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

Synchronized direct current shock (Lown, Amarasingham, and Neuman, 1962) has rapidly become established as an effective and safe method of treating cardiac arrhythmias, but controversy remains about the use of antiarrhythmic drugs in maintaining sinus rhythm following the procedure. Although quinidine is potentially dangerous (Thomson, 1956; Oram and Davies, 1964; Davies, Leak, and Oram, 1965), many authors state that it should be used prophylactically (Lown et al., 1963; Hurst et al., 1964; Korsgren et al., 1965; Morris, Peter, and McIntosh, 1966). However, Halmos (1966) and Szekely, Batson, and Stark (1966) have suggested that quinidine does not prolong the duration of sinus rhythm. In this paper we describe our experience in using direct current shock to treat 149 patients with atrial arrhythmias. The effect of prophylactic quinidine on the maintenance of sinus rhythm in a group of patients with rheumatic heart disease is compared with another group on no quinidine. A number of other factors have been analysed to determine their influence on results.