Electrophysiology of phosphodiesterase inhibitors

Phosphodiesterase inhibitors appear to uniformly enhance atrioventricular node conduction, although milrinone seems to have the least effect. Except for digoxin, this effect on atrioventricular node conduction is similar to that noted with other inotropic agents. Other electrophysiologic effects vary among patients, with enoximone being more theophylline-like in response. Because none of these drugs do not have an adverse effect on His-Purkinje conduction, they are safe to use in patients with intraventricular conduction disturbances. Significant proarrhythmia is uncommon, but can occur. The mechanisms causing these electrophysiologic changes are not well defined, but the changes may occur because of increased concentrations of cytosol cyclic adenosine monophosphate secondary to phosphodiesterase inhibition, increased cytosol calcium levels secondary to increased cyclic adenosine monophosphate, or reflex adrenergic stimulation secondary to the peripheral vasodilating effects of these drugs.