For the maintenance of sinus rhythm after cardioversion in patients with atrial fibrillation was used quinidine. The results of 6 randomized clinical trials showed that taking quinidine contributed to maintaining sinus rhythm at 1 year in 50% of patients compared with 25% of patients who did not receive it. However, the mortality rate in patients receiving quinidine increased from 0.8 to 2.9%. Which design of study conducted