Abstract
The constant pressure perfusion of the sinus node artery was performed on 12 dogs anesthetized with sodium pentobarbital (30mg/kg, i.v.). When acetylcholine (ACh) was infused continuously at different rates into the sinus node artery, the sinoatrial pacemaker was depressed and prefibrillatory stage was established at a suitable rate of infusion. Thus, a sustained atrial fibrillation was spontaneously induced or it was evoked by a single dose of either acetylcholine, norepine-phrine or nicotine during the infusion of acetylcholine. When the infusion of ACh at a higher rate depressed the sino-atrial node completely and escape A-N nodal rhythm took place, atrial fibrillation was never induced. Atrial fibrillation ceased suddenly and the sinus rhythm reappeared soon after the infusion was interrupted. This could be observed repeatedly.
A single dose of atropine blocked the sustained atrial fibrillation, while propranolol and GEDTA could block it by infusion or intravenous administration.
It is suggested that the prefibrillatory stage is necessary for maintenance of atrial fibrillation, and its mechanism is discussed.
