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Three Part Question

In [patients undergoing external DC cardioversion for atrial fibrillation] is [antero-posterior position of electrodes better than anterolateral position] in [terms of reverting to sinus rhythm]?

Clinical Scenario

You are with a 75-year old lady who had Bypass grafting 5-days ago. Pre-operatively she was in sinus rhythm but postoperatively she went into Atrial Fibrillation (AF) on day 3. Despite 2 days of Amiodarone she remains in AF. She is otherwise well and you elect to attempt cardioversion prior to discharge. In the anaesthetic room you are presented with two gel pads for the cardioversion, and the theatre assistant asks you where you would like them placed before the patient is sedated. You elect for an antero-lateral position as you have never started with an antero-posterior position before, but after the patient cardioverted after 4 attempts in this position you wonder whether you should have tried the antero-posterior position first.

Search Strategy

Medline 1966-Feb 2004 using the OVID interface.
[exp atrial fibrillation/ OR atrial fibrillation.mp OR exp atrial flutter/ OR atrial flutter.mp or AF.mp ] AND [exp electric countershock/ OR cardioversion.mp OR electroversion.mp] AND [paddle$.mp OR position$.mp OR anterior$.mp OR antero$.mp or lateral.mp or posterior.mp]

Search Outcome

A total of 167 papers were found of which 5 prospective randomized trials represented the best evidence on this subject. These papers are listed in the table [2-6]

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Kirchhof et al, 2002, Germany	108 patients who had persistent atrial fibrillation (median duration 5 months) undergoing elective external cardioversion with defibrillator paddles Group AP: antero-posterior (N=52) Group AL: antero-lateral (N=56) Shock protocol 50,100, 200, 300, 360 J used in succession. If unsuccessful a further 360 J used in alternate position.	PRCT and meta-analysis (Level 1b)	Successful cardioversion	AP 50 of 52 patients (96%). AL 44 of 56 patients (78%) P=0.009	Sample size was calculated as needing 100 patients per group but stopped early due to highly significant result Significant factors of failure was size of atrium and time of AF Methodology of meta-analysis not described Long/mid term success of cardioversion not reported
			Crossover success	AL to AP 8 of 12 successfully cardioverted. AP to AL 0 of 2 patients
			Energy required for cardioversion	AP mean 212 J. AL mean 211 J. (8% success at 50 J and 25% success at 100 J)
			Meta-analysis of 3 studies [3-5]	AP 226 of 276 pts (82%). AL 214 of 282 pts (76%) P=0.082
Alp et al, 2000, UK	59 patients who had persistent atrial fibrillation (mean 6 months) undergoing cardioversion using defibrillator paddles Group AP: Antero-posterior (N=29) Group AL: Antero-lateral (N=30) Shock Protocol: 360 J shock used initially. If unsuccessful a further 360 J shock used in alternate position	PRCT (Level 2b)	Successful cardioversion	AP 10 of 29 patients (48%). AL 18 of 30 patients (77%) p=0.048	High initial shock in protocol Given sample size required 68 patients in each arm. The study was stopped early due to reaching a 0.05 significance. (Note p<0.005 is usually required to stop a study early) 25 of 59 patients did not have an echo
			Crossover success	AP 5 of 12 patients. P=0.22
			Energy required for cardioversion	AP mean 583 J vs AL 504 J. P=0.1
Botto et al, 1999, Italy	301 patients with stable atrial fibrillation and LA size <60mm, undergoing cardioversion with disposable gel pad electrodes Group AP: Antero-posterior (N=150) Group AL: Antero-Lateral (N=151) Shock Protocol: 3 J/kg followed by 4 J/kg followed by 4 J/kg shock in alternate position if the initial shock unsuccessful	PRCT (Level 2b)	Successful cardioversion	AP 131 of 150 patients (87%). AL 114 of 151 patients (76%) P=0.013	Duration of arrhythmia was the only factor that affected the technical success of external cardioversion Pre-cardioversion Antiarrythmic drug administration was not part of the protocol
			Crossover success	Conversion by AP shock 27 of 37 patients. Conversion by AL shock 9 of 19 patients
			Energy required for cardioversion	AP group mean 383J AL group mean 451J. P=0.025
Mathew et al, 1999, N.Ireland	90 patients with persistent atrial fibrillation undergoing cardioversion with self adhesive gel pad electrodes Group AP: Antero-posterior (N=45) Group AL: Antero-Lateral (N=45) Shock Protocol: 100J, 200J, 300J, 360J	PRCT (Level 2b)	Successful cardioversion	AP 35 of 45 patients (78%). AL 38 of 45 patients (84%). P=0.42	No sample size calculations and study is underpowered to report conclusive negative findings
			Crossover success	Cross over only performed in 10 patients
			Energy required for cardioversion	AP mean 232 J vs AL mean 223 J. P=0.09
Chen and Guo, 2003, Japan	70 patients with persistent atrial fibrillation (mean time 24 months) undergoing cardioversion with self adhesive gel pad electrodes Group AP: Antero-posterior (N=39) Group AL: Antero-Lateral (N=31) Shock protocol: 100J, 150J, 200J, 300J, 360J	PRCT (level 2b)	Successful cardioversion	AP 33 of 39 patients (85%). AL 26 of 31 patients (84%)	Small group sizes again therefore making this study underpowered to report negative conclusions No anti-arrythmic medication policy
			Crossover success	Crossover not performed
			Thoracic impedance	AP mean 65 Ohms AL mean 74 Ohms. P=0.033

Comment(s)

No papers were found that directly looked at this subject exclusively in patients post cardiac surgery, but 5 prospective randomized trials were found that represent the best evidence on this subject. Of note several other non-randomized studies were found with this search strategy but they were excluded due to absence of randomization. Kirchhof et al [5] recently performed a prospective randomized trial (PRCT) with 108 patients. They found a highly significant finding when using manual defibrillator paddles with a 96% conversion rate with the AP positioning compared to a 78% conversion rate using the AL strategy. In addition 2/3rds of patients who were not converted in the AL position were converted in the AP position. They did not demonstrate a lower energy requirement with this strategy, but they did provide a meta-analysis of 3 prior studies [2-4] showing an 82% conversion with AP position versus a 76% conversion rate with AL positioning. Alp et al [4] performed a PRCT with 59 patients randomized to the two protocols. They found that only 48% of patients converted in the AP position compared to 77% in the AL position. This study contrasts with the other studies. Their shock protocol was markedly different to other studies in that they started with 360J, prior to crossing over techniques. In addition although they planned to recruit 136 patients they stopped the study early, when the p value reached 0.05 between groups. Of note it is more usual to use much more stringent p-values of the order of 0.005 when stopping a trial early is considered, in order to prevent reporting findings on the margins of significance. Botto et al [2] performed the largest PRCT in this area, with 301 patients randomized to AP or AL cardioversion using disposable gel pad electrodes. They found that the AP position was significantly superior to the AL position and they also found that a lower total energy requirement was needed using this position. Mathew et al [3] performed a PRCT in 90 patients. They found no difference between the two positions when using disposable gel pad electrodes. The AP position had a 78% success and the AL group had a success of 84%. This study did not present sample size calculations and Kirchhof et al [5] suggested that this study was too underpowered to present conclusive negative findings. In addition the mean duration of AF was over a year in this study and thus this may have reduced the successful cardioversion rate. Chen et al [6] performed a PRCT in 70 patients. They also found no difference between AP and AL positions although they measured the Trans-Thoracic Impedance with both techniques and found this to be lower in the AP position. Of note this was also a small study. The American Heart Association/ American College of Cardiology/European Society of Cardiology joint guidelines for the treatment of AF [1] state that 'the superiority of one position over another has not been established' but they did not reference 4 of the papers listed here [3;4;5;6] If all the results of the 5 PRCTs are combined we find that 259 of 315 (82%) patients were converted with AP and 240/313 (76.6%) were converted with AL position. This means that the number needed to treat with AP electrodes is 19 for every extra person converted. In addition this is a non significant result with p=0.09.

Clinical Bottom Line

There is no clinically significant difference between the antero-lateral and antero-posterior positioning of pads for cardioversion of AF, although if cardioversion fails in one of these positions the alternative position may still succeed.

References

1. Kirchhof P, Eckardt L, Loh P, et al. Anterior-posterior versus anterior-lateral electrode positions for external cardioversion of atrial fibrillation: a randomised trial. Lancet 2002;360:1275-1279.
2. Alp NJ, Rahman S, Bell JA, et al. Randomised comparison of antero-lateral versus antero-posterior paddle positions for DC cardioversion of persistent atrial fibrillation. Int J Cardiol 2000;75:211-216.
3. Botto GL, Politi A, Bonini W, et al. External cardioversion of atrial fibrillation: role of paddle position on technical efficacy and energy requirements. Heart 1999;82:726-730.
4. Mathew TP, Moore A, McIntyre M, et al. Randomised comparison of electrode positions for cardioversion of atrial fibrillation. Heart 1999;81:576-579.
5. Chen CJ, Guo GB. External cardioversion in patients with persistent atrial fibrillation: a reappraisal of the effects of electrode pad position and transthoracic impedance on cardioversion success. Jpn Heart J 2003;44:921-932.
6. Fuster V, Ryden LE, Asinger RW et al. American College of Cardiology/American Heart Association/European Society of Cardiology Board. ACC/AHA/ESC guidelines for the management of patients with atrial fibrillation: executive summary. Am. Coll. Cardiol. 2001;38:1231-1266.