Triggered activity as a cause of bigeminy.

Standard microelectrode techniques were used to study bigeminal rhythms occurring during otherwise stable triggered activity in ouabain-toxic canine Purkinje fibers. The basis for the bigeminy appeared to be an alternans phenomenon in the delayed afterdepolarizations that induced the triggered activity, as well as in the maximal diastolic potential. The occurrence of bigeminy, previously thought to result from reentry, from single delayed afterdepolarizations coupled to a triggered action potential or from parasystole, can also be considered a manifestation of sustained triggered activity.