Comparison of monophasic and biphasic shocks for transthoracic cardioversion of atrial fibrillation

Absence of Arrhythmogenicity with Biphasic Pulsed Electric Fields Delivered to Porcine Airways

Pulsed electric field (PEF) technologies treat many types of tissue. Many systems mandate synchronization to the cardiac cycle to avoid the induction of cardiac arrhythmias. Significant differences between PEF systems make the assessment of cardiac safety from one technology to another challenging. A growing body of evidence suggests that shorter duration biphasic pulses obviate the need for cardiac synchronization, even when delivered in a monopolar fashion. This study theoretically evaluates the risk profile of different PEF parameters. It then tests a monopolar, biphasic, microsecond-scale PEF technology for arrhythmogenic potential. PEF applications of increasing likelihood to induce an arrhythmia were delivered. The energy was delivered throughout the cardiac cycle, including both single and multiple packets, and then with concentrated delivery on the t-wave. There were no sustained changes to the electrocardiogram waveform or to the cardiac rhythm, despite delivering energy during the most vulnerable phase of the cardiac cycle, and delivery of multiple packets of PEF energy across the cardiac cycle. Only isolated premature-atrial contractions (PAC) were observed. This study provides evidence that certain varieties of biphasic, monopolar PEF delivery do not require synchronized energy delivery to prevent harmful arrhythmias.

Trends in the use of electrical cardioversion for atrial fibrillation: influence of major trials and guidelines on clinical practice

BACKGROUND

The purpose of the present study was to assess the trends in the use of ECV following published studies that had compared rhythm and rate control strategies on atrial fibrillation (AF), and the recommendations included in the current clinical practice guidelines.

METHODS

The REVERCAT is a population-based assessment of the use of electrical cardioversion (ECV) in treating persistent AF in Catalonia (Spain). The initial survey was conducted in 2003 and the follow-up in 2010.

RESULTS

We observed a decrease of 9% in the absolute numbers of ECV performed (436 in 2003 vs. 397 in 2010). This is equivalent to 27% when considering population increases over this period. The patients treated with ECV in 2010 were younger, had a lower prevalence of previous embolism, a higher prevalence of diabetes, and increased body weight. Underlying heart disease factors indicated, in 2010, a higher proportion of NYHA ≥ II and left ventricular ejection fraction <30%. We observed a reduction in the number of ECV performed in 16 of the 27 (67%) participating hospitals. However, there was an increase of 14% in the number of procedures performed in tertiary hospitals, and was related to the increasing use of ECV as a bridge to AF ablation. Considering the initial number of patients treated with ECV, the rate of sinus rhythm at 3 months was almost unchanged (58% in 2003 vs. 57% in 2010; p=0.9) despite the greater use of biphasic energy in 2010 and a similar prescription of anti-arrhythmic drugs.

CONCLUSIONS

Although we observed a decrease in the number of ECVs performed over the 7 year period between the two studies, this technique remains a common option for treating patients with persistent AF. The change in the characteristics of candidate patients did not translate into better outcomes.

Part 8: adult advanced cardiovascular life support: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care

The goal of therapy for bradycardia or tachycardia is to rapidly identify and treat patients who are hemodynamically unstable or symptomatic due to the arrhythmia. Drugs or, when appropriate, pacing may be used to control unstable or symptomatic bradycardia. Cardioversion or drugs or both may be used to control unstable or symptomatic tachycardia. ACLS providers should closely monitor stable patients pending expert consultation and should be prepared to aggressively treat those with evidence of decompensation.

Intracardiac atrial defibrillation

Intravascular ventricular defibrillation and intravascular atrial defibrillation have many similarities. An important factor influencing the outcome of the shock is the potential gradient field created throughout the ventricles or the atria by the shock. A minimum potential gradient is required throughout the ventricles and probably the atria in order to defibrillate. The value of this minimum potential gradient is affected by several factors, including the duration, tilt, and number of phases of the waveform. For shock strengths near the defibrillation threshold, earliest activation following failed shocks arises in a region in which the potential gradient is low. The defibrillation threshold energy can be decreased by adding a third and even a fourth defibrillation electrode in regions where the shock potential gradient is low for the shock field created by the first two defibrillation electrodes and giving two sequential shocks, each through a different set of electrodes. However, the addition of more electrodes and sequential shocks complicates both the device and its implantation. Because patients are conscious when the atrial defibrillation shock is given, they experience pain during the shock, which is one of the main drawbacks of intravascular atrial defibrillation. Unfortunately, the pain threshold for defibrillation shocks is so low that a shock less than 1 J is uncomfortable and is not much less painful than shocks several times stronger. Therefore, even though electrode configurations exist that have lower atrial defibrillation threshold energy requirements than the atrial defibrillation threshold with standard defibrillation electrode configurations used in implantable cardioverter-defibrillators (ICDs) for ventricular defibrillation, they are not clinically practical because their shocks are almost as painful as with the standard ICD electrode configurations. Such electrode configurations would make the ICD more complicated, leading to greater difficulty and longer time required for implantation.

Low Energy Biphasic Waveform Cardioversion of Atrial Arrhythmias in Pediatric Patients and Young Adults

BACKGROUND

Low-dose biphasic waveform cardioversion has been used for the termination of atrial arrhythmias in adult patients. The energy required for termination of atrial arrhythmias in pediatric patients is not known. The objective of this study is to determine the minimum energy required for successful external cardioversion of atrial arrhythmias in pediatric patients using biphasic waveform current.

METHODS

Prospective study of all patients less than 24 years of age with and without congenital heart disease undergoing synchronized cardioversion for atrial arrhythmias. Patients were assigned to receive an initial biphasic energy shock of 0.2-0.5 J/kg and if unsuccessful in terminating the arrhythmia, subsequent sequential shocks of 1 and 2 J/kg would be administered until cardioversion was achieved. The end point of the cardioversion protocol was successful cardioversion or delivery of three shocks.

RESULTS

Between June 2005 and June 2006, 16 patients underwent biphasic cardioversion for atrial flutter or fibrillation. The mean age was 14.7 +/- 6.4 years (range: 2 weeks to 24 years). The mean weight was 51 +/- 21 kg (range: 3.8-82 kg). Seven patients had normal cardiac anatomy, three had a single ventricle (Fontan), two had a Senning operation; the remaining four patients had varied forms of congenital heart disease. The median length of time that the patients were in tachycardia was 12 hours (range: 5 minutes to 2 months). Using either transthoracic echocardiography (TTE) or transesophageal echocardiography (TEE), no thrombi were identified in any patient. All patients were successfully cardioverted with biphasic waveform energy. The successful energy shock was 0.35 +/- 0.19 J/kg (range: 0.2-0.9 J/kg). All but one patient were successfully cardioverted with less than 0.5 J/kg. The transthoracic impedance range was between 41 and 144 Omega; one patient had an impedance of 506 Omega (2-week-old infant with a weight of 3.8 kg). The mean current delivered was 5.4 +/- 2.2 A (range: 1-11 A).

CONCLUSION

Low-dose energy using biphasic waveform shocks can be used for successful termination of atrial arrhythmias in pediatric patients with and without congenital heart disease.

Acute anticoagulation adjustment in patients with atrial fibrillation at risk for stroke: approaches, strategies, risks and benefits

The acute management of anticoagulation in patients with atrial fibrillation to prevent stroke and other thromboembolic complications includes the use of individualized strategies tailored to the patient and based on the situation (cardioversion, surgeries, dental procedures, cardiac interventions, other invasive procedures and initiation of, or adjustment to, warfarin dosing). The vast range of choices can cause confusion and few randomized controlled clinical trials in this area provide adequate guidance. Chronic anticoagulation management is more straightforward since clinical evidence is ample, randomized clinical trial data provides cogent informaiton and guidelines have been established. Acute management of anticoagulation in patients with atrial fibrillation to prevent thromboembolic complications is often unrecognized but is emerging as a crucial, but challenging, and increasingly complex aspect of the care of patients with atrial fibrillation. This review addresses issues regarding such patients who may be at risk for stroke and require acute adjustments of anticoagulation (in light of, or in lieu of, chronic anticoagulation). Several promising new strategies are considered in light of established medical care. This analysis provides practical recommendations based on available data and presents results from recent investigations that may provide insight into future strategies.

Biphasic transoesophageal vs. transthoracic electrical cardioversion of persistent atrial fibrillation

OBJECTIVE

To compare the efficacy and safety of transoesophageal (TOC) vs. transthoracic (TTC) electrical cardioversion, both with biphasic shocks, for sinus rhythm (SR) restoration in patients with persistent atrial fibrillation (AF).

METHODS

We randomised 210 patients (151 male, 59 female, mean age 66 +/- 9 years) with persistent AF into two groups: group 1 (n = 104) undergoing TOC with a step-up protocol of 30, 50, 70 and 100 J, and group 2 (n = 106) undergoing TTC with a step-up protocol of 70, 100, 120 and 150 J.

RESULTS

The two groups were homogeneous as for clinical and instrumental characteristics, except for left ventricular ejection fraction (50.5 +/- 10% in group 1 vs. 53 +/- 8% in group 2, P < 0.05) and thoracic impedance (63 +/- 8 Omega in group 1 vs. 66 +/- 6 Omega in group 2, P < 0.005). SR was restored in 98 (94%) group 1 patients vs. 99 (93%) group 2 patients (P = NS). First shock was effective in 48 (46%) group 1 patients vs. 54 (51%) group 2 patients (P = NS). Mean delivered energy was 50.4 +/- 23.6 and 95.1 +/- 29.6 J; mean effective energy was 47.3 +/- 20.7 and 91.2 +/- 26.6 J in group 1 and group 2, respectively. Cross-over to the highest energy level was never effective. TOC tolerability was optimal (mean discomfort score 1.2 on a 1-4 grading scale). Markers of myocardial necrosis did not increase and no procedure-related complications occurred. On logistic regression analysis, the most predictive variables of unsuccessful cardioversion were AF duration (P = 0.0001) and low left atrial appendage emptying velocity (P = 0.02).

CONCLUSIONS

Both TOC and TTC with biphasic shocks are effective and safe for SR restoration in patients with persistent AF; however, the considerably lower levels of delivered and effective energies for SR restoration allow TOC to be performed during mild sedation with optimal tolerability, thus avoiding general anaesthesia.

[Comparison of two electrode positions in electrical cardioversion of atrial fibrillation]

OBJECTIVE

This study aims to compare effectiveness of electrical cardioversion (ECV) in patients with chronic atrial fibrillation (AF) according to the electrode positions: anteroapical (A-A) or anteroposterior (A-P). That which restores the sinus rhythm (SR) using the least energy is considered superior.

DESIGN

Observational study comparing two consecutive series of patients. SCOPE. Intensive Care Unit (ICU) of second level hospital.

PATIENTS AND METHODS

Out-patients in AF referred to the ICU for biphasic ECV. The first series began with position A-A and the second one with A-P, administering up to 3 shocks (150-200-200J), changing to the alternative position if SR was not achieved and administering 2 more shocks of 200J. Age, gender, weight, baseline heart disease, ejection fraction, left atrial size, AF time, baseline vital signs, antiarrhythmic medication, reversion to SR, number of shocks, energy used and side effects were analyzed and compared between both series. RESULTS. A total of 50 patients were treated in each group. The baseline characteristics were similar except for a greater percentage of women in group A-A. The anteroapical electrode position achieved SR with significantly fewer numbers of shocks and less energy, more frequently achieving reversion on the first shock.

CONCLUSIONS

We found greater effectiveness in the electrical cardioversion of the AF with the electrodes in the anteroapical position, that we recommend as first choice. If it is not effective, the A-P position should be attempted.

Biphasic cardioversion of acute atrial fibrillation in the emergency department

INTRODUCTION

There is a trend towards accelerated management of acute atrial fibrillation (AF) in the emergency department (ED). We report our experience with biphasic cardioversion of acute AF.

METHODS

This was a prospective, descriptive study at a tertiary hospital ED over a 6 month period. Acute AF was defined as symptoms that had been present for <48 hours. Patients who received biphasic cardioversion for acute AF in the ED were enrolled. Data collected included: patient demographics, past medical history, details of biphasic cardioversion, outcome, complications, disposition, and length of stay.

RESULTS

There were 34 attempts at cardioversion in 33 patients. The mean (SD) age was 56 (16) years and 21 patients (64%) were men. Biphasic cardioversion was successful in 31 attempts (91%). In 24 attempts (71%), 100 J was selected as the initial energy level. This was successful in 21 attempts (88%). There were three minor complications related to sedation. The mean (SD) length of stay was 5.6 (2.8) hours in the ED and 15 (25) hours in the hospital. The three patients who failed to revert were older (mean age 64 years), had underlying cardiovascular disease, and spent longer in hospital (50 v 12 hours, p = 0.01). Telephone follow up was conducted with 32 patients (97%) at 3 months. Recurrence of AF occurred in 7 patients (22%). Most patients (31, 97%) were satisfied with the biphasic cardioversion.

CONCLUSIONS

Biphasic cardioversion of acute AF is effective. The majority of patients can be managed as outpatients, and there is very high patient satisfaction with this approach. An initial shock energy level of 100 J is usually effective.

Four years experience of a nurse-led elective cardioversion service within a district general hospital setting

AIMS

External direct current cardioversion is an effective method of restoring sinus rhythm (SR) in patients with persistent atrial arrhythmias. Increasing demand for hospital beds, together with a reduction in junior doctors' hours, has adversely affected cardioversion provision. A regular nurse-led cardioversion service conducted in a dedicated hospital day-unit was introduced to resolve these constraints. There are limited data on the safety or efficacy of such a service.

METHODS AND RESULTS

All cardioversions between October 2000 and October 2004 were performed by an appropriately trained specialist nurse, under general anaesthesia. Patients attended a pre-assessment clinic. Energy requirements for initial and subsequent defibrillations were guided by a local protocol in accordance with the guidelines from American Heart Association, American College of Cardiology, and the European Society of Cardiology. Rectilinear biphasic defibrillation was introduced in January 2004 with an appropriate protocol amendment. In the absence of complications, the aim was to discharge patients the same day. A total of 578 cardioversions (475 monophasic; 103 biphasic) were performed on 464 patients [72.1% male, mean (+/- SD) age 67.8 +/- 9.4 years] with atrial fibrillation (AF) (89.7%) and atrial flutter (10.3%). SR was restored in 84.0 and 100% of patients with AF and atrial flutter, respectively, which increased to 90.2 and 100% following the introduction of biphasic defibrillation. Biphasic shocks cardioverted AF with less energy (163 +/- 22 vs. 289 +/- 81 J) and less cumulative energy (230 +/- 139 vs. 455+/-255 J) than monophasic (P < 0.001 for both), despite no difference in the duration of AF (P = 0.26) or patient age (P = 0.78). Two patients required hospital admission due to transient bradycardia; both were discharged within 72 h, without the need for permanent pacing. A total of 99.6% of patients was discharged home the same day; there were no deaths.

CONCLUSION

The provision of a nurse-led elective cardioversion service is feasible and effective, without compromising safety.

The role of biphasic shocks for transthoracic cardioversion of atrial fibrillation

The modern generation of transthoracic defibrillators now employ impedance compensated biphasic waveforms. These new devices are superior to those with monophasic waveforms and practice is currently switching to biphasic defibrillators for the treatment of both ventricular and atrial fibrillation. However, there is no universal guideline for the use of biphasic defibrillators in direct current cardioversion of atrial fibrillation. This article reviews the use of biphasic defibrillation waveforms for transthoracic cardioversion of atrial fibrillation.

Randomized comparison of anterolateral versus anteroposterior electrode position for biphasic external cardioversion of atrial fibrillation

BACKGROUND

In biphasic external cardioversion (CV) of atrial fibrillation (AF), the influence of different electrode positions on efficacy and incidence of early recurrent atrial fibrillation is not known. This study compared anteroposterior (AP) vs anterolateral (AL) electrode positioning.

METHODS

Consecutive patients referred for CV of persistent AF were randomized either to an AP or an AL electrode position. Biphasic external CV was performed with standardized electrode positions and rising energy delivery.

RESULTS

Both groups (N = 123, mean age 66 years, 71% male, 83% with structural cardiovascular disease or hypertension) did not differ concerning age, sex, body mass index, chronic antiarrhythmic therapy, duration of AF, left ventricular ejection fraction, and left atrial diameter. Cumulative success rates were comparable (AP 94.9% vs AL 95.2%, P = ns). First-shock efficacy did not differ (AP 78.3% vs AL 74.6%, P = ns). Early recurrent atrial fibrillation (AF relapse < 1 minute after successful CV) occurred in 8.1% (AP 11.6% vs AL 4.8%, P = ns). Mean number of shocks was 1.3 per patient with the AP configuration and 1.4 per patient with the AL configuration (P = ns). Mean cumulative energy delivery was also comparable (AP 171 WS vs AL 198 WS, P = ns).

CONCLUSIONS

Both electrode positions are similar in biphasic external CV of AF with regard to acute success and early recurrent atrial fibrillation. Also, the number of shocks needed and energy delivery are comparable with both electrode configurations.

Impedance compensated biphasic waveforms for transthoracic cardioversion of atrial fibrillation: a multi-centre comparison of antero-apical and antero-posterior pad positions

AIMS

To compare the success rate for transthoracic direct current cardioversion (DCC) of atrial fibrillation (AF) with antero-posterior (AP) and antero-apical (AA) electrode positions using an impedance compensated biphasic (ICB) waveform.

METHODS AND RESULTS

Three-hundred and seven patients [mean age 66 (SD+/-13), 195 male] with AF were recruited in three centres. Patients were randomized to an AA (n=150) or AP (n=144) pad position. Thirteen patients with implanted pacemakers were defaulted to the AP pad position. Cardioversion was performed using an ICB waveform with a 70, 100, 150, and 200 J energy selection protocol. If the fourth shock was unsuccessful, the pads were crossed over to the alternative position for a final 200 J shock. Shock 1 was successful in 54/150 (36%) AA and 45/144 (31%) AP patients, whereas success was achieved by shock 2 in 99/150 (66%) AA and 74/144 (51%) AP, by shock 3 in 123/150 (82%) AA and 109/144 (76%) AP, and by shock 4 in 143/150 (95%) AA and 127/144 (88%) AP and after cross-over in 144/150 (96%) AA and 135/144 (94%) AP. Overall success rate was higher than expected at 95%. Pad position was not associated significantly with success. There was a trend towards an improved outcome with the AA configuration (P=0.05).

CONCLUSION

The influence of pad position for DCC of AF may be less pertinent with ICB waveforms than with monophasic waveforms.

A trial of self-adhesive patch electrodes and hand-held paddle electrodes for external cardioversion of atrial fibrillation (MOBIPAPA)

AIMS

External electrical cardioversion is the method of choice to terminate persistent atrial fibrillation. Whether the type of shock electrode affects cardioversion success is not known. We tested whether hand-held steel electrodes improve cardioversion outcome with monophasic or biphasic shocks when compared with adhesive patch electrodes.

METHODS AND RESULTS

Two hundred and one consecutive patients with persistent atrial fibrillation (147 male, mean age 63+/-1 years, duration of atrial fibrillation 6.3+/-1 months) were randomly assigned to cardioversion using either a sinusoidal monophasic or a truncated exponential biphasic shock wave form. The first half of patients were cardioverted using adhesive patch electrodes, the second half using hand-held steel paddle electrodes, and all patients using an anterior-posterior electrode position. Paddle electrodes successfully cardioverted 100/104 patients (96%) and patch electrodes 85/97 patients (88%, P=0.04). This effect was comparable to that of biphasic shocks: biphasic shocks cardioverted 102/104 patients (98%) and monophasic shocks 83/97 patients (86%, P=0.001). A beneficial effect of paddle electrodes was observed for both shock wave forms. After cross-over from an ineffective monophasic to a biphasic shock, cardioversion was successful in 198/201 (98.5%) patients. Unsuccessful cardioversion after cross-over (3/201 patients) only occurred with patch electrodes (P=0.07).

CONCLUSION

Hand-held paddle electrodes increase success of external cardioversion of atrial fibrillation in this trial. This increase is of similar magnitude as the increase in cardioversion success achieved with biphasic shocks. A combination of biphasic shocks, paddle electrodes, and an anterior-posterior electrode position renders outcome of external cardioversion almost always successful (104/104 patients in this trial).

Simplified cardioversion service with intravenous midazolam

OBJECTIVE

To assess the results of a new cardioversion service that used intravenous midazolam sedation with cardioversion performed with a biphasic defibrillator by an experienced doctor with a prior review of patients in a pre-cardioversion clinic.

METHODS

368 consecutive patients who were treated under the new service over its first 12 months (group 1) were compared with 210 consecutive patients who attended under the old system during the preceding 12 months (group 2). Patients of group 2 had cardioversion under general anaesthesia by junior doctors with a monophasic defibrillator.

RESULTS

There were no anaesthetic or respiratory complications in group 1. Of the patients in group 1, 10.3% remembered the shocks, with only 3.5% considering them unpleasant. Cardioversion was successful in 94.6% of group 1 patients after a mean energy of 117 J compared with 81.4% (p < 0.0001) and a mean energy of 242 J (p < 0.0001) for group 2 patients. Cancellations on the day of the procedure were reduced from 24% in group 2 to 3.4% in group 1.

CONCLUSIONS

The new service was found to be safe and more efficient. It has led to a large reduction in the waiting time for cardioversion.

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

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

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.

Management of atrial fibrillation

Atrial fibrillation (AF) is the most common clinically important arrhythmia in veterinary medicine. Electrical cardioversion of AF to sinus rhythm is feasible, but pharmacologic rate control is an effective and achievable treatment strategy for most veterinary patients. Recent human trials suggest that rate control and rhythm control are almost equally beneficial. Nevertheless, AF can be a challenging arrhythmia to manage, because most affected animal shave numerous other concurring problems associated with the underlying heart disease that dictate or influence the clinician's choice of treatment and monitoring strategy for each patient.