Factors affecting cardioversion of atrial arrhythmias with special reference to quinidine.

Abstract

Direct current shock was used to treat 149 patients with atrial arrhythmias. Sinus rhythm was established in 88%. Rheumatic, patients with atrial fibrillation were divided into 2 comparable groups. The 1st received quinidine (1 g per day) 24 hr before the procedure, and following successful cardioversion patients were maintained on the same daily dose. The mean serum quinidine level was 2. 2 mg 1 (SD [plus or minus] 1.1). Quinidine was not given to the 2nd group. Observed maintenance of sinus rhythm following DC shock was not statistically different in the 2 groups. In patients followed for over a year about 45% maintained sinus rhythm, contrasted with the nonrheumatic group where 70 % maintained sinus rhythm over the same period. There was little advantage in reconverting cases who reverted within a month of cardioversion. When the preceding arrhythmia was present for more than 2 years the chances of initial successful conversion and subsequent maintenance of sinus rhythm were reduced. Small "f" waves also increased the chances of initial failure but did not influence the maintenance of sinus rhythm. Heart size did not affect results, but in the rheumatic group all the failures had a cardiothoracic ratio greater than 55%. Although patients with isolated mitral stenosis complicated by atrial fibrillation and treated by valvotomy responded well to DC shock, reversion to atrial fibrillation was as frequent as in those patients with other valvular defects. In the latter group the initial failure rate was higher. Transitory post-conversion arrhythmias were common but not serious. Premedication with quinidine significantly reduced their frequency. Ten % of patients on quinidine had side effects, mainly gastrointestinal; 1 patient developed transient thrombocytopenia. In patients with rheumatic heart disease, following cardioversion, prophylactic quinidine, achieving a mean serum level of 2. 2 mg 1 does not increase the chances of maintaining sinus rhythm.