Rectilinear Biphasic Waveform Research Articles

Defibrillator maintenance policy.

Sir, A defibrillator is a life support equipment used for the purpose of sustaining life and whose failure to perform its primary function will lead to patient death in the absence of immediate intervention. Though this equipment is not used regularly, it is important that the daily check must be carried out. The manufacturer recommends 30 J (Joules) self-test as the daily test procedure for Zoll M® series defibrillator.[1] For regular maintenance and to ensure patient safety, we follow the International Electro-technical Commission (IEC) 62353 hospital safety guidelines.[2] Typically, pre-installation safety check on defibrillators is done before using it in patient care areas. During this first maintenance, two unusual problems were identified in eight of the 45 Zoll M® series defibrillators in our institution. The unit passed pre-use check at 30 J and showed ‘TEST OK’. Whereas to assess the ability of machine at higher joules, we tested by connecting to fluke defibrillator analyser[3] (model-Impulse 6000DP). It was noticed that above 100 J the machine was unable to charge, took unusually longer time (more than 30 s) for charging and unit showed error ‘defib fault 78’ (high voltage module failure). In addition, three other defibrillators passed maximum energy discharge procedure but failed internal discharge tests. During this test, the unit was charged to higher joules, but was unable to hold the charge for 60 s followed by an error code ‘defib fault 108’. As per the manufacturer, both these error codes are related to the failure of the high voltage module/capacitor section. Both these faults require replacement for proper functioning of the unit. The checklist followed is shown in Table 1. Table 1 Bi-annual maintenance by Quality Cell, Biomedical Engg. Division The matter was reported to the manufacturer who responded by recommending 3 different test procedures. First, the daily test procedure 30 J self-test which will be a low energy test to check the charging circuits, the integrity of cables, along with other circuits that are not tested during the normal power-up self-test. This includes a capacitor, high voltage module, and the bridge resistor network used with the rectilinear biphasic waveform. Hence, this test ensures these circuits are working satisfactorily at low energy. Second, a weekly check is carried out to test at higher energy level using Zoll electrocardiography (ECG) simulator. Third, the detailed half-yearly test procedure should be performed by the biomedical department in a hospital [Table 1]. Since, manufacturer recommendation involves simulator in pre-use check which are not available to the end users, we modified the daily check procedure to be carried out by the end user without diluting weekly or bi-weekly test procedure in 3 simple steps: Step 1 - perform 30 J test procedure; Step 2 - charge the unit to maximum energy level; Step 3 - the unit should hold the charged energy for 60 s without any error code displayed and discharges internally on its own. The detailed checklist for daily low energy and weekly test procedure is shown in Table 2. Table 2 Daily low energy test The proposed check procedures were tested on the problematic defibrillators and error codes appeared during internal discharge test without using defibrillator analyser and ECG simulator. This conforms to manufacture recommendation and authenticated. The bi-annual check will be executed by biomedical engineers as shown in Table 1. In conclusion, we propose a simplified three steps ‘daily check procedure’ for end users like the paramedical staff and/or doctors who are acquainted with the use of defibrillators. In addition, charging the unit to a maximum energy level at regular intervals extends the lifespan of electrical components that are not included in normal power-up self-test.

GENERATION OF RECTANGULAR BIPHASIC WAVEFORM TO DECREASE DEFIBRILLATION THRESHOLD FOR EXTERNAL DEFIBRILLATOR

Studies have shown that defibrillation threshold for current amplitude of biphasic truncated exponential (BTE) waveform has a hyperbolic strength–duration relationship. Theoretical and experimental results have shown that decreasing the tilt of BTE waveforms decreases the defibrillation threshold. On the other hand, low peak current waveform reduces probability of myocardium damage and burn. Therefore, achieving a waveform with low tilt and low peak current is desired. All DC defibrillators use a capacitor to store and deliver required energy. Because of capacitor discharging nature, the tilt of waveforms is high. In rectilinear biphasic waveform (RBW), which was generated by ZOLL M-series defibrillator, the tilt of the first phase was decreased using an adjustable resistor connected in series with current path. But the defibrillator cannot keep the current constant in the second phase and in the both phases for high transthoracic impedances (TTI) either. In this paper, for solving these problems, a circuit that generates rectangular biphasic waveform is designed. In this circuit, five resistors are used and connected in series. Then an IGBT switch is connected to each resistor in parallel. Also, control of minimum current ripple is applied in order to decide which resistors should be worked in each time. The circuit is simulated in MATLAB/Simulink and a prototype model is constructed. Results demonstrate that the tilt of the waveform is notably reduced to a value less than 10%.

Retrospective evaluation of current-based impedance compensation defibrillation in out-of-hospital cardiac arrest

ObjectiveTransthoracic impedance (TTI) is a principal parameter that influences the intracardiac current flow and defibrillation outcome. In this study, we retrospectively evaluated the performance of current-based impedance compensation defibrillation in out-of-hospital cardiac arrest (OHCA) patients. MethodsECG recordings, along with TTI measurements were collected from multiple emergency medical services (EMSs) in the USA. All the EMSs in this study used automated external defibrillators (AEDs) which employing rectilinear biphasic (RLB) waveform. The distribution and change of TTI between successive shocks, the influence of preceding shock results on the subsequent shock outcome, and the performance of current-based impedance compensation defibrillation was evaluated. ResultsA total of 1166 shocks from 594 OHCA victims were examined in this study. The average TTI for the 1st shock was 134.8Ω and a significant decrease in TTI was observed for the 2nd (p<0.001) and 3rd (p=0.033) sequential escalating shock. But TTI did not change after the 3rd shock. A higher success rate was observed for shocks with preceding defibrillation success. The success rate remained unchanged over the whole spectrum of TTI. ConclusionThe average TTI was relatively higher in this OHCA population treated with RLB defibrillation as compared with previously reported data. TTI was significantly decreased after 1st and 2nd successive escalating shock but kept constant after the 3rd shock. Preceding shock success was a better predictor of subsequent defibrillation outcome other than TTI. Current-based impedance compensation defibrillation resulted in equivalent success rate for high impedance patients when compared with those of low impedance.

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

Performance of a rectilinear biphasic waveform in defibrillation of presenting and recurrent ventricular fibrillation: A prospective multicenter study

Objectives We tested the hypothesis that shock success differs with initial and recurrent episodes of ventricular fibrillation (VF). Methods From September 2008 to March 2010 out-of-hospital cardiac arrest patients with VF as the initial rhythm at 9 study sites were defibrillated by paramedics using a rectilinear biphasic waveform. Shock success was defined as termination of VF within 5 s post-shock. We used generalized estimating equation (GEE) analysis to assess the association between shock type (initial versus refibrillation) and shock success. Results Ninety-four patients presented in VF. Mean age was 65.4 years, 78.7% were male, and 80.9% were bystander-witnessed. VF recurred in 75 (79.8%). There were 338 shocks delivered for initial ( n = 90) or recurrent ( n = 248) VF available for analysis. Initial shocks terminated VF in 79/90 (87.8%) and subsequent shocks in 209/248 (84.3%). GEE odds ratio (OR) for shock type was 1.37 (95% CI 0.68–2.74). After adjusting for potential confounders, the OR for shock type remained insignificant (1.33, 95% CI 0.60–2.53). We observed no significant difference in ROSC (54.7% versus 52.6%, absolute difference 2.1%, p = 0.87) or neurologically intact survival to hospital discharge (21.9% versus 33.3%, absolute difference 11.4%, p = 0.31) between those with and without VF recurrence. Conclusions Presenting VF was terminated with one shock in 87.8% of cases. We observed no significant difference in the frequency of shock success between initial versus recurrent VF. VF recurred in the majority of patients and did not adversely affect shock success, ROSC, or survival.

Performance of a rectilinear biphasic waveform in defibrillation of presenting and recurrent ventricular fibrillation: A prospective multicenter study

Performance of a rectilinear biphasic waveform in defibrillation of presenting and recurrent ventricular fibrillation: A prospective multicenter study

Part 6: Defibrillation

Part 6: Defibrillation

Part 6: Electrical Therapies

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

Comparison of efficacy of pulsed biphasic waveform and rectilinear biphasic waveform in a short ventricular fibrillation pig model

Aim of study The waveform designs and their relative defibrillation efficacy of external biphasic waveforms may differ remarkably among manufacturers. In this study, we compared pulsed biphasic waveform (PBW) with rectilinear biphasic waveform (RBW) and their effects on terminating ventricular fibrillation (VF). Methods VF was electrically induced and untreated for 10 s in 6 domestic pigs weighing between 56 and 70 kg. The animals were then randomized to attempt defibrillation with either a PBW or RBW shock at energy levels of 50–200 J. If the delivered shock failed to terminate VF, a 150 J rescue shock was delivered with the same waveform. After a recovery interval of 4 min, the sequences were repeated for a total of 60 test shocks. The 50% and 80% defibrillation thresholds (DFT) were then calculated for the compared waveforms. Results No differences were observed in energy DFT50 and DFT80. Although the peak current and average current of the PBW were higher than RBW, there was no change observed in ST segment following shocks with both waveforms. Conclusion In the setting of this experiment, there was no difference in terms of defibrillation efficacy and myocardial injury related to the electrical shocks of the two waveforms.

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

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

Comparison of rectilinear biphasic waveform with biphasic truncated exponential waveform in a pediatric defibrillation model

To compare the rectilinear biphasic waveform with a biphasic truncated exponential waveform for pediatric defibrillation. Prospective, randomized study. Experimental laboratory of a university-affiliated research institute. Male domestic piglets (4-24 kg). Eleven piglets (4-8 kg), which represented a patient <1 yr old, and ten piglets (16-24 kg), which represented a pediatric patient between the ages of 2 and 8 yrs, were anesthetized, intubated, and mechanically ventilated. Ventricular fibrillation was induced and maintained for 30 secs, and a predetermined shock was then delivered to defibrillate. Following defibrillation, the animal was permitted to stabilize hemodynamically for 4 mins. Fifty shocks were applied to each animal using a randomization schedule based on a predetermined permutation of 50. The 50 shocks were 25 shocks for each rectilinear biphasic and biphasic truncated exponential waveforms, comprising five shocks at five energy settings. Each group of five shocks was fixed at a predetermined energy value, depending on the body weight of the animal. Dose-response curves were constructed using logistic regression. Aortic pressure, electrocardiogram, left ventricular pressure, and left ventricular pressure value of 40 mm Hg were continually measured. Dose-response curves determined defibrillation thresholds at 50% (D50) and 90% (D90) probability of success. The rectilinear biphasic waveform defibrillated with <90% of the D50 and D90 energies required for a biphasic truncated exponential waveform. The rectilinear biphasic waveform also successfully defibrillated with significantly less energy per body weight and per heart weight compared with a biphasic truncated exponential waveform. The rectilinear biphasic waveform has superior defibrillation performance compared with a biphasic truncated exponential waveform in a piglet defibrillation model for young children.

Effects of biphasic waveforms on outcomes of cardiopulmonary resuscitation in a porcine model of prolonged cardiac arrest*

The effects of two clinically available biphasic waveforms on the success of defibrillation and postresuscitation myocardial dysfunction after prolonged ventricular fibrillation were compared with two newly designed dual-path sequential and simultaneous rectilinear biphasic waveforms. Defibrillation via sequential pulses and encircling, overlapping multiple pathway may depolarize a larger myocardial mass and facilitate transthoracic defibrillation. Animal study. Experimental laboratory. Thirty-two 40 +/- 3 kg pigs. Ventricular fibrillation was ischemically induced in 32 pigs. After 7 mins of untreated ventricular fibrillation, cardiopulmonary resuscitation was initiated and continued for 5 mins. Animals were then randomized to receive up to three shocks with a) single-path rectilinear biphasic waveform; b) single-path biphasic truncated exponential waveform; c) dual-path rectilinear biphasic sequential defibrillation; or d) dual-path rectilinear biphasic simultaneous defibrillation. Rectilinear biphasic, dual-path sequential defibrillation, and simultaneous defibrillation had significantly fewer shocks (1.1 +/- 0.4, 1.4 +/- 0.5, 1.3 +/- 0.7, respectively) before restoration of spontaneous circulation than biphasic truncated exponential waveform (2.6 +/- 1.4, p < .005) and less postresuscitation myocardial dysfunction (p < .05). Also, dual-path sequential defibrillation had higher postresuscitation ejection fraction than rectilinear biphasic and dual-path simultaneous defibrillation (p < .005). The energy requirements for terminating ischemically induced ventricular fibrillation were significantly lower and minimized early postresuscitation myocardial dysfunction in the rectilinear biphasic, dual-path sequential defibrillation, and simultaneous defibrillation than the biphasic truncated exponential waveform. Dual-path sequential defibrillation had less postresuscitation myocardial dysfunction than rectilinear biphasic and dual-path simultaneous defibrillation, but at 72 hrs these differences were no longer significant.

A simple point score system for predicting the efficacy of external rectilinear biphasic cardioversion for persistent atrial fibrillation

To develop a simple point score system that can accurately predict the optimal energy of initial rectilinear biphasic (RLB) waveform shock for cardioversion (DC) of persistent atrial fibrillation (AF). Data from 302 consecutive patients with AF who underwent a step-up protocol of sequential shocks of 50 J-from 1 up to 2 J/kg-200 J of RLB waveform DC were prospectively examined. Using a logistic regression model, three variables independently predicted the need for 2 J/kg shocks: AF duration > 7 months, previous DC, and increased left atrial (LA) diameter > 4.5 cm. A simplified point score system (REBICAF score) that spans from 0 to 4 was developed. The score gives two points for AF duration > 7 months and one point for previous DC or LA diameter > 4.5 cm. The area under the receiver operator curve (ROC) of the proposed score for predicting the need for 2 J/kg shock was 0.84. There was a progressive increase in the need for 1 J/kg, 2 J/kg, and 200 J as the point score increased (P < 0.001, chi2 test for trend). More than 90% cumulative success rate was achieved in the low- (0-1), intermediate- (2), and high-REBICAF (3-4) score subgroups with 1 J/kg, 2 J/kg, and 200 J RLB shocks, respectively. A simple point score system is useful in prediction of successful initial RLB energy for DC of AF.

Major Changes in the 2005 AHA Guidelines for CPR and ECC

The emergency cardiovascular care (ECC) scientists involved in the 2005 evidence evaluation process and the revision of the 2005 AHA Guidelines for CPR and ECC began and ended the process aware of the limitations of the resuscitation scientific evidence, optimistic about emerging data that documents the benefits of high-quality cardiopulmonary resuscitation (CPR), and determined to make recommendations that would increase survival from cardiac arrest and life-threatening emergencies. This editorial summarizes the factors that contributed to the tipping point, the point at which information and discussion either triggered support for major changes in the guidelines or reaffirmed existing recommendations. The scientists critically reviewed the sequence and priorities of the steps of CPR to identify those factors with the greatest potential impact on survival. They then developed recommendations to support those interventions that should be performed frequently and well. There was unanimous support for increased emphasis on ensuring that rescuers deliver high-quality CPR: rescuers need to provide an adequate number and depth of compressions, allow complete chest recoil after each compression, and minimize interruptions in chest compressions. The 2005 AHA Guidelines for CPR and ECC are based on the most comprehensive review of resuscitation literature ever published.1 The evidence evaluation process incorporated the input of 281 international resuscitation experts who evaluated research, topics, and hypotheses over a 36-month period before the 2005 Consensus Conference. The process included structured evidence evaluation, analysis, and documentation of the literature.2 It also included rigorous disclosure and management of potential conflicts of interest, a process summarized in two editorials.3,4 Cardiopulmonary resuscitation and emergency cardiovascular care is a relatively new field. The epidemiologic data is incomplete, and high-level evidence is insufficient to support many recommendations. Although sudden cardiac arrest (SCA) is responsible for an estimated 250 000 deaths out of the hospital in the United …

Responses to Written Notification during Out-of-hospital Care Trials Using Waiver of Informed Consent

Resuscitation research has been allowed to proceed using waiver of consent when compliance with guidelines is assured. In these circumstances, institutional review boards (IRBs) may request notification of enrolled patients. To describe the notification process developed with IRB feedback and implemented in two out-of-hospital randomized controlled trials (RCTs) in a large urban setting. This was a descriptive review of two RCTs recruiting a total of 620 patients: the Out-of-hospital Cardiac Arrest Rectilinear Biphasic to Monophasic Damped Sine Defibrillation Waveforms with Advanced Life Support Intervention Trial (ORBIT), which compared rectilinear biphasic and monophasic damped sine waveform for out-of-hospital cardiac arrest, and the Prehospital Pacing versus Conventional Treatment Effectiveness Trial (PrePACE), which compared dopamine and transcutaneous pacing for unstable bradycardia. The ORBIT study enrolled 538 patients. In 44 (8%) patients, contact information could not be obtained. Notification was attempted for 494 (92%) patients; 48 (10%) letters were returned to sender. Researchers were contacted by telephone regarding 37 (8%) subjects: 16 (43%) requested information, 14 (38%) responded positively, and one (3%) did not return follow-up calls. Overall, two (0.4%) were withdrawn from the study. The PrePACE study enrolled 82 subjects. Contact information was unavailable for one (1%). For the remaining 81 patients, four (5%) letters were returned to sender. Researchers were contacted regarding ten (13%) subjects: seven (70%) requested information, two (20%) responded positively, and one (10%) did not return follow-up calls. No patient was withdrawn from the study. Contact information may be difficult to obtain for up to 20% of out-of-hospital critical patients. In 8% to 13% of cases, patients or designates contacted researchers; most feedback was positive. Frequently, non-study-related information was requested, consuming significant resources. Using this method, fewer than 1% of patients were withdrawn from the studies.

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

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. 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. 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 200 J. The MDS energy sequence was 50 up to 360 J. 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). 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.

Out-of-hospital cardiac arrest rectilinear biphasic to monophasic damped sine defibrillation waveforms with advanced life support intervention trial (ORBIT)

Background: Although biphasic defibrillation waveforms appear to be superior to monophasic waveforms in terminating VF, their relative benefits in out-of-hospital resuscitation are incompletely understood. Prior comparisons of defibrillation waveform efficacy in out-of-hospital cardiac arrest (OHCA) are confined to patients presenting in a shockable rhythm and resuscitated by first responder (basic life support). This effectiveness study compared monophasic and biphasic defibrillation waveform for conversion of ventricular arrhythmias in all OHCA treated with advance life support (ALS). Methods and results: This prospective randomized controlled trial compared the rectilinear biphasic (RLB) waveform with the monophasic damped sine (MDS) waveform, using step-up energy levels. The study enrolled OHCA patients requiring at least one shock delivered by ALS providers, regardless of initial presenting rhythm. Shock success was defined as conversion at 5 s to organized rhythm after one to three escalating shocks. We report efficacy results for the cohort of patients treated by ALS paramedics who presented with an initially shockable rhythm who had not received a shock from a first responder (MDS: n = 83; RLB: n = 86). Shock success within the first three ascending energy shocks for RLB (120, 150, 200 J) was superior to MDS (200, 300, 360 J) for patients initially presenting in a shockable rhythm (52% versus 34%, p = 0.01). First shock conversion was 23% and12%, for RLB and MDS, respectively ( p = 0.07). There were no significant differences in return of spontaneous circulation (47% versus 47%), survival to 24 h (31% versus 27%), and survival to discharge (9% versus 7%). Mean 24 h survival rates of bystander witnessed events showed differences between waveforms in the early circulatory phase at 4–10 min post event (mean (S.D.) RLB 0.45 (0.07) versus MDS 0.31 (0.06), p = 0.0002) and demonstrated decline as time to first shock increased to 20 min. Conclusion: Shock success to an organized rhythm comparing step-up protocol for energy settings demonstrated the RLB waveform was superior to MDS in ALS treatment of OHCA. Survival rates for both waveforms are consistent with current theories on the circulatory and metabolic phases of out-of-hospital cardiac arrest.

604 Sinus rhythm maintenance after DC cardioversion of atrial fibrillation, comparison of the rectilinear biphasic waveform with the monophasic damped sine waveform

604 Sinus rhythm maintenance after DC cardioversion of atrial fibrillation, comparison of the rectilinear biphasic waveform with the monophasic damped sine waveform

604 Sinus rhythm maintenance after DC cardioversion of atrial fibrillation, comparison of the rectilinear biphasic waveform with the monophasic damped sine waveform

604 Sinus rhythm maintenance after DC cardioversion of atrial fibrillation, comparison of the rectilinear biphasic waveform with the monophasic damped sine waveform

Comparative efficacy of monophasic and biphasic waveforms for transthoracic cardioversion of atrial fibrillation and atrial flutter

Transthoracic cardioversion fails to restore sinus rhythm in 6% to 33% of patients with atrial fibrillation. This study sought to determine the relative efficacy of biphasic waveforms compared with monophasic waveforms in the treatment of atrial arrhythmias. A total of 912 patients underwent 1022 transthoracic cardioversions between May 2000 and December 2001. A monophasic damped sine waveform was used in the first 304 cases, and a rectilinear biphasic defibrillator was used in the next 718 cases. Use of a biphasic waveform was associated with 94% success in conversion to sinus rhythm compared with 84% with a monophasic waveform (P < .001). The cumulative energy required to restore sinus rhythm was lower with biphasic shocks in both atrial fibrillation and atrial flutter groups (554 +/- 413 J for monophasic vs 199 +/- 216 J for biphasic shocks in the atrial fibrillation group, P < .001; 251 +/- 302 J vs 108 +/- 184 J, respectively, in the atrial flutter group, P < .001). In a multivariate analysis, use of a biphasic shock was associated with a 3.9-fold increase in success of cardioversion. When used to cardiovert atrial arrhythmias, the rectilinear biphasic waveform was associated with higher success rates and lower cumulative energies than the monophasic damped sine waveform.