Biphasic versus monophasic shock waveform for conversion of atrial fibrillation: the results of an international randomized,double-blind multicenter trial

OBJECTIVES: This study compared a biphasic waveform with a conventional monophasic waveform for cardioversion of atrial fibrillation (AF). BACKGROUND: Biphasic shock waveforms have been demonstrated to be superior to monophasic shocks for termination of ventricular fibrillation, but data regarding biphasic shocks for conversion of AF are still emerging. METHODS: In an international, multicenter, randomized, double-blind clinical trial, we compared the effectiveness of damped sine wave monophasic versus impedance-compensated truncated exponential biphasic shocks for the cardioversion of AF. Patients received up to five shocks, as necessary for conversion: 100 J, 150 J, 200 J, a fourth shock at maximum output for the initial waveform (200 J biphasic, 360 J monophasic) and a final cross-over shock at maximum output of the alternate waveform. RESULTS: Analysis included 107 monophasic and 96 biphasic patients. The success rate was higher for biphasic than for monophasic shocks at each of the three shared energy levels (100 J: 60% vs. 22%, p < 0.0001; 150 J: 77% vs. 44%, p < 0.0001; 200 J: 90% vs. 53%, p < 0.0001). Through four shocks, at a maximum of 200 J, biphasic performance was similar to monophasic performance at 360 J (91% vs. 85%, p = 0.29). Biphasic patients required fewer shocks (1.7 +/- 1.0 vs. 2.8 +/- 1.2, p < 0.0001) and lower total energy delivered (217 +/- 176 J vs. 548 +/- 331 J, p < 0.0001). The biphasic shock waveform was also associated with a lower frequency of dermal injury (17% vs. 41%, p < 0.0001). CONCLUSIONS: For the cardioversion of AF, a biphasic shock waveform has greater efficacy, requires fewer shocks and lower delivered energy, and results in less dermal injury than a monophasic shock waveform.     

Transthoracic defibrillation of short-lasting ventricular fibrillation: a randomised trial for comparison of the efficacy of low-energy biphasic rectilinear and monophasic damped sine shocks

BACKGROUND: Biphasic rectilinear shocks are more effective than monophasic shocks for transthoracic atrial defibrillation and for ventricular arrhythmias during electrophysiological testing.We undertook the present study to compare the efficacy of 100 J rectilinear biphasic waveform shocks with 150 J monophasic damped sine waveform shocks for transthoracic defibrillation of true ventricular fibrillation during defibrillation threshold testing (DFT).The second aim of the study was to analyse the influence of patch positions on the efficacy of defibrillation. METHODS: 50 episodes of 14 patients (age ranging from 37 to 82 years) who underwent DFT testing were randomised for back-up shocks with either a sequence of 100 and 200 J biphasic waveform, or a sequence of 150 and 360 J conventional monophasic shocks. A binary search protocol was used at implantation and before hospital discharge. Patients were also randomised to an anteroposterior position versus a right-anterior-apical position. A crossover was performed between implantation and pre-hospital discharge for biphasic versus monophasic sequence as well as for the 2 different positions. RESULTS: After failed internal shocks, 27 episodes were treated with biphasic, and 23 with monophasic shocks.The first attempt by the external device did not terminate II episodes (2 biphasic, 9 monophasic).The first shock efficacy was significantly greater with biphasic than with monophasic shocks (p < 0.02).The overall success rate was 93% with biphasic shocks and 64% with monophasic shocks. In multivariate regression analysis including patch position, arrhythmia duration, type of waveform, testing order and session, only waveform was associated with successful defibrillation (p < 0.02). CONCLUSION: For transthoracic defibrillation of ventricular fibrillation, low-energy rectilinear biphasic shocks are more effective than monophasic shocks.The position of the defibrillation shock pads has no influence on the biphasic shock efficacy, but anteroposterior pad position is more effective using monophasic shocks.     

Biphasic Versus Monophasic Shock Waveform for Conversion of Atrial Fibrillation

Cardioversion of atrial fibrillation (AF) using traditional monophasic shock waveform is unsuccessful in up to 20% of cases, and often requires several shocks of up to 360 J. Based on the success with biphasic shock waveform in converting ventricular fibrillation, it was postulated that biphasic shocks would allow cardioversion with lower energy. In a international multicenter, double-blind, randomized trial of 203 patients, damped sine wave monophasic shocks were compared with impedance-compensated truncated exponential biphasic waveform shocks. Patients received up to five shocks: 100 J, 150 J, 200 J, a fourth shock at maximum output for the initial waveform (200 J biphasic, 360 J monophasic) and a final cross-over shock at maximum output of the alternate waveform. For each energy level, the biphasic waveform compared favorably to the monophasic waveform in successful cardioversion (100 J: 60% versus 22%, P < 0.0001; 150 J: 77% versus 44%, p < 0.0001; 200 J: 90% versus 53%, p < 0.0001). Success with 200 J biphasic was equivalent to 360 J monophasic shock (91% versus 85%, p = 0.29). Patients randomized to biphasic waveform required fewer shocks and lower total energy delivered; in addition, this waveform was associated with less dermal injury and no blistering. Biphasic shocks converted AF present for less than 48 hours with 80% efficacy, but conversion of AF present for more than 48 hours and more than 1 year the success rate was only 63 and 20%, respectively. The results of this study is similar to other investigations comparing biphasic and monophasic shock waveforms for conversion of atrial fibrillation. We recommend starting with biphasic energy of 100 J for atrial fibrillation of less than 48 hours duration, but using higher energies (150 J, 200 J or greater) when AF has been present for longer periods.     

Efficacy of transthoracic cardioversion of atrial fibrillation using a biphasic, truncated exponential shock waveform at variable initial shock energies

Biphasic shocks are more effective than damped sine wave monophasic shocks for transthoracic cardioversion (CV) of atrial fibrillation (AF), but the optimal protocol for CV with biphasic shocks has not been defined. We conducted a prospective, randomized study of 120 consecutive patients with persistent AF to delineate the dose-response curve for CV of AF with a biphasic truncated exponential shock waveform and to identify clinical predictors of shock efficacy. Our data suggest that the initial shock energy for CV with this waveform should be 200 J if the patient weighs <90 kg and 360 J if the patient weighs >/=90 kg.     

Comparison of a novel rectilinear biphasic waveform with a damped sine wave monophasic waveform for transthoracic ventricular defibrillation. ZOLL Investigators.

OBJECTIVES: We compared the efficacy of a novel rectilinear biphasic waveform, consisting of a constant current first phase, with a damped sine wave monophasic waveform during transthoracic defibrillation. BACKGROUND: Multiple studies have shown that for endocardial defibrillation, biphasic waveforms have a greater efficacy than monophasic waveforms. More recently, a 130-J truncated exponential biphasic waveform was shown to have equivalent efficacy to a 200-J damped sine wave monophasic waveform for transthoracic ventricular defibrillation. However, the optimal type of biphasic waveform is unknown. METHODS: In this prospective, randomized, multicenter trial, 184 patients who underwent ventricular defibrillation were randomized to receive a 200-J damped sine wave monophasic or 120-J rectilinear biphasic shock. RESULTS: First-shock efficacy of the biphasic waveform was significantly greater than that of the monophasic waveform (99% vs. 93%, p = 0.05) and was achieved with nearly 60% less delivered current (14 +/- 1 vs. 33 +/- 7 A, p < 0.0001). Although the efficacy of the biphasic and monophasic waveforms was comparable in patients with an impedance < 70 ohms (100% [biphasic] vs. 95% [monophasic], p = NS), the biphasic waveform was significantly more effective in patients with an impedance > or = 70 ohms (99% [biphasic] vs. 86% [monophasic], p = 0.02). CONCLUSIONS: This study demonstrates a superior efficacy of rectilinear biphasic shocks as compared with monophasic shocks for transthoracic ventricular defibrillation, particularly in patients with a high transthoracic impedance. More important, biphasic shocks defibrillated with nearly 60% less current. The combination of increased efficacy and decreased current requirements suggests that biphasic shocks as compared with monophasic shocks are advantageous for transthoracic ventricular defibrillation.     

Monophasic versus biphasic waveform shocks for atrial fibrillation cardioversion in patients with concomitant amiodarone therapy.

AIMS: With transthoracic cardioversion of atrial fibrillation (AF), biphasic are more effective than monophasic waveforms. We sought to determine the ideal energy levels for biphasic waveforms. Methods We compared biphasic truncated exponential waveforms with monophasic damped sine waveform defibrillators, in a prospective, single-centre, randomized (1:1 ratio) study. The study included 154 patients receiving concomitant amiodarone; 77 received serial biphasic (50, 100, 150, up to 175 J) and 77 monophasic shocks (100, 200, 300, up to 360 J), as necessary. Results First-shock efficacy was similar in the two groups (57 vs. 55%, P = 0.871, respectively), as were serial-shocks (90 vs. 92%, P = 0.780). Both groups received equal numbers of shocks (1.8 +/- 1.1 vs. 1.7 +/- 1.0, P = 0.921). In both groups, serum creatine kinase levels showed a small but significant increase. The increase was, however, higher in the monophasic group. CONCLUSION: In patients with concomitant amiodarone therapy, biphasic truncated exponential shocks, using half the energy, were as effective as monophasic damped sine shocks. The biphasic scheme was not more efficacious for cardioverting AF. In our population, a first shock of at least 100 J seemed advisable with either waveform. If necessary, escalating shocks must be performed, but ideal levels of increase per shock are still uncertain for biphasic waveforms.     

Biphasic versus monophasic cardioversion in shock-resistant atrial fibrillation:

Biphasic versus Monophasic Cardioversion. INTRODUCTION: Cardioversion of atrial fibrillation using monophasic transthoracic shocks occasionally is ineffective. Biphasic cardioversion requires less energy than monophasic cardioversion, but its efficacy in shock-resistant atrial fibrillation is unknown. Thus, we compared the efficacy of cardioversion using biphasic versus monophasic waveform shocks in patients with atrial fibrillation previously refractory to monophasic cardioversion. METHODS AND RESULTS: Fifty-six patients with prior failed monophasic cardioversion were randomized to either a 360-J monophasic damped sinusoidal shock or biphasic truncated exponential shocks at 150 J, followed by 200 J and then 360 J, if necessary. If either waveform failed, patients were crossed over to the other waveform. The primary endpoint was defined as the proportion of patients achieving sinus rhythm following initial randomized therapy. Stepwise multivariate logistic regression examined independent predictors of shock success, including patient age, sex, left atrial diameter, body mass index, drug therapy, and waveform. Twenty-eight patients were randomized to the biphasic shocks and 28 to the monophasic shocks. Sinus rhythm was restored in 61% of patients with biphasic versus 18% with monophasic shocks (P = 0.001). Seventy-eight percent success was achieved in patients who crossed over to the biphasic shock after failing monophasic cardioversion, whereas only 33% were successfully cardioverted with a monophasic shock after crossover from biphasic shock (P = 0.02). Overall, 69% of patients who received a biphasic shock at any point in the protocol were cardioverted successfully, compared to 21% with the monophasic shock (P < 0.0001). The type of shock was the strongest predictor of shock success (P = 0.0001) in multivariate logistic regression. CONCLUSION: An ascending sequence of 150-, 200-, and 360-J transthoracic biphasic cardioversion shocks are successful more often than a single 360-J monophasic shock. Thus, biphasic shocks should be the recommended configuration of choice for all cardioversions.     

Effect of shock polarity on the efficacy of transthoracic atrial defibrillation

Background The energy requirement for internal ventricular defibrillation is reduced by reversal of shock polarity. The influence of shock polarity on the efficacy of transthoracic atrial defibrillation is unknown. Methods This prospective, randomized study enrolled 110 consecutive patients who were referred for elective cardioversion of persistent atrial fibrillation (AF). The electrodes were placed in the anteroposterior position. The patients were randomized to receive either standard (anterior pad = cathode) or reversed polarity (anterior pad = anode) shocks with a damped sinusoidal monophasic waveform. A step-up protocol was used to estimate the cardioversion threshold. The initial shock energy was 50 J, with subsequent increments to 100, 200, 300, and 360 J in the event of cardioversion failure. Results Sixty-four percent of the patient population were men, with a mean age of 66 ± 13 years and a mean duration of AF of 242 ± 556 days. The overall success rates of cardioversion were 84% for standard polarity and 78% for reversed polarity (P not significant). Among the patients who were successfully cardioverted, the mean atrial defibrillation threshold was 198 ± 103 J for standard polarity and 212 ± 107 J for reversed polarity (P not significant). Conclusions Reversal of shock polarity does not improve transthoracic cardioversion efficacy with a standard damped sinusoidal monophasic waveform. Alternate strategies should be considered for patients who fail external cardioversion, such as adjunctive pharmacologic treatment, use of a biphasic shock waveform, or internal cardioversion. (Am Heart J 2002;143:541-5.)     

Prospective, randomized comparison of two biphasic waveforms for the efficacy and safety of transthoracic biphasic cardioversion of atrial fibrillation

OBJECTIVES: The purpose of this study was to determine if there is a difference in commercially available biphasic waveforms. BACKGROUND: Although the superiority of biphasic over monophasic waveforms for external cardioversion of atrial fibrillation (AF) is established, the relative efficacy of available biphasic waveforms is less clear. METHODS: We compared the effectiveness of a biphasic truncated exponential (BTE) waveform and a biphasic rectilinear (BR) waveform for external cardioversion of AF. Patients (N = 188) with AF were randomized to receive transthoracic BR shocks (50, 75, 100, 120, 150, 200 J) or BTE shocks (50, 70, 100, 125, 150, 200, 300, 360 J). Shock strength was escalated until success or maximum energy dose was achieved. If maximum shock strength failed, patients received the maximum shock of the opposite waveform. Analysis included 141 patients (71 BR, 70 BTE; mean age 66.5 +/- 13.7. Forty-seven randomized patients were excluded because of flutter on precardioversion ECG upon blinded review (n = 25), presence of intracardiac thrombus (n = 7), or protocol deviation (n = 15). Groups were similar with regard to clinical and echocardiographic characteristics. RESULTS: The success rate was similar for the two waveforms (93% BR vs 97 BTE, P = .44), although cumulative selected and delivered energy was less in the BTE group. Only AF duration was significantly different between successful and unsuccessful patients. No significant complications occurred. CONCLUSIONS: Biphasic waveforms were very effective in transthoracic cardioversion of AF, and complication rates were low. No significant difference in efficacy was observed between BR and BTE waveforms. Impedance was not an important determinant of success for either biphasic waveform.     

Novel rectangular biphasic and monophasic waveforms delivered by a radiofrequency-powered defibrillator compared with conventional capacitor-based waveforms in transvenous cardioversion of atrial fibrillation.

AIMS: To investigate the feasibility and efficacy of novel low-tilt biphasic waveforms in transvenous cardioversion of atrial fibrillation (AF), delivered by a radiofrequency-powered defibrillator. METHODS AND RESULTS: The investigation was performed in three phases in an animal model of AF: a feasibility and efficacy study (in 10 adult Large White Landrace swine), comparison with low-tilt monophasic and standard capacitor-based waveforms, and an assessment of sequential shocks delivered over several pathways (in 15 adult Suffolk sheep). Defibrillation electrodes were positioned transvenously under fluoroscopic control in the high lateral right atrium and distal coronary sinus. When multiple defibrillation pathways were tested, a third electrode was also attached to the lower interatrial septum. The electrodes were then connected to a radiofrequency (RF)-powered defibrillator or a standard defibrillator. After confirmation of successful induction of sustained AF, defibrillation was attempted. Percentage success was calculated from the effects of all shocks delivered to all the animals within each set of experiments. Of the low-tilt (RF) biphasic waveforms delivered during internal atrial cardioversion, 100% success was achieved with a 6/6 ms 100/-50 V waveform (1.45+/-0.01 J). This waveform was similar in efficacy to low-tilt (RF) monophasic waveforms (88 vs. 92% success, 1.58+/-0.01 vs. 2.67+/-0.03 J; P=NS; delivered energy 41% lower) and superior to equivalent voltage standard monophasic (50% success, 0.67+/-0.00 J; P<0.001) and biphasic waveforms (72% success, 0.69+/-0.00 J; P=0.03). Sequential shocks delivered over dual pathways did not improve the efficacy of low-tilt biphasic waveforms. CONCLUSION: A low-tilt biphasic waveform from a RF-powered defibrillator (6/6 ms 100/-50 V) is more efficacious than standard monophasic or biphasic waveforms (equivalent voltage) and is similar in efficacy to low-tilt monophasic waveforms.     

Reduced Cardioversion Thresholds for Atrial Fibrillation and Flutter Using the Rectilinear Biphasic Waveform

Background: The RLB waveform has been shown to be superior in overall efficacy to the MDS waveform for cardioversion of AF in one prospective study and one large retrospective analysis. However, little is known about the efficacy of the RLB waveform at lower energies.Objective: This study was undertaken to define the cardioversion thresholds for atrial fibrillation (AF) and flutter (FL) using the rectilinear biphasic (RLB) waveform and compare these to the cardioversion threshold using the conventional monophasic damped sine (MDS) waveform.Methods: All patients underwent transthoracic cardioversion of persistent AF and FL. We performed step-up cardioversion thresholds for AF in 180 RLB patients and 38 MDS patients and compared those results. We also performed cardioversion threshold determinations in 39 RLB patients with typical right atrial FL. For the RLB patients, an initial energy setting of 5 Joules (J) was selected, with increasing energy steps until success, up to 200J. The MDS energy sequence was 50 up to 360J.Results: The average selected energy threshold for AF using the RLB waveform was 70.6 J (median = 50 J) versus 193.4 J (median=150 J) for the MDS waveform (p < 0.001). For FL, the average cardioversion threshold using the RLB waveform was 33.2 J (median = 20 J; p < 0.001 vs. AF with the RLB waveform).Conclusions: Our results show that the transthoracic AF cardioversion threshold using the RLB waveform is significantly lower than the MDS waveform. As expected, the cardioversion threshold for FL was significantly lower than that of AF using the RLB waveform.     

Ambulatory electrocardioversion of atrial fibrillation by means of biphasic versus monophasic shock delivery. A prospective randomized study

Transthoracic electrical cardioversion using a monophasic waveform is the most common method converting persistent atrial fibrillation into sinus rhythm. Recently, cardioversion with a new biphasic waveform has shown promising results for treatment of atrial fibrillation. We undertook a randomized prospective trial comparing the efficacy and safety of the two waveforms for ambulatory cardioversion of atrial fibrillation. A total of 118 consecutive patients (mean age 62 years [SD 11]) presenting with persistent atrial fibrillation (mean duration 8 months [SD 11]) for ambulatory electrical cardioversion were randomized to receive either monophasic (n = 57) or biphasic shocks (n = 61). We used a standardized step-up protocol with increasing shock energies (100-360 joules) in either group. In all patients an anterior-posterior shock electrode position was used. If sinus rhythm was not achieved with the third (360 joules) shock, cardioversion was repeated with the opposite waveform. The two groups did not differ in demographic or disease-related data. The success rate was 100% for the biphasic and 73.7% for the monophasic waveform (p < 0.001). Biphasic patients required fewer shocks (1.5 versus 2.9) and a lower mean cumulative energy (203 versus 570 joules) (p < 0.001). Twelve out of 15 unsuccessfully treated monophasic patients were converted with biphasic shocks. The success rate for all 118 patients was 97.5%. No major acute complications were observed. For ambulatory transthoracic cardioversion of persistent atrial fibrillation biphasic shocks are of greater efficacy and require less energy than monophasic shocks. The procedure can be performed ambulatory and is safe regardless of shock waveform used.     

The Effects of Ventricular Fibrillation Duration and a Preceding Unsuccessful Shock on the Probability of Defibrillation Success Using Biphasic Waveforms in Pigs

Influence of VF Duration on Defibrillation Efficacy. introduction: While the defibrillation threshold has been reported to increase with ventricular fibrillation (VF) duration for monophasic waveforms, the effect of VF duration for biphasic waveforms is unknown. Methods and Results: The ED 50 requirements (the 50% probability of defibrillation success) for an endocardial lead system, which included a subcutaneous array, were determined by logistic regression using a recursive up-down algorithm for a biphasic waveform ((6/6 msec). The study was performed in two parts, each with eight pigs. In part 1, ED 50 was compared for shocks delivered after 10 seconds of VF and for shocks delivered after 20 seconds of VF following a failed first shock at 10 seconds. Energy at ED 50 decreased from 6.5 ± 0.9, J for shocks delivered after 10 seconds of VF to 4.9 ± 0.8, J (P < 0.01) for shocks delivered after 20 seconds. To determine if improved second shock efficacy was a result of preconditioning by the failed first shock or a function of VF duration, part 2 of the study compared defibrillation efficacy between shocks delivered after 10 seconds of VF with shocks delivered after 20 seconds of VF with and without a failed first shock at 10 seconds. Mean energy at ED 50 decreased from 10.1 ± 2.4, J for shocks delivered after 10 seconds of VF to 7.9 ± 2.4 J (P < 0.01) and 7.5 ± 3.2 J (P < 0.01) for shocks delivered after 20 seconds of VF with and without a failed first shock, respectively. The mean energy at KD 50 for shocks delivered after 20 seconds of VK with and without a failed first shock was not significantly different (P = 0.53). A strong linear correlation for energy at ED 50 was found between shocks delivered after 10 seconds of VF and shocks delivered after 20 seconds of VF following a failed first shock (r = 0.95, P < 0.01). Conclusion: (1) As opposed to monophasic shocks, ED 50 is significantly lower for biphasic shocks delivered after 20 seconds of VF compared with shocks delivered after 10 seconds of VF in pigs. (2) An unsuccessful biphasic shock in pigs does not affect the defibrillation efficacy for a subsequent shock. (3) ED 50 for a biphasic shock delivered after 20 seconds of VK is linearly related to ED 50 for a shock delivered after 10 seconds of VK.     

Comparison of biphasic and monophasic waveforms in epicardial atrial defibrillation

Objectives. Because biphasic waveforms have previously been shown to be more efficient than monophasic waveforms in defibrillation of the ventricle, we compared the efficiency of the two waveforms in defibrillation of the atria.Background. The development of an implantable atrial defibrillator would offer significant advantages over current approaches to the management of atrial fibrillation. Patient tolerance of atrial shocks from such a device, however, would depend critically on the deployment of an efficient waveform.Methods. Both the monophasic and biphasic shocks were of 8-ms duration, and the biphasic was a dual-capacitor waveform with equal first- and second-phase duration and leading-edge voltage. One hundred randomized atrial shocks were evaluated in 21 patients during cardiopulmonary bypass. Atrial fibrillation was induced by the application of alternating current. Atrial shocks were delivered through customized, contoured epicardial paddles applied to the posterior left atrial wall (surface area 11 cm²) and to the anterior right atrial wall (surface area 26 cm²).Results. For the monophasic waveform the delivered energy (joules) associated with 50% success (E₅₀) was 1.44 J (95% confidence interval [CI] 0 to 11.2) and with 80% (E₈₀) success 3.9 J (95% CI 2.42 to 109.8); for the biphasic waveform 50% success was achieved with 0.37 J (95% CI 0.36 to 0.38) (p = NS) and 80% success with 0.57 J (95% CI 0.56 to 0.58) (p < 0.05).Conclusions. A biphasic waveform is more efficient than a monophasic waveform in atrial defibrillation. This may have implications for the development of an implantable atrial defibrillator for paroxysmal atrial fibrillation in addition to improvement of elective transthoracic and endocardial cardioversion of chronic atrial fibrillation.     

An Update on Electrical Cardioversion of Atrial Fibrillation

Atrial fibrillation is the most frequently encountered sustained arrhythmia in clinical practice. Electrical cardioversion of atrial fibrillation using damped sine wave shocks has been a mainstay of therapy for nearly 4 decades; its limitation remains a failure rate that approaches 20%. Although several alternatives have been proposed, including delivering 720 J shocks using dual monophasic defibrillators, ibutilide pretreatment and internal cardioversion, each of these approaches has significant limitations, which preclude its routine use. Recent data demonstrate that routine use of biphasic shocks for cardioversion of atrial fibrillation is associated with a marked improvement in cardioversion efficacy and suggest that biphasic shocks may be the preferred method for the transthoracic electrical cardioversion of atrial fibrillation.     

Immediate termination of fibrillation at 50% probability of overall success correlates with defibrillation dose-response curve width

INTRODUCTION: Issues in transthoracic defibrillation, including waveform shape, fixed versus escalating dose protocol, and low- versus high-energy shocks, can be addressed by examining the defibrillation dose-response curve. We tested the hypothesis that, for commonly used defibrillation waveforms, the steepness of the overall defibrillation dose-response curve, measured as normalized curve width, correlates with the probability of a successful defibrillation being immediate at the shock intensity producing 50% success. METHODS AND RESULTS: We used 16 isolated rabbit hearts to determine probability of overall success as a function of shock intensity and probability that a successful defibrillation is immediate rather than progressive (followed by several extrasystoles) at the shock intensity producing 50% overall defibrillation success. Two waveform pairs were tested--a monophasic damped sine versus a biphasic truncated exponential waveform commonly used for transthoracic defibrillation, and a monophasic/biphasic truncated exponential waveform pair similar to those used in internal cardioverter defibrillators. There was a close correlation between probability of a successful defibrillation being immediate at 150 and normalized curve width for the defibrillation dose-response curve. CONCLUSION: Our findings suggest that a high probability of successful defibrillation being immediate at low shock intensities is correlated with a narrow normalized curve width for the defibrillation dose-response curve.     

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

OBJECTIVES: The 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). BACKGROUND: We 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. METHODS: Twenty 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. RESULTS: Monophasic 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. CONCLUSIONS: Lower-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.     

Encircling overlapping multipulse shock waveforms for transthoracic defibrillation

Objectives. This study was performed to determine the efficacy of new encircling overlapping multipulse, multipathway waveforms for transthoracic defibrillation.

Background. Alternative waveforms for transthoracic defibrillation may improve shock success.

Methods. First, we determined the shock success achieved by three different waveforms at varying energies (18–150 J) in 21 mongrel dogs after short-duration ventricular fibrillation. The waveforms tested included the traditional damped sinusoidal waveform, a single pathway biphasic waveform, and a new encircling overlapping multipulse waveform delivered from six electrode pads oriented circumferentially. Second, in 11 swine we compared the efficacy of encircling overlapping multipulse shocks given from six electrode pads and three capacitors versus encircling overlapping shocks given from a device utilizing three electrodes and one capacitor.

Results. In the first experiment, the encircling overlapping waveform performed significantly better than biphasic and damped sinusoidal waveforms at lower energies. The shock success rate of the overlapping waveform (six pads) ranged from 67 ± 4% (at 18–49 J energy) to 99 ± 3% at ≥150 J; at comparable energies biphasic waveform shock success ranged from 26 ± 5% (p < 0.01 vs. encircling overlapping waveforms) to 99 ± 5% (p = NS). Damped sinusoidal waveform shock success ranged from 4 ± 1% (p < 0.01 vs. encircling overlapping waveform) to 73 ± 9% (p = NS). In the second experiment the three electrode pads, one capacitor encircling waveform achieved shock success rates comparable with the six-pad, three-capacitor waveform; at 18–49 J, success rates were 45 ± 15% versus 57 ± 12%, respectively (p = NS). At 100 J, success rates for both were 100%.

Conclusions. We conclude that encircling overlapping multipulse multipathway waveforms facilitate transthoracic defibrillation at low energies. These waveforms can be generated from a device that requires only three electrodes and one capacitor.     

Impact of biphasic electrical cardioversion of atrial fibrillation on early recurrent atrial fibrillation and shock efficacy

INTRODUCTION: Early recurrent atrial fibrillation (ERAF) after external cardioversion of atrial fibrillation (AF) occurs in 12% to 26% of patients. Whether biphasic cardioversion has an impact on the incidence of ERAF after cardioversion of AF is unclear. METHODS AND RESULTS: Consecutive patients (n = 216, mean age 66 years, 71% male, 88% with structural cardiovascular disease or hypertension) underwent cardioversion with a biphasic (Bi) or monophasic (Mo) shock waveform in randomized fashion. Energies used were 120-150-200-200 Ws (Bi) or 200-300-360-360 Ws (Mo). The two study groups (Bi vs Mo) did not differ with regard to age, sex, body mass index, underlying cardiovascular disease, left atrial diameter, left ventricular ejection fraction, duration of AF fibrillation, and antiarrhythmic drug therapy. Mean delivered energy was significantly lower in the Bi group (Bi: 186 +/- 143 Ws vs Mo: 324 +/- 227 Ws; P < 0.001). Overall incidence of ERAF (AF relapse within 1 minute after successful cardioversion) was 8.9% and showed no difference between the two groups (Bi: 8.1% vs Mo: 9.7%, P = NS). Cardioversion was successful in 95.4% of patients. The success rate was comparable in both groups (Bi: 94.3% vs Mo 96.8%; P = NS). First shock efficacy did not differ between Bi and Mo (76.4% vs 67.7%; P = NS). Mean number of shocks were 1.4 shocks per patient in both groups. CONCLUSION: Biphasic cardioversion allows comparable success rates with significantly lower energies. However, the incidence of ERAF is not influenced by biphasic cardioversion. With the energies used, biphasic and monophasic shock waveforms are comparable with regard to first shock and cumulative shock efficacy.     

Comparison of the rectilinear biphasic waveform with the monophasic damped sine waveform for external cardioversion of atrial fibrillation and flutter

External cardioversion using the monophasic damped sine (MDS) waveform is successful 70% to 94% of the time when using up to 360 J. The rectilinear biphasic (RLB) defibrillator has been shown to be superior in efficacy to the MDS waveform in atrial cardioversion in a small randomized study. This larger, retrospective study compares the results of the RLB waveform with those of the MDS waveform for cardioversion of atrial fibrillation (AF) and atrial flutter in a large cohort of patients. We performed 1,877 external cardioversion procedures in 1,361 patients for AF and atrial flutter by using the RLB defibrillator. We compared these results with those of the MDS defibrillator in 2,025 patients who underwent 2,818 cardioversion procedures. The overall success rates for the RLB defibrillator were 99.1% for AF and 99.2% for atrial flutter, and the corresponding success rates for the MDS defibrillator were 92.4% and 99.8% (p <0.001; RLB superior for AF). The median overall successful energy level for the MDS waveform was 200 J, whereas the corresponding RLB energy level was 100 J. Multivariate analyses demonstrated that underlying clinical conditions or use of antiarrhythmic drugs does not significantly affect overall success rates. Our results from >4,000 procedures confirmed and extended those of the previous report by showing a very high success rate for cardioversion of AF and atrial flutter using the RLB waveform. The MDS waveform was equally effective for atrial flutter but significantly less effective in terminating AF.