DF success rate and accuracy. Methods. ECG data, including 1410 DFs, were obtained from 748 cardiac arrest patients from multiple areas in the US. A 4.1 secs ECG window ending at 0.5 sec before DF was analyzed and AMSA calculated prior to first DF and subsequent DFs delivered in cases of DF-resistant VF. Successful DF was defined as return of an organized rhythm within 60 sec. For first and subsequent DFs, AMSA threshold values were analyzed with regard to their ability to discriminate among successful and not successful DFs. Sensitivity, specificity, accuracy, and positive predictive value (DF success rate) of an AMSA based decision algorithm were calculated. The DF performance was then compared between two DF decision algorithms with and without AMSA threshold, respectively. Results. A total of 1221 qualified DF events from 607 patients, with 578 first DF attempts and 543 subsequent ones for DF-resistant VF, were included in the analyses. For the DF decision algorithm without AMSA, the DF success rate and accuracy were 27%/27% for the first DFs, 9%/9% for the subsequent DFs, respectively. An optimized AMSA threshold was found to be 14 mV-Hz for first DFs and 12 mV-Hz for subsequent ones. Incorporation of these AMSA thresholds into a DF decision algorithm increased both DF success rate and accuracy. The first DF achieved a DF success rate of 54% and an accuracy of 75% while subsequent DF attempts achieved 42% in DF success rate and 89% in accuracy. These results translated into an increase of DF success rate and accuracy by 100% and 180% for the first DFs, and 360% and 880% for the subsequent DFs. Conclusions. In this population, a defibrillation decision algorithm incorporating an AMSA threshold was confirmed to be capable to predict DF success with high accuracy. Different optimized AMSA thresholds can be selected for first and subsequent DF attempts to predict DF success with high accuracy may be selected in the case of first and subsequent DFs.

A low tilt waveform in the transthoracic defibrillation of ventricular arrhythmias during cardiac arrest

AimMost commercially available defibrillators utilise a high tilt waveform. Work in atrial fibrillation has shown improved defibrillation success using low tilt waveforms. We hypothesise that a novel low tilt biphasic waveform will be non-inferior to a standard tilt waveform whilst delivering lower energy for the defibrillation of ventricular arrhythmias. MethodsPatients in cardiac arrest who experienced ventricular arrhythmias received shocks from a novel low tilt waveform defibrillator at 120J or a standard tilt waveform defibrillator at 150J. Resuscitation guidelines were followed as per Resuscitation Council UK, 2005. A shock was successful when the ventricular arrhythmia was terminated for ≥5s following shock delivery. ResultsA total of 113 cardiac arrest cases were included. The low tilt device was used for 56 cases and the standard tilt device for 57 cases. The presenting rhythm was ventricular fibrillation (VF) in 71.7% (81/113), pulseless electrical activity (PEA) in 15.9% (18/113), ventricular tachycardia (VT) in 9.7% (11/113), asystole in 1.8% (2/113) and narrow complex rhythm in 0.9% (1/113). The low tilt device resulted in first shock success in 86% (48/56 cases) vs. the standard tilt device first shock success of 77% (44/57 cases). There was no significant difference in first shock success between the two devices (p=0.36). ConclusionThe low tilt waveform used in this study demonstrated first shock success rates in keeping with a commercially available high tilt defibrillator which could result in less myocardial damage due to reduced energy requirements.

Clinical experience with shock-wave lithotripsy using the Siemens Modularis Vario lithotripter

PurposeTo assess the effectiveness of a lithotripter (Modularis Vario; Siemens, AG Healthcare, Munich, Germany) in the management of renal and ureteric stones. Patients and methodsIn all, 1146 adult patients with renal or ureteric stones were treated at one urological centre using the latest model of the Modularis Vario lithotripter. The effectiveness of lithotripsy and re-treatment rate were assessed. Data were obtained on stone location, stone size, shock wave usage, success rate, and complications. ResultsBetween May 2007 and November 2009, 698 patients with renal stones and 448 with ureteric stones underwent extracorporeal shock-wave lithotripsy (ESWL). The mean (SD) renal stone size was 12.8 (3.8) mm; a mean of 1.36 sessions was required, with a mean (SD) number of 3744 (1961) shocks delivered per renal stone. After 3months, the success rate defined as the patient being stone-free or with residual fragments of <4mm; for renal stones the rate was 91.1%, with a 6.9% complication rate in the form of steinstrasse and severe renal colic. The mean (SD) ureteric stone size was 10.4 (2.7) mm. A mean of 1.37 sessions was required, with a mean (SD) of 4551 (2467) shocks delivered for each ureteric stone. The success rate for ureteric stones was 89.5%, with a 5.6% complication rate. The overall efficiency quotient was 0.66. ConclusionThe Siemens Modularis Vario lithotripter is a safe and effective machine for treating renal and ureteric stones.