Effects of intravenous ajmaline on atrial excitability and conduction in man

Slow conduction of early extrastimuli and short refractory periods are some of the factors underlying atrial fibrillation in man. In order to study the effect of ajmaline, a class I antiarrhythmic agent, on these variables, we have performed electrophysiologic studies in 13 patients with and without atrial arrhythmias, before and after the intravenous administration of 1 mg kg-1 of ajmaline chlorhydrate. During paced rhythm with a 600 ms cycle length, extrastimuli were applied to the right atrial appendage, and conduction to the low septal right atrium and the coronary sinus were measured. Ajmaline prolonged P wave duration from 111 +/- 15 to 140 +/- 24 ms (P less than 0.001), conduction of baseline stimuli to low septal right atrium from 69 +/- 14 to 95 +/- 21 ms (P less than 0.001) and to coronary sinus from 127 +/- 18 to 165 +/- 29 ms (P less than 0.001). Atrial effective refractory period increased from 207 +/- 23 to 255 +/- 27 ms (P less than 0.001). Maximum conduction delay of early extrastimuli decreased at the low septal right atrium from 43 +/- 22 to 29 +/- 16 ms (P less than 0.25) and at the coronary sinus from 47 +/- 22 to 21 +/- 14 ms (P less than 0.001). These results show interesting electrophysiologic effects of ajmaline on atrial tissue, with reversion of some of the abnormalities underlying atrial fibrillation, and suggest an antiarrhythmic effect.