Evaluation of the defibrillation threshold in atrial fibrillation by transoesophageal cardioversion using a biphasic impulse

Introduction: Recurrent atrial fibrillation (AF) in the setting of haemodynamic disturbances requires frequently repeated cardioversions, which is associated with the risk of myocardial damage. It is thus necessary to identify methods which can minimise the cardioverter impulse energy. Aim: To define the defibrillation threshold in recent-onset AF using a biphasic impulse, following an infusion of magnesium, potassium, and amiodarone. Methods: Transoesophageal cardioversion was performed in 32 patients with AF lasting ≤48 hours, in whom prior administration of 40 mEq K + , 4.0 g MgSO4 and 300 mg amiodarone did not restore sinus rhythm. Cardioversion was performed under short intravenous anaesthesia using a biphasic impulse travelling from a multi-annular oesophageal electrode to two electrodes on the anterior chest wall. The initial energy was set to 1 J, which was subsequently increased according to the following protocol: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 40, 50 and 70 J. Results: Electrical cardioversion following the administration of electrolytes and amiodarone restored sinus rhythm in all the patients (100% efficacy). The mean defibrillation threshold was 12.9±14.3 J, with a minimal effective energy of 1 J and a maximum effective energy of 70 J. The defibrillation threshold was in the range from 1 to 10 J in 75% of the patients. The mean cumulative energy transferred between electrodes during evaluation of the defibrillation threshold was 39.7 J (SD, 38.8). Conclusions: Transoesophageal cardioversion using a low-energy (mean, 12.9 J; range, 1–70 J) biphasic impulse, following the intravenous administration of potassium chloride and amiodarone, was 100% effective in restoring sinus rhythm in AF.