Electrophysiological effects of ajmaline in isolated cardiac tissue

The electrophysiological effects of increasing molar concentrations of ajmaline were studied in isolated cardiac tissue, including sino-atrial node and Purkinje fibre. Ajmaline produced significant shortening of the plateau of Purkinje fibre action potential associated with marked depression of dV/dt and directly measured conduction velocity. A negative chronotropic effect was noted both in the sinus node and in spontaneously beating Purkinje fibres. Ajmaline's major electrophysiological effect appears to be depression of Purkinje fibre conduction velocity.