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.     

Internal Cardioversion of Persistent Atrial Fibrillation Using Rectilinear Biphasic Waveform

Internal electrical cardioversion is currently used in patients with persistent atrial fibrillation resistant to external electrical cardioversion. In external cardioversion, biphasic waveforms have shown a greater efficacy than monomorphic waveforms. The present study aimed to test the safety and efficacy of rectilinear biphasic waveform in converting patients with persistent atrial fibrillation to sinus rhythm using internal electrical cardioversion, and to compare it with that of classical monophasic waveform. Twenty-seven consecutive patients with persistent AF received 31 internal cardioversions, using monophasic waveform in 11 (group I), and rectilinear biphasic waveform in 20 cases (group II). Baseline patients characteristics were similar in both groups. Multipolar catheters were positioned in the distal coronary sinus and in the high right atrium. Synchronised shocks were delivered using an escalating protocol of 2, 5, 10, 15, 20, 30, and 50 Joules. In group I, 1 patient was resistant to maximal energy (success rate 91%). The mean energy of the maximal shock was 18 ± 13 J. In group II, all patients were converted to sinus rhythm. The mean energy of the maximal shock was 9 ± 5 J (p < 0.01 vs. group I). No significant complications occurred. At 3 months follow-up, 45% of group I and 60% of group II patients remained in sinus rhythm (p = NS).We conclude that internal cardioversion using rectilinear biphasic waveform is feasible and safe, and requires less energy than classical monophasic waveforms.     

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.     

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.     

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.     

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.     

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.     

Transvenous internal cardioversion for atrial fibrillation: a randomized study on defibrillation threshold and tolerability of asymmetrical compared with symmetrical shocks.

The aim of the study was to compare, according to a randomized cross-over design, two different biphasic waveforms (6.5/2.5 ms and 3.0/3.0 ms phases duration, respectively) for low energy internal atrial cardioversion with regard to energy requirements for cardioversion and shock induced discomfort. METHODS: Nineteen patients with chronic persistent atrial fibrillation (AF)(mean duration 16+/-20 months) were submitted to internal atrial cardioversion (shock delivery between catheters in right atrium and coronary sinus, respectively) and were randomly allocated to baseline cardioversion with an asymmetrical biphasic shock (6.5/2.5 ms) or with a symmetrical biphasic shock (3.0/3.0 ms), according to a step up protocol. After baseline cardioversion, a sustained AF was reinduced and the patients crossed to the alternative waveform. The procedure was performed without routine administration of sedatives and shock induced discomfort was monitored by a subjective score (1 to 5). Sedatives or anesthetics were administered at patient's request. RESULTS: The procedure was effective in all the patients and was performed without need for sedatives/anesthetics in 17/19 patients (89%). Leading edge voltage of effective shocks resulted lower for asymmetrical shocks compared to symmetrical shocks (290+/-76 vs. 337+/-104 V, P<0.001) with no statistically significant differences in delivered energy (7.74+/-4.25 vs. 8.65+/-5.94 J). Moreover shock induced discomfort resulted lower for asymmetrical shocks compared to symmetrical (pain score=4.18+/-0.73 vs. 4.59+/-0.62, P<0.02). Shock impedence of effective shocks was 59+/-10 ohms for both waveforms. No significant complications occurred during the procedure and no ventricular arrhythmia was observed after atrial cardioversion. Transient bradycardia requiring support ventricular pacing was observed in one patient. CONCLUSIONS: Delivery of biphasic asymmetrical shocks (6.5/2.5 ms) results in lower leading edge voltage of effective shocks and better patients tolerability compared with conventional biphasic symmetrical shocks (3.0/3.0 ms). These findings are of interest both for transvenous internal cardioversion of chronic persistent AF and for implantable atrial defibrillators.     

A randomized trial comparing monophasic and biphasic waveform shocks for external cardioversion of atrial fibrillation

Background

We compared efficacy of and pain felt after biphasic truncated exponential (BTE) and monophasic damped sine (MDS) shocks in patients undergoing external cardioversion of atrial fibrillation (AF).

Methods

Patients with AF were randomized to BTE or MDS waveform cardioversion. Successive shocks were delivered at 70, 100, 200, and 360 J until successful cardioversion, with one 360 J attempt of the alternate waveform when all 4 shocks failed. Success was determined by blinded over-read of electrocardiograms. Peak current was calculated from energy and impedance. Patients rated their pain at 1 and 24 hours after cardioversion.

Results

Fourteen of 37 (38%) patients treated with MDS and 34 of 35 (97%) treated with BTE shocks were cardioverted at ≤200 J (P < .0001). Success rates of MDS versus BTE shocks were 5.4% versus 60% for 70 J, 19% versus 80% for ≤100 J, and 86% versus 97% for ≤360 J. BTE shocks cardioverted with less peak current (14.0 ± 4.3 vs 39.5 ± 11.2 A, P < .0001), less energy (97 ± 47 vs 278 ± 120 J, P < .0001), and less cumulative energy (146 ± 116 vs 546 ± 265 J, P < .0001). Patients felt less pain after BTE than MDS shocks at 1 hour (P < .0001) and 24 hours (P < .0001) after cardioversion.

Conclusion

This BTE waveform is superior to the MDS waveform for cardioversion of AF, requiring much less energy and current, and causing less postprocedural pain.     

Evaluation of the defibrillation threshold in atrial fibrillation by transoesophageal cardioversion using a biphasic impulse

INTRODUCTION: Recurrent atrial fibrillation (AF) in the setting of haemodynamic disturbances requires frequently repeated cardioversions, which is associated with the risk of myocardial damage. It is thus necessary to identify methods which can minimise the cardioverter impulse energy. AIM: To define the defibrillation threshold in recent-onset AF using a biphasic impulse, following an infusion of magnesium, potassium, and amiodarone. METHODS: Transoesophageal cardioversion was performed in 32 patients with AF lasting < or =48 hours, in whom prior administration of 40 mEq K+, 4.0 g MgSO4 and 300 mg amiodarone did not restore sinus rhythm. Cardioversion was performed under short intravenous anaesthesia using a biphasic impulse travelling from a multi-annular oesophageal electrode to two electrodes on the anterior chest wall. The initial energy was set to 1 J, which was subsequently increased according to the following protocol: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 40, 50 and 70 J. RESULTS: Electrical cardioversion following the administration of electrolytes and amiodarone restored sinus rhythm in all the patients (100% efficacy). The mean defibrillation threshold was 12.9+/-14.3 J, with a minimal effective energy of 1 J and a maximum effective energy of 70 J. The defibrillation threshold was in the range from 1 to 10 J in 75% of the patients. The mean cumulative energy transferred between electrodes during evaluation of the defibrillation threshold was 39.7 J (SD, 38.8). CONCLUSIONS: Transoesophageal cardioversion using a low-energy (mean, 12.9 J; range, 1-70 J) biphasic impulse, following the intravenous administration of potassium chloride and amiodarone, was 100% effective in restoring sinus rhythm in AF.     

Electrical cardioversion of atrial fibrillation

External direct current cardioversion remains the most common and effective method for restoration of normal sinus rhythm in patients with persistent AF. The development of biphasic defibrillators allows for higher success rates of conversion using standard energy levels. For persistent AF, an initial energy of 200 J is recommended for biphasic defibrillators, and 300 to 360 J are recommended for monophasic defibrillators, with the electrodes placed in the anterior posterior position. For refractory cases, alternatives are available such as dual defibrillators or internal cardioversion. Antiarrhythmic drugs may enhance the results of cardioversion by helping overcome shock failure or by preventing immediate recurrence of AF. Thromboembolism is the most important complication associated with cardioversion, but it can be prevented by providing 3 weeks of anticoagulation before the procedure or by excluding the presence of thrombi by transesophageal echocardiography, followed by an additional 4 weeks of anticoagulation.     

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.     

Waveform optimization for internal cardioversion of atrial fibrillation

Introduction

A novel atrial defibrillator was developed at the Royal Victoria Hospital in collaboration with the Nanotechnology and Integrated Bio-Engineering Centre, University of Ulster. This device is powered by an external pulse of radiofrequency energy and designed to cardiovert using low-tilt monophasic waveform (LTMW) and low-tilt biphasic waveform (LTBW), 12 milliseconds pulse width. This study compared the safety and efficacy of LTMW with LTBW for transvenous cardioversion of atrial fibrillation (AF).

Methods

Patients were anticoagulated with warfarin to maintain International Normalized Ratio between 2 and 3 for 4 weeks prior cardioversion. Warfarin international normalized ratio level was maintained in between 2 and 3 for 4 weeks prior cardioversion. St Jude's defibrillating catheter was positioned in the distal coronary sinus and right atrium and connected to the defibrillator via a junction box. After a test shock using a dummy load, the patient was cardioverted in a step-up progression from 50 to 300 V. Shock success was defined as return of sinus rhythm for 30 seconds or more. If cardioversion was unsuccessful at peak voltage, the patient was crossed over to the other arm of the waveform type and cardioverted at peak voltage.

Results

Thirty patients were randomized equally to LTBW and LTMW (15 each). Seven out of 15 patients (46%) cardioverted to sinus rhythm with LTBW, and 1 (6%) of 15, with LTMW (P = .035). Including crossover patients, 14 patients (46%) converted to sinus rhythm. After crossover, 4 patients were cardioverted with LTBW and 2 with LTMW. Overall mean voltage, current, and energy used for cardioversion were 270.53 ± 35.96 V, 3.68 ± 0.80 A, and 9.12 ± 3.73 J, respectively, and intracardiac impedance was 70.82 ± 13.46 Ω. For patients who were successfully cardioverted, mean voltage, current, energy, and intracardiac impedance were 268.28 ± 42.41 V, 3.52 ± 0.63 A, 8.51 ± 3.16 J, and 73.92 ± 12.01 Ω. There were no major adverse complications during the study. Cardiac markers measured postcardioversion were unremarkable.

Conclusion

Low-tilt biphasic waveform was more efficacious for low-energy transvenous cardioversion of AF. A significant proportion of patients were successfully cardioverted to sinus rhythm with low energy. Radiofrequency-powered defibrillation can be safely used for transvenous cardioversion of AF.     

Restoring Sinus Rhythm in Atrial Fibrillation: Electrical or Pharmacological Cardioversion

Restoration of sinus rhythm represents a desirable endpoint in patients with persistent (nonselfterminating) episode of paroxysmal atrial fibrillation (AF) and in selected patients with chronic AF. The decision whether to cardiovert AF pharmacologically or electrically is unresolved. Pharmacological cardioversion with oral quinidine first used to terminate recent onset AF is no longer used in Europe because its safety has been questioned. Other oral antiarrhythmic agents were used orally in this indication including procaînamide, disopyramide, and oral amiodarone. More recently, oral flecaînide and oral propafenone have been used in recent onset AF. Success rates ranging between 67% and 95% were reported in placebo-controlled studies. Pharmacological cardioversion can also routinely be obtained in hospital practice using intravenous injection of an antiarrhythmic agent. Intravenous digoxin, although commonly used, has shown in controlled studies to be no better than placebo. Intravenous amiodarone in open studies was associated with high success rates. Intravenous flecaînide, intravenous propafenone, and intravenous cibenzoline have been reported to be sucessful in recent onset AF. It is important to keep in mind that pharmacological cardioversion carries the risk of flutter with 1:1 conduction and ventricular proarrhythmia. The safety of pharmacological cardioversion using oral agents should be assessed in a hospital environment before allowing outpatient use. External (transthoracic) electrical cardioversion remains the technique of choice for restoring sinus rhythm in chronic AF. The success rates range from 65% to 90%. A technique of high energy electrical DC (200J or 300J) internal cardioversion has been shown to be useful in patients who failed external conversion. Recently, a technique for low-energy (> 6J) cardioversion of AF using biphasic shocks, electrode catheters positioned in the right atrium (cathode), and the coronary sinus (anode), was found to restore sinus rhythm in 70%-88% of patients. Internal cardioversion is emerging as a therapeutic alternative in selected groups of AF patients, particularly in those who failed external cardioversion.     

Effect of Electrode Configuration and Capacitor Size on Internal Atrial Defibrillation Threshold Using Leads Currently Used for Ventricular Defibrillation.

Background: Previous studies have shown that endocardial atrial defibrillation, using lead configurations specifically designed for ventricular defibrillation, is feasible but the substantial patient discomfort might prevent the widespread use of the technique unless significant improvements in shock tolerability are achieved. It has been suggested that the peak voltage or the peak current but not the total energy delivered determines the patient pain perception and therefore, lower defibrillating voltage and current achieved with modifications in lead and waveforms may increase shock tolerability. This study was undertaken to evaluate the effect, on the atrial defibrillation threshold (ADFT), of the addition of a patch electrode (mimicking the can electrode) to the right ventricle (RV)-superior vena cava (SVC) lead configuration. The influence of capacitor size on ADFT using the RV-SVC+skin patch configuration was also assessed.Methods: In 10 patients (pts) (Group 1) cardioversion thresholds were evaluated using biphasic shocks in two different configurations: 1) right ventricle (RV) to superior vena cava (SVC); 2) RV to SVC+skin patch. In a second group of twelve patients (Group 2) atrial defibrillation thresholds of biphasic waveforms that differed with the total capacitance (90 or 170 µF) were assessed using the RV to SVC+skin patch configuration.Results: In Group 1 AF was terminated in 10/10 pts (100 %) with both configurations. There was no significant difference in delivered energy at the defibrillation threshold between the two configurations (7.1 ± 5.1 J vs 7.1 ± 2.6 J; p < 0.05). In group 2 AF was terminated in 12/12 pts (100%) with both waveforms. The 170 µF waveform provided a significantly lower defibrillating voltage (323.7 ± 74.6 V vs 380 ± 70.2 V; p < 0.03) and current (8.1 ± 2.7 A vs 10.0 ± 2.3 A; p < 0.04) than the 90 µF waveform. All pts, in both groups, perceived the shock of the lowest energy tested (180 V) as painful or uncomfortable.Conclusions: The addition of a patch electrode to the RV-SVC lead configuration does not reduce the ADFT. Shocks from larger capacitors defibrillate with lower voltage and current but pts still perceive low energy subthreshold shocks as painful or uncomfortable.     

Internal low-energy cardioversion: a therapeutic option for restoring sinus rhythm in chronic atrial fibrillation after failure of external cardioversion.

AIMS: Conventional external cardioversion remains the technique of choice for restoration of sinus rhythm in patients with chronic atrial fibrillation (AF). Recent reports have suggested that internal low-energy cardioversion is efficient and safe in terminating AF in patients with failed external cardioversion. METHODS AND RESULTS: In 20 of 118 consecutive patients with spontaneous chronic AF (>7/days), who underwent low-energy cardioversion, one or more attempts at restoring sinus rhythm with external cardioversion had failed. Low-energy internal cardioversion was performed under light sedation. Shocks were delivered (using an external custom defibrillator) between two nonapolar catheters positioned in the right atrium (cathode) and in the coronary sinus (anode). Heart disease was present in 12 and absent in eight patients ('lone' atrial fibrillation). Atrial fibrillation was established for a period ranging from 12 days to 53 months. Low-energy internal cardioversion restored sinus rhythm in 15 of the 20 patients (75%) with a mean energy of 4.5+/-1.2 J, a mean conversion voltage of 355+/-53 V and a mean impedance of 63+/-8 ohms. No complications were observed. With a mean follow-up of 6+/-7 months, 11 patients (73%) were in stable sinus rhythm. CONCLUSIONS: This study provides evidence in support of low-energy internal cardioversion as a valuable therapeutic option in patients in whom conventional external cardioversion failed. This technique is safe and does not require general anaesthesia.     

Low-Energy Internal Cardioversion for Atrial Fibrillation Resistant to External Cardioversion

Internal Cardioversion. introduction : This report describes the electrical conversion of atrial fibrillation in two morbidly obese patients refractory to external cardioversion at 360 J.
Methods and Results : The two patients were lightly sedated and underwent placement of decapolar catheters in the coronary sinus and right atrial appendage. All ten electrodes of each decapolar catheter were electrically coupled, and defibrillation was attempted at successively increasing levels using a biphasic decaying exponential waveform generated by an external defibrillator. Both patients were returned to normal sinus rhythm using <10 J without complication.
Conclusion : Internal cardioversion is effective in restoration of sinus rhythm in some patients refractory to conventional forms of therapy     

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.     

Plateau waveform shape allows a much higher patient shock energy tolerance in AF patients

Objectives: To evaluate the possible pain reduction of the plateau waveform in atrial fibrillation (AF) patients. Background: Previous studies have indicated that reduced amplitude waveforms would be less painful than a conventional (65/65% tilt) biphasic waveform. Computer modeling suggested that a moderately long (10–12 msec) plateau (flat topped) shock waveform would deliver equivalent effectiveness with the lowest possible peak amplitude. Methods: We enrolled 27 patients at two sites with persistent AF with a total of 220 shocks delivered during internal atrial cardioversion using an interleaved crossover design. Patient response was scored in three ways: (1) a verbally reported discomfort score, (2) visual analog scale (VAS), and (3) a blinded observer reporting a contraction score. Results: All scores were significantly reduced (P < 0.0001) by the plateau waveform with impressive statistics: Verbal discomfort (3.51 ± 0.13 to 2.89 ± 0.12), VAS (7.00 ± 0.56 to 5.91 ± 0.36), and contraction scores (1.94 ± 0.12 to 1.62 ± 0.12). The average pain threshold shift (TS) for the Verbal score was 2.34, while that for the VAS score was 2.30. (This means that the patient typically could tolerate 2.34 times as much energy with the plateau waveform for the same level of verbally reported discomfort.) The contraction TS was less at 1.57. Response scores were also corrected for the shock sequence number to control for the sensitization effect from multiple shocks. This increased the TS for the Verbal score to 3.58, but the shock number was not significant for the VAS. A pulmonary artery electrode return was associated with lower pain compared with a coronary sinus position. Conclusion: A plateau shaped biphasic waveform resulted in significantly increased shock energy pain tolerances. Controlling for session sensitization, patients tolerated over three times as much energy for the same verbally reported discomfort score.     

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.