Effects of atrial fibrillation on left and right atrial dimensions, pressures, and compliances.

The effects of atrial fibrillation on left and right atrial dimensions, pressures, and compliances were examined in two groups of seven barbiturate-anesthetized open-chest pigs. Atrial diameters and pressures were recorded during atrioventricular (AV) pace and thereafter during atrial fibrillation. Both rhythms were studied with constant ventricular rate after complete AV block. Left atrial maximal diameter, which appeared at the end of the atrial filling phase, decreased from 32.4 (28.9-36.7; median and 95% confidence interval) to 31.3 (28.4-35.7) mm after induction of atrial fibrillation. The right atrial maximal diameter also decreased, although not significantly. Atrial pressure at the peak of the v wave rose from 7.0 (5.5-8.5) to 9.6 (8.3-11.2) mmHg in the left atrium and from 5.0 (4.3-5.6) to 7.3 (6.2-8.7) mmHg in the right atrium. Left and right atrial chamber stiffness constants increased from 0.25 (0.19-0.48) to 0.41 (0.28-0.66) mm-1 and from 0.21 (0.11-0.31) to 0.33 (0.30-0.39) mm-1, respectively. Instantaneous diastolic atrial compliance decreased in both atria after induction of atrial fibrillation. Thus, during atrial fibrillation with regular ventricular rate, changes in atrial diameter, pressure, and compliance take place.