Indian Pacing Electrophysiol. J.

ISSN 0972-6292

Home Page Current Issue List of Editors

Indian Pacing Electrophysiol. J. 2005;5(4):289-295                 Review Article

The Role of Biphasic Shocks for Transthoracic Cardioversion of Atrial Fibrillation

Download PDF 204 KB 

Simon J Walsh, MD MRCP; Ben M Glover, MB BCh MRCP; AA Jennifer Adgey, MD FRCP FACC

Regional Medical Cardiology Centre, Royal Victoria Hospital, Belfast.

Address for correspondence: Professor AA Jennifer Adgey, The Regional Medical Cardiology Centre,
Royal Victoria Hospital, Grosvenor Road, Belfast, Northern Ireland, BT12 6BA.


            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.
Keywords: Atrial fibrillation, defibrillation, direct current cardioversion, biphasic waveform

            Electrical cardioversion is a commonly performed procedure for the treatment of atrial fibrillation (AF) that has been successfully employed since the 1960’s.1 Early devices used both alternating and direct current for defibrillation. However, by the 1960’s it was apparent that alternating current was more detrimental to the heart and direct current has been used in defibrillators since. Direct current cardioversion (DCC) was performed with critically damped monophasic waveforms for over 2 decades. However, these are produced with inductors used in conjunction with capacitors.2 Inductors are electrical components that are too large for implantable devices. As interest in implantable defibrillators increased, research was subsequently driven towards truncated capacitor-based discharges. These waveforms were simple to produce, and improved capacitor technology facilitated their production in suitably sized implantable devices. We have described the production of these waveforms previously.3
            It was recognised subsequently that biphasic waveforms offered distinct advantages over monophasic waveforms in ventricular defibrillation (in terms of superior or equivalent efficacy at lower peak voltage, current and total delivered energy). These results stimulated further research into biphasic waveforms for defibrillation of AF, where similar results were reported for internal and external cardioversion.

Why choose biphasic waveforms for transthoracic DCC of AF?

            Some physicians have questioned whether biphasic waveforms offer significant advantages over monophasic defibrillators. It has been noted that monophasic waveforms result in similar rates of cardioversion by the maximum energy of a treatment protocol. It is already known that DCC does not result in cardiac damage at currently applied energies.4 In addition, the use of biphasic waveforms does not appear to reduce the early recurrence of atrial fibrillation.5
            Many studies have shown that lower energy impedance compensated biphasic (ICB) waveforms are equivalent or superior to the higher energy monophasic waveforms (Table 1).5-13 These new devices are successful with fewer shocks,7 will offer successful cardioversion to patients where monophasic shocks have failed14 and may obviate the need for transvenous cardioversion.15 Skin burns are less common with biphasic waveforms 7 with the likelihood of a skin burn increasing proportionally with the total energy delivered with both monophasic7 and biphasic devices.16 In addition, biphasic waveforms have been shown to cause less muscle damage9 and do not cause elevation of myoglobin and cardiac troponin I levels after DCC.17 In summary, success can be achieved with biphasic waveforms at lower energy and with minimal deleterious effects for the patient.
            Manufacturers are no longer producing monophasic defibrillators. These older devices will be superseded and replaced by those with biphasic waveforms. This will result in an inevitable shift in practice toward biphasic DCC of atrial arrhythmias.

Table 1. Studies comparing monophasic and biphasic devices for DCC in atrial fibrillation.

MP: Monophasic   
BP: Biphasic

Electrode positioning in DC Cardioversion

            Antero-posterior (AP) and antero-apical (AA) electrode positions are commonly employed during DCC of AF. There has been considerable debate as to whether any one position is optimal. Historically, AP configurations have been considered to provide a better “shock vector” through the atria compared with the AA configuration.18,19 Several antero-posterior configurations were described and theories were proposed to explain the advantages of these electrode positions, with a right anterior to left posterior configuration suggested where the underlying pathology involves both atria, whilst a left anterior to posterior configuration is better when the left atrium was primarily affected.19 However, it is known that only a small percentage (~4%) of current delivered by the transthoracic route reaches the heart in an AA configuration,20 whilst the majority of current is shunted around the heart (around the thoracic cage or through the lungs). The path taken by current using AP electrodes is not described, and small variations in electrode positions may have a very small influence on outcome. Kerber had previously indicated that there was no significant difference between apex-anterior, apex-posterior and anterior-posterior configurations with monophasic waveforms achieving greater than 90% success in all groups.21 Two studies have suggested that the use of an AP configuration may be superior when monophasic waveforms are employed for DCC of AF.22,23 However, neither measured transthoracic impedance (TTI) with the varying electrode configurations.
            TTI is known to be an important determinant of both atrial24 and ventricular defibrillation.25 Modern biphasic defibrillators compensate for differing transthoracic impedances. These devices alter the delivered waveforms in order to deliver similar defibrillation energy “doses” to patients at extremes of transthoracic impedance. Thus those with a low TTI (typically smaller and lighter) receive a limited voltage and current to deliver a set energy, whilst those with a high TTI (larger and heavier patients) receive more voltage and current to deliver the same given energy to the heart.
            Kirchhof and colleagues have recently examined the midline AP configuration with non-impedance compensated monophasic and impedance compensated biphasic waveforms using hand-held paddles (a factor that is known to reduce TTI).26 This position was reported to be highly efficacious.26. TTI was not reported. To date, AA and various AP configurations have been described with biphasic waveforms and the results are highly efficacious when a modern ICB defibrillator is employed. We have recently compared AA and AP electrode positions using a biphasic waveform and found that the AP position was associated with a lower TTI in a large number of patients. However, when a modern biphasic defibrillator with impedance compensation was employed for DCC, there was a trend towards an improved outcome with the AA position.27 Our results suggest that reducing the influence of TTI with a modern device, and the utilisation of a biphasic waveform reduces the effect and importance of electrode position. We currently use the AA position for DCC in our institution.

Energy selection

            There are 2 distinct approaches to energy selection for DCC. Some physicians feel that it is best to select the highest possible energy in order to maximize the chance of initial success, minimize the number of shocks and lessen the exposure to sedative agents. Others prefer to follow an escalating energy protocol. Lown’s rationale for this approach was to minimise post-shock arrhythmia.18 This method also allows cardioversion at the lowest energy for each individual patient and may prevent high cumulative doses in some.
            At present each manufacturer recommends different energy selection protocols for their devices. Whilst lower energy shocks may be efficacious in patients with AF of short duration (1 week or less), published studies show that shocks of ≥150 J will result in a success rate of ~80% (Table 2). Two manufacturers offer the capability of higher energy biphasic waveforms (up to 360 J). Current evidence suggests that the majority of patients will be successfully cardioverted by 200 J shocks, and it appears that only a very small percentage of patients benefit from higher energy biphasic shocks. In addition, preliminary results from an ongoing multicentre study demonstrated that first shock success was significantly higher and fewer shocks were administered when a non-escalating energy selection protocol starting at 200J was employed (compared with an escalating protocol starting at 100J, maximum energy 200J).28

<>Table 2. Evidence for energy levels and pad positions in biphasic direct current cardioversion of atrial fibrillation.

*2 shocks delivered at same energy
Cross-over from Med-Phys to Zoll
AA: Antero-apical
Med-Phys: Medtronic-Physiocontrol
AP: Antero-posterior

What is the place of direct current cardioversion in the era of the rate control strategy?

            Recent clinical trials have demonstrated that a rate control and anticoagulate strategy is acceptable for many patients with AF. The AFFIRM29 and RACE30 studies demonstrated that aggressive pursuit of sinus rhythm is not necessary in many patients. Nevertheless, many patients with AF will be acutely or chronically symptomatic necessitating cardioversion. Furthermore, those with a precipitating cause may have their arrhythmia abolished for the long term when the acute insult is resolved. Therefore, DCC will remain an important therapeutic option for a large proportion of patients with AF.


            Direct current cardioversion of AF using biphasic waveforms is highly efficacious and is superior to monophasic waveforms. All manufacturers’ devices have been shown to be effective for this procedure. The choice of electrode position appears to be less important when impedance compensated biphasic waveforms are employed for DCC. An initial energy of at least 150 J should be selected for DCC of AF, although only a small minority of patients will benefit from shocks of greater than 200 J.


1. Lown B, Perlroth MG, Kaidbey S, Abe T, Harken DE. Cardioversion of atrial fibrillation. N Engl J Med 1963;269:325-331

2.  Lown B. Defibrillation and cardioversion. Cardiovascular Research 2002;55:220-224.

3. Adgey AAJ, Walsh SJ. Theory and practice of defibrillation: (1) Atrial fibrillation and DC conversion. Heart. 2004;90:1493-1498.

4. Rao ACR, Naeem N, John C, Collinson PO, Canepa-Anson R, Joseph SP. Direct current cardioversion does not cause cardiac damage: evidence from cardiac troponin T estimation. Heart 1998;80:229-230

5. Siaplaouras S, Buob A, Rotter C, Bohm M, Jung J. Impact of biphasic electrical cardioversion of atrial fibrillation on early recurrent atrial fibrillation and shock efficacy. J Cardiovasc Electrophysiol. 2004;15:895-897

6. Mittal S, Ayati S, Stein KM, Schwartzman D, Cavlovich D, Tchou PJ, et al. Transthoracic cardioversion of atrial fibrillation. Comparison of rectilinear biphasic versus damped sine wave monophasic shocks. Circulation 2000;101:1282-1287

7.  Page RL, Kerber RE, Russell JK, Trouton T, Waktare J, Gallik D, et al for the BiCard Investigators. Biphasic versus monophasic shock waveform for conversion of atrial fibrillation. J Am Coll Cardiol 2002;39:1956-1963

8. Scholten M, Szili-Torok T, Klootwijk P, Jordaens L. Comparison of monophasic and biphasic shocks for transthoracic cardioversion of atrial fibrillation. Heart 2003;89:1032-1034

9. Marinsek M, Larkin GL, Zohar P, Bervar M, Pekolj-Bicanic M, Mocnik FS, et al. Efficacy and impact of monophasic versus biphasic countershocks for transthoracic cardioversion of persistent atrial fibrillation. Am J Cardiol 2003;92:988-991

10. Rho RW, Page RL. Biphasic versus monophasic shock waveform for conversion of atrial fibrillation. Card Electrophysiol Rev 2003;7:290-291

11. Koster RW, Dorian P, Chapman FW, Schmitt PW, O’Grady SG, Walker RG. A randomized trial comparing monophasic and biphasic waveform shocks for external cardioversion of atrial fibrillation. Am Heart J. 2004;147:e20.

12. Niebauer MJ, Brewer JE, Chung MK, Tchou PJ. Comparison of the rectilinear biphasic waveform with the monophasic damped sine waveform for external cardioversion of atrial fibrillation and flutter. Am J Cardiol. 2004;93:1495-1499.

13. Gurevitz OT, Ammash NM, Malouf JF, Chandrasekaran K, Rosales AG, Ballman KV. Comparative efficacy of monophasic and biphasic waveforms for transthoracic cardioversion of atrial fibrillation and atrial flutter. Am Heart J. 2005;149:316-321.

14. Khaykin Y, Newman D, Kowalewski M, Korley V, Dorian P. Biphasic versus monophasic cardioversion in shock-resistant atrial fibrillation. J Cardiovasc Electrophysiol 2003;14:868-872

Fuster V, Ryden LE, Asinger RW, Cannom DS, Crijns HJ, Frye RL, et al. 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 and the European Society of Cardiology Committee for Practice Guidelines and Policy Conferences (Committee to Develop Guidelines for the Management of Patients With Atrial Fibrillation) Developed in Collaboration With the North American Society of Pacing and Electrophysiology. Eur Heart J 2001;22:1852-1923

16. Neal S, Ngarmukos T, Lessard D, Rosenthal L. Comparison of the efficacy and safety of two biphasic defibrillator waveforms for the conversion of atrial fibrillation to sinus rhythm. Am J Cardiol 2003;92:810-814

Kosior DA, Opolski G, Tadeusiak W, Chwyczko T, Wozakowska-Kaplon B, Stawicki S, et al. Serum troponin I and myoglobin after monophasic versus biphasic transthoracic shocks for cardioversion of persistent atrial fibrillation. Pacing Clin Electrophysiol. 2005;28 Suppl 1:S128-132

18.  Lown B. Electrical reversion of cardiac arrhythmias. Br Heart J 1967;29:469-489

Ewy GA. Optimal technique for electrical cardioversion of atrial fibrillation. Circulation 1992; 86:1645-1647

20. Lerman BB, Deale OC. Relation between transcardiac and transthoracic current during defibrillation in humans. Circulation Research 1990;67:1420-1426

Kerber RE, Jensen SR, Grayzel J, Kennedy J, Hoyt R.  Elective cardioversion: influence of paddle-electrode location and size on success rates and energy requirements. N Engl J Med 1981;305:658-662

Botto GL, Politi A, Bonini W, Broffoni T, Bonatti R. External cardioversion of atrial fibrillation: role of paddle position on technical efficacy and energy requirements. Heart 1999;82:726-730

23. Kirchhof P, Eckardt L, Loh P, Weber K, Fischer R-J, Seidl K-H. Anterior-posterior versus anterior-lateral electrode positions for external cardioversion of atrial fibrillation: a randomised trial. Lancet 2002;360:1275-1279

24. Dalzell GWN, Anderson J, Adgey AAJ. Factors determining success and energy requirements for cardioversion of atrial fibrillation. Q J Med 1990;76:903-913

25. Dalzell GWN, Cunningham SR, Anderson J, Adgey AAJ. Electrode pad size, transthoracic impedance and success of external ventricular defibrillation. Am J Cardiol 1989;64:741-744

26. Kirchhof P, Monnig G, Wasmer K, Heinecke A, Breithardt G, Eckardt L, et al. A trial of self-adhesive patch electrodes and hand-held paddle electrodes for external cardioversion of atrial fibrillation (MOBIPAPA). Eur Heart J 2005;26:1292-1297

27. Walsh SJ, McCarty D, McClelland AJ, Owens CG, Trouton TG, Harbinson MT, et al. Impedance compensated biphasic waveforms for transthoracic cardioversion of atrial fibrillation: a multi-centre comparison of antero-apical and antero-posterior pad positions. Eur Heart J 2005;26:1298-1302

Glover BM, Walsh SJ, McCann CJ, Moore MJ, Dalzell GWN, Trouton T, et al. Energy Setting of Biphasic Shocks For Direct Current Cardioversion of Atrial Fibrillation. Irish J of Med Sci. 2005 (In Press)

29. The Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) Investigators. A comparison of rate control and rhythm control in patients with atrial fibrillation. N Engl J Med 2002;347:1825-1833

30. Van Gelder IC, Hagens VE, Bosker HA, Kingma JH, Kamp O, Kingma T, et al. A comparison of rate control and rhythm control in patients with recurrent persistent atrial fibrillation. N Engl J Med 2002;347:1834-1840

31. Kim ML, Kim SG, Park DS, Gross JN, Ferrick KJ, Palma EC, et al. Comparison of rectilinear biphasic waveform energy versus truncated exponential biphasic waveform energy for transthoracic cardioversion of atrial fibrillation. Am J Card 2004;94:1438-1440.

32. Rashba EJ, Gold MR, Crawford FA, Leman RB, Peters RW, Shorofsky SR. Efficacy of transthoracic cardioversion of atrial fibrillation using a biphasic trancated exponential shock waveform at variable initial shock energies. Am J Cardiol 2004; 94: 1572-1574

33. Ricard P, Levy S, Boccara G, Lakhal E, Bardy G. External cardioversion of atrial fibrillation: comparison of biphasic vs monophasic waveform shocks. Europace 2001, 3: 96-9

Home Page Current Issue List of Editors