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Figure 4 Atrial fibrillation induced by 1 µmol/l acetylcholine (ACh) (A) and 0.1 µmol/l ACh and 2 µmol/l isoproterenol (B). In the control experiment, an ACh concentration of 1 µmol/l was the threshold that repeatedly induced atrial fibrillation (AF) in that dog. The perfusion onset led to sinus rhythm slowing. Seven seconds after the start of perfusion, the atrial premature beat triggered AF. The perfusion was immediately stopped, and the paroxysm lasted for 12 s. Perfusion with ACh and isoproterenol resulted in less sinus rhythm slowing, and the paroxysm arose from a stable and faster rhythm than that before perfusion. Notably, the ACh concentration used to induce AF was 10 times less than that without isoproterenol. This paroxysm started with some delay and lasted for 90 s (not shown). CL = cycle length; E1 and E2 = atrial bipolar electrograms; P2 = blood pressure recording; II = standard electrocardiographic lead II.
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