ATRIAL FIBRILLATION
Monophasic versus biphasic waveform shocks for atrial fibrillation cardioversion in patients with concomitant amiodarone therapy
Heart Institute (INCOR-HCFMUSP), University of São Paulo Medical School, Av. Doutor Enéas Carvalho Aguiar 44, 05403.000 São Paulo, Brazil
Manuscript submitted 24 March 2006. Accepted after revision 4 November 2006.
* Corresponding author. Tel: +55 1130695387; fax: +55 1130695348. E-mail address: caio.vianna{at}incor.usp.br
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Abstract |
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Aims With transthoracic cardioversion of atrial fibrillation (AF), biphasic are more effective than monophasic waveforms. We sought to determine the ideal energy levels for biphasic waveforms.
Methods We compared biphasic truncated exponential waveforms with monophasic damped sine waveform defibrillators, in a prospective, single-centre, randomized (1:1 ratio) study. The study included 154 patients receiving concomitant amiodarone; 77 received serial biphasic (50, 100, 150, up to 175 J) and 77 monophasic shocks (100, 200, 300, up to 360 J), as necessary.
Results First-shock efficacy was similar in the two groups (57 vs. 55%, P = 0.871, respectively), as were serial-shocks (90 vs. 92%, P = 0.780). Both groups received equal numbers of shocks (1.8 ± 1.1 vs. 1.7 ± 1.0, P = 0.921). In both groups, serum creatine kinase levels showed a small but significant increase. The increase was, however, higher in the monophasic group.
Conclusion In patients with concomitant amiodarone therapy, biphasic truncated exponential shocks, using half the energy, were as effective as monophasic damped sine shocks. The biphasic scheme was not more efficacious for cardioverting AF. In our population, a first shock of at least 100 J seemed advisable with either waveform. If necessary, escalating shocks must be performed, but ideal levels of increase per shock are still uncertain for biphasic waveforms.
Key Words: Atrial fibrillation, Electric countershock, Amiodarone
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Introduction |
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Monophasic and biphasic defibrillators are available for transthoracic conversion of atrial fibrillation (AF). Until recently, most available defibrillators produced monophasic damped sine waveform shocks. However, most manual defibrillators sold today are biphasic and produce exponential truncated or rectilinear waveforms.
Biphasic waveforms are more effective than standard monophasic shocks, and require less energy per shock,1
–9 but the ideal levels of energy have not been determined. For this purpose, we compared the effectiveness of a biphasic defibrillator producing exponential truncated waveforms, using half the energy delivered per shock, with a standard monophasic defibrillator producing damped sine waveforms.
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Methods |
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This was a prospective, single-centre, randomized (1:1 ratio) study, and all patients were treated in our Emergency Department. Atrial fibrillation was defined as the absence of organized atrial activity, the presence of fibrillatory atrial waves, and irregular ventricular activity. Patients were enrolled over a 12-month period.
Inclusion criteria were patients with AF eligible for elective transthoracic cardioversion. Exclusion criteria were the following: (i) age < 18 years; (ii) known or suspected pregnancy; (iii) pacemaker dependent; (iv) insufficient data to estimate the AF duration; (v) estimated duration of AF > 1 year (vi) regular oral treatment with antiarrhythmic drugs except amiodarone, digoxin, sotalol, other beta-blockers, verapamil, and diltiazem; (vii) haemodynamic instability (severe arterial hypotension, loss of consciousness, or signs of heart failure); and (viii) thoracic pain or suspected acute coronary syndromes.
Patients were defibrillated soon after admission if AF duration was 
48 h, or when AF was > 48 h, if they were adequately anticoagulated with warfarin. In patients not on warfarin or with inadequate INR values whose AF duration was > 48 h, warfarin was initiated (or its dose adjusted) and maintained for at least 3 weeks before transthoracic cardioversion.
Before shocks, patients received intravenous amiodarone hydrochloride infusion, 5 mg/kg, for 30 min, except if they were already on regular treatment with oral amiodarone or heart rate was < 60 bpm. Patients were excluded if AF was reverted during a 30 min period after intravenous amiodarone; otherwise, transthoracic shocks were employed.
The selected patients were randomized to receive biphasic or monophasic shocks, with a 1:1 ratio, by a computer programme. We used a Medtronic Physio-Control Lifepak 12-3D biphasic VLP-model defibrillator (Redmond, WA, USA), producing exponential truncated waveform shocks, using standard elliptical paddles, measuring 12.5 cm x 7.5 cm. The biphasic defibrillator determined the transthoracic impedance of the patients at the onset of delivered shocks, which were automatically adjusted, in current amplitude and pulse duration,9 according to the impedance of each patient. We used a Hewlett Packard (Palo Alto, CA, USA) Codemaster-XL, M1722A-model monophasic defibrillator, producing damped sine waveform shocks. No equipment was used to measure impedance and compensation. Standard rectangular paddles, measuring 10.5 cm x 8.5 cm were used.
Sedation was achieved with intravenous propofol, as necessary. Both paddles were placed on the anterior surface of the thorax, after skin cleansing and shaving, if necessary. In both groups, the ‘sternal’ paddle was placed in the right subclavicular position, and the ‘apex’ paddle on the fifth or sixth intercostal space, at the left anterior axillary thoracic line. The shocks were synchronized to the QRS complex and applied during the end expiratory phase. Only one physician performed all transthoracic cardioversions, and he learned of the randomization immediately before the shocks.
Patients randomized to the biphasic defibrillator received a sequence of 4 shocks of 50, 100, 150, up to 175 J, with intervals of at least 1 min, as necessary for cardioversion. Patients randomized to the monophasic defibrillator received a sequence of 4 shocks of 100, 200, 300, up to 360 J, if necessary, according to an algorithm proposed by Guidelines-2000 for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care.8 After conversion of the rhythm with any level of energy, the patients were observed for 1 h, and if AF recurred during this time, the sequence of shocks was resumed. If the patient had no reversion of the arrhythmia after the fourth shock in the sequence, he was considered to have had unsuccessful reversion of AF. Successful cardioversion was defined as restored sinus rhythm for 1 h after the shocks.
Basal demographic (age, sex, weight, height, anteroposterior thoracic diameter, body surface area, and body mass index) and clinical variables (oximetry, axillary temperature, heart rate, arterial pressure, duration of AF, underlying diseases, and use of drugs) were assessed.
Serum levels of creatine kinase (CK) and MB isoenzyme (CKMB) were assessed immediately before the shocks and 24 h afterwards. Creatine kinase and CKMB were measured using the ultraviolet kinetic method, temperature 25°C.
The institutional committee on human research approved the study. The study complies with the Declaration of Helsinki. All selected patients were informed about this protocol and signed the consent form.
Statistical analysis
The sample size was calculated assuming estimated cumulative efficacy of 83% in monophasic patients, and to detect a 15% difference in favour of the biphasic group, with a significance level of 0.05 and power of 80%, in a two-tailed fashion. This required at least 72 patients in each arm of the study. Biphasic results are presented before monophasic results. Quantitative values are presented as mean ± SD and discontinuous values as frequencies and percentages. Quantitative values were compared using two-sided paired or unpaired Student t tests, or by Wilcoxon signed rank or Mann–Whitney U tests for non-Gaussian distributions. Discontinuous variables were compared with the 
2 test or Fisher's exact test when indicated. We used Spearman rank-order correlation to analyse the cumulative delivered energy in each patient with CK and CKMB levels after shocks. A multivariate stepwise logistic regression was performed to determine the variables independently associated with unsuccessful cardioversion, considering all 154 patients. The logistic regression model was constructed with all variables (Tables 1 and 2) with P < 0.15 by the univariate analysis. For all analyses, statistical significance was considered when P < 0.05.
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Results |
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Patient population
Of 226 patients selected for elective external cardioversion, 172 without previous oral amiodarone use and with a heart rate
60 bpm received intravenous amiodarone infusion based on a protocol. Of these, 72 (42%) had AF reverted by the amiodarone and were excluded (100 patients were included). Another 54 patients with previous regular treatment with oral amiodarone were also included but did not receive amiodarone infusion. Therefore, 154 patients were enrolled in the study and were randomized to biphasic or monophasic defibrillators (77 patients in each group). The demographic data and population characteristics are in Tables 1 and 2. The biphasic group had more men than did the monophasic group (75% vs. 57%, P = 0.027). Biphasic shock patients were younger than those receiving monophasic shocks (55.1 ± 13.5 vs. 60.1 ± 13.3 years, P = 0.022). The other demographic and clinical characteristics were not significantly different between groups.
No clinical complications were observed during or after the shocks in any patient in either group.
Results of transthoracic cardioversion
The effectiveness of biphasic and monophasic shocks is summarized in Table 3. No differences were observed in efficacy of the first-shock or cumulative efficacy after all serial shocks between groups. On average, both groups received the same number of shocks, and biphasic group patients received almost half of all cumulative energy compared with the monophasic group.
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Creatine kinase significantly increased in both groups. (from 36.8 ± 14.5 U/L to 53.8 ± 48.8 U/L, P = 0.004, in biphasic, from 37.1 ± 19.2 U/L to 180.3 ± 303.9 U/L, P < 0.0001, in monophasic groups). Creatine kinase MB isoenzyme showed no significant increase in both groups. Comparison between biphasic and monophasic patients who received the same cumulative delivered energy, specifically 300 J, showed that CK after 24 h was lower in biphasic patients (35.2 ± 14.7 vs. 224.3 ± 292.9, P < 0.0001). Considering all patients in both groups, we found a linear correlation between cumulative delivered energy with both CK and CKMB levels 24 h after the shocks (CK, r = 0.606, P < 0.0001, and CKMB, r = 0.363, P < 0.0001).
The multivariate logistic regression model to determine independent predictors of unsuccessful cardioversion (all variables with P < 0.15 by univariate analysis) included: AF duration > 2 months (P = 0.002) and idiopathic dilated cardiomyopathy (P = 0.009) (positive correlations with unsuccessful cardioversion), heart rate > 100 bpm (P = 0.057), valvular disease (P = 0.073), chronic oral amiodarone use (P = 0.140); and chronic oral beta-blocker use, excluded sotalol (P = 0.141) (these variables with negative correlations with unsuccessful cardioversion, that is, a tendency to less failure). Three other not significant variables by univariate analysis must be mentioned: chronic warfarin use (P = 0.163), AF duration > 48 h (P = 0.168) (both with a positive tendency to failure), and idiopathic AF (P = 0.303) (with a negative tendency to failure). The failure rates of patients with chronic oral amiodarone vs. patients receiving intravenous infusion amiodarone before the shocks were, respectively, 1.3 vs. 7.8% (P = 0.140). After multivariate analysis, only AF duration longer than 2 months persisted as an independent predictor of unsuccessful cardioversion (adjusted odds ratio = 8.5, 95% confidence interval 2.0–34.1, P = 0.003).
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Discussion |
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It is well known that biphasic devices have greater efficacy than monophasic defibrillators for AF cardioversion.1
–9 Monophasic defibrillators deliver waveforms with one direction of current, and biphasic devices invert the current direction in the last phase of the shock. Biphasic defibrillators automatically adjust the delivered energy according to an impedance analysis.2,7,9 This study was designed to compare the efficacy of a biphasic truncated exponential defibrillator, using half the energy per shock, with a standard damped sine monophasic defibrillator, in patients with concomitant amiodarone therapy. An advantage for AF reversion efficacy was not demonstrated. Both groups received the same number of shocks. The effectiveness of the first shock and of the serial-shocks was similar in the two groups.
Our study confirmed that CK increases more with monophasic than with biphasic shocks, even when equal levels of energy are accumulated. This result indicates that a strategy using biphasic shocks with half the energy can be applied in rare conditions, as when avoidance of skeletal musculature damage is desirable. Previous studies have demonstrated that CK elevations are not clinically significant, including those with high levels of energy delivered with either waveform.1,6,10,11 In addition, CKMB and troponin serum levels did not significantly change.6,10–12
Rate of AF relapse is high unless a concomitant antiarrhythmic drug is given.1 This study enrolled only patients who received amiodarone before treatment. This is the usual practice in our emergency department. Amiodarone can revert AF, facilitate efficacy of external electrical cardioversion, and prevent relapses, as can other drugs (ibutilide, propafenone, dofetilide, and flecainide).1,5 We included only patients using amiodarone so that we could study a specific, homogeneous patient population, in line with the majority of our patients. The efficacy of intravenous amiodarone infusion to revert AF is still uncertain. In this study, of 172 patients without previous oral amiodarone, intravenous infusion reverted AF in 42%, during a short 30 min period after infusion. Success after all serial shocks was high in both groups (Table 3), and amiodarone certainly facilitated these good results equally in the two groups.
Our results support the Guidelines for transthoracic cardioversion of AF, which recommend a first shock between 100 and 120 J for biphasic and 100 and 200 J for monophasic waveforms.2 If necessary, additional shocks should be applied in a stepwise fashion. After an ineffective first shock, the ideal sequence of additional shocks is still uncertain. As a practical opinion, we believe that both biphasic truncated exponential and monophasic damped sine waveform defibrillators should apply a similar sequence of shocks starting with 100 J, until consensus is established.
This study cannot be directly applied to defibrillators producing biphasic rectilinear waveforms. Rectilinear waveforms seem to have superior efficacy compared with truncated exponential waveforms,4,5,9 but these defibrillators deliver shocks with a maximum energy of 200 J, which implies a different plan of serial shocks.
Study limitations
All patients in this study were previously treated with oral amiodarone, or an intravenous dose was given immediately before shocks, which is routine practice in some medical centres.
This was not a double-blind study, although only one physician accomplished all transthoracic cardioversions, and he learned of the randomization just at the moment of shock administration.
Conclusions
In a specific population of patients with concomitant amiodarone therapy, we compared two methodologies of electrical cardioversion of AF. The result was favourable to biphasic defibrillators, because both groups were equally effective, but the biphasic shocks used half energy. This strategy can be employed when skeletal musculature damage needs to be avoided. However, an appreciable benefit using half energy with biphasic defibrillators was not observed. Our results indicate a first shock with at least 100 J for both waveforms to be efficacious. If necessary, escalating shocks must be performed, but ideal levels of increase per shock are still uncertain for biphasic waveforms. Prospective studies to determine the ideal levels of energy for biphasic shocks should be performed.
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References |
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[1] ACC/AHA/ESC Guidelines for the management of patients with atrial fibrillation: Executive Summary A report of the American College of Cardiology/American Heart Association Task Force on practice guidelines:the European Society of Cardiology Committee for Practice Guidelines and Policy Conferences (Committee to Develop Guidelines for the Management of Patients with Atrial Fibrillation). Circulation 2001; 104: 2118–50.
[2] The 2005 American Heart Association Guidelines for Cardiopulmonary Resuscitation: Emergency Cardiovascular Care ECC Committee, Subcommittees and Task Forces of the American Heart Association. Part 5: electrical therapies. automatic external defibrillators, defibrillation, cardioversion, and pacing. Circulation 2005; 112: IV35–46.
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[12] Cemin R, Rauhe W, Marini M, Pescoller F, Pitscheider W. Serum troponin I level after external electrical direct current synchronized cardioversion in patients with normal or reduced ejection fraction: no evidence of myocytes injury. Clin Cardiol 2005; 28: 467–70.[Medline]
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