European Heart Journal (2000) 21, 848–855doi:10.1053/euhj.1999.1870, available online at http://www.idealibrary.com on

Transoesophageal low-energy cardioversion of atrialfibrillation

Results with the oesophageal–right atrial lead configuration

M. Santini, C. Pandozi, F. Colivicchi, F. Ammirati, M. Carmela Scianaro, A. Castro,F. Lamberti and G. Gentilucci

Department of Cardiology, San Filippo Neri Hospital, Rome, Italy

Revision submitted 30 July 1999, and accepted 4 August 1999.

Correspondence: Claudio Pandozi, MD, via Madonna di Fatima,22, 00147 Rome, Italy.

Introduction

Low energy intracardiac cardioversion has been recentlyintroduced as a safe and effective method to restoresinus rhythm in patients with both paroxysmal andpersistent atrial fibrillation[1–6]. In preliminary studiessuch a procedure has been proposed and employed afterthe failure of conventional external cardioversion orin patients with high transthoracic impedance and/orcontraindications to general anaesthesia[6].

Only mild and brief sedation is required during lowenergy intracardiac cardioversion. Despite its efficacyand safety, the spread of this new methodology inclinical practice is limited by the need for an electro-

0195-668X/00/100848+08 $35.00/0

physiology laboratory with fluoroscopy and of specifictechnical competence for lead positioning, either in thecoronary sinus or in the left pulmonary artery. Thepresence of a lead in the coronary sinus or in the leftpulmonary artery, which are both in direct contact withthe left atrium, allows a significant reduction in the atrialdefibrillation threshold[4].

The oesophagus is an anatomical structure in directcontact with the left atrium and several authors havereported preliminary experimental or clinical experi-ences of transoesophageal cardioversion for persistentatrial fibrillation[7–9]. In such studies the energy deliverywas performed between an oesophageal lead and astandard cutaneous paddle on the anterior chest wall[7].Energy requirements were found to be significantlylower with such a procedure when compared with thestandard external cardioversion, but general anaesthesiacould not be avoided[9].

Background Low energy internal cardioversion is a safeand effective procedure to restore sinus rhythm in patientswith atrial fibrillation refractory to external cardioversion.However the procedure is invasive and fluoroscopy ismandatory.

Aim of the study To assess the efficacy, safety andtolerability of a new simplified procedure of low energyinternal cardioversion.

Methods Twenty-five consecutive patients (19 males and 6females) with persistent atrial fibrillation were submitted tolow energy internal cardioversion using a step-up protocol(in steps of 50 V, starting from 300 V). A large surface arealead (cathode) was positioned in the oesophagus, 45 cmfrom the nasal orifice. A second large surface area lead(anode) was positioned in the right atrium. A quadripolarlead was positioned at the right ventricular apex to achieveventricular synchronization and back-up pacing. Oeso-phageal endoscopy was performed within 24 h of the end of

the procedure and repeated after 48 h, if injury to theoesophageal mucosa had occurred.

Results Sinus rhythm was restored in 23 patients (92%)with a mean delivered energy of 15·74 J (range 5–27) and amean impedance of 48 �. In two patients, endoscopyrevealed that small burns had occurred in the oesophagealmucosa. Such lesions spontaneously healed after 48 h.

Conclusions This new technique of performing low en-ergy internal cardioversion is effective and safe and avoidsthe positioning of a lead in the coronary sinus or in the leftpulmonary artery, thereby simplifying the procedure.(Eur Heart J 2000; 21: 848–855)� 2000 The European Society of Cardiology

Key Words: Atrial fibrillation, cardioversion, oesophagealcardioversion, endocavitary cardioversion.

See page 785 for the Editorial comment on this article

� 2000 The European Society of Cardiology

Transoesophageal cardioversion of AF 849

We therefore concluded that low energy internalcardioversion could be performed with a new configur-ation, employing a first lead in the oesophagus and asecond lead in the right atrium; such a new approachshould be effected with a low defibrillation thresholdand the consequent avoidance of general anaesthesia.Moreover, this simplified approach could have anapplication in small cardiological centres devoid ofspecific electrophysiological experience.

The aim of the present clinical study was to assess thesafety and efficacy of low energy internal cardioversionperformed with a right atrial–oesophageal configurationand to verify the possibility of performing such aprocedure without general anaesthesia.

Methods

Patient selection

The study was carried out in 25 consecutive patientswith persistent atrial fibrillation. The study was ap-proved by our Institutional Ethical Committee, and allthe patients provided written informed consent.

The diagnosis of atrial fibrillation was based on thesurface ECG, with the following criteria: presence offluctuation of the baseline without regular P or F waves,with totally irregular RR intervals. Thyroid dysfunctionhad been previously ruled out in all patients. Significantliver disease had been previously excluded in all patientsby history, clinical assessment and blood chemistry.

Eight patients were on amiodarone, nine on propa-fenone, eight in therapeutic washout. The patients inwashout were treated with intravenous propafenone(2 mg . kg�1) after sinus rhythm restoration. Allpatients were fully orally anticoagulated for at least 3weeks before the procedure. Anticoagulation was re-duced 2 days before the procedure to obtain an Inter-national Normalized Ratio value of about 2. Full oral

anticoagulation was restarted after cardioversion andwas continued for at least 30 days in cases of sinusrhythm persistence. After the procedure all patients werestarted on heparin which was discontinued when thera-peutic International Normalized Ratio values (2·5–3)were again reached.

Lead position

Three catheters were used for each patient. One custom-made decapolar large active surface area (520 mm2) lead(FIAB, Vicchio, FI, Italy) was introduced in the right orleft nostril and advanced into the oesophagus with thepatient’s cooperation, to a depth between 40 and 45 cmand until the distal pair of electrodes recorded a largeventricular electrogram and the proximal pairs recordedthe fibrillating atrial activity. A second lead with a distaldefibrillating coil having a large active surface area(500 mm2) (InControl, Inc., Redmond, WA, U.S.A.)was positioned in the right atrium.

In the first 15 patients it was introduced via thefemoral vein under fluoroscopic control, while in thefollowing 10 patients the lead was introduced in the rightinternal jugular vein and then positioned in the rightatrium under echocardiographic control (Fig. 1). Thecorrect position of this lead in the right atrium wasconfirmed by fluoroscopy. A third quadripolar standardlead was introduced via the femoral vein and positionedat the right ventricular apex to allow synchronizationof the shock on the QRS. An example of the leadconfiguration is given in Fig. 2.

Figure 1 The lead introduced through the right internaljugular vein is positioned in the right atrium under echocardio-graphic control. In this short-axis echocardiographic view, thearrow shows the catheter inside the right atrium.

Cardioversion

All the catheters were connected to a Telectronics 4510implant support device, combining features of a pacing-sensing system analyser and a cardioverter/defibrillator,

Eur Heart J, Vol. 21, issue 10, May 2000

850 M. Santini et al.

provided with 150 �F capacitor. A truncated, biphasic(3+3 ms) exponential waveform was used. The lead inthe oesophagus was used as the cathode and that in theright atrium as the anode.

Beginning from 300 V, the voltage was increasedprogressively by 50 V until restoration of sinus rhythmor an energy of 27 J was reached. All shocks wereseparated by an interval of at least 1 min. The voltage,both the total and delivered energy and the impedanceof each shock, were automatically measured by thedevice. All patients were sedated with intravenousDiazepam (standard dose: 5 mg in 2 min) before theshock delivery.

After each shock the patients were requested to gradevery carefully the discomfort with a score from 1 to 5:1=not felt, 2=felt without discomfort, 3, 4, 5=mild,moderate and severe discomfort, respectively.

If successful cardioversion was not achieved anotherlead with a distal defibrillating coil (InControl, Inc,Redmond, WA, U.S.A.) was positioned in the coronarysinus via the right internal jugular vein and cardio-version was again attempted with the coronary sinus–right atrium configuration. Oesophageal endoscopy wasperformed within 24 h from the procedure and repeatedafter 48 h if any oesophageal mucosa damage wasobserved.

Follow-upIn all patients an ECG was recorded every 6 h for 3 daysafter the procedure. After discharge, ECG and physicalexamination were performed once a week for the firstmonth and once a month thereafter. Patients were askedto come to the hospital for additional examinationswhenever symptoms recurred.

Eur Heart J, Vol. 21, issue 10, May 2000

Statistical analysis

Data are presented as mean values�SD. Differences incontinuous variables were analysed by paired and un-paired Student’s t-test or ANOVA as appropriate, andcomparisons between groups were performed by mul-tiple Bonferroni test. Difference in categorical variableswere analysed by Chi-square test, with Yates’ correctionif needed. A value of P<0·05 was considered statisticallysignificant.

Results

The clinical data of our patients are reported in Table 1.Twenty patients were men and five women, with a meanage of 60·68�7·46 years; the mean body weight was72·92�14·66 kg; the mean height was 165·24�8·25 cmand the mean body surface area was 1·42�0·19 m2. Themean atrial fibrillation duration was 290·20�277·79days, median 165 days, range 20–1080 days. The meanleft atrial size, as measured by echocardiography, was45·88�5·19 mm (range 38–58 mm).

The underlying heart disease were as follows: valvularheart disease (six patients), hypertension (eight patients),dilated cardiomyopathy (three patients), coronary heartdisease[4]. Four patients had lone atrial fibrillation.

Figure 2 Left-anterior oblique view of the leads used forcardioversion. The decapolar lead (cathode) is positioned in theoesophagus, while a second lead with a large surface active areacoil (anode) is introduced through the internal jugular vein intothe right atrium. The two leads embrace a large part of theatrial mass, including the septum. A third lead in the rightventricular apex allows the synchronization of the shock on theQRS.

Response to cardioversion

Successful cardioversion was obtained in 23/25 patients(92%) with a mean of 5·30�2·48 shocks/patient (range1–9). An example of successful termination of atrialfibrillation is shown in Fig. 3.

Transoesophageal cardioversion of AF 851

The intracardiac cardioversion data of the successfullytreated patients are reported in Table 2. The meanenergy required for cardioversion was 15·74�7·37 J(range: 5–27 J), the mean voltage 517·39�125·78 V(range: 300–700 V) and the mean impedance 48·0�6·14 � (range: 34–60 �). The mean duration of theprocedure was 40·7�6·22 min and the mean time offluoroscopy 4·09�2·57 min. In all patients in whom theright atrial lead was positioned under echocardiographiccontrol, fluoroscopy confirmed the correct position ofthe catheter in the right atrium. In these cases the atriallead had been introduced for a mean of 23�1·9 cm(range 20–25 cm).

In patients in whom the atrial lead was positionedthrough the femoral vein guided by fluoroscopy theprocedure duration was similar to those in whom it waspositioned through the internal jugular vein guided byechocardiography (42·26�6·36 min vs 38�4·47 min,respectively). Also, the fluoroscopy time was similar inthe two groups (4·6�2·99 vs 3·3�1·05 min) as well asthe mean discomfort score of the effective shock(3·3�0·6 vs 3·4�0·7).

As shown by the mean discomfort score, the pro-cedure was tolerated under sedation by all the patientsand general anaesthesia was never requested althoughoffered before the procedure.

The two patients who failed cardioversion with theoesophageal–right atrial configuration were cardio-verted with the coronary sinus–right atrial vector;nevertheless, these patients showed an atrial defibril-lation threshold of 24 and 27 J, higher than that re-ported in the literature with this configuration inpatients with persistent atrial fibrillation[4,6].

Safety of the procedure

A total of 190 oesophageal shocks were delivered in the25 patients. All the shocks were properly synchronizedon the QRS complex and no proarrhythmic effect wasnoted. In two patients small burns of the oesophagealmucosa were detected by endoscopy performed 24 hafter the procedure (Fig. 4a). These two patients hadreceived seven and nine shocks with a peak energy of 14and 20 J, respectively. However, the patients remainedtotally asymptomatic and the lesions spontaneously dis-appeared 48 h after the procedure (Fig. 4b). No othercomplications were noted.

Table 1 Clinical characteristics of patients

Patients Sex Age(years)

Weight(kg)

Height(cm)

BSA(m2)

AFdur(days)

LA(mm) Disease Therapy

M.A. F 58 91 150 1·85 180 44 Hypert WODG.V. F 67 54 152 1·49 90 48 Valvul WOP.B. M 65 75 167 1·84 720 38 CHD AmioV.F. M 61 94 175 2·09 135 44 Hypert PropafI.S. M 58 78 168 1·88 1080 45 Valvul WOI.A. M 58 78 168 1·88 140 43 CMD AmioB.M. M 63 64 160 1·67 60 46 Valvul PropafC.P. M 58 63 160 1·66 160 43 CHD AmioR.F. M 59 73 166 1·81 90 45 Valvul PropafF.G. M 67 90 178 2·08 720 43 Hypert WOP.A. M 75 70 178 1·87 365 58 CMD AmioS.A. M 49 64 160 1·67 20 43 Hypert PropafP.M. M 63 90 178 2·08 720 39 Lone PropafD.E. M 67 70 178 1·87 720 51 CHD AmioE.N. M 58 75 167 1·84 240 50 Valvul PropafB.V. M 59 73 166 1·81 60 57 CMD AmioB.A. M 65 64 160 1·67 120 46 Hypert WOO.G. M 73 85 170 1·95 180 48 Hypert PropafN.T. M 68 110 160 2·1 75 42 Lone WOV.I. M 45 72 175 1·86 150 53 Hypert AmioS.M. F 56 50 157 1·45 240 46 Hypert PropafP.C. F 62 68 160 1·72 180 51 Valvul PropafL.F. F 52 45 158 1·42 300 44 CHD AmioB.V. M 46 63 160 1·66 360 38 Lone WOR.F. M 65 64 160 1·67 150 42 Lone WOMean 60·68 72·92 165·24 1·42 290·20 45·88SD 7·46 14·66 8·25 0·19 277·79 5·19Median 61·5 77·5 155 1·76 165 43

M=male; F=female; BSA=body surface area; LA=left atrium diameter; AFdur=duration ofatrial fibrillation; Valvul=valvular disease; Hyper=hypertension; Amio=amiodarone; WO=wash-out; CAD=coronary artery disease; Lone=lone atrial fibrillation; DMC=dilated myocardiopathy.

Follow-up

The mean follow-up period was 188�61 days (range:60–240 days). No late symptom possibly related to the

Eur Heart J, Vol. 21, issue 10, May 2000

852 M. Santini et al.

shocks in the oesophagus were reported by the patients.Eleven of the 23 cardioverted patients (48%) had arecurrence of atrial fibrillation during the follow-upperiod. Nine of the 11 recurrences (82%) occurred in thefirst 2 weeks.

Discussion

Main findings in the study

Low energy internal cardioversion employing an oeso-phageal lead was found to be effective in restoring sinusrhythm in 92% of patients with long-term persistentatrial fibrillation. Besides this high success rate, themean atrial defibrillation threshold was sufficiently lowto allow the avoidance of general anaesthesia in allcases. In the study population the procedure was foundto be safe and well tolerated. Endoscopy revealed onlyminimal asymptomatic and transient damage to theoesophageal mucosa in a minority of cases. Finally, theprocedure could be performed in a simplified manner byintroducing the right atrial lead through the internaljugular vein under echocardiography control.

2000 4000 6000 80000

2000 4000 6000 80000

9 J 400 V

I

IIIII

aVR

aVL

aVF

VS

V2

V3

V4

V5

V6

Figure 3 Example of successful cardioversion obtained with the oesophageal–right atrialconfiguration. A 9 joule energy shock, synchronized on the QRS, restores the sinus rhythm.Complexes 1 and 2 following shock are paced (or fusion) beats. The transient ST-T elevation couldbe suggestive of a transient electrical injury, probably not related to the modality of cardioversion.

Role of low energy internal cardioversion inclinical practice

Low energy internal cardioversion should be consideredas a routine procedure for the treatment of specific

Eur Heart J, Vol. 21, issue 10, May 2000

subsets of patients with atrial fibrillation. In particular,such a methodology is clearly indicated in all thosesubjects with contraindications to general anaesthesia,high transthoracic impedance and resistance to externalcardioversion[6]. However, to date, several factors havelimited the spread of low energy internal cardioversionin clinical practice. In fact, in initial series, patients haveoften experienced non negligible discomfort during theprocedure, possibly owing to the relevant number ofshocks delivered in step-up research protocols[4,6]. How-ever, several recent improvements in the energy deliverymode have increased patients’ tolerance for low energyinternal cardioversion. In particular, the use of a singleeffective shock[10], of biphasic waveforms[11], of reducedpeak voltages[12], of rounded peak voltages[13] and ofsequential shocks delivered through dual-current path-ways[14], together with mild sedation, have all contrib-uted to a significant reduction in the discomfort whilemaintaining a high success rate.

A second major limitation to the spread of low energyinternal cardioversion in clinical practice is its relativecomplexity and consequent technical requirements. Lowenergy internal cardioversion is an invasive method,usually performed in an electrophysiology laboratorywith fluoroscopy and needs the positioning of at leastone lead in the coronary sinus or in the left pulmonaryartery. The overall complexity of such an approach hasrendered the spread of the method to cardiologicalcentres devoid of specific experience in electrophysiology

Transoesophageal cardioversion of AF 853

almost impossible. A new procedure without such limi-tations would possibly reach a wider clinical practice.

Table 2 Intracardiac cardioversion data of the successfully treated patients

Patients Vein Proc.time Flu.time n shocks Energy Volt Ohm

M.A. femoral 34 3 3 9 400 40DG.V. femoral 46 6 9 27 700 34P.B. femoral 36 4 5 14 500 41V.F. femoral 44 5 8 24 650 50I.S. femoral 47 3 9 27 700 48I.A. femoral 39 3 3 9 400 55B.M. femoral 51 9 4 11 450 54C.P. femoral 32 2 1 5 300 45R.F. femoral 55 13 5 14 500 38F.G. femoral 46 4 9 27 700 50P.A. femoral 43 6 7 20 600 43S.A. femoral 37 2 3 9 400 57P.M. femoral 40 3 7 20 600 46D.E. femoral 45 2 9 27 700 50E.N. femoral 46 3 7 24 650 50B.V. jugular 36 5 2 7 350 60B.A. jugular 45 4 7 20 600 47O.G. jugular 37 2 5 14 500 47N.T. jugular 35 4 3 9 400 47V.I. jugular 38 4 3 9 400 47S.M. jugular 34 2 4 11 450 52P.C. jugular 38 3 5 14 500 49L.F. jugular 32 2 4 11 450 54Mean 40·70 4·09 5·30 15·74 517·39 48SD 6·22 2·57 2·48 7·37 125·78 6·14Median 33 2·5 3·5 10 425 47

Proc.time=procedure time; flu.time=fluoroscopy time.

Results with oesophageal cardioversion

In this study significant effort was made in order tosimplify low energy internal cardioversion, while retain-ing the high effectiveness already shown for such atherapeutic approach.

In our series, low energy internal cardioversion modi-fied with the use of an oesophageal lead was found to beeffective in restoring sinus rhythm recovery in 92% ofpatients with persistent atrial fibrillation. Even if theenergy required with this new configuration is higherthan that currently used with conventional low energyinternal cardioversion (right atrium–coronary sinus,right atrium–left pulmonary artery)[1–6], the mean atrialdefibrillation threshold was sufficiently low to avoidgeneral anaesthesia in all cases.

The procedure was found to be safe and well toler-ated, as only minimal asymptomatic and transient dam-age to the oesophageal mucosa could be noted in aminority of cases by endoscopy. An even more simplifiedapproach was then performed in a significant percentageof cases: the right atrial lead was introduced through theinternal jugular vein under echocardiographic control.This opened up new prospects for the clinical use ofsuch a procedure. For all these reasons, our experiencesignificantly differs from available studies in which

transoesophageal cardioversion was performed using acutaneous patch as a cathode[8,9]. McKeown and co-workers[9] reported a success rate of 79·5% for oeso-phageal cardioversion with an external lead. However,despite a mean energy delivery of 63·1 J, in several casesthe high defibrillation threshold required an energy ofup to 200 J to achieve sinus rhythm restoration;consequently most patients had to undergo generalanaesthesia during the procedure.

The high energy required for successful cardioversionfound in this preliminary experience could be, at least inpart, explained by the use of conventional defibrillationdevices employing monophasic or sinusoidal waveforms.In a recent study from Marangoni et al.[15] sinus rhythmrestoration was achieved in a significant percentage ofpatients (86%) using a custom made oesophageal leadsimilar to ours and an external patch.

Although the waveform used was not specified, theatrial defibrillation threshold was found to be as high as50 J and consequently general anaesthesia was manda-tory in all cases. It is conceivable that the use of externalpatches for cardioversion, even in conjunction with anoesophageal lead and with optimal waveforms, impliesthe need of higher energies to achieve results similar tolow energy internal cardioversion.

The lead configuration proposed in this study seemsto offer significant advantages with respect to thesemethodologies. The use of an oesophageal together withan intracardiac lead allows a higher success rate,a lower defibrillation threshold and the avoidance of

Eur Heart J, Vol. 21, issue 10, May 2000

854 M. Santini et al.

general anaesthesia in all patients. Furthermore, the useof endoscopy after shock delivery showed that theprocedure was safe and that asymptomatic transientdamage to the oesophageal mucosa is rare, presentsspontaneous healing and does not warrant any specifictherapeutic intervention. Such a low prevalence of oeso-phageal damage was expected, as in previous studieseven the use of repeated shocks of 100 J did not causesignificant symptoms or functional impairment[9]. How-ever, our study represents the first experience in whichoesophageal lesions have been systematically searchedfor by endoscopy.

Finally, a major advantage of the new lead configur-ation proposed in this study is that it avoids leadpositioning in the coronary sinus or the left pulmonaryartery, thereby simplifying the procedure and wideningits use to cardiological centres with minimal technical

Figure 4 Endoscopy performed 24 h after the procedureshows small burns in the oesophageal mucosa (a). Suchlesions spontaneously disappeared 48 h after the procedure(b).

Eur Heart J, Vol. 21, issue 10, May 2000

References

[1] Murgatroyd FD, Slade AK, Sopher M, Rowland E, WardDE, Camm J. Efficacy and tolerability of transvenous lowenergy internal cardioversion of paroxysmal atrial fibrillationin humans. J Am Coll Cardiol 1995; 25: 1347–53.

[2] Alt E, Schmitt C, Ammer R et al. Initial experience withintracardiac atrial defibrillation in patients with chronic atrialfibrillation. PACE 1994; 17: 1067–78.

competence. We are aware that, although the invasive-ness of the proposed procedure could be considered lowcompared to other conventional electrode configur-ations of atrial internal cardioversion (the number of theleads introduced in the heart is reduced), it still remainsinvasive because one lead has to be positioned in theright ventricular apex and another in the right atrium.Another recent approach, is the use of a single catheterwith both defibrillation electrodes and a pacing/sensingright ventricle electrode[16]. This could be considered lessinvasive. In our opinion this recent approach is lessinvasive than the conventional electrodes configurations,but it does not reduce the complexity of the procedurebecause the distal coil of the lead has to be positioned inthe left pulmonary artery (only in the left pulmonaryartery, because if the distal coil of the lead is positionedin the coronary sinus, the pacing/sensing electrode willnot be in contact with the right ventricle making thesynchronization of the shock on the QRS very difficultand often impossible).

Perspectives and conclusions

In this study, the atrial lead was positioned in the rightatrium under echocardiographic control in a significantpercentage of patients (40%); fluoroscopy was subse-quently used only to confirm the correct position of thelead in the atrium. Such an approach proved effective inall cases and precise lead positioning was obtained in allpatients without any complications.

We believe that the straight course of the jugular veintowards the superior cava vein and the right atriumallows a simple approach for lead positioning and doesnot require specific skilled manoeuvres.

We have shown that a simplified method for lowenergy internal cardioversion is now available for clini-cal purposes and that by employing an oesophageal leadand possibly by positioning the intracardiac lead underechocardiographic control such a new method mayspread in cardiological practice.

Moreover, in the future, the procedure could theoreti-cally be performed without the use of fluoroscopy,avoiding the need for a ventricular lead by synchroniz-ing the shock on the QRS of the surface ECG of anexternal defibrillator provided with biphasic shockwaveform. Before starting a new research protocol toevaluate this latter possibility, further studies are neededin order to define the efficacy and safety of the newmethodology described in our study.

[

Transoesophageal cardioversion of AF 855

[3] Levy S, Ricard P, Lau C et al. Multicenter low energytransvenous atrial defibrillation (XAD) trial results in differ-ent subset of atrial fibrillation. J Am Coll Cardiol 1997; 29:750–5.

[4] Levy S, Ricard P, Gueunoun M et al. Low-energy cardio-version of spontaneous atrial fibrillation. Immediate andlong-term results. Circulation 1997; 96: 253–9.

[5] Schmitt C, Alt E, Plewan A et al. Low energy intracardiaccardioversion after failed conventional external cardioversionof atrial fibrillation. J Am Coll Cardiol 1996; 28: 994–9.

[6] Santini M, Pandozi C, Toscano S et al. Low energy intra-cardiac cardioversion of persistent atrial fibrillation. PACE1998; 21: 2641–50.

[7] Yamanouchi Y, Kumagay K, Tashiro N, Hiroki T, ArakawaK. Transesophageal low-energy synchronous cardioversion ofatrial flutter/fibrillation in the dog. Am Heart J 1992; 123:417–20.

[8] McNally EM, Meyer EC, Langendorf R. Elective counter-shock in unanesthetized patients with use of an esophagealelectrode. Circulation 1966; 23: 124–7.

[9] McKeown PP, Croal S, Allen D, Anderson J, Adgey JD.Transesophageal cardioversion. Am Heart J 1993; 125:396–404.

10] Santini M, Pandozi C, Altamura G et al. Single shock lowenergy intracardiac cardioversion of chronic atrial fibrillation.J Int Card Electrophysiol 1999; 3: 45–51.

[11] Cooper RAS, Alferness CA, Smith WM, Ideker RA. Internalcardioversion of atrial fibrillation in sheep. Circulation 1993;87: 1673–86.

[12] Ammer R, Alt E, Ayers G et al. Pain threshold for low energyintracardiac cardioversion of atrial fibrillation with low or nosedation. PACE 1996; 19 [Pt. II]: 230–6.

[13] Harbinson MT, Allen JD, Zafar I et al. Rounded biphasicWaveform reduces energy requirements for transvenous cath-eter cardioversion of atrial fibrillation and flutter. PACE 1996;19 [Pt. II]: 226–9.

[14] Cooper RAS, Plumb VJ, Epstein AE, Kay GN, Ideker RE.Marked reduction in internal atrial defibrillation thresholdwith dual-current pathways and sequential shocks in humans.Circulation 1998; 97: 2527–35.

[15] Marangoni E, Lissoni F, Bucci L, Orlandi M. Rationale foresophageal cardioversion of atrial fibrillation. Proceedings ofthe International Symposium on Progress in Clinical Pacing1998. Rome, Italy, 1–4 December 1998, Edited by MassimoSantini, Futura Media Services, Inc. Armonk, NY, 43–7.

[16] Bocconcelli P, Mancino M, Mariani M, Pierantozzi A,Andraghetti A, Sgarbi E. Single catheter low energy endo-cardial cardioversion of atrial fibrillation (Abstr). PACE 1999;22 [Pt. II]: A 182.

Eur Heart J, Vol. 21, issue 10, May 2000