A comparison of biphasic and monophasic waveform defibrillation after prolonged ventricular fibrillation

STUDY OBJECTIVE: 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 duration of untreated ventricular fibrillation (VF), including the effects of epinephrine. DESIGN: Prospective, randomized, animal study. SETTING: Animal laboratory and university-affiliated research and educational institute. PARTICIPANTS: Domestic pigs. INTERVENTIONS: VF 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 RESULTS: No 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. CONCLUSIONS: Lower-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.     

Monophasic versus biphasic transthoracic countershock after prolonged ventricular fibrillation in a swine model

OBJECTIVE: We sought to compare the defibrillation efficacy of a low-energy biphasic truncated exponential (BTE) waveform and a conventional higher-energy monophasic truncated exponential (MTE) waveform after prolonged ventricular fibrillation (VF). BACKGROUND: Low energy biphasic countershocks have been shown to be effective after brief episodes of VF (15 to 30 s) and to produce few postshock electrocardiogram abnormalities. METHODS: Swine were randomized to MTE (n = 18) or BTE (n = 20) after 5 min of VF. The first MTE shock dose was 200 J, and first BTE dose 150 J. If required, up to two additional shocks were administered (300, 360 J MTE; 150, 150 J BTE). If VF persisted manual cardiopulmonary resuscitation (CPR) was begun, and shocks were administered until VF was terminated. Successful defibrillation was defined as termination of VF regardless of postshock rhythm. If countershock terminated VF but was followed by a nonperfusing rhythm, CPR was performed until a perfusing rhythm developed. Arterial pressure, left ventricular (LV) pressure, first derivative of LV pressure and cardiac output were measured at intervals for 60 min postresuscitation. RESULTS: The odds ratio of first-shock success with BTE versus MTE was 0.67 (p = 0.55). The rate of termination of VF with the second or third shocks was similar between groups, as was the incidence of postshock pulseless electrical activity (15/18 MTE, 18/20 BTE) and CPR time for those animals that were resuscitated. Hemodynamic variables were not significantly different between groups at 15, 30 and 60 min after resuscitation. CONCLUSIONS: Monophasic and biphasic waveforms were equally effective in terminating prolonged VF with the first shock, and there was no apparent clinical disadvantage of subsequent low-energy biphasic shocks compared with progressive energy monophasic shocks. Lower-energy shocks were not associated with less postresuscitation myocardial dysfunction.     

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.     

The effects of biphasic waveform design on post-resuscitation myocardial function

OBJECTIVES: This study examined the effects of biphasic truncated exponential waveform design on survival and post-resuscitation myocardial function after prolonged ventricular fibrillation (VF). BACKGROUND: Biphasic waveforms are more effective than monophasic waveforms for successful defibrillation, but optimization of energy and current levels to minimize post-resuscitation myocardial dysfunction has been largely unexplored. We examined a low-capacitance waveform typical of low-energy application (low-energy biphasic truncated exponential [BTEL]; 100 microF, < or =200 J) and a high-capacitance waveform typical of high-energy application (high-energy biphasic truncated exponential [BTEH]; 200 microF, > or =200 J). METHODS: Four groups of anesthetized 40- to 45-kg pigs were investigated. After 7 min of electrically induced VF, a 15-min resuscitation attempt was made using sequences of up to three defibrillation shocks followed by 1 min of cardiopulmonary resuscitation. Animals were randomized to BTEL at 150 J or 200 J or to BTEH at 200 J or 360 J. RESULTS: Resuscitation was unsuccessful in three of the five animals treated with BTEH at 200 J. All other attempts were successful. Significant therapy effects were observed for survival (p = 0.035), left ventricular ejection fraction (p < 0.001), stroke volume (p < 0.001), fractional area change (p < 0.001), cardiac output (p = 0.044), and mean aortic pressure (p < 0.001). Hemodynamic outcomes were negatively associated with energy and average current but positively associated with peak current. Peak current was the only significant predictor of survival (p < 0.001). CONCLUSIONS: Maximum survival and minimum myocardial dysfunction were observed with the low-capacitance 150-J waveform, which delivered higher peak current while minimizing energy and average current.     

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.     

双相电震致心律失常性的降低及其与高效除颤的关系

双相电震比单相电震除颤更有效，但其机制未明。除颤的易损性上限（ＵＬＶ）假说认为一个无效电震是由于它再次诱发了心室颤动（ＶＦ），因此研究ＶＦ诱发的机制可能有助于理解除颤的机制。单、双相电震以电震强度（ＳＳ）与偶联间期（ＣＩ）及波形随机结合的方式施加于Ｌａｎｇｅｎｄｏｒｆ灌流的兔离体心脏上，比较心脏对单、双相电震的ＶＦ易损性。结果心脏对双相电震的反应有如下几点不同于其对单相电震的反应：①易损区（ＡＯＶ）小（８．９±４．２个区域单位ｖｓ１３．９±６．０个区域单位，Ｐ＜０．０５）。②易损区与非心律失常反应区之间的过渡区窄（１４．７±４．８个区域单位ｖｓ２９．９±６．４个区域单位，Ｐ＜０．００１）。③双相电震将整个ＡＯＶ向更长的ＣＩ移动（左边界右移了１１．０±８．８ｍｓ，右边界右移了６．０±５．２ｍｓ，Ｐ均＜０．０１）。这种双相电震致心律失常性的降低可有助进一步解释双相电震除颤阈值降低的现象。     

Better outcome after pediatric defibrillation dosage than adult dosage in a swine model of pediatric ventricular fibrillation

OBJECTIVES: This study was designed to compare outcome after adult defibrillation dosing versus pediatric dosing in a piglet model of prolonged prehospital ventricular fibrillation (VF). BACKGROUND: Weight-based 2 to 4 J/kg monophasic defibrillation dosing is recommended for children in VF, but impractical for automated external defibrillator (AED) use. Present AEDs can only provide adult shock doses or newly developed attenuated adult doses intended for children. A single escalating energy sequence (50/75/86 J) of attenuated adult-dose biphasic shocks (pediatric dosing) is at least as effective as escalating monophasic weight-based dosing for prolonged VF in piglets, but this approach has not been compared to standard adult biphasic dosing. METHODS: Following 7 min of untreated VF, piglets weighing 13 to 26 kg (19 +/- 1 kg) received either biphasic 50/75/86 J (pediatric dose) or biphasic 200/300/360 J (adult dose) therapies during simulated prehospital life support. RESULTS: Return of spontaneous circulation was attained in 15 of 16 pediatric-dose piglets and 14 of 16 adult-dose piglets. Four hours postresuscitation, pediatric dosing resulted in fewer elevations of cardiac troponin T (0 of 12 piglets vs. 6 of 11 piglets, p = 0.005) and less depression of left ventricular ejection fraction (p < 0.05). Most importantly, more piglets survived to 24 h with good neurologic scores after pediatric shocks than adult shocks (13 of 16 piglets vs. 4 of 16 piglets, p = 0.004). CONCLUSIONS: In this model, pediatric shocks resulted in superior outcome compared with adult shocks. These data suggest that adult defibrillation dosing may be harmful to pediatric patients with VF and support the use of attenuating electrodes with adult biphasic AEDs to defibrillate children.     

Optimization of transthoracic ventricular defibrillation-biphasic and triphasic shocks,waveform rounding,and synchronized shock delivery

The aim of this study is to optimize the truncated exponential waveform for transthoracic ventricular defibrillation. Discharge of a capacitor gives a fast-rising waveform with a spike; rounding of the waveform slows the rate of rise and removes the spike. Defibrillation thresholds for electrically induced VF were determined for rounded and conventional biphasic and triphasic waveforms (apex-anterior paddles; 130 microF capacitor; 3-10 ms phase duration), and for the Lown waveform in 29 anesthetized pigs. Rounding of the leading edge of the biphasic waveform reduced the threshold voltage and current for defibrillation at 3 + 3 ms and 6 + 6 ms phase duration, relative to the conventional unrounded biphasic or the Lown waveforms. The threshold delivered energy was lower for rounded truncated exponential biphasic shocks at 3 + 3 ms (55.3 +/- 2.5 J) than at 6 + 6 ms (67.6 +/- 2.9 J; reduction 15.9 +/- 3.8%; P <.001; n = 29) phase duration. Triphasic shocks (total duration 6-12 ms) showed no advantages over biphasic shocks in this model. The rounded waveform (6 + 6 ms phase duration) had a reduced delivered energy at threshold (9%) with transthoracic shock delivery synchronized to peak (71.1 +/- 4.2 J) or trough (71.5 +/- 4.9 J) of the high amplitude body surface electrocardiogram signal in ventricular fibrillation, compared with unsynchronized shocks (78.7 +/- 4.7 J; P <.05). In this study a biphasic, rounded waveform of total duration 6 or 12 ms, was optimal for the correction of electrically-induced ventricular fibrillation. Synchronization to the peak or trough of the high amplitude electrocardiogram signal gave a further reduction in the energy to defibrillate.     

Prospective comparison of biphasic and monophasic shocks for implantable cardioverter-defibrillators using endocardial leads.

Bidirectional shocks using 2 current pathways have been used in endocardial lead systems for implantable cardioverter-defibrillators, but the optimal shock waveform for endocardial defibrillation is unknown. The clinical efficacy and electrical characteristics of bidirectional monophasic and biphasic shocks for endocardial cardioversion-defibrillation of fast monomorphic or polymorphic ventricular tachycardia (VT), or ventricular fibrillation (VF) were evaluated. Thirty-three patients (mean age 60 +/- 12 years, and mean left ventricular ejection fraction 34 +/- 13%) were studied. Defibrillation catheter electrodes were located in the right ventricular apex and superior vena cava/right atrial junction. A triple-electrode configuration including the 2 catheter electrodes and a left thoracic patch was used to deliver bidirectional shocks from the right ventricular cathode to an atrial anode (pathway 1) and the thoracic patch (pathway 2). The shock waveforms examined were sequential and simultaneous monophasic, and simultaneous biphasic. The efficacy of 580 V (20 J) shocks for fast monomorphic VT were comparable for the 3 waveforms (73% for sequential monophasic, 73% for simultaneous monophasic, and 100% for simultaneous biphasic). However, for polymorphic VT and VF, 580 V sequential monophasic shocks had a significantly lower efficacy (25%) than did simultaneous monophasic (75%; p = 0.01) or biphasic (89%; p less than 0.001) shocks. Single-shock defibrillation thresholds with simultaneous biphasic shocks were significantly lower (9 +/- 5 J) than were those with simultaneous monophasic shocks (15 +/- 4 J; p less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)     

Early Out-of-Hospital Experience with an Impedance-Compensating Low-Energy Biphasic Waveform Automatic External Defibrillator

Impedance-compensating low-energy biphasic truncated exponential(BTE) waveforms are effective in transthoracic defibrillation ofshort-duration ventricular fibrillation (VF). However, the BTE waveform hasnot been examined in out-of-hospital cardiac arrest (OHCA) with patients inprolonged VF often associated with myocardial ischemia. The objective ofthis study was to evaluate the BTE waveform automatic externaldefibrillator (AED) in the out-of-hospital setting with long-duration VF.AEDs incorporating a 150-J BTE waveform were placed in 12 police squad carsand 4 paramedic-staffed advanced life support ambulances. AEDs were appliedto arrested patients by first-arriving personnel, whether police orparamedics. Data were obtained from PC Data Cards within the AED.Defibrillation was defined as at least transient termination of VF. Tenpatients, 64 ± 14 years, were treated for VF with BTE shocks.Another 8 patients were in nonshockable rhythms and the AEDs,appropriately, did not advise a shock. Five of the 10 VF arrests werewitnessed with a 911 call-to-shock time of 6.6 ± 1.7 minutes. VFdetection and defibrillation occurred in all 10 patients. Spontaneouscirculation was restored in 3 of 5 witnessed arrest patients and 1 survivedto discharge home. Fifty-one VF episodes were converted with 62 shocks. Presenting VF amplitude and rate were 0.43 ± 0.22 (0.13-0.86) mV and232 ± 62 (122-353) beats/min, respectively, and defibrillation wasachieved with the first shock in 7 of 10 patients. Including transientconversions, defibrillation occurred in 42 of 51 VF episodes (82%)with one BTE shock. Shock impedance was 85 ± 10 (39-138) ohms.Delivered energy and peak voltage were 152 ± 2 J and 1754 ±4 V, respectively. The average number of shocks per VF episode was 1.2± 0.5 (1-3). More than one shock was needed in only 9 episodes; nonerequired >3 shocks to defibrillate. Impedance-compensating low-energyBTE waveforms terminated VF in OHCA patients with a conversion rateexceeding that of higher energy monophasic waveforms. VF was terminated inall patients, including those with high impedance.     

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.     

The quality of chest compressions during cardiopulmonary resuscitation overrides importance of timing of defibrillation

BACKGROUND: We address the quality of chest compressions and the impact on initial defibrillation or initial chest compressions after sudden death. METHODS: Ventricular fibrillation was induced by occlusion of the left anterior descending coronary artery in 24 domestic pigs with a mean (+/- SD) weight of 40 +/- 2 kg. Cardiac arrest was left untreated for 5 min. Animals were then randomized to receive chest compressions-first or defibrillation-first and were further randomized to "optimal" or "conventional" chest compressions. A total of four groups of animals were investigated using a factorial design. For optimal chest compressions, the anterior posterior diameter of the chest was reduced by 25%, representing approximately 6 cm. Only 70% of this depth, or approximately 4.2 cm, represented conventional chest compressions. Chest compressions were delivered with a mechanical chest compressor. Defibrillation was attempted with a single biphasic 150-J shock. Postresuscitation myocardial function was echocardiographically assessed. RESULTS: Coronary perfusion pressures and end-tidal Pco(2) were significantly lower with conventional chest compressions. With optimal chest compressions, either as an initial intervention or after defibrillation, each animal was successfully resuscitated. Fewer shocks were required prior to the return of spontaneous circulation after initial optimal chest compressions. No animals were resuscitated when conventional chest compressions preceded the defibrillation attempt. When defibrillation was attempted as the initial intervention followed by conventional chest compressions, two of six animals were resuscitated. CONCLUSIONS: In this animal model of cardiac arrest, it was the quality of the chest compressions, rather then the priority of either initial defibrillation or initial chest compressions, that was the predominant determinant of successful resuscitation.     

External cardioversion of atrial fibrillation: comparison of biphasic vs monophasic waveform shocks.

AIMS: It is well established in transthoracic ventricular defibrillation that biphasic truncated waveform shocks are associated with superior defibrillation efficacy when compared with damped sine wave monophasic waveform shocks. The aim of this study was to explore whether biphasic waveform shocks were superior to monophasic waveform shocks for external cardioversion of atrial fibrillation (AF). METHODS AND RESULTS: Fifty-seven patients in whom cardioversion of AF was indicated were randomized in this prospective study, to transthoracic cardioversion with either monophasic damped sine waveform shocks or biphasic impedance compensating waveform shocks. In the group randomized to monophasic waveform shocks (27 patients), a first shock of 150 J was delivered, followed (if necessary) by a 360 J shock. In the biphasic waveform group (30 patients), the first shock had an energy of 150 J and (if necessary) a second 150 J was delivered. All shocks were delivered in the anterolateral chest pad position. Sinus rhythm was restored in 16 patients (51%) with the first monophasic shock and in 27 patients (86%) with the first biphasic shock. The difference was statistically significant (P=0.02). After the second shock, sinus rhythm was obtained in a total of 24 patients (88%) with monophasic shocks and in 28 patients (93%) with biphasic shocks. No complication was observed in either group and cardiac enzymes (CK, CKmb, troponin I, myoglobin) did not show any significant changes. CONCLUSION: This study suggests that at the same energy level of 150 J, biphasic impedance compensating waveform shocks are superior to monophasic damped sine waveform shocks cardioversion of atrial fibrillation.     

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.     

Postresuscitation stunning: postfibrillatory myocardial dysfunction caused by reduced myofilament Ca2+ responsiveness after ventricular fibrillation-induced myocyte Ca2+ overload

INTRODUCTION: Resuscitation from ventricular fibrillation (VF), particularly from prolonged VF, frequently is complicated by postfibrillatory myocardial dysfunction (postresuscitation stunning). We tested whether this dysfunction can be caused by reduced myofilament Ca2+ responsiveness after VF-induced myocyte Ca2+ overload. We also tested whether electrical defibrillation shocks contribute to this dysfunction. METHODS AND RESULTS: Myofilament Ca2+ responsiveness was estimated as ratio of left ventricular developed pressure over myocyte Ca2+ transient amplitudes (assessed as indo-1 fluorescence) in isolated perfused rat hearts before, during, and after VF (1.5 or 10 min) comparing three modes of defibrillation (biphasic electrical shocks, lidocaine, or spontaneous). We found that, independent of these defibrillation modes, myofilament Ca2+ responsiveness was significantly reduced, particularly after prolonged VF, although hearts were not ischemic or acidotic during and after VF (unchanged coronary flow, myocardial oxygen consumption, and pH of the coronary effluent). This reduction was associated with VF-induced myocyte Ca2+ overload and increasing or decreasing Ca2+ overload during VF (using 1 microM diltiazem or 6 mM extracellular calcium) led to parallel changes of myofilament Ca2+ responsiveness. However, myofilament Ca2+ responsiveness was not associated with the defibrillation shock energy (range 0.1-15.0 J/g wet heart weight). CONCLUSION: Postfibrillatory myocardial dysfunction can be caused by reduced myofilament Ca2+ responsiveness after VF-induced myocyte Ca2+ overload. Electrical defibrillation shocks (up to 15 J/g wet heart weight), however, do not significantly contribute to this dysfunction. Our findings suggest that early additional therapy targeting intracellular Ca2+ overload may normalize myocyte Ca2+ and partially prevent postresuscitation stunning.     

A prospective randomized evaluation of biphasic versus monophasic waveform pulses on defibrillation efficacy in humans

Biphasic waveforms have been suggested as a superior waveform for ventricular defibrillation. To test this premise, a prospective randomized intraoperative evaluation of defibrillation efficacy of monophasic and biphasic waveform pulses was performed in 22 survivors of out of hospital ventricular fibrillation who were undergoing cardiac surgery for implantation of an automatic defibrillator. The initial waveform used in a patient for defibrillation testing, either monophasic or biphasic, was randomly selected. Subsequently, each patient served as his or her own control for defibrillation testing of the other waveform. The defibrillation threshold was defined as the lowest pulse amplitude that would effectively terminate ventricular fibrillation with a single discharge delivered 10 s after initiation of an episode of ventricular fibrillation induced with alternating current. Each defibrillation pulse was recorded oscilloscopically, and defibrillation pulse voltage, current, resistance and stored energy were measured. Fifteen (68%) of the 22 patients had a lower defibrillation threshold with the biphasic pulse, 3 (14%) had a lower threshold with the monophasic pulse and 4 (18%) had equal defibrillation thresholds (within 1.0 J) regardless of waveform. The mean leading edge defibrillation threshold voltage was 317 +/- 105 V when the monophasic pulse was used and 267 +/- 102 V (16% less) when the biphasic pulse was used (p = 0.008). Mean leading edge defibrillation threshold current was 7.9 +/- 3.7 A when the monophasic pulse was used and 6.8 +/- 3.8 A (14% less) when the biphasic pulse was used (p = 0.051).(ABSTRACT TRUNCATED AT 250 WORDS)     

Multicenter study of principles-based waveforms for external defibrillation

STUDY OBJECTIVE: The efficacy of a shock waveform for external defibrillation depends on the waveform characteristics. Recently, design principles based on cardiac electrophysiology have been developed to determine optimal waveform characteristics. The objective of this clinical trial was to evaluate the efficacy of principles-based monophasic and biphasic waveforms for external defibrillation. METHODS: A prospective, randomized, blinded, multicenter study of 118 patients undergoing electrophysiologic testing or receiving an implantable defibrillator was conducted. Ventricular fibrillation was induced, and defibrillation was attempted in each patient with a biphasic and a monophasic waveform. Patients were randomly placed into 2 groups: group 1 received shocks of escalating energy, and group 2 received only high-energy shocks. RESULTS: The biphasic waveform achieved a first-shock success rate of 100% in group 1 (95% confidence interval [CI] 95.1% to 100%) and group 2 (95% CI 94.6% to 100%), with average delivered energies of 201+/-17 J and 295+/-28 J, respectively. The monophasic waveform demonstrated a 96.7% (95% CI 89.1% to 100%) first-shock success rate and average delivered energy of 215+/-12 J for group 1 and a 98.2% (95% CI 91.7% to 100%) first-shock success rate and average delivered energy of 352+/-13 J for group 2. CONCLUSION: Using principles of electrophysiology, it is possible to design both biphasic and monophasic waveforms for external defibrillation that achieve a high first-shock efficacy.     

Lidocaine Increases the Proarrhythmic Effects of Monophasic but not Biphasic Shocks

INTRODUCTION: Lidocaine increases monophasic shock defibrillation energy requirement (DER) values but does not alter biphasic shock DER values. However, the mechanism of this drug/shock waveform interaction is unknown. It may be that lidocaine increases the proarrhythmic actions of monophasic shocks but not biphasic shocks. Thus, lidocaine may increase monophasic shock DER values by increasing myocardial vulnerability to shock-induced ventricular fibrillation. METHODS AND RESULTS: Area of myocardial vulnerability (AOV), defined by a two-dimensional grid according to shock strength (y-axis) and shock coupling interval (x-axis), was assessed for biphasic shocks (n = 11) and monophasic shocks (n = 13) in intact swine hearts. Shocks were randomly delivered during right ventricular pacing at 10 shock strengths (50 to 500 V) and five coupling intervals (160 to 240 msec). AOV was defined as the number of points within the test grid that induced ventricular fibrillation. AOV, upper limit of vulnerability (ULV), and DER values were determined at baseline and during systemic infusion of lidocaine (10 mg/kg/hour). Lidocaine increased AOV, ULV, and DER values by 35%, 23%, and 36%, respectively, for monophasic shocks. However, lidocaine did not alter AOV, ULV, or DER values for biphasic shocks. CONCLUSION: Lidocaine increases the AOV to monophasic shocks, which is directly related to changes in ULV and DER values. This implies that lidocaine increases the proarrhythmic activity of monophasic shocks but not biphasic shocks. This may explain why lidocaine increases monophasic shock DER values.     

Comparison of four clinically used external defibrillators for transesophageal defibrillation

Introduction

Defibrillation thresholds (DFT) are lower when using biphasic instead of monophasic shock waveforms. In addition, transesophageal defibrillation can decrease the defibrillation threshold compared to thransthoracic defibrillation due to a different shock vector. We compared the defibrillation thresholds of a monophasic and three biphasic defibrillators in transesophageal defibrillation.

Methods

Ventricular fibrillation was electrically induced in 12 domestic pigs. Transesophageal defibrillation was performed between two cutaneous patch electrodes and one esophageal electrode. The lowest energy level with successful defibrillation was defined as the DFT. Using four commercially available defibrillators, DFTs were determined for monophasic, truncated exponential biphasic and rectilinear biphasic shock waveforms.

Results

DFTs for biphasic transesophageal shocks were significantly lower than for monophasic shocks, reducing DFT to about 50%. There was no significant difference between the three biphasic defibrillators with regard to DFT.

Conclusions

The choice of shock waveform can further decrease the already low DFT in transesophageal defibrillation. Similar to transthoracic defibrillation, biphasic shock waveforms yield lower DFTs in transesophageal defibrillation compared to monophasic shocks. The use of different biphasic waveforms does not seem to have a major effect on DFT in transesophageal defibrillation.     

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.