Cardiac lesions in dairy cows with idiopathic atrial fibrillation

Histopathological examination of the heart, particularly the right atrium including the sinoatrial (SA) node, was carried out in 9 Holstein dairy cows with idiopathic atrial fibrillation (AP; AF group) and 12 healthy cows of the same breed (control group) in order to establish the correlation between idiopathic AF and histopathological changes in the heart in dairy cows. None of the 9 cows had clinical evidence of other diseases, and they consisted of 5 cases of short-term AF which lasted a few days or weeks, and 4 cases of long-term AF which lasted more than 1 month. The pathological changes found in the present series included multifocal or fairly large areas of myocardial fibrosis in the right atrium (in all the 9 cows of the AF group and 2 of the 12 controls - however, the changes were qualitatively and quantitatively much more severe in the former group); SA nodal architecture changes (in 3 of the 4 cows with long-term AF); and atrial dilatation (in 3 of the 4 cows with long-term AF). The results suggest that the fibrotic lesions of the right atrial myocardium may represent the anatomical changes that underlie idiopathic AF in dairy cows.