Dual Versus Single Shock for Cardioversion of Atrial Fibrillation

The investigators aim to investigate the immediate success rate (rate of termination of atrial fibrillation) of dual shock cardioversion compared with standard single shock cardioversion in patients with baseline characteristics adversely influencing successful cardioversion. Baseline characteristics known to reduce the success rate of single shock cardioversion include: increased body mass index (BMI), chronic obstructive pulmonary disease, sleep apnea, enlarged left atrium, longer duration of atrial fibrillation and use of amiodarone.