A possible profibrillatory effect on the atria of an elevated atrial
pressure and the site of atrial stimulation was examined. In 15
anesthetized dogs, right or left atrial or biatrial pacing was applied
at a high rate (300-600/min) for 5 seconds at double threshold intensity
under a wide range of atrial pressures achieved by venous or arterial
transfusion or bleeding. Induction of atrial fibrillation in 236 of
1,971 pacing runs was associated with a significantly higher (P < 0.001)
atrial pressure (21.6 +/- 12.2 mmHg, mean +/- SD) than maintenance of
sinus rhythm (16.8 +/- 11.1 mmHg in 1,735 of 1,971 pacing runs).
Stimulation of the right atrium resulted in atrial fibrillation more
frequently than left atrial or biatrial stimulation, with biatrial
stimulation less frequent than right or left atrial stimulation. The
induction of atrial fibrillation was related to the atrial pressure and
to the site of stimulation but not to the pacing rate or the prepacing
heart rate. The prepacing heart rate, associated with failure to induce
sustained atrial fibrillation, was higher than that associated with
atrial fibrillation in 12 of 15 experiments (significantly in 6) and not
significantly lower in 3 of 15. Atrial fibrillation lasting 1 minute or
more was more frequently associated with simultaneous stimulation of
both atria than of either atrium alone. Thus, an elevated atrial
pressure may facilitate the induction of atrial fibrillation. The site
of stimulation also plays an important role for both the induction and
maintenance of atrial fibrillation in this model
