Electrophysiological properties in man of L 9394, a substance chemically related to amiodarone.

The effects of L 9394, a new compound closely related to amiodarone, were investigated in 44 patients by electrophysiological studies. Thirty two patients were given an intravenous injection of one of the following doses: 0.5, 1, 1.5 or 2 mg/kg. Conduction times of the A-V node (A-H interval) and of the His-Purkinje system (H-V interval) were measured by recording the His bundle potential. Refractory periods were determined by the extrastimulus technique. In the remaining 12 subjects, the action of L 9394 on sinus node was assessed. Sinus node recovery time was measured by rapid atrial stimulation and estimated atrial-sinoatrial conduction time deduced from the effects of atrial premature stimulation on sinus node activity. Results were as follows: (1) A-V nodal conduction was depressed after L9394. The A-H interval increased in direct proportion to the dose. Similarly, the effective and functional refractory periods of the A-V node were prolonged, more markedly after higher doses. (2) No change was shown in the His-Purkinje system. The H-V interval was unaltered. (3) L 9394 had no significant effects on the atrial or ventricular muscle. (4) Sinus cycle length as well as sinus node recovery time did not change significantly. In 7/12 patients, results of premature atrial stimulation suggested the formation of a sinoatrial block.