Prospective assessment of the minimum energy needed for external electrical cardioversion of atrial fibrillation

Constitutively Active Acetylcholine-Dependent Potassium Current Increases Atrial Defibrillation Threshold by Favoring Post-Shock Re-Initiation

Electrical cardioversion (ECV), a mainstay in atrial fibrillation (AF) treatment, is unsuccessful in up to 10–20% of patients. An important aspect of the remodeling process caused by AF is the constitutive activition of the atrium-specific acetylcholine-dependent potassium current (I_K,ACh → I_K,ACh-c), which is associated with ECV failure. This study investigated the role of I_K,ACh-c in ECV failure and setting the atrial defibrillation threshold (aDFT) in optically mapped neonatal rat cardiomyocyte monolayers. AF was induced by burst pacing followed by application of biphasic shocks of 25–100 V to determine aDFT. Blocking I_K,ACh-c by tertiapin significantly decreased DFT, which correlated with a significant increase in wavelength during reentry. Genetic knockdown experiments, using lentiviral vectors encoding a Kcnj5-specific shRNA to modulate I_K,ACh-c, yielded similar results. Mechanistically, failed ECV was attributed to incomplete phase singularity (PS) removal or reemergence of PSs (i.e. re-initiation) through unidirectional propagation of shock-induced action potentials. Re-initiation occurred at significantly higher voltages than incomplete PS-removal and was inhibited by I_K,ACh-c blockade. Whole-heart mapping confirmed our findings showing a 60% increase in ECV success rate after I_K,ACh-c blockade. This study provides new mechanistic insight into failing ECV of AF and identifies I_K,ACh-c as possible atrium-specific target to increase ECV effectiveness, while decreasing its harmfulness.

Relation of early termination of persistent atrial fibrillation by cardioversion or drugs to ablation outcomes

Current ablation consensus documents define persistent atrial fibrillation (AF) as AF lasting >1 week to 1 year or AF requiring cardioversion or pharmacologic conversion in <1 week. These 2 persistent AF subgroups may have different clinical characteristics and ablation outcomes. We compared 179 patients whose persistent AF was always terminated in <1 week by cardioversion/drugs to 244 whose AF actually lasted >1 week to 1 year. Patients with AF termination in <1 week by cardioversion/drugs had smaller left atrial (LA) size (4.1 ± 0.6 vs 4.5 ± 0.7 cm, p <0.0001), a longer AF history (7.5 ± 7.5 vs 6.0 ± 7.2 years, p = 0.035), more failed drugs (1.6 ± 1.0 vs 1.3 ± 1.0, p = 0.004), lower body mass index (28.5 ± 5.5 vs 30.3 ± 5.5, p = 0.0008), and fewer cardiomyopathies (3.9% vs 11.1%, p = 0.01). Cox multivariate analysis showed that LA size (p = 0.02), female gender (p = 0.001), and coronary artery disease (p = 0.03) predict ablation failure. There was a linear relation between duration of longest AF episode and LA size (p = 0.0001). Longest AF episode duration was the only factor predicting LA size (p = 0.001). Kaplan-Meier analysis showed more patients with AF termination in <1 week by cardioversion/drugs were free of AF after ablation (p = 0.042) than those whose AF actually lasted >1 week to 1 year. Once AF lasted >1 week, duration up to 1 year did not affect ablation success. In conclusion, patients whose persistent AF is always terminated by drugs/cardioversion in <1 week have different clinical characteristics and better ablation outcomes than patients whose AF persists beyond 1 week. This suggests that maintaining sinus rhythm before ablation is beneficial and that the definition of AF2 may need revision.

Noninvasive time and frequency predictors of long-standing atrial fibrillation early recurrence after electrical cardioversion

BACKGROUND

Several clinical factors have been studied to predict atrial fibrillation (AF) recurrence after electrical cardioversion (ECV) with limited predictive value.

METHODS

 A method able to predict robustly long-standing AF early recurrence by characterizing noninvasively the electrical atrial activity (AA) with parameters related to its time course and spectral features is presented. To this respect, 63 patients (20 men and 43 women; mean age 73.4 ± 9.0 years; under antiarrhythmic drug treatment with amiodarone) who were referred for ECV of persistent AF were studied. During a 4-week follow-up, AF recurrence was observed in 41 patients (65.1%).

RESULTS

 RR variability and the studied AA spectral features, including dominant atrial frequency (DAF), its first harmonic and their amplitude, provided poor statistical differences between groups. On the contrary, f waves power (fWP) and Sample Entropy (SampEn) of the AA behaved as very good predictors. Patients who relapsed to AF presented lower fWP (0.036 ± 0.019 vs 0.081 ± 0.029 n.u.(2) , P < 0.001) and higher SampEn (0.107 ± 0.022 vs 0.086 ± 0.033, P < 0.01). Furthermore, fWP presented the highest predictive accuracy of 82.5%, whereas SampEn provided a 79.4%. The remaining features revealed accuracies lower than 70%. A stepwise discriminant analysis (SDA) provided a model based on fWP and SampEn with 90.5% of accuracy.

CONCLUSIONS

 The fWP has proved to predict long-standing AF early recurrence after ECV and can be combined with SampEn to improve its diagnostic ability. Furthermore, a thorough analysis of the results allowed outlining possible associations between these two features and the concomitant status of atrial remodeling.

Indexed left atrial volume predicts the recurrence of non-valvular atrial fibrillation after successful cardioversion

AIMS

Atrial fibrillation (AFib) induces remodelling of the left atrium (LA). Indexed LA volume (iLAV) as more accurate measure of LA size has not been evaluated as predictor of recurrence of AFib after cardioversion.

METHODS AND RESULTS

We identified 411 adults (mean age 64.1 ± 11.4 years, 34.5% women) who underwent successful cardioversion and with no history of other atrial arrhythmia, stroke, congenital heart disease, valvular dysfunction, surgery, thyroid dysfunction, acute or chronic inflammatory disease, and pacemaker. All echocardiographic data were retrieved from the laboratory database. iLAV was measured off-line using Simpson's method. Clinical characteristics and recurrence of clinical AFib were determined by review of medical records. Patients with scheduled follow-up of at least 6 months were included. About 250 patients (60.8%) developed AFib recurrence after a median (25th-75th percentile) follow-up of 345.0 (210.0-540.0) days. Patients with AFib recurrence had significantly greater iLAV than patients without AFib recurrence (39.7 ± 8.4 vs. 31.4 ± 4.6, P < 0.001). Each mL/m(2) increase in iLAV was associated with a 30% increased risk of AFib recurrence [odds ratio (OR) 1.30, confidence interval (CI) 1.23-1.38, P < 0.001]. In a multivariable model, each mL/m(2) increase in iLAV was independently associated with a 21% increase in the risk of AFib recurrence (OR 1.21, CI 1.11-1.30, P < 0.001). The areas under receiver operating characteristic curves, generated to compare LA diameter and iLAV as predictors of AFib recurrence, were 0.59 ± 0.3 and 0.85 ± 0.2, respectively (P < 0.001).

CONCLUSION

The present study is the first to show that larger iLAV before cardioversion, as a more accurate measure of LA remodelling than LA diameter, is strongly and independently associated with higher risks of AFib recurrence.

Time and frequency recurrence analysis of persistent atrial fibrillation after electrical cardioversion

Electrical cardioversion (ECV) has become a mainstay of therapy for the treatment of persistent atrial fibrillation (AF), which is an arrhythmia that affects up to 1% of the general population. The procedure is initially effective, but it is also characterized by a high rate of AF recurrence. As a consequence, it would be clinically useful to predict normal sinus rhythm (NSR) maintenance after ECV before it is attempted. In this respect, several clinical, echocardiographic and demographic parameters have been analyzed by other authors. However, these indices are weak predictors of ECV outcome. In this work, surface electrocardiographic (ECG) recordings were used to extract the atrial activity (AA) signal and parametrize the fibrillatory (f) waves, both in time and frequency, to obtain AF recurrence predictors. Parameters as f waves amplitude (fWA), AA mean power, dominant atrial frequency (DAF), its first harmonic, etc were studied. Obtained results showed that fWA was the most significant predictor of AF recurrence 1 month later. Concretely, 72.73% of the patients resulting in NSR, 83.87% relapsing to AF and 80.0% with unsuccessful ECV, were correctly identified. Therefore, fWA classified satisfactorily 79.37% of the analyzed patients. In addition, a forward stepwise discriminant analysis, with a leave-one-out cross validation approach, proved that fWA and DAF combination provided an improved diagnostic ability of 85.71%. In this case 86.36%, 83.87% and 90% of the patients who resulted in NSR, relapsed to AF and with unsuccessful ECV, were correctly discerned, respectively. In conclusion, fWA could be considered as a promising predictor of ECV outcome during the first month following the procedure. Additionally, time and frequency indices could yield complementary information useful to predict the cardioversion outcome. Finally, further studies are needed to validate the robustness of these parameters and the repeatability of the obtained results on wider databases.

Does left atrial appendage peak emptying flow velocity predict the electrical energy required to achieve successful direct-current cardioversion in patients with persistent atrial fibrillation?

BACKGROUND

The relation of left atrial (LA) appendage peak emptying flow velocity (LAAEV) with energy requirement for successful direct-current cardioversion (DCCV) in persistent atrial fibrillation (AF) is unknown. LAAEV correlates with success of cardioversion of AF to sinus rhythm, both of which are related to the LA size and the chronicity of AF. We tested the hypothesis that LAAEV can predict optimal energy required for DCCV in persistent AF (>48 hours).

METHODS

We studied 1050 consecutive patients with persistent AF who underwent successful transesophageal echocardiographically guided DCCV from 2000 to 2005. After excluding patients with atrial flutter and those receiving antiarrhythmic drugs, 454 patients qualified for the study.

RESULTS

LAAEV did not correlate with cardioversion energy (r = 0.06, P = .23) or number of shocks required for successful DCCV (r = 0.05, P = .33). The only predictor of energy required for successful cardioversion was the chronicity of AF.

CONCLUSION

LAAEV does not predict electrical energy required for successful cardioversion in persistent AF.

Practical management of common atrial arrhythmias 1: cardioversion

This is the first in a series of four practical articles highlighting the important management steps for non-cardiologists and non-cardiac electrophysiologists dealing with patients with atrial fibrillation and common atrial flutter. This article will deal with care pathways and management principles for cardioversion of atrial arrhythmias.

[Electrical and pharmacological strategies for early cardioversion of atrial fibrillation]

Cardioversion of atrial fibrillation as an element of rhythm control strategy is indicated in patients with first episode of atrial fibrillation, hemodynamic instability, recurrent atrial fibrillation with low probability of spontaneous conversion, or severe symptoms. Early cardioversion is performed within 48 h of onset of atrial fibrillation. The best point in time is still unknown. It can be performed by pharmacological, or, preferentially, by electrical cardioversion. The advantages of electrical cardioversion are higher efficacy and no proarrhythmic risk, however, short time general anaesthesia is needed. Electrical cardioversion is most effective when biphasic shocks are delivered. For pharmacological cardioversion, several antiarrhythmic drugs are available which have to be considered individually. Thromboembolic risk does not differ between the two methods. Early cardioversion and maintenance of sinus rhythm is most effective in atrial fibrillation of short duration, normal left atrial size and no or only mild structural heart disease.

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

AIMS

To develop a simple point score system that can accurately predict the optimal energy of initial rectilinear biphasic (RLB) waveform shock for cardioversion (DC) of persistent atrial fibrillation (AF).

METHODS AND RESULTS

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

CONCLUSION

A simple point score system is useful in prediction of successful initial RLB energy for DC of AF.

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

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.

Management of new-onset atrial fibrillation in the emergency department: is there any predictive factor for early successful cardioversion?

OBJECTIVES

The aim of this retrospective study was to assess the initial management of atrial fibrillation (AF) in the emergency department (ED) and to identify predictive factors of early conversion to sinus rhythm, which could justify a short stay in the ED observation unit (EDOU) instead of longer hospitalization.

PATIENTS AND METHODS

All patients with acute AF, either of new onset or recurrent, admitted to our hospital during a 12-month period were included in the study. Hospital records were reviewed retrospectively. The success of conversion to sinus rhythm was recorded in association with a series of clinical and laboratory factors.

RESULTS

Sixty-seven patients (39 men and 28 women), with a mean age of 63.6+/-12.2 years, were studied. The most frequent presenting symptom was palpitations (n=40, 59.7%). In forty-two patients (62.7%) the duration of symptoms was less than 48 h. Digoxine was the anti-arrhythmic agent most frequently administered (n=26, 38.8%), followed by amiodarone (n=17, 25.4%). Fifty patients (73.1%) converted to sinus rhythm and for 45 of them conversion took place during their stay in the ED or in the EDOU. Factors associated with early conversion to sinus rhythm were aged younger than 65 years (P=0.021) and symptom duration of less than 48 h (P=0.001). On the other hand, the presence of signs of heart failure was significantly associated with unsuccessful early cardioversion (P=0.001).

CONCLUSIONS

The majority of patients admitted with AF of acute onset had early conversion to sinus rhythm. AF in young patients, with a duration of symptoms of less than 48 h and without signs of heart failure can be managed in the EDOU, thus avoiding a longer hospitalization.

Simple electrocardiographic markers for the prediction of paroxysmal atrial fibrillation in hyperthyroidism

BACKGROUND

Hyperthyroidism is a major cause of paroxysmal atrial fibrillation (AF). The purpose of this study was to evaluate the predictors of AF in the patients with clinical and subclinical hyperthyroidism.

METHODS AND RESULTS

The study population consisted of four groups: group I (57 euthyroid healthy persons), group II (33 patients with subclinical hyperthyroidism), group III (69 patients with overt hyperthyroidism) and group IV (31 patients with overt hyperthyroidism and documented paroxysmal AF). The maximum P wave duration (P maximum) in group IV (114 +/- 8 ms) was significantly higher than group I (102 +/- 7 ms, p < 0.001), group II (106 +/- 7 ms, p < 0.001) and group III (108 +/- 9 ms, p0.005). The P wave dispersion (PWD) was measured as 46 +/- 9 ms in group IV and this was significantly higher than group I (29 +/- 8 ms, p < 0.001), group II (36 +/- 9 ms, p < 0.001) and grup III (38 +/- 8 ms, p = 0.001). The P maximum and PWD were higher in the patients with subclinical hyperthyroidism compared to healthy individuals. Univariate regression analysis revealed that age, P maximum and PWD, multivariate analysis showed that P maximum and PWD were significant predictors of paroxysmal AF. A PWD value of 37.5 ms separated group IV from others with a sensitivity of 90%, specificity of 85%, and positive predictive accuracy of 77%.

CONCLUSION

Simply measuring P maximum and PWD values, we could identify the patients with high risk for the development of AF and these simple ECG parameters may help in clinical judgement to determine the requirement for treatment in the patients with subclinical hyperthyroidism.

High energy external cardioversion for refractory atrial fibrillation in postoperative tetralogy of fallot

Long-term complications of surgical repair of Tetralogy of Fallot include atrial arrhythmias. These can be difficult to treat, and loss of sinus rhythm can lead to profound hemodynamic consequences in the presence of residual structural abnormalities. We describe the first report of high-energy external cardioversion in a 46-year-old man with repaired tetralogy of Fallot with atrial fibrillation refractory to conversion with normal energy. This represents an alternative to internal cardioversion or rate control for these patients.

Efficacy of Biphasic Shock for Transthoracic Cardioversion of Persistent Atrial Fibrillation:. Can We Predict Energy Requirements?

Although electrical cardioversion of atrial fibrillation (AF) is frequently performed, initial energy requirements for cardioversion of persistent AF is still a matter of debate. The aim of the study was to determine the efficacy of biphasic shocks for transthoracic cardioversion of persistent AF and to predict adequate initial energy. A prospective study enrolled 94 consecutive patients with persistent AF, who were referred for elective cardioversion with a biphasic waveform. The paddles were placed in the anterolateral position. A step-up protocol was used to estimate the cardioversion threshold. The initial shock energy was 50 J, with subsequent increments to 100, 200, and 300 J in the event of cardioversion failure. The mean age of the study group was of about 65 years (6 +/- 11 years) and a median duration of AF was 65 days (3-324). Sixty-two out of 94 patients were men, 55% of the study population was classified as having well-controlled hypertension. The overall success rate of cardioversion was 89%, with a mean 2.2 +/- 1.4 shocks, and effective J 217.8 +/- 113 delivered during repeated cardioversions. The success rate of low energy shocks: 50 and 50 +100 J was 51%. By logistic regression analysis the only independent predictor of success at low energy shock was shorter duration of AF (r =-0.51; P = 0.02). Patients with shorter duration of AF have a higher probability for successful cardioversion with low energy. In patients with longer AF duration, a 200 J shock should be considered for cardioversion as the initial energy.

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.

Comparison of the efficacy and safety of two biphasic defibrillator waveforms for the conversion of atrial fibrillation to sinus rhythm

The overall efficacy of transthoracic biphasic shocks delivered for conversion of atrial fibrillation (AF) has been demonstrated. We compared 2 different energy waveforms, either the biphasic rectilinear (BRL) waveform or the biphasic truncated exponential (BTE) waveform, in the conversion of AF to sinus rhythm. The relation between energy required for the conversion of AF, the type of biphasic waveform, and patient characteristics were examined. Serum levels of cardiac troponin I were measured before and after cardioversion, as well as postprocedural skin erythema and discomfort. In this prospective trial, 101 patients (mean age 61 +/- 15 years, 72 men [71%]) referred for elective electrical cardioversion of AF were randomized to either a BTE or a BRL device. Shocks were delivered in a step-up fashion beginning with 50 J (then 100 J, 200 J, repeat 200 J, and then crossover to 360 J). One hundred patients were successfully converted to sinus rhythm (99% success rate). There was no difference in efficacy at any energy level used, regardless of the duration of the arrhythmia. In addition, there was no difference in cumulative success. Troponin I did not significantly increase after cardioversion, regardless of the total energy used. A positive correlation between skin erythema and skin discomfort after shock (24 to 48 hours) was seen with increasing cumulative energies. There was also a positive trend toward increasing energy requirements as chest circumference and body mass index increased. Thus, biphasic waveforms are safe and effective at converting AF to sinus rhythm. In this study population, there was no clinical difference between the BRL and the BTE waveforms.

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

OBJECTIVE

To compare the efficacy of cardioversion in patients with atrial fibrillation between monophasic damped sine waveform and rectilinear biphasic waveform shocks at a high initial energy level and with a conventional paddle position.

DESIGN

Prospective randomised study.

PATIENTS AND SETTING

227 patients admitted for cardioversion of atrial fibrillation to a tertiary referral centre.

RESULTS

70% of 109 patients treated with an initial 200 J monophasic shock were cardioverted to sinus rhythm, compared with 80% of 118 patients treated with an initial 120 J biphasic shock (NS). After the second shock (360 J monophasic or 200 J biphasic), 90% of the patients were in sinus rhythm in both groups. The mean cumulative energy used for successful cardioversion was 306 J for monophasic shocks and 159 J for biphasic shocks (p < 0.001).

CONCLUSIONS

A protocol using monophasic waveform shocks in a 200-360 J sequence has the same efficacy (90%) as a protocol using rectilinear biphasic waveform shocks in a 120-200 J sequence. This equal efficacy is achieved with a significantly lower mean delivered energy level using the rectilinear biphasic shock waveform. The potential advantage of lower energy delivery for cardioversion of atrial fibrillation needs further study.

External Cardioversion in Patients With Persistent Atrial Fibrillation A Reappraisal of the Effects of Electrode Pad Position and Transthoracic Impedance on Cardioversion Success

The optimal methods to perform external cardioversion of atrial fibrillation (AF) have yet to be conclusively determined. This study was performed to examine the relative efficacy of different pad positions on cardioversion success and the relationship between the transthoracic impedance (TTI) and energy requirement for AF cardioversion. Seventy patients with persistent AF undergoing elective cardioversion were randomly assigned to an electrode pad position situated either over the ventricular apex-right infraclavicular area (AL group, n = 31 ) or over the right lower sternal border-left infrascapular area close to the spine (AP group, n = 39). Energy was delivered at an initial 100 joules (J) and then increased to 150 J, 200 J, 300 J, and 360 J if needed. Energy and TTI readings were recorded. Mean TTI was significantly lower in the AP group than in the AL group. However, the cumulative success rates at each energy level were similar in the two groups (23% vs 19.4%, 41% vs 45.2%, 66.7% vs 74.2%, 79.5% vs 77.4%, and 84.6% vs 83.9% at 100 J, 150 J, 200 J, 300 J and 360 J, respectively). In the AP group, converters showed slightly lower TTI compared to nonconverters. In the AL group, converters showed significantly lower TTI compared to nonconverters. However, for all patients as a group, TTI was the only predictor for cardioversion success and showed a significant relationship to the energy required for cardioversion, which can be described by a quadratic equation. Rather than pad position. TTI is the single factor that significantly affects cardioversion and correlates with energy requirement. The relationship between energy requirement and TTI further allows estimation of energy requirements to achieve a successfil cardioversion.

Anterior-posterior versus anterior-lateral electrode positions for external cardioversion of atrial fibrillation: a randomised trial

BACKGROUND

External cardioversion is a readily available treatment for persistent atrial fibrillation. Although anatomical and electrophysiological considerations suggest that an anterior-posterior electrode position should create a more homogeneous shock-field gradient throughout the atria than an anterior-lateral position, both electrode positions are equally recommended for external cardioversion in current guidelines. We undertook a randomised trial comparing the two positions with the endpoint of successful cardioversion.

METHODS

108 consecutive patients (mean age 60 years [SD 16]) with persistent atrial fibrillation (median duration 5 months, range 0.1-120) underwent elective external cardioversion by a standardised step-up protocol with increasing shock strengths (50-360 J). Electrode positions were randomly assigned as anterior-lateral or anterior-posterior. If sinus rhythm was not achieved with 360 J energy, a single cross-over shock (360 J) was applied with the other electrode configuration. A planned interim analysis was done after these patients had been recruited; it was by intention to treat.

FINDINGS

Cardioversion was successful in a higher proportion of the anterior-posterior than the anterior-lateral group (50 of 52 [96%] vs 44 of 56 [78%], difference 23.7% (95% CI 9.1-37.8, p=0.009). Cross-over from the anterior-lateral to the anterior-posterior electrode position was successful in eight of 12 patients, whereas cross-over in the other direction was not successful (two patients). After cross-over, cardioversion was successful in 102 of 108 randomised patients (94%).

INTERPRETATION

An anterior-posterior electrode position is more effective than the anterior-lateral position for external cardioversion of persistent atrial fibrillation. These results should be considered in clinical practice, for the design of defibrillation electrode pads, and when guidelines for cardioversion of atrial fibrillation are updated.

Effect of shock polarity on the efficacy of transthoracic atrial defibrillation

BACKGROUND

The energy requirement for internal ventricular defibrillation is reduced by reversal of shock polarity. The influence of shock polarity on the efficacy of transthoracic atrial defibrillation is unknown.

METHODS

This prospective, randomized study enrolled 110 consecutive patients who were referred for elective cardioversion of persistent atrial fibrillation (AF). The electrodes were placed in the anteroposterior position. The patients were randomized to receive either standard (anterior pad = cathode) or reversed polarity (anterior pad = anode) shocks with a damped sinusoidal monophasic waveform. A step-up protocol was used to estimate the cardioversion threshold. The initial shock energy was 50 J, with subsequent increments to 100, 200, 300, and 360 J in the event of cardioversion failure.

RESULTS

Sixty-four percent of the patient population were men, with a mean age of 66 +/- 13 years and a mean duration of AF of 242 +/- 556 days. The overall success rates of cardioversion were 84% for standard polarity and 78% for reversed polarity (P not significant). Among the patients who were successfully cardioverted, the mean atrial defibrillation threshold was 198 +/- 103 J for standard polarity and 212 +/- 107 J for reversed polarity (P not significant).

CONCLUSIONS

Reversal of shock polarity does not improve transthoracic cardioversion efficacy with a standard damped sinusoidal monophasic waveform. Alternate strategies should be considered for patients who fail external cardioversion, such as adjunctive pharmacologic treatment, use of a biphasic shock waveform, or internal cardioversion.

Atrial mechanical performance after internal and external cardioversion of atrial fibrillation: an echocardiographic study

OBJECTIVES

To compare the time course of resumption of mechanical performance of the left and right atrium after the novel method of internal low-energy cardioversion (CV) and conventional external CV of atrial fibrillation (AF).

BACKGROUND

Right atrial performance has been shown to normalize before the left atrium after external CV. However, no data on atrial function after internal CV are available.

PATIENTS AND INTERVENTIONS

Sixty-three patients with chronic AF were randomized to participate in either external or internal CV.

MEASUREMENTS

Echocardiographic examinations were carried out before as well as immediately after CV (day 0), and at days 1, 7, and 28 thereafter for the determination of cardiac dimensions, volumes, and transvalvular flow patterns.

RESULTS

After randomized internal CV or external CV, stable sinus rhythm was restored in 59 patients. Irrespective of the mode of CV, the right atrium resumed its mechanical function immediately after CV, whereas the left atrium was stunned beyond day 7. The mode of CV, internal or external, had no influence on the recovery of atrial mechanical function.

CONCLUSIONS

The right atrium resumes its normal function immediately after internal as well as external CV, whereas left atrium function is delayed. In contrast to the assumption that low-energy internal CV would impact less on atrial mechanical recovery, the type of method of CV used has no effect on such recovery.

Initial energy setting, outcome and efficiency in direct current cardioversion of atrial fibrillation and flutter

OBJECTIVES

The purpose of this study was to design a more efficient protocol for the electrical cardioversion of atrial arrhythmias.

BACKGROUND

Guidelines for electrical cardioversion of atrial arrhythmias recommend starting with low energy shocks, which are often ineffective.

METHODS

We recorded the sequence of shocks in 1,838 attempts at cardioversion for atrial fibrillation (AF) and 678 attempts at cardioversion for atrial flutter. These data were used to calculate the probability of success for each shock of a standard series and the probability of success with a single shock at each intensity. In 150 cases, a rhythm strip with the time of each shock allowed us to calculate the time expended on unsuccessful shocks.

RESULTS

We analyzed the effects of 5,152 shocks delivered to patients for AF and 1,238 shocks delivered to patients for atrial flutter. The probability of success on the first shock in AF of > 30 days duration was 5.5% at < 200 J, 35% at 200 J and 56% at 360 J. In atrial flutter, an initial 100 J shock worked in 68%. In AF of >30 days duration, shocks of < 200 J had a 6.1% probability of success; this fell to 2.2% with a duration >180 days. In those with AF for >180 days, the initial use of a 360 J shock was associated with the eventual use of less electrical energy than with an initial shock of < or =100 J (581 +/- 316 J vs. 758 +/- 433 J, p < 0.01, Mann-Whitney U test).

CONCLUSIONS

An initial energy setting of > or =360 J can achieve cardioversion of AF more efficiently in patients than traditional protocols, particularly with AF of longer duration.

Initial energy for elective external cardioversion of persistent atrial fibrillation

We conducted a prospective randomized study to determine the safety and efficacy rate of 3 commonly used energy levels (100, 200, and 360 J) for elective direct-current cardioversion of persistent atrial fibrillation. When compared with 100 and 200 J, the initial success rate with 360 J was significantly higher (14%, 39%, and 95%, respectively), and patients randomized to 360 J ultimately required less total energy and a lower number of shocks.

Transthoracic cardioversion of atrial fibrillation: comparison of rectilinear biphasic versus damped sine wave monophasic shocks

BACKGROUND

Clinical studies have shown that biphasic shocks are more effective than monophasic shocks for ventricular defibrillation. The purpose of this study was to compare the efficacy of a rectilinear biphasic waveform with a standard damped sine wave monophasic waveform for the transthoracic cardioversion of atrial fibrillation.

METHODS AND RESULTS

In this prospective, randomized, multicenter trial, patients undergoing transthoracic cardioversion of atrial fibrillation were randomized to receive either damped sine wave monophasic or rectilinear biphasic shocks. Patients randomized to the monophasic protocol (n=77) received sequential shocks of 100, 200, 300, and 360 J. Patients randomized to the biphasic protocol (n=88) received sequential shocks of 70, 120, 150, and 170 J. First-shock efficacy with the 70-J biphasic waveform (60 of 88 patients, 68%) was significantly greater than that with the 100-J monophasic waveform (16 of 77 patients, 21%, P<0.0001), and it was achieved with 50% less delivered current (11+/-1 versus 22+/-4 A, P<0.0001). Similarly, the cumulative efficacy with the biphasic waveform (83 of 88 patients, 94%) was significantly greater than that with the monophasic waveform (61 of 77 patients, 79%; P=0.005). The following 3 variables were independently associated with successful cardioversion: use of a biphasic waveform (relative risk, 4.2; 95% confidence intervals, 1.3 to 13.9; P=0.02), transthoracic impedance (relative risk, 0.64 per 10-Omega increase in impedance; 95% confidence intervals, 0.46 to 0.90; P=0.005), and duration of atrial fibrillation (relative risk, 0.97 per 30 days of atrial fibrillation; 95% confidence intervals, 0.96 to 0.99; P=0.02).

CONCLUSIONS

For transthoracic cardioversion of atrial fibrillation, rectilinear biphasic shocks have greater efficacy (and require less energy) than damped sine wave monophasic shocks.

External cardioversion of atrial fibrillation: role of paddle position on technical efficacy and energy requirements

AIM

To define the effect of defibrillator paddle position on technical success and dc shock energy requirements of external cardioversion of atrial fibrillation.

METHODS

301 patients (mean (SD) age 62 (11) years) with stable atrial fibrillation were randomly assigned to elective external cardioversion using anterolateral paddle position (ventricular apex-right infraclavicular area; group AL (151 patients)) or anteroposterior paddle position (sternal body-angle of the left scapula; group AP (150 patients)). A step up protocol was used, delivering a 3 J/kg body weight dc shock, then a 4 J/kg shock (maximum 360 J), and finally a second 4 J/kg shock using the alternative paddle location.

RESULTS

The two groups were comparable for the all clinical variables evaluated. The cumulative percentage of patients successfully converted to sinus rhythm was 58% in group AL and 67% in group AP with low energy dc shock (NS); this rose to 76% in group AL and to 87% in group AP with high energy dc shock (p = 0.013). Thirty seven patients in group AL and 19 in group AP experienced dc shock with the alternative paddle position; atrial fibrillation persisted in 10/37 in group AL and in 10/19 in group AP. Mean dc shock energy requirements were lower for group AP patients than for group AL patients, at 383 (235) v 451 (287) J, p = 0.025. Arrhythmia duration was the only factor that affected the technical success of external cardioversion (successful: 281 patients, 80 (109) days; unsuccessful: 20 patients, 193 (229) days; p < 0.0001). The success rate was lower if atrial fibrillation persisted for > 6 months: 29 of 37 (78%) v 252 of 264 (95%); p = 0.0001.

CONCLUSIONS

An anteroposterior defibrillator paddle position is superior to an anterolateral location with regard to technical success in external cardioversion of stable atrial fibrillation, and permits lower dc shock energy requirements. Arrhythmia duration is the only clinical variable that can limit the restoration of sinus rhythm.

Marked reduction in atrial defibrillation thresholds with repeated internal cardioversion

OBJECTIVES

This study was performed to assess the atrial defibrillation threshold in patients with recurrent atrial fibrillation (AF) using repeated internal cardioversion.

BACKGROUND

Previous studies in patients with chronic AF undergoing internal cardioversion have shown this method to be effective and safe. However, current energy requirements might preclude patients with longer-lasting AF from being eligible for an implantable atrial defibrillator.

METHODS

Internal shocks were delivered via defibrillation electrodes placed in the right atrium (cathode) and the coronary sinus (anode) or the right atrium (cathode) and the left pulmonary artery. After cardioversion, patients were orally treated with sotalol (mean 189 +/- 63 mg/day). Eighty consecutive patients with chronic AF (mean duration 291 +/- 237 days) underwent internal cardioversion, and sinus rhythm was restored in 74 patients. Eighteen patients underwent repeated internal cardioversion using the same electrode position and shock configuration after recurrence of AF (mean duration 34 +/- 25 days).

RESULTS

In these 18 patients, the overall mean defibrillation threshold was 6.67 +/- 3.09 J for the first cardioversion and 3.83 +/- 2.62 J for the second (p = 0.003). Mean lead impedance was 55.6 +/- 5.1 ohms and 57.1 +/- 3.7 ohms, respectively (not significant). For sedation, 6.7 +/- 2.9 mg and 3.9 +/- 2.2 mg midazolam were administered intravenously (p = 0.003), and the pain score (0 = not felt, 10 = intolerable) was 5.1 +/- 1.9 and 2.7 +/- 1.8 (p = 0.001). Uni- and multivariate analyses revealed only the duration of AF before cardioversion to be of relevance, lasting 175 +/- 113 days before the first and 34 +/- 25 days before the second cardioversion in these 18 patients (p = 0.002).

CONCLUSIONS

If the duration of AF is reduced, a significant reduction in defibrillation energy requirements for internal cardioversion ensues. This might extend the group of patients eligible for an implantable atrial defibrillator despite relatively high initial defibrillation thresholds.

Randomised comparison of electrode positions for cardioversion of atrial fibrillation

OBJECTIVE

To compare the relative efficacy of anteroanterior v anteroposterior electrode pad positions for external cardioversion of atrial fibrillation.

DESIGN

Prospective randomised trial.

SETTING

Tertiary referral cardiology centre in the United Kingdom.

PATIENTS

90 patients undergoing elective cardioversion for atrial fibrillation.

INTERVENTIONS

Cardioversion was attempted with self adhesive electrode pads with an area of 106 cm2 placed either in the anteroanterior (AA) or anteroposterior (AP) positions. Initial shock was 100 J which, if unsuccessful, was followed by 200 J, 300 J, and 360 J if required. Peak current and transthoracic impedance were measured.

MAIN OUTCOME MEASURES

Cardioversion success rate and energy requirements.

RESULTS

Cardioversion was successful in 81% of the patients (73/90). There was no statistically significant difference in the cardioversion success rate (AA 84%, 38/45 patients; AP 78%, 35/45 patients; p = 0.42) or mean (SD) energy requirement for all patients (AA 223 (96.1) J; AP 232 (110) J) or for patients who were successfully cardioverted (AA 197.9 (82.4) J; AP 195.4 (97.2) J; p = 0.9) between the two pad positions. The mean transthoracic impedance (TTI) for the first shock (AA 77.5 (18.4) ohms; AP 73.7 (18.7) ohms; p = 0.34) was not significantly different between the two groups. TTI correlated significantly with body mass index, percentage body fat, and chest AP diameter. There was a progressive decrease in TTI with serial shocks. While aetiology and TTI were the two independent significant predictive factors for energy requirement, duration of atrial fibrillation was the only independent predictor of cardioversion success in a multivariate analysis.

CONCLUSIONS

Electrode pad position is not a determinant of cardioversion success rate or energy requirement.