Monophasic Waveform Defibrillation 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.

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 < 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 < 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.

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.

Part 4: CPR Overview

Cardiopulmonary resuscitation (CPR) is a series of lifesaving actions that improve the chance of survival following cardiac arrest.1 Although the optimal approach to CPR may vary, depending on the rescuer, the victim, and the available resources, the fundamental challenge remains: how to achieve early and effective CPR. Given this challenge, recognition of arrest and prompt action by the rescuer continue to be priorities for the 2010 AHA Guidelines for CPR and ECC. This chapter provides an overview of cardiac arrest epidemiology, the principles behind each link in the Chain of Survival, an overview of the core components of CPR (see Table 1), and the approaches of the 2010 AHA Guidelines for CPR and ECC to improving the quality of CPR. The goal of this chapter is to integrate resuscitation science with real-world practice in order to improve the outcomes of CPR. View this table: Table 1. Summary of Key BLS Components for Adults, Children and Infants Despite important advances in prevention, cardiac arrest remains a substantial public health problem and a leading cause of death in many parts of the world.2 Cardiac arrest occurs both in and out of the hospital. In the US and Canada, approximately 350 000 people/year (approximately half of them in-hospital) suffer a cardiac arrest and receive attempted resuscitation.3,–,7 This estimate does not include the substantial number of victims who suffer an arrest without attempted resuscitation. While attempted resuscitation is not always appropriate, there are many lives and life-years lost because appropriate resuscitation is not attempted. The estimated incidence of EMS-treated out-of-hospital cardiac arrest in the US and Canada is about 50 to 55/100 000 persons/year and approximately 25% of these present with pulseless ventricular arrhythmias.3,8 The estimated incidence of in-hospital cardiac arrest is 3 to 6/1000 admissions4,– …

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...

Left Ventricular Function after Monophasic and Biphasic Waveform Defibrillation: The Impact of Cardiopulmonary Resuscitation Time on Contractile Indices

AbstractPrevious work has suggested that low‐energy biphasic waveform defibrillation (BWD) is followed by less post‐resuscitation left ventricular (LV) dysfunction when compared with higher‐energy monophasic waveform defibrillation (MWD). To the best of the authors' knowledge, the effect of cardiopulmonary resuscitation (CPR) duration and total ischemia time on LV function after countershock, controlling for waveform type, has not been evaluated. Objective: To determine the effect of CPR duration on LV function after MWD and BWD. Methods: VF was electrically induced in anesthetized and instrumented swine. After 5 minutes of VF, the animals were randomized to MWD (n = 22) or one of two BWDs (n = 46). If countershock terminated VF but was followed by a nonperfusing rhythm, conventional manual CPR without drug therapy was performed until restoration of spontaneous circulation (ROSC), defined as a systolic arterial pressure >60 mm Hg for 10 minutes without vasopressor support. Systolic LV pressure (LVP), LV dP/dt (first derivative of pressure measured over time), and cardiac output (CO) were measured at intervals for 60 minutes postresuscitation. CPR times (times to ROSC) and hemodynamic variables for the three groups were compared. Multivariable linear regression was performed to assess the contribution of defibrillation waveform, total joules, and CPR time on LVP, LV dP/dt, and CO at 15, 30, and 60 minutes postresuscitation. Results: When analyzed as groups, significant differences in median number of shocks to terminate VF, total joules, or CPR time were not observed between waveform groups. Regression analysis demonstrated that increasing CPR time was associated with a significant effect on indices of LV function at 15 and 30 minutes postresuscitation. Global LV function was not influenced by waveform type or total joules. Conclusions: Adjustment for CPR time, a determinant of total myocardial ischemia time, is necessary when defibrillation waveforms are compared for their effect on postresuscitation cardiac function and short‐term outcome.

Left ventricular function after monophasic and biphasic waveform defibrillation: the impact of cardiopulmonary resuscitation time on contractile indices.

Previous work has suggested that low-energy biphasic waveform defibrillation (BWD) is followed by less post-resuscitation left ventricular (LV) dysfunction when compared with higher-energy monophasic waveform defibrillation (MWD). To the best of the authors' knowledge, the effect of cardiopulmonary resuscitation (CPR) duration and total ischemia time on LV function after countershock, controlling for waveform type, has not been evaluated. To determine the effect of CPR duration on LV function after MWD and BWD. VF was electrically induced in anesthetized and instrumented swine. After 5 minutes of VF, the animals were randomized to MWD (n = 22) or one of two BWDs (n = 46). If countershock terminated VF but was followed by a nonperfusing rhythm, conventional manual CPR without drug therapy was performed until restoration of spontaneous circulation (ROSC), defined as a systolic arterial pressure >60 mm Hg for 10 minutes without vasopressor support. Systolic LV pressure (LVP), LV dP/dt (first derivative of pressure measured over time), and cardiac output (CO) were measured at intervals for 60 minutes postresuscitation. CPR times (times to ROSC) and hemodynamic variables for the three groups were compared. Multivariable linear regression was performed to assess the contribution of defibrillation waveform, total joules, and CPR time on LVP, LV dP/dt, and CO at 15, 30, and 60 minutes postresuscitation. When analyzed as groups, significant differences in median number of shocks to terminate VF, total joules, or CPR time were not observed between waveform groups. Regression analysis demonstrated that increasing CPR time was associated with a significant effect on indices of LV function at 15 and 30 minutes postresuscitation. Global LV function was not influenced by waveform type or total joules. Adjustment for CPR time, a determinant of total myocardial ischemia time, is necessary when defibrillation waveforms are compared for their effect on postresuscitation cardiac function and short-term outcome.

A Comparison of Biphasic and Monophasic Waveform Defibrillation After Prolonged Ventricular Fibrillation

Study objectiveTo compare the effects of biphasic defibrillation waveforms and conventional monophasic defibrillation waveforms on the success of initial defibrillation, postresuscitation myocardial function, and duration of survival after prolonged duration of untreated ventricular fibrillation (VF), including the effects of epinephrine. DesignProspective, randomized, animal study. SettingAnimal laboratory and university-affiliated research and educational institute. ParticipantsDomestic pigs. InterventionsVF was induced in 20 anesthetized domestic pigs receiving mechanical ventilation. After 10 min of untreated VF, the animals were randomized. Defibrillation was attempted with up to three 150-J biphasic waveform shocks or a conventional sequence of 200-J, 300-J, and 360-J monophasic waveform shocks. When reversal of VF was unsuccessful, precordial compression was performed for 1 min, with or without administration of epinephrine. The protocol was repeated until spontaneous circulation was restored or for a maximum of 15 min. Measurements and resultsNo significant differences in the success of initial resuscitation or in the duration of survival were observed. However, significantly less impairment of myocardial function followed biphasic shocks. Administration of epinephrine reduced the total electrical energy required for successful resuscitation with both biphasic and monophasic waveform shocks. ConclusionsLower-energy biphasic waveform shocks were as effective as conventional higher-energy monophasic waveform shocks for restoration of spontaneous circulation after 10 min of untreated VF. Significantly better postresuscitation myocardial function was observed after biphasic waveform defibrillation. Administration of epinephrine after prolonged cardiac arrest decreased the total energy required for successful resuscitation.

Effects of Biphasic vs Monophasic Defibrillation on the Scaling Exponent in a Swine Model of Prolonged Ventricular Fibrillation

Mathematical analyses of ventricular fibrillation (VF) have resulted in the derivation of a measure termed the scaling exponent (ScE) that characterizes the duration of VF and probability of defibrillation success. The purpose of this study was to compare the effects of biphasic defibrillation waveform (BDW) and monophasic defibrillation waveform (MDW) rescue shocks on ScE in a swine model of prolonged VF. Utstein guidelines for the laboratory study of cardiopulmonary resuscitation were followed. Twenty mixed-breed domestic swine (mass range 20.5-26.8 kg) were instrumented and randomized to receive either MDW or BDW rescue shocks. Ventricular fibrillation was induced and untreated for a nonintervention interval of 8 minutes. Rescue shocks were delivered at 8, 10, and 12 minutes of elapsed VF time. The energy sequence for the three MDW shocks was 70, 100, and 150 J (approximately 3, 4, and 6 J/kg). All BDW shocks were delivered at 50 J (approximately 2.5 J/kg). Only VF was shocked. Chest compressions and drugs were not provided. Rhythm analysis and ScE calculation were performed offline. Continuous and discontinuous linear regression models were fit to plots of ScE vs time. Defibrillation success and progression of ScE slope were analyzed using Fisher's exact test, paired t-tests, and repeated-measures analysis of variance (ANOVA). Baseline characteristics were similar for both groups. Successful termination of VF occurred on the first rescue shock in 1 of 10 (10%) in the MDW group and 3 of 10 (30%) in the BDW group; this difference was not statistically significant (p = 0.58). No other defibrillation successes were observed. No animals achieved return of spontaneous circulation. The ScE values during the protocol progressed from 1.330 (95% CI = 1.287 to 1.373) to 1.724 (95% CI = 1.603 to 1.845) for MDW and 1.338 (95% CI = 1.261 to 1.415) to 1.639 (95% CI = 1.530 to 1.745) for BDW. Both groups showed a trend toward increasing ScE values with successive rescue shocks. Repeated-measures ANOVA using both continuous and discontinuous models demonstrated no difference in overall ScE slope progression between study groups. Mode of defibrillation waveform (BDW vs MDW) does not appear to impact ScE trends. Additional studies must be performed to better evaluate the clinical implications of this finding.

Low-energy biphasic waveform defibrillation reduces the severity of postresuscitation myocardial dysfunction.

Both clinical and experimental studies have demonstrated substantial impairment of ventricular function after resuscitation from cardiac arrest. Indeed, postresuscitation myocardial dysfunction has been implicated as a potentially important mechanism, accounting for fatal outcomes after successful resuscitation in 70% of victims within the first 72 hrs. Recent experimental studies implicated the total electrical energy delivered during defibrillation as an important correlate with the severity of postresuscitation myocardial dysfunction and postresuscitation survival. This prompted us to investigate the option of using lower electrical energy biphasic waveform defibrillation. We compared the effects of low-energy biphasic waveform defibrillation with conventional monophasic waveform defibrillation after a short (4 mins), intermediate (7 mins), or prolonged (10 mins) interval of untreated ventricular fibrillation. Biphasic waveform defibrillation with a fixed energy of 150 joules proved to be as effective as conventional monophasic damped sine waveform defibrillation for restoration of spontaneous circulation, with significantly lower delivered energy. This was associated with significantly less severity of postresuscitation myocardial dysfunction. The low-energy biphasic waveform defibrillation is, therefore, likely to be the future direction of transthoracic defibrillation in settings of cardiopulmonary resuscitation.

The effects of biphasic and conventional monophasic defibrillation on postresuscitation myocardial function

OBJECTIVESThe purpose of this study was to compare the effects of biphasic defibrillation waveforms and conventional monophasic defibrillation waveforms on the success of initial defibrillation, postresuscitation myocardial function and duration of survival after prolonged ventricular fibrillation (VF).BACKGROUNDWe have recently demonstrated that the severity of postresuscitation myocardial dysfunction was closely related to the magnitude of the electrical energy of the delivered defibrillation shock. In the present study, the effects of fixed 150-J low-energy biphasic waveform shocks were compared with conventional monophasic waveform shocks after prolonged VF.METHODSTwenty anesthetized, mechanically ventilated domestic pigs were investigated. VF was induced with an AC current delivered to the right ventricular endocardium. After either 4 or 7 min of untreated ventricular fibrillation (VF), the animals were randomized for attempted defibrillation with up to three 150-J biphasic waveform shocks or conventional sequence of 200-, 300- or 360-J monophasic waveform shocks. If VF was not reversed, a 1-min interval of precordial compression preceded a second sequence of up to three shocks. The protocol was repeated until spontaneous circulation was restored or for a total of 15 min.RESULTSMonophasic waveform defibrillation after 4 or 7 min of untreated VF resuscitated eight of 10 pigs. All 10 pigs treated with biphasic waveform defibrillation were successfully resuscitated. Transesophageal echo-Doppler, arterial pressure and heart rate measurements demonstrated significantly less impairment of cardiovascular function after biphasic defibrillation.CONCLUSIONSLower-energy biphasic waveform shocks were as effective as conventional higher energy monophasic waveform shocks for restoration of spontaneous circulation after 4 and 7 min of untreated VF. Significantly better postresuscitation myocardial function was observed after biphasic waveform defibrillation.

49. Waveform Design Based on Cardiac Electrophysiology Can Improve Transchest Defibrillation

Introduction: Monophasic defibrillation waveforms are presently the standard of care in clinical use for trans-thoracic defibrillation. Recently, there has been renewed interest in biphasic waveforms. This interest reflects the superior performance demonstrated with biphasic waveforms in implantable defibrillators (ICD). External defibrillation research on two biphasic truncated exponential waveforms has been reported in which the waveforms were compared clinically to a damped sine waveform. A limitation of these transthoracic waveforms is the insufficiency of fundamental design principles used to determine the waveform characteristics.Methods: We developed design principles to determine the optimal waveform characteristics of an external biphasic truncated exponential waveform based on myocardial cell response model. The cell response model incorporates critical transthoracic elements into a recently published and experimentally validated intracardiac model used to design ICD waveforms. We determined the optimal leading-edge voltage (LEV), phase durations (in milliseconds, Ph1 D, Ph2 D), and delivered energies (ED) for the reported external biphasic waveforms (WF) using the model with 78 W for trans-chest resistance. We compared our results against those reported for the biphasic waveforms.

Biphasic Waveform Defibrillation Using a Three‐Electrode Transvenous Lead System in Humans

Biphasic waveform defibrillation is not always more efficacious than monophasic waveform defibrillation. Waveform efficacy appears to vary with the lead system used. In this prospective, randomized study, defibrillation efficacy with biphasic and monophasic single capacitor 120-microF, 65% tilt pulses was compared for a lead system consisting of right ventricular (RV), chest patch (CP), and superior vena cava (SVC) electrodes. Although this lead system is commonly used with monophasic pulses in transvenous defibrillators, few studies have examined the defibrillation efficacy of this lead system in man for biphasic waveform defibrillation. Fourteen cardiac arrest survivors undergoing defibrillator implantation were included in the study using pulses delivered from a cathodal RV electrode simultaneously to anodal SVC and CP electrodes. Biphasic and monophasic waveforms were recorded oscilloscopically to acquire defibrillation threshold (DFT) data on leading edge voltage requirements and for stored energy. The monophasic DFT voltage was 661 +/- 177 V compared to the biphasic DFT voltage of 451 +/- 185 V (P < 0.0001). The monophasic DFT stored energy was 28.0 +/- 13.4 J compared to the biphasic DFT stored energy of 14.1 +/- 12.4 J (P < 0.0001). The stored energy DFT was < or = 15 J in only 2 of 14 patients (15%) with monophasic defibrillation but < or = 15 J in 10 of 14 (71%) patients with biphasic defibrillation. These findings indicate that biphasic defibrillation with an RV, SVC, CP transvenous electrode system is substantially more efficient than monophasic defibrillation, allowing for higher numbers of patients to receive transvenous defibrillators with a relatively simple lead system at a satisfactory cutoff DFT safety margin of 15 J.

Functional damage to the heart caused by monophasic and biphasic defibrillation waveforms

Although external cardiac defibrillation is generally recognized to be highly effective, repeated discharges of submaximal or maximal energy may lead to marked disturbances of myocardial contraction and relaxation [2-4], postcardioversion arrhythmias (including fibrillation) [1,9-11], and electromechanical dissociation and/or asystole [2,10], as well as to serious morphological lesions in the myocard ium, including infarction [8,10]. The quoted studies, however, are mainly concerned with monophasic defibrillation waveforms widely used in the West, whereas more effective, but less well studied, biphasic waveforms are used in countries of the former USSR. In the present study, functional damage caused to the heart by monophasic waveforms (Edmark pulses) were compared to those caused by asymmetrical quasisinusoidal biphasic waveforms (Gurvitch pulses).

Comparison of biphasic and monophasic defibrillation waveforms in an isolated rabbit heart preparation

The aims were to develop a Langendorff rabbit heart model and to compare monophasic and biphasic defibrillation pulses. Hearts were perfused with a Krebs-Henseleit solution and two 1.4 cm2 Pt-Ir mesh patch electrodes were sutured onto the ventricles. A 5 ms monophasic or 10 ms biphasic pulse, with randomly selected voltages of 30, 50, 70, 90, 110, or 130 V, defibrillated the heart after 10 s of fibrillation. 11 adult male New Zealand white rabbits weighing 2.8(0.27) kg, were used for the studies. A total of 72 fibrillation and defibrillation sequences were conducted in each preparation. The results were fitted to a sigmoidal dose-response curve by logistic regression analysis. Voltage and energy values from the fitted data at 50% and 80% success (V50, V80, E50, E80) indicated a significantly lower (p less than 0.05) defibrillation threshold voltage and energy for the biphasic waveform [V50 = 48 (SD19) V, V80 = 87(27) V, E50 = 0.15(0.12) J, E80 = 0.48(0.29) J] compared with the monophasic waveform [V50 = 79(20) V, V80 = 110(20) V, E50 = 0.27(0.12) J, E80 = 0.5(0.12) J]. There was no observed difference in defibrillation success rate between the first and second halves of any study. The Langendorff rabbit heart model is suitable for assessing electrical fibrillation and defibrillation mechanisms. Defibrillation can be achieved with a lower energy when using a biphasic rather than a monophasic pulse.

Electrode system influence on biphasic waveform defibrillation efficacy in humans.

Several clinical studies have demonstrated a general superiority of biphasic waveform defibrillation compared with monophasic waveform defibrillation using epicardial lead systems. To test the breadth of utility of biphasic waveforms in humans, a prospective, randomized evaluation of defibrillation efficacy of monophasic and single capacitor biphasic waveform pulses was performed for two distinct nonthoracotomy lead systems as well as for an epicardial electrode system in 51 cardiac arrest survivors undergoing automatic defibrillator implantation. The configurations tested consisted of a right ventricular-left ventricular (RV-LV) epicardial patch-patch system, an RV catheter-chest patch (CP) nonthoracotomy system, and a coronary sinus (CS) catheter-RV catheter nonthoracotomy system. For each configuration, the defibrillation current and voltage waveforms were recorded via a digital oscilloscope to measure defibrillation threshold voltage, current, resistance, and stored energy. Biphasic waveform defibrillation proved more efficient than monophasic waveform defibrillation for the epicardial RV-LV system (4.8 +/- 4.1 versus 6.7 +/- 4.9 J, p = 0.047) and the nonthoracotomy RV-CP system (23.4 +/- 11.1 versus 34.3 +/- 10.4 J, p = 0.0042). Biphasic waveform defibrillation thresholds were not significantly lower than monophasic waveform defibrillation thresholds for the CS-RV nonthoracotomy system (15.6 +/- 7.2 versus 20.0 +/- 11.5 J, p = 0.11). Biphasic waveform defibrillation proved more efficacious than monophasic waveform defibrillation in 13 of 20 patients (65%) with RV-LV epicardial patches, 10 of 15 patients (67%) with an RV-CP nonthoracotomy system, and nine of 16 patients (56%) with an RV-CS nonthoracotomy system. Biphasic pulsing was useful with nonthoracotomy lead systems as well as with epicardial lead systems. However, the degree of biphasic waveform defibrillation superiority appeared to be electrode system dependent. Furthermore, for a few individuals, biphasic waveform defibrillation proved less efficient than monophasic waveform defibrillation, regardless of the lead system used.