Effects of amiodarone on triggered activity induced by overdrive stimulation in Ca2+ overloaded ventricular muscle from guinea pig.

1. The acute effects of amiodarone, a powerful antiarrhythmic drug, on transient depolarizations (TDs) and/or triggered activity (TA) induced by an overdrive stimulation in the condition of low potassium (2.7 mM) and high calcium (5.4 mM) solution were evaluated on isolated ventricular papillary muscles from guinea pig, by means of conventional microelectrode techniques. 2. The amplitude of the induced TDs was enhanced by increase in stimulus number and frequency during overdrive stimulation, and the coupling interval of TDs was shortened. 3. Amiodarone (4.4 x 10(-5) M) significantly decreased the amplitude of TDs, and prolonged the coupling interval. 4. On the other hand, superfusion with a higher concentration (4.4 x 10(-4) M) of amiodarone tended to induce automatic activity. 5. Possible implications with respect to the antiarrhythmic activity of amiodarone are discussed.