Biphasic Waveform Defibrillation Research Articles

Amplitude of spectral area of ventricular fibrillation as a guide for low energy defibrillation level in patients with out-of-hospital cardiac arrest

Abstract Funding Acknowledgements Type of funding sources: None. Introduction The optimal energy level for shock in biphasic waveform defibrillation represents a significant knowledge gap. Different energy regimens have been trialed; however, a selection criterion which may help in adopting one approach over another has never been identified. Choosing the maximum energy may be an option but current-induced myocardial damage should not be neglected and an effort to tailor energy delivery is desirable. Purpose To assess whether amplitude spectral area (AMSA) of VF can guide the dose-regimens of defibrillation in out-of-hospital cardiac arrest (OHCA) patients. Methods This is a multicenter study based on the data from some of the largest OHCA registers in Europe, which enrolled 830 OHCA patients who received at least one shock during advanced resuscitation. AMSA values were calculated by retrospectively analyzing the data collected by the Corpuls 3 and LIFEPAK 12/15 monitors/defibrillators and by using a 2-second-pre-shock ECG interval. Results Among 830 OHCAs, 2135 shocks were delivered from a minimum energy level of 150 J to a maximum of 360 J. The AMSA values of efficacious shocks delivered at 150 J were higher compared to those of efficacious shock at 360 J [13.1 (IQR 10.2-17.1) vs 11.8 (IQR 8.3-15.2) HzxmV; p<0.01). In a multivariate analysis corrected for time to each shock, sex, age, amiodarone administration and study center, AMSA values, and not the dose of the shock energy, was significantly associated with the probability of shock success [OR 5.8, (95%CI 4.7-7.3); p< 0.01]. By dividing the total shocks into three tertiles based on AMSA values (T1: 0.8-6.9 Hz×mV; T2: 6.9-11.8 Hz×mV; T3: 11.8-63.2 Hz×mV), the rate of shock success at low energy was significantly higher in the tertile with highest AMSA values (T3: 38% vs T2: 15% vs T1: 5%; p<0.01). Particularly in T3, low energy was more effective than high energy shocks (38% vs 23%, p < 0.001). Conclusion This is the first study to identify a datapoint to guide decision-making with regards to defibrillation with lower energy levels. AMSA could indeed guide the selection of energy levels in order to optimize efficaciousness in restoring a perfusing rhythm while minimizing the contribution to myocardial dysfunction.

The Impact of Cardiopulmonary Resuscitation Guidelines Updates Against Out-of-Hospital Shockable Cardiac Arrest: A Population-Based Cohort Study

Background: International cardiopulmonary resuscitation (CPR) guidelines based on the best available evidence from resuscitation science have been updated since 2000. However, few nationwide population-based studies have been investigated comprehensive efficacy of those updates for out-of-hospital cardiac arrest (OHCA). Methods: From the All-Japan Utstein Registry between 2005 and 2015, we enrolled 73 578 adults who had witnessed shockable (ventricular fibrillation or pulseless ventricular tachycardia) OHCA. We examined temporal trends over eleven years (2005 on the Guidelines 2000 era, from 2006 to 2010 on the consensus on CPR and emergency cardiovascular care science with treatment recommendations [CoSTR] 2005 era, and from 2011 to 2015 on the CoSTR 2010 era). The primary end point was favorable neurological outcome (Cerebral Performance Category of 1 or 2) at 30 days after OHCA. Findings: Of 73 578 study patients, 61,080 (83%) were witnessed by bystander and 12 498 (17%) by emergency medical services (EMS) responder. After adjustment for Utstein variables, odds ratios for favorable 30-day neurological outcome increased year by year (reference, 2005): the bystander-witnessed group, 1∙19 (95% CI 1∙03-1∙37) in 2006, 2∙40 (95% CI 2∙10-2∙74) in 2010, 2∙45 (95% CI 2∙14-2∙80) in 2011 and 3∙02 (95% CI 2∙63-3∙46) in 2015; the EMS responder-witnessed group, 1∙27 (95% CI 1∙01-1∙60) in 2007, 1∙28 (95% CI 1∙02-1∙60) in 2010, 1∙54 (95% CI 1∙23-1∙94) in 2011 and 1∙58 (95% CI 1∙26-1∙99) in 2015. Similar results were seen in the subgroups receiving EMS-dispatcher CPR instruction, bystander chest compression-only CPR, early defibrillation, biphasic waveform defibrillators or advanced airway management. However, there was no evidence for any benefit from the addition of epinephrine. Interpretation: The international CPR guidelines updates for shockable OHCA had improved neurologically intact survival year by year. However, epinephrine is a topic for the future. Clinical Trial Registration Details: This study is registered with the University Hospital Medical Information Network Clinical Trials Registry, UMI09918. Funding Information: None. Declaration of Interests: We declare no competing interests. Ethics Approval Statement: A subcommittee of resuscitation science in the Japanese Circulation Society conducted this study with approval from the ethics committee at Nihon University Hospital.

First-time evaluation of ascending compared to rectangular transthoracic defibrillation waveforms in modelled out-of-hospital cardiac arrest

Aim of the studyPrognosis in out-of-hospital cardiac arrest (OHCA) depends on cardiopulmonary resuscitation (CPR) duration. Therefore, the optimal biphasic defibrillation waveform shows high conversion rates besides low energy. Matthew Fishler theoretically predicted it to be truncated ascending exponential. We realised a prototypic defibrillator and compared ascending with conventional rectangular waveforms in modelled OHCA and CPR. MethodsApproved by the authorities, 57 healthy swine (Landrace ​× ​Piétrain) were randomised to ASCDefib (n 26) or CONVDefib (n 26). Five swine served as sham control. We induced ventricular fibrillation (VF) electrically in anaesthetised swine randomised to ASCDefib or CONVDefib and discontinued mechanical ventilation. After 5 ​min of untreated cardiac arrest, we started CPR with mechanical chest compressions and ventilation. We performed transthoracic biphasic defibrillations after 2, 4, 6 and 8 ​min CPR targeting 4 ​J/kg in either group. Depending on the randomised group, the defibrillation protocol was either three ascending followed by one rectangular waveform (ASCDefib) or three rectangular followed by one ascending waveform (CONVDefib). ResultsUnder our model-specific conditions, VF was initially terminated by 13/80 ascending waveforms and 13/79 rectangular waveforms and persistent return of spontaneous circulation was achieved in 8/26 (ASCDefib) vs. 10/26 (CONVDefib) animals. Mean current rather than waveform design was predictive for defibrillation success in a generalised linear model. ConclusionContrary to theoretical assumptions, transthoracic biphasic defibrillation with ascending waveforms is not superior to rectangular waveforms in modelled OHCA. We advocate defibrillation dosage to be guided by current, that has proven its predictive value again. Institutional protocol number84–02.04.2017.A176.

Ascending Defibrillation Waveform Significantly Reduces Myocardial Morphological Damage and InjuryCurrent.

This study tested the hypothesis that a biphasic defibrillation waveform with an ascending first phase (ASC) causes less myocardial damage by pathology and injury current than a standard biphasic truncated exponential (BTE) waveform in a swine model. Although lifesaving, defibrillation shocks have significant iatrogenic effects that reduce their benefit for patient survival. An ASC waveform with an 8-ms linear ramp followed by an additional positive 0.5-ms decaying portion withamplitudes of 20J (ASC 20J) and 25J (ASC 25J) was used. The control was a 25-J BTE conventional waveform (BTE25J) RESULTS: The ASC 20J and ASC 25J shocks were both successful in 6 of 6 pigs, but the BTE 25J was successful in only 6of 14 pigs (p<0.05). Post-shock ST-segment elevation (injury current) in the right ventricular electrode was significantly greater with BTE 25J than with ASC 20J and ASC 25J. With a blinded pathology reading, hemorrhage, inflammation, thrombi, and necrosis 24h post-shock were significantly greater with BTE 25J than with ASC 20J and ASC 25J. Troponin levels were also markedly lower at 3, 4, 5, and 6h post-shock. Defibrillation shocks cause electrophysiological, histological, and biochemical signs of myocardial damage and necrosis. These signs of damage are markedly less for an ASC waveform than for a conventional BTEwaveform.

Biphasic Waveform External Defibrillation Starting Energy and In-Hospital Cardiac Arrest Survival: Retrospective Cohort Study From the Get With the Guidelines-Resuscitation Registry

ABSTRACT Biphasic waveform defibrillators permit effective defibrillation of ventricular tachycardia and ventricular fibrillation (VT/VF) at lower energies. Little data is available on trends in th...

Association between transthoracic impedance and electrical cardioversion success with biphasic defibrillators: An analysis of 1055 shocks for atrial fibrillation and flutter.

The relevance of transthoracic impedance (TTI) to electrical cardioversion (ECV) success for atrial tachyarrhythmias when using biphasic waveform defibrillators is unknown. TTI is predictive of ECV success with contemporary defibrillators. De-identified data stored in biphasic defibrillator memory cards from ECV attempts for atrial fibrillation (AF) or atrial flutter (AFL) over a 2-year period at our center were evaluated. ECV success, defined as arrhythmia termination and ≥ 1 sinus beat, was adjudicated by 2 blinded cardiac electrophysiologists. The association between TTI and ECV success was assessed via Cochrane-Armitage trend and Spearman rank correlation tests, as well as simple and multivariable logistic regression. The influence of TTI on the number of shocks and on cumulative energy delivered per patient was also examined. 703 patients (593 with AF, 110 with AFL) receiving 1055 shocks were included. Last shock success was achieved in 88.0% and 98.2% of patients with AF and AFL, respectively. In patients with AF, TTI was positively associated with last shock failure (Ptrend =0.019), the need for multiple shocks (Ptrend <0.001), and cumulative energy delivered (ρ = 0.348; P < 0.001). After adjusting for first shock energy, 10-Ω increments in TTI were associated with odds ratios of 1.36 (95% CI: 1.24-1.49) and 1.22 (95% CI: 1.09-1.37) for first and last shock failure, respectively (P < 0.001 for both). Although contemporary defibrillators are designed to compensate for TTI, this variable continues to be associated with ECV failure in patients with AF. Strategies to lower TTI during ECV for AF may improve procedural success.

Dynamic evaluation of myocardial dysfunction in rats after cardiopulmonary resuscitation

Objective To observe the dynamic changes of myocardial structure and dysfunction during post-resuscitation period in order to establish a rat mode of post-resuscitation myocardial dysfunction after cardiac arrest resulted from electric stimulation-induced ventricular fibrillation (VF) and cardiopulmonary resuscitation (CPR). Methods A total of 40 male Sprague-Dawley (SD) rats were randomly(random number) assigned into post-resuscitation (PR) 4 h, PR 12 h, PR 24 h, PR 72 h and sham groups. VF was induced by an alternating electric current delivered to the right ventricular endocardium and untreated for 8 min. Biphasic waveform defibrillation was attempted and mechanical ventilation was synchronized after 6 min of CPR. Myocardial function was assessed with serum myocardial enzyme activity, echocardiography, mitochondrial respiratory function and histopathologic findings at different intervals. Results Thirty-two animals were successfully resuscitated with restoration of spontaneous circulation (ROSC) in 86% (32/37)rats. Compared with sham group, severe systolic and diastolic heart failure were found at 4 h after ROSC and then gradually improved without significant difference(P>0.05) in ejection fraction at PR 72 h after ROSC was found, whereas thickened ventricular wall and increased myocardial performance index as well as interstitial proliferation were observed at 72 h after ROSC. Conclusions A rat model of post-resuscitation myocardial dysfunction after cardiac arrest resulted from electric stimulation-induced VF and CPR was successfully established. Key words: Cardiac arrest; Cardiopulmonary resuscitation; Myocardial dysfunction; Mitochondrion; Animal model

Biphasic versus monophasic waveforms for transthoracic defibrillation in out-of-hospital cardiac arrest.

Transthoracic defibrillation is a potentially life-saving treatment for people with ventricular fibrillation (VF) and haemodynamically unstable ventricular tachycardia (VT). In recent years, biphasic waveforms have become more commonly used for defibrillation than monophasic waveforms. Clinical trials of internal defibrillation and transthoracic defibrillation of short-duration arrhythmias of up to 30 seconds have demonstrated the superiority of biphasic waveforms over monophasic waveforms. However, out-of-hospital cardiac arrest (OHCA) involves a duration of VF/VT of several minutes before defibrillation is attempted. To determine the efficacy and safety of biphasic defibrillation waveforms, compared to monophasic, for resuscitation of people experiencing out-of-hospital cardiac arrest. We searched the following electronic databases for potentially relevant studies up to 10 September 2014: the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE and EMBASE. Also we checked the bibliographies of relevant studies and review articles, contacted authors of published reviews and reviewed webpages (including those of device manufacturers) relevant to the review topic. We handsearched the abstracts of conference proceedings for the American Heart Association, American College of Cardiology, European Society of Cardiology, European Resuscitation Council, Society of Critical Care Medicine and European Society of Intensive Care Medicine. Regarding language restrictions, we did not apply any. We included randomised controlled trials (RCTs) that compared biphasic and monophasic waveform defibrillation in adults with OHCA. Two review authors independently screened the literature search results. Two review authors independently extracted data from the included trials and performed 'Risk of bias' assessments. We resolved any disagreements by discussion and consensus. The primary outcome was the risk of failure to achieve return of spontaneous circulation (ROSC). Secondary outcomes included risk of failure to revert VF to an organised rhythm following the first shock or up to three shocks, survival to hospital admission and survival to discharge. We included four trials (552 participants) that compared biphasic and monophasic waveform defibrillation in people with OHCA. Based on the assessment of five quality domains, we identified two trials that were at high risk of bias, one trial at unclear risk of bias and one trial at low risk of bias. The risk ratio (RR) for failure to achieve ROSC after biphasic compared to monophasic waveform defibrillation was 0.86 (95% CI 0.62 to 1.20; four trials, 552 participants). The RR for failure to defibrillate on the first shock following biphasic defibrillation compared to monophasic was 0.84 (95% CI 0.70 to 1.01; three trials, 450 participants); and 0.81 (95% CI 0.61 to 1.09; two trials, 317 participants) for one to three stacked shocks. The RR for failure to achieve ROSC after the first shock was 0.92 (95% CI 0.81 to 1.04; two trials, 285 participants). Biphasic waveforms did not reduce the risk of death before hospital admission (RR 1.05, 95% CI 0.90 to 1.23; three trials, 383 participants) or before hospital discharge (RR 1.05, 95% CI 0.78 to 1.42; four trials, 550 participants). There was no statistically significant heterogeneity in any of the pooled analyses. None of the included trials reported adverse events. It is uncertain whether biphasic defibrillators have an important effect on defibrillation success in people with OHCA. Further large studies are needed to provide adequate statistical power.

A Grouped Up-and-Down Method Used for Efficacy Comparison Between Two Different Defibrillation Waveforms.

Electrical defibrillation, which consists of delivering a therapeutic dose of the electrical current to the fibrillating heart with the aid of a defibrillator, is still the only effective way to treat life-threatening ventricular fibrillation (VF). However, the efficacy of electrical therapy for terminating VF is highly dependent on the waveform applied. When new defibrillation waveforms or techniques are developed, their efficacy needs to be accurately evaluated and compared to those in use. A common method for the comparison of defibrillation efficacy is to estimate and compare the individual defibrillation threshold (DFT) by constructing dose response curves or using an up-and-down method. Since DFT is calculated by repetitive and sequential shocks, there will be variability for each measurement and for each individual. This creates a considerable uncertainty for paired comparison. In this paper, a novel grouped up-and-down method is developed for the comparison of defibrillation efficacy between two different defibrillation waveforms or techniques. The efficacy of two commonly used biphasic defibrillation waveforms was compared in a porcine model of cardiac arrest using the developed method. Experimental results demonstrate that the proposed method is more sensitive for efficacy comparison and requires less defibrillation attempts compared with traditional DFT methods.

Abstract 237: Comparative Efficacy of Biphasic Waveform Defibrillation Energies for In-Hospital Cardiac Arrest: Insights from the Get With The Guidelines--Resuscitation Registry

Background: Biphasic waveforms have become the predominant choice for defibrillation of cardiac arrest due to pulseless ventricular tachycardia or ventricular fibrillation (VT/VF). However, little is known about the relative efficacy of different first shock energy levels for defibrillation of VT/VF. Methods: Within the Get With The Guidelines - Resuscitation multicenter observational registry, we identified adults who received biphasic waveform defibrillation for in-hospital cardiac arrest due to VT/VF between 2005 and 2012. Using hierarchical regression to adjust for patient arrest characteristics and comorbidities while accounting for clustered observations by hospital, we examined the risk-adjusted association between the energy level (100J, 120J, 150J, 200J, 300J, or 360J) of the first defibrillation attempt and patient outcomes. Our primary outcome was termination of VT/VF following the first shock, with secondary outcomes of return of spontaneous circulation (ROSC), 24 hour survival, and survival to discharge. Results: Among 12,417 adults suffering VT/VF arrest treated with biphasic defibrillation, the most common first shock energy was 200 J (55.5%) Compared with 200 J, defibrillation with 120 J was more likely to result in termination of VT/VF and 24 hour survival and 150J was associated with greater 24 hour survival and survival to discharge. In contrast, energies higher than 200 J showed no difference in termination of VT/VF, but were associated with lower survival (see Table). Conclusion: Among adults with in-hospital cardiac arrest due to VT/VF, defibrillation with 200 J is the most common energy used for initial defibrillation with a biphasic waveform. However, initial defibrillation with lower energy levels is associated with greater odds of VT/VF termination, 24 hour survival, and survival to discharge. Further study is needed to inform the optimal energy for initial defibrillation of cardiac arrest due to VT/VF.

Abstract 310: Body Mass Index and Initial Defibrillation for In-Hospital Cardiac Arrest

Background: Higher transthoracic impedance may influence the success of defibrillation. We evaluated the relationship between body mass index (BMI) and post-defibrillation outcomes for in-hospital ventricular fibrillation or pulseless ventricular tachycardia (VF/VT). Methods: Within the Get With The Guidelines - Resuscitation multicenter observational registry, we identified adult patients who received biphasic waveform defibrillation for in-hospital VT/VF cardiac arrest between 2008 and2012. We evaluated the relationship between BMI and defibrillation outcomes using a generalized linear mixed regression to adjust for patient arrest characteristics and comorbidities while accounting for within hospital clustering. The primary outcome was successful termination of VF/VT. Secondary outcomes included termination of VF/VT to an organized rhythm with pulse, return of spontaneous circulation ≥ 20 minutes (ROSC), survival at 24 hours, and survival to discharge. Results: A total of 10,561 adult subjects with VF/VT from 268 hospitals were analyzed. BMI was not associated with termination of VT/VF following defibrillation. However, compared to normal BMI patients, underweight and morbidly obese patients were less likely to have termination of VT/VF with restoration of a pulse. Further, underweight patients were less likely to survive to 24 hours and discharge. In contrast, overweight and obese patients were more likely to survive to 24 hours and discharge (see Table). Summary: Successful termination of VF/VT was not associated with BMI. However, a non-linear relationship exists between BMI and termination of VF/VT to an organized rhythm with pulse, ROSC, survival at 24 h and survival at discharge.

Average current is better than peak current as therapeutic dosage for biphasic waveforms in a ventricular fibrillation pig model of cardiac arrest

ObjectiveDefibrillation current has been shown to be a clinically more relevant dosing unit than energy. However, the effects of average and peak current in determining shock outcome are still undetermined. The aim of this study was to investigate the relationship between average current, peak current and defibrillation success when different biphasic waveforms were employed. MethodsVentricular fibrillation (VF) was electrically induced in 22 domestic male pigs. Animals were then randomized to receive defibrillation using one of two different biphasic waveforms. A grouped up-and-down defibrillation threshold-testing protocol was used to maintain the average success rate of 50% in the neighborhood. In 14 animals (Study A), defibrillations were accomplished with either biphasic truncated exponential (BTE) or rectilinear biphasic waveforms. In eight animals (Study B), shocks were delivered using two BTE waveforms that had identical peak current but different waveform durations. ResultsBoth average and peak currents were associated with defibrillation success when BTE and rectilinear waveforms were investigated. However, when pathway impedance was less than 90Ω for the BTE waveform, bivariate correlation coefficient was 0.36 (p=0.001) for the average current, but only 0.21 (p=0.06) for the peak current in Study A. In Study B, a high defibrillation success (67.9% vs. 38.8%, p<0.001) was observed when the waveform delivered more average current (14.9±2.1A vs. 13.5±1.7A, p<0.001) while keeping the peak current unchanged. ConclusionIn this porcine model of VF, average current was better than peak current to be an adequate parameter to describe the therapeutic dosage when biphasic defibrillation waveforms were used.The institutional protocol number: P0805.

Abstract 181: Patterns of Waveform and Energy Use in Defibrillation for Cardiac Arrest: Insights from the Get With The Guidelines-Resuscitation Registry

Background: Early defibrillation for termination of life-threatening arrhythmias is key to survival of cardiac arrest. Biphasic waveform defibrillation has been suggested as superior to monophasic waveform defibrillation, but little is known about trends in defibrillation waveform and energy used for in-hospital cardiac arrest. Methods: Within Get With The Guidelines-Resuscitation, a national registry of in-hospital cardiac arrest, we identified subjects over age 18 with an in-hospital cardiac arrest due to ventricular fibrillation or pulseless ventricular tachycardia between 2005 and 2012. We restricted the study cohort to this time period, as defibrillation waveform and energy were not captured prior to 2005. We examined calendar year trends in defibrillation waveform and energy of first defibrillation attempt using the chi-square test. Results: A total of 22,108 patients from 504 facilities were identified. In 2005, in which there were 2898 in-hospital cardiac arrest cases, 1911 (66%) events were treated with biphasic defibrillation and 987 (34%) with monophasic defibrillation. By 2012, nearly all (97% [1460/1502]) events were treated with biphasic defibrillation; p for trend &lt; 0.0001 (see Figure). For biphasic defibrillation, the predominant energy used for first defibrillation attempt was 200 J (55.91% of events) with 150 J being the next most common (18.21% of events) with a trend toward more frequent use of 200 J (p &lt; 0.0001). Conclusion: Biphasic defibrillation at 200 J is now the predominant waveform and energy used for initial defibrillation during in-hospital cardiac arrest. Additional work is needed to determine if a rise in use of biphasic defibrillation is improving outcomes.

Contribution of out-of-hospital factors to a reduction in cardiac arrest mortality after witnessed ventricular fibrillation or tachycardia

BackgroundMortality rates in Osaka for cardiac arrest after witnessed ventricular tachycardia (VT) or ventricular fibrillation (VF) have decreased dramatically. We sought to estimate the contribution of changes in out-of-hospital care to this decrease. MethodsWe applied a previously validated statistical model, IMPACT, to data obtained from the Utstein Osaka Project, which registers all cardiopulmonary arrests in Osaka. The outcome was death within the first month after the arrest. Sensitivity analysis was conducted by simulating an increase in the use of public access defibrillators (PADs). ResultsFrom 1999 through 2008, age- and sex-adjusted standardized 1-month mortality fell from 88.6% to 57.1%. There were 105 fewer deaths than expected in 2008 (295 deaths). The IMPACT model explained 62.5% of the decrease (67 deaths) in the 1-month mortality. The main contributors to the decrease in mortality were an increase in the use of biphasic waveform defibrillators, and a shortened time to first shock. These were partly offset by an increase in the administration of epinephrine by emergency medical services personnel. According to the simulation, an increase in PAD use from 1.9% to 34.4% would reduce mortality from the observed 57.1% to 49.5%. ConclusionsModeling suggests that improvement in out-of-hospital care accounted for approximately 60% of the decline in deaths following witnessed VT or VF arrests in Osaka between 1999 and 2008. Increased usage of PADs could further improve these outcomes.

History, Principle and Techniques for Waveform Optimization in External Defibrillations

Cardiac defibrillation consists of delivering a therapeutic dose of electrical current to the fibrillating heart with the aid of a device named defibrillator. Defibrillation waveform, which is the temporal pattern of its amplitude measured by voltage or current, is one of the principle determinants of defibrillation efficacy. The purpose for the optimization of the waveform is to improve the defibrillation efficacy while decrease the risk of shock induced cardiac injury. The optimization is achieved by adjusting the defibrillation waveform parameters, including voltage, current, pulse duration, tilt, polarity and morphology. This paper reviewed the history, principle and recent techniques on waveform optimization techniques that related to external defibrillation. The patents presented demonstrate the decreased energy requirement, increased efficacy, and self-adjusting optimal waveforms based on the patient parameter measurements. Keywords: Waveform Optimization, Cardiac Arrest, External Defibrillation, Ventricular Fibrillation, Waveform design, Electrical defibrillation, Biphasic defibrillation waveform, Self adjusting optimal waveform, Triphasic waveforms, cardiopulmonary resuscitation, BTE waveform, myocardial injury, Damped biphasic truncated waveform, Rectilinear biphasic waveform

Simultaneous Comparison of Many Triphasic Defibrillation Waveforms

Biphasic defibrillation waveforms are now accepted as being more effective at terminating ventricular fibrillation (VF) than monophasic waveforms. If two phases are better than one, this naturally leads to the hypothesis that additional phases improve efficacy. This study tests the hypothesis by adding one additional phase. We examined the efficacy of 18 different triphasic waveforms simultaneously.We tested the rate of recovery, i.e., successful defibrillation, of 21 guinea pigs (820-1,050 g) using triphasic, monophasic and biphasic defibrillation waveforms. The biphasic and monophasic were control waveforms. VF was electrically induced twenty times per animal and a single defibrillation attempt was made using a test waveform VF episode. Every waveform was adjusted to the energy required to defibrillate that animal 50% of the time, using a biphasic waveform as a control. The success rate of each triphasic waveform was pair-wise compared to the biphasic and monophasic control using the adjusted McNemar statistical test.Of the 18 triphasic waveforms tested, two were significantly poorer than the monophasic control (p<0.05). One was superior to the biphasic waveform (p<0.1), but not statistically so. We concluded that, while adding a phase to a monophasic waveform does improve efficacy, adding an additional phase to a biphasic waveform does not necessarily improve efficacy.

Part 6: Electrical Therapies

The recommendations for electrical therapies described in this section are designed to improve survival from SCA and life-threatening arrhythmias. Whenever defibrillation is attempted, rescuers must coordinate high-quality CPR with defibrillation to minimize interruptions in chest compressions and to ensure immediate resumption of chest compressions after shock delivery. The high first-shock efficacy of newer biphasic defibrillators led to the recommendation of single shocks plus immediate CPR instead of 3-shock sequences that were recommended prior to 2005 to treat VF. Further data are needed to refine recommendations for energy levels for defibrillation and cardioversion using biphasic waveforms.

Comparison of neurological outcomes following witnessed out-of-hospital ventricular fibrillation defibrillated with either biphasic or monophasic automated external defibrillators

Background:Biphasic waveform defibrillation results in higher rates of termination of fibrillation than monophasic waveform defibrillation but has not been shown to improve survival outcomes.Objective:To compare the effectiveness of a biphasic...

Increased prevalence of sustained return of spontaneous circulation following transition to biphasic waveform defibrillation

We sought to assess the prevalence of shock-induced sustained return of spontaneous circulation (ROSC) and neurologically intact discharge survival before (1990-1997) and after (1998-2006) transition to biphasic waveform defibrillation in our population-controlled EMS setting. All victims of out-of-hospital cardiac arrest with ventricular fibrillation as the initial rhythm from November 1990 to December 2006 were included for analysis. Data were acquired prospectively and analyzed retrospectively during two periods: before (period 1) and after (period 2) transition from monophasic damped sine to biphasic truncated exponential and rectilinear biphasic waveform defibrillation. We compared the prevalence of sustained ROSC and survival in the two periods. Very high survival was observed during both periods. During period 1, sustained ROSC with shocks only was obtained in 37 (27.6%) patients; in period 2, sustained ROSC was obtained in 39 (40.2%) (p=0.04). Fifty-three (39.6%) survived to neurologically intact discharge in period 1, and 45 (46.4%) in period 2 (p=0.29). For bystander-witnessed arrests, ROSC was obtained in 34 (31.5%) in period 1 and 34 (45.3%) in period 2 (p=0.06). Forty-eight (44.4%) survived in period 1 and 39 (52.0%) in period 2 (p=0.31). We observed no other significant differences in patient or EMS-performance characteristics in the two time periods. Return of sustained pulses with shocks alone increased after transition to biphasic waveform defibrillation, with no other differences to explain the increase. High survival was noted in both periods, with a trend toward higher survival in the second period.

Abstract 87: Cyclosporin A does not Prevent Myocardial Dysfunction after Resuscitation from Cardiac Arrest in Rats

Objective: We have previously reported in a rat model of VF and closed-chest resuscitation that cytochrome c is released into the bloodstream after resuscitation from cardiac arrest attaining plasma levels inversely proportional to survival. Recent evidence indicates that release of cytochrome c during ischemia and reperfusion may be a manifestation of prolonged opening of the mitochondrial permeability transition pore (mPTP). In this study, we investigated whether cyclosporin A (CsA, an inhibitor of mPTP opening) can prevent post-resuscitation (PR) myocardial dysfunction and improve survival. Methods: VF was electrically induced and left untreated for 10 mins. Resuscitation was attempted by 8 mins of chest compression followed by biphasic waveform defibrillation. Rats were randomized to received a bolus CsA (10 mg/kg) five minutes before inducing VF (n=6), immediately before starting chest compression (n=6), or to receive vehicle control before inducing VF (n=3) or before starting chest compression (n=3). CsA-treated (n=12) and vehicle-treated (n=6) rats were pooled for this analysis after noticing no differences between subgroups. Resuscitated rats were monitored for up to 6 hours. Results: All rats were successfully resuscitated. Treatment with CsA did not improve PR myocardial function (Table ). Survival time was comparable between CsA-treated (321±67 mins) and vehicle-treated (331±67 mins) rats. Conclusions: In our rat model of VF and resuscitation, CsA failed to prevent PR myocardial dysfunction and improve survival. These data contrast with numerous studies demonstrating a protective effect in isolated heart models of ischemia and reperfusion. Two possible explanations are the mPTP does not open in this unique setting of cardiac arrest and resuscitation, and the optimal in vivo dose of CsA needs to be determined as the protective effects of CsA are dose dependent. Hemodynamic and Left Ventricular Function