Electrical cardioversion of atrial fibrillation

Cardiol Clin 22 (2004) 101–111

Electrical cardioversion of atrial fibrillationJose A. Joglar, MD*, Robert C. Kowal, MD, PhD

Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern

Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, TX 75390-8837, USA

Atrial fibrillation (AF) is the most common

chronic arrhythmia encountered in clinical prac-tice, affecting an estimated 2.2 million Americansand present in 8% to 10% of those over 80 years

old [1]. As the United States population ages, theincidence and prevalence of AF is expected toincrease. Although the Atrial Fibrillation Follow-

Up of Rhythm Management (AFFIRM) studydemonstrated no clinical benefit from attempts tomaintain sinus rhythm in AF patients with

suppressive antiarrhythmic agents and repeatedcardioversions, cardioversion was employed asinitial management in both arms of the study [2].In addition, restoration of sinus rhythm may be

an important therapeutic goal in patients who areyounger or highly symptomatic. Therefore, car-dioversion remains an important and frequently

employed intervention in patients with AF.Transthoracic direct-current cardioversion has

become the standard method for terminating AF

since it was first described by Lown et al in 1962 [3].Since then, this technique has been used extensive-ly, and it has been determined to be safe and

effective.Extensive research completed over the lastdecade has resulted in a better understanding of themechanisms of defibrillation, the development ofnewer technologies and energy waveforms, and

novel optimization strategies to improve efficacyrates, patient safety, and success in refractory cases.

Waveforms and energy selection

An important advance over the last decade has

been the development of alternate waveforms for

* Corresponding author.

E-mail address: [email protected]

(J.A. Joglar).

0733-8651/04/$ - see front matter � 2004 Elsevier Inc. All rig

doi:10.1016/S0733-8651(03)00119-X

defibrillation. Traditional defibrillators deliver

monophasic shocks. The electrical energy isdelivered in a single polarity, meaning that ittravels in a single direction, primarily with

a damped sinusoidal waveform. Biphasic defibril-lation waveforms were developed in an attempt toimprove conversion rates. In contrast to mono-

phasic waveforms, biphasic waveforms involvea reversal of current at a specific time in the energyshock (Fig. 1). The advantage of biphasic shocks

derives from its ability to lower the defibrillationthreshold by creating longer postshock refracto-riness in a greater percentage of myocytes thanwith monophasic shocks [4]. Biphasic waveforms

are employed in all implantable defibrillators,because they have shown to reduce energyrequirements by 25% to 45% [5,6]. They also

are used in automated external defibrillators [7].Another advantage of biphasic defibrillators isthat they adjust delivered current according to

transthoracic impedance (see Fig.1). It is inevita-ble that biphasic defibrillators ultimately willreplace monophasic models; nevertheless, many

monophasic waveform devices around the worldremain operational, and as such, both technolo-gies are discussed in this article.

Studies of monophasic waveform

Historically, there has been disagreement re-garding the best initial energy to select for electivecardioversion of AF. The controversy emanatedfrom the fact that AF duration influences the

amount of energy required for successful cardio-version. Using monophasic shocks, Ricard et aldemonstrated that for AF of less than 24 hours

duration, energies equal or less than 200 Joules (J)were successful in 98% of patients [8]. For AF ofover 48 hours’ duration, the energy requirements

hts reserved.

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102 J.A. Joglar, R.C. Kowal / Cardiol Clin 22 (2004) 101–111

were higher. The authors performed a prospectiverandomized study evaluating three different initial

energies (100, 200, and 360 J) for electivecardioversion of persistent AF using monophasicdefibrillators [9]. The study included 64 patientswith persistent AF of over 48 hours’ duration. The

Fig. 1. Different waveforms for defibrillation. (Top)

Traditional damped sinusoidal monophasic. (Middle)

Truncated exponential biphasic adjustment of current

according to transthoracic impedance occurs by changes

in the pulse duration of the first phase. (Bottom) The

rectilinear biphasic waveform maintains a constant

current during the first phase to adjust for differences

in transthoracic impedance. (From Takata TS, Page RL,

Joglar JA. Automated external defibrillators: technical

considerations and clinical promise. Ann Intern Med

2001;135:990–8; with permission.)

initial success rate was 14% with 100 J, 39% with200 J, and 95% with 360 J (P < 0.0001).Furthermore, when the patients were started at

the lower energy levels, they ultimately receiveda higher total energy and higher number ofshocks, whereas no adverse effects were seen whena high initial energy was employed (Fig. 2) [9]. For

conversion of atrial flutter, Pinski et al demon-strated that 100 J of energy achieved an 85%conversion rate versus a 70% conversion rate

when only 50 J were used [10].

Studies of biphasic waveform

More recent studies have confirmed the supe-riority of biphasic over monophasic shocks for

cardioversion of AF [11,12]. In a prospectiverandomized study, Mittal et al demonstrated thesuperiority of the rectilinear biphasic waveform

over damped sinusoidal monophasic waveformfor elective cardioversion of AF [11]. In theirstudy, the conversion efficacy of the biphasic

shocks was markedly superior to monophasicshocks at all energy levels (Fig. 3). One importantaspect of this type of waveform is that itcompensates for transthoracic impedance by

maintaining a constant current during the firstphase of defibrillation. Therefore, the superiorityof biphasic over monophasic waveforms was more

dramatic in those with high transthoracic imped-ances (> 70 ohms), who are therefore less likely toconvert with monophasic shocks (see Fig. 3) [11].

Page et al compared a damped sinusoidal mono-phasic waveform to a truncated exponentialbiphasic waveform [12]. Patients underwenta step-up protocol, where they received up to five

shocks, 100, 150, 200, 200 J biphasic or 360 Jmonophasic, and a final crossover shock at themaximum output of the alternate waveform. At

the first three energy levels, the biphasic waveformwas dramatically superior to the monophasicwaveform (60% versus 22% at 100 J, 77% versus

44% at 150 J, and 90% versus 53% at 200 J).Furthermore, the patients receiving biphasicshocks required fewer shocks and experienced

significantly less dermal injury [12].Therefore, for cardioversion of patients with

persistent AF, it is recommended that an initialenergy of 200 J be selected when biphasic

waveform defibrillators are used. In patientswith AF of less than 24 hours duration, 100 Jwill be appropriate for most patients. If mono-

phasic waveform defibrillators are used, a higherinitial cardioversion energy should be selected(300 to 360 J). For patients undergoing cardio-

103J.A. Joglar, R.C. Kowal / Cardiol Clin 22 (2004) 101–111

version for atrial flutter, the optimal initialenergy selection is 100 J.

General technique

Success rates of transthoracic cardioversionare high if one employs proper technique,

especially if biphasic waveforms are used. Factorsthat might impact success rate negatively includebody size, presence of idiopathic dilated cardio-

myopathy, and AF duration (Fig. 4). Left atrialenlargement should not preclude an attempt atcardioversion, because it is not a factor thatstrongly predicts adverse outcome [13].

The most important determinant of successfuldefibrillation is the amount of current that travelsacross the myocardium, because a critical mass of

tissue must be depolarized for successful arrhyth-mia termination. Transthoracic impedance isquite variable in people, reported from 20 to 150

ohms, with an average of 70 to 80 ohms [14].Because the amount of delivered current deter-mines successful defibrillation, and current is

inversely proportional to the impedance betweenthe electrodes, determinants of transthoracicimpedance can influence the efficacy of defibrilla-tion. Factors that affect transthoracic impedance

include chest size, electrode size and composition,electrode–tissue interface, the time between repeatdirect currents (DC) shocks, prior sternotomy,

phase of respiration, and whether pressure isapplied to the chest. Because the maximal amountof energy in defibrillators generally is fixed, these

factors should be optimized to enhance cardio-version success, especially when monophasicwaveforms shocks are applied, as modern bi-phasic defibrillators measure transthoracic imped-

ance and adjust the delivered current accordingly.Ewy et al observed that the optimal electrode

size for defibrillation to be 12 to 13 cm in diameter

[15]. In this study, larger electrodes did not resultin adequate energy density for defibrillation. Withsmaller electrodes, current is concentrated, which

may result in myocardial damage [16]. The

Fig. 2. When performing elective cardioversion of

persistent AF using monophasic defibrillators, compared

with 100 or 200 J, the higher level (360 J) resulted in higher

success rate (A), fewer number of shocks (B), and less total

energy (C). *P =<0.0001; +P =<0.05. (From Joglar

JA, Hamdan MH, Ramaswamy K, Zagrodzky JD,

Sheehan CJ, Nelson LL, et al. Initial energy for elective

external cardioversion of persistent atrial fibrillation. Am

J Cardiol 2000;86:348–50; with permission.)

c


Fig. 3. (A) Defibrillation of persistent AF was significantly more effective with a rectilinear biphasic waveform than with

traditional monophasic waveform, even when lower energies were used. (B) Because of impedance compensation, which

ensures a constant current during the first phase, the different in benefit was seen mainly in patients with high

transthoracic impedance. (From 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;101:1282–7; with permission.)

minimal electrode size is 80 cm2, and total forboth at least 150 cm2 [17].

The placement of electrodes can impact out-come and has been investigated. Because the rightand left atria are positioned one behind the other,toward the posterior aspect of the thorax, an

electrical vector in the anterior–posterior directionshould be more effective than the standardanterior-lateral direction for ventricular defibrilla-

tion. Botto et al randomized 301 patients with

persistent AF to cardioversion using paddles in theanterior–lateral (ventricular apex-right infraclavic-

ular area) or a modified anterior–posterior posi-tion with the anterior paddle to the right of thesternum and the posterior paddle on the angle ofthe left scapula. A step-up protocol was used, with

a first shock of 3 J/kg, a second of 4 J/kg (max 360J), and, if necessary, a last shock at the highestenergy with alternate paddle location. They

demonstrated a higher conversion rate with


Fig. 4. Success rate of direct current cardioversion inversely correlates with AF duration. (From Elhendy A, Gentile F,

Khandheria BK, Hammill SC, Gersh BJ, Bailey KR, et al. Predictors of unsuccessful electrical cardioversion in atrial

fibrillation. Am J Cardiol 2002;89:83–6; with permission.)

modified anterior–posterior position, and statisti-cally significant lower energy requirements (Fig. 5).Of interest, nine of their patients who failed to

convert with anterior–posterior electrodes hadsuccess with the anterior–lateral position, stressingthe fact that in individual patients, any of these

positions may be more effective [18]. In anotherstudy, Kirchhof et al randomized 108 patients, alsowith persistent AF, to anterior–posterior or

anterior–lateral electrodes position using a step-up protocol (50 to 360 J), followed by a lastmaximal output cross-over shock. Before cross-over, success was 96% for the anterior–posterior

group, compared with 78% in the anterior–lateral(P=0.009). After cross-over, an additional eightpatients initially randomized to anterior–lateral

converted [19]. Kerber et al did not observea difference between electrode positions duringatrial cardioversion, but their study included

a significant number of patients with flutter thatinvolved only the right atrium. Furthermore, theydid document higher transthoracic impedance with

the anterior–lateral position [20]. Therefore, thedata support the use of an anterior–posteriorelectrode position for the cardioversion of AF,although this may be less important with biphasic

shocks and adjusted currents [21].In women, placement of the anterior electrode

should be adjacent or under the breast, since

placing it over the breast will result in a higherimpedance [22]. In patients with permanent pace-makers, the electrodes should be positioned as far

as possible from the pacemaker and in anterior–posterior position so that the energy vector isperpendicular to the pacing system. The device

should be interrogated immediately before andafter cardioversion to verify appropriate function[23].

Because air is not a good conductor ofelectricity, administering the shock during theexpiratory phase of respiration is beneficial [24].

Kerber et al demonstrated that pressure applied tothe chest during cardioversion resulted in lowertransthoracic impedance [25]. Cohen et al were

able to cardiovert four of five refractory patientssuccessfully by using active chest compression anddocumented in one patient a 13 ohm reduction intransthoracic impedance [26]. The time between

successive shocks is also important. Dahl et aldemonstrated progressive decrements in trans-thoracic impedance with repeated shocks, espe-

cially when the time between shocks was longest(3-minute, versus 15-second or 1-minute intervals)[27]. Kerber also demonstrated as much as a 24%

decline in transthoracic impedance in the earlypostoperative period following sternotomy [28].

Finally, shocks must be synchronized to the

QRS complex to prevent inadvertent inductionof ventricular fibrillation caused by delivery ofa shock in the vulnerable period of the T wave.Adequate sedation is essential to maximize

patient comfort. In randomized study, propofoland methohexital demonstrated similar efficacy,and both provided a more rapid onset of action

than midazolam [29].

Refractory cases

Fortunately, if one adheres to appropriate

technique, especially with the use of biphasic


Fig. 5. The two electrode configurations used by Botto et al for comparison. The anterior–posterior configuration was

demonstrated to be more effective that the anterior–lateral configuration. For this configuration, the anterior electrode is

to the right of the sternum at the third intercostal space, and the posterior electrode is just at the angle of the left scapula.

Therefore, it is not true anterior–posterior, but right anterior, left posterior. This position is recommended by Lown and

other authors for cardioversion of AF, because the shocking vector directly crosses both atria [56]. (From 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;82:726–30; with permission.)

waveforms, failure to defibrillate is uncommon.Nevertheless, in rare patients in whom standardcardioversion is not successful, additional optionsmust be pursued. There are two potential negative

outcomes from cardioversion that are importantto recognize and distinguish. First, there is shockfailure, where no sinus beats are identified.

Second, there is immediate or early recurrence ofatrial fibrillation (IRAF, ERAF), where sinusrhythm is restored, but AF recurs any time from

the first minute (IRAF) to days (ERAF). Rossiand Lown reported a 16% incidence of recurrentAF within 1 minute of cardioversion [30].

Therefore, a continuous ECG recording shouldbe available during cardioversion for carefulinspection of the postcardioversion rhythm, be-cause different strategies are required for these

two different negative outcomes, and at times itmight be difficult to distinguish them.

For overcoming shock failure, Saliba et al

reported the rapid, sequential use of two defib-rillators with 720 J of total energy in a group ofpatients with large body habitus (mean weight was

117 kg) who previously had failed to convert withthe standard technique [31]. They used two sets ofpatch electrodes in the anterior–posterior positionnext to each other, and a single operator delivered

the energy simultaneously. By using this tech-nique, they successfully restored normal sinusrhythm in 46 of 55 (84%) of these previously

refractory patients, with no significant complica-

tions. Other options include drug-facilitatedcardioversion and internal cardioversion.

Drugs to facilitate cardioversion

Antiarrhythmic drugs can be effective for

overcoming shock failure and for preventingimmediate AF recurrences. In a randomizedstudy, Oral et al demonstrated that the class III

agent ibutilide increased the success of electricalcardioversion from 72% to 100% [32]. Further-more, all patients who failed to convert initiallylater were cardioverted successfully after they

crossed over to the ibutilide arm. There was nodifference between the groups in immediate re-currence; therefore, the drug was effective only for

prevention of shock failure. Cappucci et alrandomized 92 patients with persistent AF toamiodarone 400 mg/day for 1 month before

cardioversion, diltiazem 180 mg/day before car-dioversion and a glucose/insulin/potassium in-fusion given 24 hours before cardioversion, ordiltiazem alone. Immediate cardioversion success

was higher with amiodarone compared with theother two groups (87%, 58%, and 65%, re-spectively) [33]. One limitation of amiodarone was

that to enhance cardioversion success, pretreat-ment for weeks was required. In contrast, ibutilidehas the advantage of immediate use in the setting

of shock failure without the required pretreat-ment. In both studies, the success rate in the


Fig. 6. The combination of amiodarone and irbesartan is superior to amiodarone alone in maintaining sinus rhythm

after cardioversion. As the Kaplan-Meier graph demonstrates, the difference was in great part because of a reduction in

immediate AF recurrence. (From Madrid AH, Bueno MG, Rebollo JMG, Marin I, Pena G, Bernal E, et al. Use of

irbesartan to maintain sinus rhythm in patients with long-lasting persistent atrial fibrillation. A prospective randomized

study. Circulation 2002;106:331–6; with permission.)

control groups was low for current standards

using biphasic defibrillators; nevertheless, ibutilideis still an option when needed.

Suppression of immediate AF recurrence could

result in good intermediate-term arrhythmiacontrol. Van Noord et al treated 27 patientswho had unsuccessful cardioversion with a 4-week

load of amiodarone, after which cardioversionwas repeated. Of those patients in whom theinitial cardioversion failed because of shock

failure (n= 16), only 31% were in sinus rhythmat 1 month, compared with 91% for those withinitial failure caused by immediate recurrence(n = 11) [34].

Immediate AF recurrences can be preventedwith antiarrhythmic drugs. Rossi and Lowndemonstrated a higher cardioversion success rate

after quinidine loading (92%with quinidine versus64% control) mainly by preventing immediate AFrecurrence [30]. Bianconi and et al randomized 100

patients to receive the class IC antiarrhythmic

propafenone (750 mg/day) for 2 days before

cardioversion or placebo. There was no differencein shock failure between the two groups; however,immediate recurrence occurred less often in the

propafenone group and allowed for more patientsto be discharged at 2 days in sinus rhythm (73.5%versus 52.9%, P < 0.05) [35]. Even better results

were reported by DeSimone et al, who in additionto propafenone, gave a short course of verapamil.This intervention decreased the 2-day AF recur-

rence to less than 5%, theoretically by improvingelectrical remodeling [36].

Other drugs not considered antiarrhythmic inthe traditional sense can be effective in preventing

immediate recurrence of AF. In a recent study,Madrid et al demonstrated that the combinationof amiodarone with the angiotensin receptor

blocker, irbesartan, reduced immediate AF re-currence compared with amiodarone alone(Fig. 6) [37]. The mechanism postulated includes

prevention of AF-induced electrical remodeling


directly or indirectly by other mechanisms such asprevention of fibrosis or modulation of sympa-thetic tone. The use of these and other drugs is the

focus of extensive research.

Internal cardioversion

In addition to the use of physical techniques and

pharmacological agents, internal atrial defibrilla-tion has been developed to achieve atrial conver-sion in difficult cases. Because high chest wallimpedance is often the reason for failed conversion,

internal cardioversion serves as a means of circum-venting this obstacle to restoration of sinus rhythm.The technique involves placement of catheters with

large electrode surface areas in the lateral rightatrium and either the coronary sinus or the leftpulmonary artery. Energy is delivered across this

vector synchronous to theQRS.Delivery followingshort RR intervals (< 300 milliseconds) should beavoided [38,39]. Bypassing the chest wall by means

of internal energy delivery leads to a substantialreduction in defibrillation threshold. In severalstudies, the mean defibrillation energy requiredranged from 5 to 7 J [40,41]. The duration of AF

appears to be themost powerful predictor of energyrequirements. As a result, internal cardioversioncan be performed with mild sedation rather than

general anesthesia in most cases, making thetechnique particularly useful in patients at highrisk for anesthesia-related complications.

Other than its role in patients already un-dergoing electrophysiological study, internal car-dioversion appears to be most useful in individualsrefractory to standard transthoracic cardioversion.

In a study of 55 patients with AF refractory toexternal cardioversion, Gasparini et al reportedsuccessful internal cardioversion in 95% of these

subjects without complications [41]. Although 31%suffered recurrence ofAFwithin 1week, 40%of thepopulation remained in sinus rhythm following

a mean follow-up of 18 months. Similarly, reportshave demonstrated an effective role for internalcardioversion in extremely obese patients [42].

Internal cardioversion is not without limita-tion. The invasive nature of the procedure, re-quiring fluoroscopic guidance for catheterplacement and prolonged postprocedure observa-

tion, makes the approach substantially moreexpensive than standard external cardioversion.Furthermore, anticoagulation must be terminated

before the procedure, necessitating the use ofheparin in the peri-procedure period to limit theriskofperi-conversion stroke.Finally,Verdino et al

observed that of 20 patients referred for internalcardioversion, 16 were converted to sinus rhythmsuccessfully, with an additional attempt at external

cardioversion employing careful electrode place-ment an the use of significant chest wall pressure,suggesting that internal cardioversion likely isneeded for only a small minority of patients [43].

Adverse effects and anticoagulation

Cardioversion of AF generally is considered

safe with a low rate of complications. Thepotential risks are related mainly to dermal injury,arrhythmias, and embolic events. In patients whoundergo cardioversion without receiving antico-

agulation, the risk of embolic events has beenreported to be as high as 6% [44]. This most likelyis the result of postcardioversion atrial stunning,

which is a delay in resumption of atrial mechan-ical function despite organized electrical activity.It is therefore general practice that patients receive

anticoagulation for at least 3 weeks beforecardioversion and continue it for 4 weeks post-procedure, unless the arrhythmia duration isknown to be less than 48 hours [23]. Such

a strategy decreases the overall risk of stroke toless than 1% (range 0.5% to 0.8%) [45,46]. Whentransesophageal echocardiography is used to

guide cardioversion, the risk is similarly low,provided that anticoagulation is maintained dur-ing the cardioversion and at least 4 weeks

afterwards [45]. Although the risk of stroke aftercardioversion of atrial flutter has been reported tobe significantly lower [44], some authors have

reported an incidence similar to cardioversion ofAF [47]. Therefore the authors and othersrecommend anticoagulating patients with atrialflutter in a fashion similar to that with AF

patients [48].In the past, concerns were raised about

myocardial damage from direct current cardio-

version based on studies demonstrating a raise increatine kinase (CK) and CK-MB [49]. Sub-sequently, using more cardiospecific markers

(troponins I and T), these concerns were easedafter several studies demonstrated no damagefrom elective cardioversion [50–52]. Transient ST

segment elevation, which resolves within 1.5minutes, can be observed in up to 19% of patientsundergoing cardioversion [53]. The etiology of thechanges remains unknown, but it has been

postulated that they might just be sustaineddepolarization of the regional myocardium


exposed to the highest current density [54].Regardless of the mechanism, no evidence ofmyocardial damage has been documented as theresult of these changes.

Dermal injury is common and usually outlinesthe borders of the defibrillation electrodes. Thenature of these lesions, often referred to as burns,

was described by Pagan-Carlo et al [55]. Theyperformed biopsies on 30 patients who sufferedthermal injury after elective cardioversion of AF

and flutter and compared them to biopsiesobtained from two normal subjects. They demon-strated variable degrees of epidermal necrosis and

confirmed the lesions to be consistent with first-degree burns, although they also found variablenumbers of neutrophils and eosinophils, suggest-ing a possible hypersensitivity reaction compo-

nent. Page et al reported a reduction in theincidence of symptomatic skin burns by morethan half with the use of biphasic defibrillators

compared with monophasic defibrillators [12].

Summary

External direct current cardioversion remainsthe most common and effective method for

restoration of normal sinus rhythm in patients withpersistent AF. The development of biphasic defib-rillators allows for higher success rates of conver-

sion using standard energy levels. For persistentAF, an initial energy of 200 J is recommended forbiphasic defibrillators, and 300 to 360 J are

recommended for monophasic defibrillators, withthe electrodes placed in the anterior–posteriorposition. For refractory cases, alternatives are

available such as dual defibrillators or internalcardioversion. Antiarrhythmic drugs may enhancethe results of cardioversion by helping overcomeshock failure or by preventing immediate recur-

rence of AF. Thromboembolism is the mostimportant complication associated with cardiover-sion, but it can be prevented by providing 3 weeks

of anticoagulation before the procedure or byexcluding the presence of thrombi by transesopha-geal echocardiography, followed by an additional

4 weeks of anticoagulation.

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Electrical cardioversion of atrial fibrillation