Defibrillation Waveforms Research Articles

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.

Minor Variations in Electrode Pad Placement Impact Defibrillation Success

Defibrillation is essential for resuscitating patients with ventricular fibrillation (VF), but shocks often fail to defibrillate. We hypothesized that small variations in pad placement affect shock success, and that defibrillation waveform and shock dose could compensate for suboptimal pad placement. In 10 swine experiments, electrode pads were attached at 3 adjacent anterolateral positions, less than 3 centimeters apart. At each position, 24 episodes of VF were induced and shocked, 8 episodes for each of 3 defibrillation therapies. This resulted in 9 tested combinations of pad position and defibrillation therapy, with 80 episodes of VF for each combination. An episode consisted of 15 seconds of untreated VF, followed by a first shock and, if necessary, a repeat shock. Episodes were separated by four minutes of recovery. Both electrode pad position and therapy order were randomized by experiment. Primary outcome was defined as successful VF termination after the first shock; secondary outcome was the cumulative success of the first and second shocks. First shock efficacy varied widely across the 9 tested combinations of pad position and defibrillation therapy, ranging from 11.3% to 86.3%. When grouped by therapy, first shock efficacy varied significantly between the 3 pad positions: 38.3%, 48.3%, 36.7% (p = 0.02, ANOVA), and, when grouped by pad position, it varied significantly between therapies: 15.0%, 32.5%, 75.8% (p < 0.001, ANOVA). Cumulative 2-shock success varied significantly with therapy (p < 0.001, ANOVA) but not with pad position (p = 0.30, ANOVA). The lowest first shock success was at one position in 6 of 10 animals, at another position in 4 of 10 animals, and never at the third position. Small variations in pad placement can significantly affect defibrillation shock efficacy. However, anatomical variation between individuals and the challenging conditions of real-world resuscitations make optimal pad placement impractical. Suboptimal pad placement can be overcome with defibrillation waveform and shock dose.

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.

Construction of Energy-Optimal Smooth Monophasic Defibrillation Pulse Waveforms Using Cardiomyocyte Membrane Model

The goal is to help create smooth energy-optimal monophasic pulse waveforms for defibrillation using the Luo-Rudy cardiomyocyte membrane computer model. The waveforms were described with the help of the piecewise linear function. Each line segment provides a transition from one present level of the transmembrane potential to the next with a minimal energy value. The duration of the last segment was defined as a minimum duration at which an action potential occurs. Monophasic waveforms of segments 3, 10 and 29 were built using different increments of the transmembrane potential. The pulse energy efficiency was evaluated according to their threshold energy ratios in mA2·ms/cm4. There was virtually no difference between the threshold energy ratios of the three waveforms constructed and those of the previously studied energy-optimal half- sine waveform: 241 - 242 and 243 mA2·ms/cm4. The pulse waveform constructed is characterized by a low rise and fall as the duration of the rise is ~1.5 times longer than that of the fall. Conclusion: Energy-optimal smooth monophasic pulse waveforms have the same threshold energy ratio as the optimal half-sine one which was studied before. The latter is equivalent to the first phase of biphasic quasisinusoidal Gurvich-Venin pulse which has been used in Russia since 1972. Thus, the use of the Luo-Rudy cardiomyocyte membrane model appears to offer no possibilities for a substantial increase in the energy efficiency (threshold energy ratio reduction) of the classical monophasic defibrillation pulse waveforms.

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.

Low‐Tilt Monophasic and Biphasic Waveforms Compared with Standard Biphasic Waveforms in the Transvenous Defibrillation of Ventricular Fibrillation

Commercially available implantable defibrillators utilize a high-tilt waveform. Studies in atrial fibrillation and transthoracic defibrillation of ventricular fibrillation (VF) have shown improved defibrillation efficacy using low-tilt (LT) waveforms. We investigated the feasibility, efficacy, and safety of a LT waveform in the transvenous defibrillation of VF and hypothesized that it would be more efficacious than standard tilted biphasic (STB) waveforms. The investigation was performed in four phases in a porcine model: an efficacy study of LT monophasic waveforms (n= 9), an efficacy study of LT biphasic waveforms (n= 9), a comparison study between the most successful LT waveforms and clinically available STB waveforms (n= 15), and a safety study (n= 9). A total of 1,056 shocks were delivered (phase 1: 288, phase 2: 288, phase 3: 480). The LT biphasic 8/4-ms waveform was significantly more likely to successfully defibrillate than the LT monophasic and STB waveforms with an odds ratio of 122.3 (95% confidence interval: 32.5, 460.2, P< 0.001). The calculated defibrillation threshold (E50) for the LT 8/4-ms waveform was 12.7 J compared to 43.5 J and 45.5 J for STB waveforms 6/6 ms and 8/4 ms, respectively, and 47.7 J for LT 12-ms waveform. The LT 8/4-ms waveform had no lasting detrimental effect on cardiac function, and any transient hemodynamical or biochemical changes observed were comparable to those observed with STB waveforms. LT waveforms are effective and appear safe in transvenous defibrillation in a porcine model of VF. The LT biphasic 8/4-ms waveform is more efficacious than conventional waveforms.

Do clinical examination gloves provide adequate electrical insulation for safe hands-on defibrillation? II: Material integrity following exposure to defibrillation waveforms

IntroductionMaintaining contact with the patient during defibrillator discharge has been proposed as a method for reducing no flow time but carries an associated risk of electrocution of the rescuer. This study describes an investigation to determine if typical clinical examination gloves possess the dielectric strength needed to prevent breakdown at defibrillation voltages; a factor essential to protect the rescuer. MethodsFour types of examination glove typically used in a clinical environment were tested with two types of defibrillation waveform commonly used. For each type of glove, 10 samples were tested initially using a monophasic defibrillation waveform and then, using a fresh sample of gloves, with a Biphasic waveform. For each glove the number of shocks required before electrical breakdown occurred was recorded. ResultsKimberly Clark KC300 (nitrile), Kimberly Clark KC500 purple (nitrile), PH Medisavers GN90 (nitrile) and Bodyguards GL6622 (Vinyl) were tested using a monophasic defibrillation waveform and broke down after a median of 1, 4.5, 1 and 1 shocks respectively. The equivalent values for Biphasic defibrillator were 2, >10, 2.5 and 1 shocks. DiscussionTypical clinical examination gloves do not possess the dielectric strength required to protect a rescuer from defibrillation voltages during hands-on chest compressions.

Defibrillation Waveform Duration Adjustment Increases the Proportion of Acceptable Defibrillation Thresholds in Patients Implanted with Single-Coil Defibrillation Leads

The aim of this study was to determine whether defibrillation waveform duration adjustment with single-coil defibrillation leads can be used to increase the proportion of patients with satisfactory defibrillation thresholds (DFTs). A retrospective analysis of the DFT levels for 105 patients with implantable cardioverter-defibrillator devices and a single-coil defibrillation lead was performed. Two groups of patients were compared: 34 patients who had undergone waveform tuning (group A) and 71 patients with a fixed-tilt waveform (group B). Additional data including demographics, etiology, New York Heart Association functional class, left ventricular ejection fraction, high-voltage lead impedance and medications were gathered to determine what effect these variables had on the DFT levels. Of the 34 patients who had undergone waveform adjustment (group A), 27 (79%) were found to have satisfactory DFTs, while 41 (58%) of the 71 patients with fixed-tilt devices (group B) had satisfactory DFTs. Waveform duration adjustment was found to significantly increase the proportion of patients with satisfactory DFTs (p = 0.03).

Comparison of Fixed Tilt and Tuned Defibrillation Waveforms: The PROMISE Study

All modern defibrillation systems use biphasic shock waveforms. Typically a fixed tilt waveform is used for implantable defibrillators (ICDs), but a tuned waveform with duration based on shock impedance may be superior based on theoretical calculations. The objective of this study was to compare defibrillation efficacy of fixed tilt and tuned waveforms. PROMISE was designed as a prospective, within-patient, randomized study of defibrillation thresholds (DFTs) comparing a tuned (assuming a 3.5 milliseconds membrane time constant) versus a 50/50% tilt waveform. All patients had a left pectoral implant (active can) and testing was performed with a single coil shocking configuration ("SVC coil OFF"). DFTs were measured in random order with a binary search method in 52 patients, using the high-voltage lead impedance to select the pulse widths for both waveforms. At the DFT, the tuned waveform had similar delivered energy (10.5 ± 6.3 vs 9.5 ± 5.5 J, P = 0.47), stored energy (13.6 ± 7.9 vs 11.3 ± 6.3 J, P = 0.06), peak current (7.5 ± 3.0 vs 6.8 ± 2.2 A, P = 0.09), and delivered voltage (451.0 ± 134.5 vs 411.5 ± 120.7 V, P = 0.05) compared with the 50/50% tilt waveform. The DFTs for 3.5-millisecond time constant based tuned and 50/50% tilt waveforms are similar using a single coil, left pectoral active can.

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.

Ventricular pacing threshold after transthoracic external defibrillation with two different waveforms: an experimental study

Although an increase in the ventricular pacing threshold (VPT) has been observed after administration of transthoracic shock for ventricular defibrillation, few studies have evaluated the phenomenon with respect to the defibrillation waveform energy. Therefore, this study examined the VPT behaviour after transthoracic shock with a monophasic or biphasic energy waveform. Domestic Landrace male piglets implanted with a permanent pacemaker stimulation system were divided into three groups: no ventricular fibrillation (VF) induction and transthoracic shock with monophasic or biphasic energy (group I); VF induction, 1 min of observation without intervention, 2 min of external cardiac massage, and transthoracic shock with monophasic or biphasic energy (group II); and VF induction, 2 min of observation without intervention, 4 min of external cardiac massage, and transthoracic shock with monophasic or biphasic energy (group III). After external shock, the VPT was evaluated every minute for 10 min. A total of 143 experiments were performed. At the end of the observation period, groups I and II showed steady VPT values. Group III showed an increase in VPT with monophasic or biphasic external energy, with no difference between the external energy sources. The monophasic but not the biphasic waveform was associated with higher VPT values when the VF was longer. Defibrillation does not have a significant impact on pacing threshold, but a longer VF period is related to a higher VPT after defibrillation with monophasic waveform.

CONTINUOUS COMPRESSION WITHOUT DEFIBRILLATION FAVOURED NO SHORT-TERM SURVIVAL IN PROLONGED VENTRICULAR FIBRILLATION

CONTINUOUS COMPRESSION WITHOUT DEFIBRILLATION FAVOURED NO SHORT-TERM SURVIVAL IN PROLONGED VENTRICULAR FIBRILLATION

Comparison of Outcomes After Use of Biphasic or Monophasic Defibrillators Among Out-of-Hospital Cardiac Arrest Patients

The use and popularity of the biphasic waveform defibrillator as a replacement for the monophasic waveform defibrillator are increasing, but it is unclear whether this can improve the rate of survival among out-of-hospital cardiac arrest patients. This study aimed to verify the hypothesis that the outcome of out-of-hospital cardiac arrest patients who received defibrillation shock with the biphasic waveform defibrillator was better than that of patients who received defibrillation shock with the monophasic defibrillator. This prospective, nationwide, population-based, observational study included 21 172 out-of-hospital cardiac arrest patients with initial ventricular fibrillation or pulseless ventricular tachycardia from January 1, 2005, through December 31, 2007. Defibrillation shock was performed by monophasic defibrillator on 8224 (39%) patients and by biphasic defibrillator on 12 948 (61%) patients. The rate of survival at 1 month with minimal neurological impairment was 11.6% (951/8192) in the monophasic defibrillator group and 12.8% (1653/12 928) in the biphasic defibrillator group. Hierarchical logistic regression analysis using a generalized estimation equation showed no significant difference between the biphasic and monophasic groups in 1-month survival with minimal neurological impairment (adjusted odds ratio, 1.07; 95% confidence interval, 0.91-1.26; P=0.42). Confirmatory propensity score analyses showed similar results. Although monophasic defibrillators are being replaced by biphasic defibrillators, our nationwide population-based observational study failed to demonstrate a statistically significant association between defibrillation waveform and 1-month survival rate with minimal neurological impairment.

Efficacy of Tuned Waveforms Based on Different Membrane Time Constants on Defibrillation Thresholds: Primary Results from the POWER Trial

The efficacy of tuned defibrillation waveforms versus the nominal fixed-tilt waveform has been previously studied. However, the optimal membrane time constant for tuning was not known. The POWER (Pulsewidth Optimized Waveform Evaluation tRial) trial was designed to determine the optimal membrane time constant for programming "tuned" biphasic waveforms. This acute, multicenter study included 121 implantable cardioverter-defibrillator/cardiac resynchronization therapy defibrillator patients who were randomized at implant to any two of the three membrane time constant waveforms (2.5, 3.5, and 4.5 ms). Fixed pulse widths were programmed using the measured high voltage shock impedance. The defibrillation threshold (DFT) estimates were obtained using a hybrid protocol starting with an upper limit of vulnerability estimate followed by a step-up/step-down ventricular fibrillation induction process. DFT voltage was significantly lower using 3.5- and 4.5-ms waveforms as compared to the 2.5-ms waveform (P = 0.004 and 0.035, respectively). DFT voltage with both 3.5- and 4.5-ms waveforms was ≤ that obtained with the 2.5-ms waveform in 78.5% of the cases. The mean difference in DFT voltage using the 3.5-ms waveform and the 4.5-ms waveform was not significant (P = 0.4). However, the 3.5-ms waveform gave a lower DFT than the 4.5-ms waveform in 19 patients although the reverse was true in only nine (P = 0.02 not significant for multiple comparisons). The use of a 3.5- or 4.5-ms time constant-based waveforms had lower DFTs when compared to the 2.5-ms waveform. This study suggests that the first defibrillation attempt at implantation should be with 3.5- or 4.5-ms time constant-based waveforms. The 3.5-ms-based waveform trended toward the best choice.

A comparison of rectilinear and truncated exponential biphasic waveforms in elective cardioversion of atrial fibrillation: A prospective randomized controlled trial

BackgroundSeveral different biphasic waveforms are used clinically, but few studies have compared their efficacy. The two main waveforms are the biphasic rectilinear (BR) and biphasic truncated exponential (BTE) waveforms, both of which have important differences, particularly at the extremes of transthoracic impedance. ObjectiveTo compare the efficacy of two commonly used defibrillation waveforms in the elective cardioversion of atrial fibrillation. MethodsIn a prospective randomized controlled study, sequential adult patients undergoing elective cardioversion for AF were recruited. Patients were randomized to receive synchronized defibrillation using either a BR or BTE waveform, both using a 50J, 100J, 150J, 200J, 200J selected energy escalating protocol. Failure to cardiovert after the fifth shock was classed as failed defibrillation. The power of this study was 80% with 5% significance level to detect a difference of 20% or greater between groups. Survival analysis was used to compare the total energy delivered to achieve successful cardioversion between groups. ResultsA total of 202 patients were recruited, of which data are complete for 199 (100 BR; 99 BTE). Median number of shocks to achieve cardioversion was 2 for the BR waveform and 3 for the BTE waveform (P=0.059). In the BR waveform group, 95/100 (95.0%) achieved sinus rhythm. In the BTE waveform group, 90/99 (90.9%) achieved sinus rhythm and this group required on average 117.1J more energy to achieve the outcome compared to the BR waveform group (P=0.838). ConclusionsBR and BTE waveforms show similar high efficacy in the elective cardioversion of atrial fibrillation.

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.

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