Determination of sample size Considering a 20% increase (i.e. from 10% at baseline to 30%) in incidence of silent cerebral lesions following electrical cardioversion, the required number of patients to reject the null-hypothesis with 90% power and at the 0.05 significance level (two-sided) is 35. To allow for drop-outs, 40 patients will be included in the study. The sample size calculations were performed in the software "nQuery Advisor" version 7.0.