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.
E-mail:
jennifer.adgey@royalhospitals.n-i.nhs.uk
Abstract
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
Introduction
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 failed
14 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
monophasic
7 and biphasic
devices.
16 In addition,
biphasic waveforms have been shown to cause less muscle damage
9 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 atrial
24
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 AFFIRM
29 and RACE
30
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.
Conclusions
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.
References
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
15. 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
17.
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
19.
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
21. 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
22. 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
28. 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
