Regarding waveforms: Assuming the cumulative efficacy, defined as success rate after all delivered shocks, for one of the waveforms is 95%, and for the other waveform ≥80%, a sample size of 75 patients in each group is needed to achieve a power of 80% in rejecting the null hypothesis (that the difference in cumulative efficacy is ≥15%). Continuous variables (number of shocks, delivered energy etc.) are expressed as mean ± SD or median values and compared with Students t-test or equivalent non-parametric test. Categorical variables (e.g. successful cardioversion) are expressed as percentages and compared using the Chi-square or Fisher's exact test (where appropriate). P ≤ 0.05 is considered statistically significant for all comparisons.