Background. Postoperative atrial fibrillation after cardiac operation is co
mmon. Despite the identification of risk factors associated with postoperat
ive atrial fibrillation, the pathophysiologic mechanisms remain unclear. My
olysis has been recently described to be associated with maintenance of atr
ial fibrillation in experimental animals. In this study, we attempted to id
entify histopathologic changes in atria that might predict the development
of postoperative atrial fibrillation, and specifically address its associat
ion with myolysis.
Methods. Right appendicular atrial tissue was sampled before and after card
iopulmonary bypass from 60 patients in sinus rhythm who underwent elective
coronary artery bypass grafting.
Results. Fifteen patients (25%) developed postoperative atrial fibrillation
. Histopathologic abnormalities were found in most patients (52 of 60). How
ever, only myolysis and lipofuscin levels were found to be an independent h
istologic finding associated with the development of postoperative atrial f
ibrillation. Electron microscopy showed that myolytic vacuoles were not mem
brane bound, and were associated with lipofuscin deposits. Neither mitochon
drial pathology nor apoptosis was detected in the atria before or after ope
Conclusions. Abnormalities in biopsies before cardiopulmonary bypass can in
dicate the susceptibility to develop postoperative atrial fibrillation. Thi
s implies that the status of the atrium before cardiopulmonary bypass is a
major determinant in the development of this common complication. (C) 2001
by The Society of Thoracic Surgeons.