Forty patients with chronic
atrial fibrillation, apparently unrelated to any overt
heart disease, were randomly allocated to two groups after restoration of sinus rhythm by direct current
shock. The patients in group A were given 4 daily doses of
quinidine polygalacturonate, while those in group B were given 2 daily doses of a long-acting
quinidine preparation,
quinidine arabogalactan sulphate. The percentage of early relapses (within the first month following DC
shock) was not significantly different in the two groups: 44-4% in group A and 35% in group B (P greater than 0-50). On the other hand, there were fewer late relapses with long-acting
quinidine. After 18 months of treatment, 27-8% of patient in group A remained in sinus rhythm, compared with 61% in group B (P less than 0-05). The average amount of
quinidine actually ingested by the patients in group A was smaller than that in group B. However, this could not entirely account for the difference observed in the incidence of relapse since with short-acting
quinidine the proportion of patients remaining in sinu rhythm was similar whether the dose was decreased or not. The incidence of gastrointestinal side-effects was the same in the two groups and there were no seriou complications that could be attributed to treatment. It is concluded that long-acting
quinidine preparations are more effective than conventional
quinidine in preventing late relapses of
atrial fibrillation.