Read your latest personalised notifications
No account yet? Start here
Don't miss out
Ok, got it
Prof. Bulent Gorenek ,
While the indications for cardioversion in atrial fibrillation are widely communicated in the literature, the procedure itself is seldom described. Here, we will review basic principles and techniques of direct current and internal cardioversion, from patient preparation to energy waveforms requirements and paddle positioning, as well as complications, implantable devices and pretreatment with antiarrhythmic drugs.
Direct current cardioversion is one of the most effective means of converting atrial fibrillation into sinus rhythm. Medical cardioversion is one alternative, however direct current cardioversion has the highest overall success rate (1,2). In all, patients who require cardioversion will often undergo direct current cardioversion rather than pharmacologic conversion because of its:
Cardioversion should be performed with the patient in a fasting state, under adequate general anaesthesia. The anaesthetic agent must 1) provide analgesia and sedation, and 2) cause the least cardiovascular compromise while allowing for rapid recovery (10-12). Oxygen saturation and electrolytes should be normal and anticoagulation status monitored. Drug levels, such as digoxin and antiarrhythmic agents, should be within the therapeutic range. Digoxin shouldn't be withheld unless there is a suggestion of digitalis excess or toxicity (11). A baseline 12-lead electrocardiogram should be recorded, and venous cannulation should be secured. A pacing catheter may be placed prophylactically in the right ventricle if sick sinus syndrome is suspected. For back-up, external pacing pads may be used for both cardioversion and for prophylaxis should asystole or bradycardia ensue. Overnight hospitalisation is seldom required (10).
Biphasic Waveforms superior to Monophasic Waveforms
Whether cardioversion will succeed depends on whether delivery of current flow through the heart is adequate or not (13). The major determinants of current delivery are 1) the nature of the shock waveform (mono or biphasic) 2) level of delivered energy. In terms of shock waveform, both monophasic and biphasic waveforms are used. Currently, most evidence favors the use of biphasic external defibrillators due to their categorically lower energy requirements and greater efficacy (14,15). Indeed, in a study of 912 patients with AF and atrial flutter, restoration of sinus rhythm was higher in patients who had received biphasic waveforms (94 versus 84 percent for monophasic waveforms) and with lower cumulative energy (199 J versus 554 J) (16). Biphasic waveforms may be of special interest in patients who have failed to revert with the use of monophasic waveforms (17). Furthermore, fewer shocks are required, thereby potentially reducing procedure times and thus, requirements for intravenous sedation. A lower incidence of skin burns (18) and less skeletal muscle damage (19) have also been reported. Additionally biphasic waveforms result in fewer post-shock arrhythmias, and a shorter period of myocardial stunning (20).
The amount of energy needed for initial attempts of DCC has been controversial. Once satisfactory synchronisation is obtained, sedation or anaesthesia is initiated, and a shock is delivered. After shock delivery, if conversion is unsuccessful, higher energy repeat direct current cardioversion is attempted. This can be repeated until the arrhythmia terminates or the decision is made to abandon direct current cardioversion. Using a monophasic waveform, the energy required will often be >200 joules (21), with possibly more being required in obese patients and long-standing atrial fibrillation (22,23). However, biphasic devices have been shown more effective in two randomised clinical trials and to require less energy delivery than monophasic devices (19,24). Higher biphasic energies as a first direct cardioversion shock for patients who are overweight or have a higher transthoracic impedance might be recommended. The Best-AF trial demonstrated that, when biphasic waveforms were used, there was a significant increase in the first-shock success for direct current cardioversion if the initial energy selected was 200 J rather than 100 J (25). In patients who were overweight or obese, first-shock success was significantly greater if a higher-energy shock was selected. However, in patients with a normal or low body mass index there was no difference in the first-shock success regardless of whether 100 J or 200 J was used. The initial energy may be lower for cardioversion of atrial flutter (25). In a review including 985 cardioversions in 840 patients with atrial flutter, the median energy level for successful cardioversion was 50 joules with a biphasic defibrillator and 200 joules with a monophasic defibrillator (26).
Lown et al. recommended an anteroposterior electrode configuration over anteroanterior positioning (27,28) however the two current conventional orientations that are commonly used for electrode placement are anteroposterior and anterolateral. A number of studies have examined the effect one over the other and showed that less energy is required and higher success rates are achieved when using the anteroposterior position (20-32). Some reports, nevertheless, have failed to confirm these findings (33,34). In some patients one position and not the other, may be effective; thus, it has been suggested that if initial shocks are unsuccessful in terminating the arrhythmia, the electrodes should be relocated and cardioversion repeated (31). Thus when cardioversion fails, shocks can be repeated at highest energy until the arrhythmia terminates or a decision is made to abandon direct current cardioversion. Repositioning the paddles should also be done in case of failure. Furthermore, the double-paddle technique is another alternative as well as pharmacologic facilitation of cardioversion: in one study, patients who had AF and had failed 360-J monophasic cardioversion were loaded with amiodarone orally. If repeat 360-J monophasic cardioversion persisted in failing, the patients underwent the double-paddle technique: two monophasic defibrillators were used with two sets of paddles for each patient; each defibrillator was set for a synchronous shock at the maximum output of 360 J; they then were discharged simultaneously, resulting in successful conversion of 13 out of 15 patients (35).
Internal cardioversion is performed with the patient under conscious sedation or general anaesthesia. Because of the potential risk of bleeding, warfarin therapy is usually withheld in view of the procedure and resumed afterward. Temporary anticoagulation before and after the procedure can be accomplished with heparin. Internal cardioversion is indicated:
Despite such significant advantages, the spread of this new methodology in clinical practice has been limited by the need of a laboratory of electrophysiology with fluoroscopy and of specific technical competence for lead positioning, either in the coronary sinus or in the left pulmonary artery. Simplification of the procedure is obviously very important for the future of internal cardioversion, particularly because of the recent improvement in success rates of external cardioversion using biphasic shocks, higher energy shocks or pre-treatment with drugs before cardioversion (24,42,43).
Despite its widespread clinical use, controversy surrounds the electrophysiologic mechanisms by which direct current cardioversion terminates atrial fibrillation involving multiple microreentrant circuits. Most investigators agree that defibrillation occurs when a certain amount of current density reaches the myocardium. However, it is unclear what amount of current density is needed and what energy setting is necessary to achieve homogeneous current density. Complications associated with direct current cardioversion are mainly risks related to general anaesthesia, thromboembolic events and postcardioversion arrhythmias. Overall however, risk is low in patients who are selected adequately (44) - only a 1–2% risk of thromboembolic events (45-47). Thromboembolic events, nevertheless, are more likely to occur in patients with atrial fibrillation who have not been anticoagulated prior to cardioversion. Patients with a previous embolism do not have an increased risk of embolisation if anticoagulation is adequate (48). The estimated incidence of thromboembolism varies, but in a large non-randomised series that included 437 patients, embolism occurred in 5.3 % of non-anticoagulated patients compared to 0.8 % of those receiving anticoagulation (49). Many kinds of arrhythmias, especially ventricular and supraventricular premature beats, bradycardia, sinus arrest, may arise following cardioversion and commonly subside spontaneously (50). More dangerous arrhythmias, such as ventricular tachycardia and fibrillation, may arise in the face of hypokalemia, digitalis intoxication, or inadequate synchronisation (51,52).
Patients with Implantable Devices
Patients who have implanted permanent pacemakers or cardioverter-defibrillators can undergo external cardioversion with minimal risk to their devices and themselves, provided appropriate precautions are taken. Devices are typically implanted anteriorly, so the electrode paddle should be at least 8 cm from the pacemaker battery and an anteroposterior paddle position is recommended (2,53,54). Elective cardioversion should be begun with low-energies in order to avoid damage to the pacemaker circuitry and the electrode-myocardial interface. After cardioversion, the pacemaker should be interrogated and evaluated to ensure normal pacemaker function (2).
Pretreatment with Antiarrhythmic DrugsPretreatment or repeat treatment with antiarrhythmic drugs such as ibutilide, amiodarone, sotalol, propafenone or flecainide increases the likelihood of restoration of sinus rhythm and helps prevent recurrent atrial fibrillation (2). Enhanced efficacy may involve decreasing the energy required to achieve cardioversion, prolonging atrial refractory periods, and suppressing atrial ectopy that may cause early recurrence of atrial fibrillation (55-55). Antiarrhythmic medications may be initiated out of hospital or in hospital immediately prior to direct-current cardioversion.
Direct current cardioversion is an effective means of restoring sinus rhythm in patients with atrial fibrillation - improving patient outcomes is thus usually in our hands. Attention to proper technique for direct current cardioversion has the power to optimise efficacy.
However, post-cardioversion, potential life-threatening complications such as post-cardioversion arrhythmias and thromboembolism remain a possibility.
1. Electrical conversion of atrial fibrillation: immediate and long-term results and selection of patients. Morris JJ Jr, Peter RH, McIntosh HD. Ann Intern Med. 1966;65:216 –231.2.Guidelines for the management of atrial fibrillation: the Task Force for the Management of Atrial Fibrillation of the European Society of Cardiology.Camm AJ, Kirchhof P, Lip GY, Schotten U, Savelieva I, Ernst S, Van Gelder IC, Al-Attar N, Hindricks G, Prendergast B, Heidbuchel H, Alfieri O, Angelini A, Atar D, Colonna P, De Caterina R, De Sutter J, Goette A, Gorenek B, Heldal M, Hohloser SH, Kolh P, Le Heuzey JY, Ponikowski P, Rutten FH. Eur Heart J. 2010;31:2369-4293. Initial energy sitting, outcome and efficiency in direct current cardioversion of atrial fibrillation.Gallagher MM, Guo XH, Poloniecki JD, Guan Yap Y, Ward D, Camm AJ. J Am Coll Cardiol 2001;38:1498-504.4. Chronic atrial fibrillation: long term results of direct current cardioversionLundstrom T, Ryden L. Acta Med Scand 1988;223:53-9.5. Electrical reversion of cardiac arrhythmias. Lown B. Br Heart J 1967;29:469-89.6. Factors determining success and energy requirement for cardioversion of atrial fibrillation.Dalzell GW, Anderson J, Adgey AA. Q J Med 1990;76:903-13.7. Echocardiographic and clinical predictors for outcome of elective cardioversion ofatrial fibrillation.Dittrich HC, Erikson JS, Schneideman T, Blacky AR, Savides T, Nicod PH. . Am J Cardiol 1989;63:193-7.8. Initial energy setting, outcome and efficiency in direct current cardioversion of atrial fibrillation and flutter.Gallagher, MM, Guo, XH, Poloniecki, JD, et al. J Am Coll Cardiol 2001; 38:1498.9. Electrical reversion of cardiac arrhythmiasLown, B.Br Heart J 1967; 29:469. 10. Safety and efficacy of in-office cardioversion for treatment of supraventricular arrhythmias.Lesser MF. Am J Cardiol 1990;66:1267–8.11. Absence of cardioversion-induced ventricular arrhythmias in patients with therapeutic digoxin levels.Mann, DL, Maisel, AS, Atwood, JE, et al. J Am Coll Cardiol 1985; 5:882. 12. Stoneham MD. Anaesthesia for cardioversion. Anaesthesia 1996 ;51:565-713. Epicardial mapping of ventricular defibrillation with monophasicand biphasic shocks in dogs.Zhou X, Daubert JP, Wolf PD, et al. Circ Res 1993;72:145–6014. Prediction of uneventful cardioversion and maintenance of sinus rhythm from direct current electrical cardioversion of chronic atrial fibrillation and flutter.Van Gelder, IC, Crijns, HJ, Van Gilst, WH, et al. Am J Cardiol 1991; 68:41.15. Early recurrences of atrial fibrillation after electrical cardioversion: A result of fibrillation-induced electrical remodeling of the atriaTieleman, RG, Van Gelder, IC, Crijns, HJGM, et al. J Am Coll Cardiol 1998; 31:167.16. Comparative efficacy of monophasic and biphasic waveforms for transthoracic cardioversion of atrial fibrillation and atrial flutter.Gurevitz OT, Ammash NM, Malouf JF, Chandrasekaran K, Rosales AG, Ballman KV, Hammill SC, White RD, Gersh BJ, Friedman PA. Am Heart J 2005; 149:316-21.17. Biphasic versus monophasic cardioversion in shock-resistant atrial fibrillation. Khaykin Y, Newman D, Kowalewski M, Korley V, Dorian P.Cardiovasc Electrophysiol 2003;14:868-72.18. BiCard Investigators. Biphasic versus monophasic shock waveform for conversion of atrial fibrillation.Page RL, Kerber RE, Russell JK, et al. J Am Coll Cardiol 2002;39:1956–63.19. Efficacy and impact of monophasic versus biphasic countershocks for transthoracic cardioversion of persistent atrial fibrillationMarinsek M, Larkin GL, Zohar P, et al. Am J Cardiol 2003;92:988–91. 20. Post-shock myocardial stunning: a prospective randomized double-blind comparison of monophasic and biphasic waveforms.Ambler JJ. Resuscitation 2006;68:329–33. 21. Prospective assessment of the minimum energy needed for external cardioversion of atrial fibrillation. Ricard P, Levy S, Trigano J, et al. Am J Cardiol 1997;79:815-6.22. Initial energy sitting, outcome and efficiency in direct current cardioversion of atrial fibrillation.Gallagher MM, Guo XH, Poloniecki JD, Guan Yap Y, Ward D, Camm AJ. J Am Coll Cardiol 2001;38:1498-504.23. A new algorithm for transthoracic cardioversion of atrial fibrillation based on body weight.Rashba EJ, Bouhouch R, Koshy S, et al. Am J Cardiol 2001;88:1043-5.24. Transthoracic cardioversion of atrial fibrillation. Comparison of rectilinear versus damped sine wave monophasic shocks.Mittal S, Ayati S, Stein KM, et al. Circulation 2000;101:1282-7.25. Biphasic energy selection for transthoracic cardioversion of atrial fibrillation.Glover BM, Walsh SJ, McCann CJ, Moore MJ, Manoharan G, Dalzell GW, McAllister A, McClements B, McEneaney DJ, Trouton TG, Mathew TP, Adgey AA. The BEST AF Trial. Heart 2008 ;94:884-7.26. Comparison of the rectilinear biphasic waveform with the monophasic damped sine waveform for external cardioversion of atrial fibrillation and flutter.Niebauer MJ, Brewer JE, Chung MK, Tchou PJ. . Am J Cardiol 2004 15;93:1495-9.27. New method for terminating cardiac arrhythmias: use of sychronized capacitor discharge.Lown B, Amarasingham R, Neuman J. JAMA 1962;182:548–55.28. Cardioversion of atrial fibrillation: a report on the treatment of 65 episodes in 50 patients.Lown B, Perlroth MG, Kaidbey S, et al. N Engl J Med 1963;269:325–31.29. Anterior-posterior versus anterior-lateralelectrode positions for external cardioversion of atrial fibrillation.Kirchhof P, Eckardt L, Loh P, et al. Lancet 2002;360:1275-9.30. The technique of cardioversion. Lown B, Kleiger R, Wolff G. Am Heart J 1964;67:282-4.31. External cardioversion of atrial fibrillation: role of paddle position on technique efficacy and energy requirements.
Prof. Bulent-Gorenek, Ankara, Turkey.Authors' disclosures: None declared.
Our mission: To reduce the burden of cardiovascular disease.
© 2019 European Society of Cardiology. All rights reserved.