Adenosine decreases the fibrillation threshold in atrial myocardium.

The action of adenosine on the fibrillation threshold, effective refractory period, electric diastolic threshold and mechanical activity of the atrial and ventricular myocardium was studied in vivo and in vitro. In anaesthetized, open-chest cats, the atrial fibrillation threshold significantly decreased under adenosine-infusion (1 mumols/kg/min). In electrically stimulated atrial myocardium of cats, adenosine (10 mumols/l-1 mmol/l) was capable of evoking a concentration-dependent decrease in electric diastolic threshold and shortening the functional refractory period. Adenosine decreased also the contractile force. The shortening on the functional refractory period was more prominent in electrically driven guinea-pig left atrial myocardium. This action could be antagonized by aminophylline, a competitive antagonist on P1 purinoceptors. In ventricular myocardium, adenosine did not influence the fibrillation threshold, the electric diastolic threshold, the functional refractory period or contractile force. On the basis of these observations it can be assumed that the above changes in the extracellular electrophysiological parameters may play a role in the pathomechanism of atrial fibrillation occasionally manifested during treatment with adenosine in patients as well as in dogs.