AN ECHOCARDIOGRAPHIC STUDY OF ATRIAL-FIBRILLATION IN HORSES - BEFORE AND AFTER CONVERSION TO SINUS RHYTHM

Two-dimensional and M-mode echocardiograms were recorded from 41 horse s before they were successfully treated for atrial fibrillation, In ad dition, these examinations were performed in a subgroup of 20 horses a fter treatment, and the results were compared with pretreatment values . Atrial fibrillation in this group of horses was associated with a re duction of mean left ventricular fractional shortening (mean 31% +/- 5 .24%), and 22 of the 41 horses were below the reference range, The rem aining mean M-mode variables were within the normal reference range, a lthough 12 horses had increased left ventricular lumen dimensions in s ystole, and 8 horses had decreased left ventricular ejection times. Ab normal motion of the mitral valve was present in all horses and was ch aracterized by the absence of A peaks, which were replaced by small di astolic undulations in 55% of the horses, In horses 1 to 20, after con version to sinus rhythm, the mean fractional shortening increased (35. 34% +/- 5.4%, P = .004), but there were no significant differences in heart rate or left ventricular lumen diameters in systole or diastole, These results suggest that ventricular function may be compromised by the presence of atrial fibrillation. However, this improved after cor rection of the arrhythmia.