Abstract
DC countershock abolished 92 of 101 episodes of atrial fibrillation in 86 patients, an incidence of 91 per cent. Supraventricular arrhythmias were not infrequent immediately after countershock. These were transient and did not complicate the procedure nor were they hazardous to the patient. On two occasions a slow atrioventricular nodal rhythm appeared followed by recurrence of atrial fibrillation a few hours later. Sinus node activity did not return in these patients. Ventricular tachycardia, fibrillation, or standstill did not occur in this series. The following arrhythmias were observed immediately after countershock but prior to the establishment of a regular sinus rhythm: atrioventricular dissociation, 12 times; passive atrioventricular nodal rhythm, five times; atrioventricular nodal tachycardia, five times; atrial flutter or tachycardia, four times. The conversion of fibrillation to flutter by countershock implies that the effect of the electric current was merely to shorten the length of the circulating wave, a phenomenon that can also be observed in the treatment of atrial fibrillation with quinidine. Disorders of rhythm, probably having a different mechanism, were also observed after countershock had established a regular sinus pacemaker. In the group not treated with quinidine prior to countershock (74 episodes) atrial extrasystoles were seen 26 times (35 per cent); atrioventricular nodal extrasystoles or escapes, 18 times (24.3 per cent); atrial flutter or tachycardia, six times (8.1 per cent); atrial fibrillation, eight times (18 per cent); atrioventricular nodal tachycardias, twice (2.6 per cent); and a bizarre, multifocal atrial arrhythmia, once (1.3 per cent). The arrhythmias considered to be responsible for the recurrence of atrial fibrillation and also the possible mechanisms involved were discussed. Pretreatment with quinidine was effective in reducing the incidence of arrhythmias occurring after conversion (27 episodes), atrial extrasystoles six times (22 per cent), atrioventricular nodal extrasystoles or escapes six times (22 per cent); atrial flutter or tachycardia three times (11 per cent); atrial fibrillation once (3.7 per cent); and atrioventricular nodal tachycardia once (3.7 per cent).
