ArticlesAnterior-posterior versus anterior-lateral electrode positions for external cardioversion of atrial fibrillation: a randomised trial
Introduction
Atrial fibrillation is the most common sustained cardiac arrhythmia, and incidence is increasing in an ageing population.1 Atrial fibrillation causes important morbidity and mortality through loss of haemodynamic function of the atria, uncontrolled ventricular rate, and risk of stroke.2, 3 Restoration of sinus rhythm is therefore a main treatment goal in patients with persistent atrial fibrillation.4 Transthoracic external electrical cardioversion is the standard method to restore sinus rhythm in such patients,5, 6 but it is not successful in every case.4, 7, 8 Means of improving the method of external cardioversion are therefore clinically and socioeconomically important.
Termination of fibrillatory activity can be achieved by creation of a shock-field gradient of at least 5 V/cm throughout the fibrillating myocardium for a few milliseconds.9, 10, 11 Since the right and left atria are positioned one behind the other, an electrical shock field between the anterior and posterior thorax may be more efficient at achieving such a shock-field gradient in the atria than that with electrodes positioned anteriorly and laterally on the anterior thorax. Furthermore, some evidence suggests that transthoracic impedance is lower for anterior-posterior electrodes.12, 13
Botto and colleagues14 suggested that anterior-posterior paddle positions may increase cardioversion success rates, but others have found no difference7, 15 or have even suggested that anterior-lateral electrode positions may be better.16 Present guidelines therefore equally recommend either electrode position for external cardioversion.8, 17
In a 1998 statement by a study group of the Working Group on Arrhythmias of the European Society of Cardiology,4 the need for better classification of atrial fibrillation was emphasised, as were the implications for studies that assess maintenance of sinus rhythm. These considerations were not taken into account fully by previous studies. We therefore designed a prospective randomised trial to test whether an anterior-posterior electrode position improves cardioversion success compared with an anterior-lateral position during external cardioversion of persistent atrial fibrillation.
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Patients
We screened all patients aged 18–80 years who were undergoing cardioversion at the Department of Cardiology of the University of Munster, Germany between May, 1999, and November, 2000. Patients with a pectorally implanted pacemaker or defibrillator were not included in this trial, but were cardioverted in the anterior-posterior position.8 Care was taken to exclude patients with atrial flutter or rapid atrial tachycardias; skilled cardiologists, including at least one electrophysiologically
Results
We terminated the study after the interim analysis. At that time, 167 patients had been screened, and 100 were eligible and gave consent. At the termination point, cardioversion had been successful in a significantly higher proportion of patients treated in the anterior-posterior electrode position than in the anterior-lateral position (49 [98%] of 50 vs 39 [78%] of 50, difference 0·22 [95% CI 0–089·0·352]; p=0·004). During the time needed for the interim analysis, eight further patients were
Discussion
In this study, external cardioversion of persistent atrial fibrillation was more likely to be successful when an anterior-posterior electrode position was used. Furthermore, a change from the anterior-lateral to the anterior-posterior electrode position resulted in sinus rhythm in eight of 12 patients for whom cardioversion attempts had failed with the anterior-lateral electrode position. These findings suggest that an anterior-posterior electrode position is more effective for external
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