ATRIAL PRESSURE AND EXPERIMENTAL ATRIAL-FIBRILLATION

A possible profibrillatory effect on the atria of an elevated atrial p ressure and the site of atrial stimulation was examined. In 15 anesthe tized dogs, right or left atrial or biatrial pacing was applied at a h igh rate (300-600/min) for 5 seconds at double threshold intensity und er a wide range of atrial pressures achieved by venous or arterial tra nsfusion or bleeding. Induction of atrial fibrillation in 236 of 1,971 pacing runs was associated with a significantly higher (P < 0.001) at rial pressure (21.6 +/- 12.2 mmHg, mean +/- SD) than maintenance of si nus rhythm (16.8 +/- 11.1 mmHg in 1,735 of 1,971 pacing runs). Stimula tion of the right atrium resulted in atrial fibrillation more frequent ly 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 sit e of stimulation but not to the pacing rate or the prepacing heart rat e. The prepacing heart rate, associated with failure to induce sustain ed atrial fibrillation, was higher than that associated with atrial fi brillation in 12 of 15 experiments (significantly in 6) and not signif icantly 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 m ay facilitate the induction of atrial fibrillation. The site of stimul ation also plays an important role for both the induction and maintena nce of atrial fibrillation in this model.