[The effects of digoxin administration on normal and pathological sinus node function. An electrophysiological study (author's transl)].

In 12 normal subjects (group I), in 12 subjects with asymptomatic sinus bradycardia (group II) and in 18 patients with symptomatic sick sinus syndrome (group III), sinus node cycle length (SNCL), sinus node recovery time (SNRT), corrected sinus node recovery time (CSNRT), sino-atrial conduction time (SACT), have been evaluated before and after an acute digoxin administration. Mean value of SNCL lengthened significantly in all groups. Mean value of SNRT increased moderately in the first group, remarkably in the third group, whereas it showed a mild but statistically insignificant increase in the second group. Mean value of CSNRT was significantly lengthened only in the third group. Mean value of SACT showed a mild but statistically insignificant lengthening in all groups. In order to investigate the importance of the parasympathetic action induced by digitalis, in 4 normal subjects, in 4 patients with asymptomatic sinus bradycardia, and in 10 patients with symptomatic sick sinus syndrome, SNCL, CSNRT and SACT has been evaluated after an intravenously, administration of atropine, following digoxin. In the paper the intricate mechanisms by which digitalis affects the parameters of sinus nodal function especially in patients with symptomatic sick sinus syndrome, are discussed. In disagreement with the mot papers reported in the literature we think that an acute digoxin administration is able to worsen the electrophysiological parameters of sinus nodal function especially in patients with symptomatic sick sinus syndrome.