ATRIAL CONTRACTILE PERFORMANCE AFTER CESSATION OF ATRIAL-FIBRILLATION

Atrial fibrillation is associated with a fall in cardiac output, and cardioversion to sinus rhythm is frequently attempted. After cardioversion, atrial contractile performance might be depressed. It is, however, unclear whether or not atrial contractile performance is altered following atrial fibrillation periods lasting <1 wk. Atrial contractile performance after short-term paroxysmal atrial fibrillation was examined in seven barbiturate-anesthetized, open-chest pip paced at constant ventricular rate after complete atrioventricular block. Percent left atrial systolic shortening (systolic shortening of left atrial diameter in percent of atrial diameter at onset of atrial contraction, %LASS) increased from 100 to 116.2% (107.7-121.8) (median and 95% confidence interval) immediately after cessation of a fibrillation period of 1 min. A brief phase of atrial hypercontractility (% LASS significantly above control) was also demonstrated after fibrillation periods of 5 and 15 min. A subsequent phase of atrial hypocontractility (%LASS significantly below control) was recorded after atrial fibrillation periods of 5, 15, and 30 min. After the 30-min fibrillation period, atrial hypocontractility was most pronounced and reached a nadir of 86.8% (75.1-93.3).