Quinidine in maintenance of sinus rhythm after electroconversion of chronic atrial fibrillation. A controlled clinical study.

One hundred patients were subjected to a controlled study of the effectiveness of quinidine treat- ment upon the maintenance of sinus rhythm after electroconversion. The quinidine series was treated with a long-acting preparation of quinidine sulphate, which was given in a dosage to achieve serum levels between 4 and 6 mg/l. The control series received no quinidine. The mainten- ance rate did not differ significantly in the two series during the first three months, but for the remaining observation time until I2 months a sigmficant difference in favour of quinidine was present. Identical results were found in a cross-over experiment, in which 24 patients served as their own controls. Further analysis broughtforward that quinidine was effective only if the atrial fibrillation had lasted for less than one year before electroconversion. Complications due to the use of quinidine were negligible during the observation time.