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J Thorac Cardiovasc Surg 2006;131:1364-1372
© 2006 The American Association for Thoracic Surgery

Cardiopulmonary Support and Physiology

Relationship between atrial histopathology and atrial fibrillation after coronary bypass surgery

^a Department of Surgical Sciences, Cardiac Surgery Division, Varese University Hospital, University of Insubria, Varese, Italy
^c Department of Human Morphology, Pathology Division, Varese University Hospital, University of Insubria, Varese, Italy
^b Department of Surgical and Perioperative Sciences, Heart Center, Cardiothoracic Division, Umeå University Hospital, Umeå, Sweden.

Received for publication October 16, 2005; revisions received December 18, 2005; accepted for publication January 30, 2006.

^_* Address for reprints: Giovanni Mariscalco, MD, Department of Surgical Sciences, Cardiothoracic Division, Varese University Hospital, I-21100, Varese, Italy (Email: giovannimariscalco{at}yahoo.it).

BACKGROUND: Postoperative atrial fibrillation is common after coronary surgery. The cellular condition of atrial myocytes might play a part in the postoperative development of atrial fibrillation. Our study aimed to investigate whether patients in whom postoperative atrial fibrillation develops show pre-existent alterations in histopathology of the right atrium and how such changes are expressed in relation to the use of cardiopulmonary bypass.

METHODS: Seventy patients undergoing elective coronary revascularization were prospectively randomized to on-pump conventional surgery (conventional coronary artery bypass grafting, n = 35) or off-pump surgery on the beating heart (off-pump coronary artery bypass grafting, n = 35). Samples from the right atrial appendage were immediately collected after opening the pericardium. In the on-pump group samples were also taken after weaning from cardiopulmonary bypass. Focusing on degenerative alterations, histology was studied by means of light microscopy and for confirmation of particular findings by means of electronic microscopy.

RESULTS: Twenty-two (31%) patients had postoperative atrial fibrillation, with the rate not being different between the off-pump coronary artery bypass grafting and conventional coronary artery bypass grafting groups (P = .797). Left atrial enlargement and inotropic requirement were related to atrial fibrillation. Interstitial fibrosis, vacuolization, and nuclear derangement of myocytes were the histologic abnormalities associated with the development of postoperative atrial fibrillation. However, in multivariate analysis fibrosis was confounded by myocyte vacuolization (P = .002) and nuclear derangement (P = .016), representing independent atrial fibrillation predictors. As expected, the conventional coronary artery bypass grafting and off-pump coronary artery bypass grafting groups showed similar histology, but more importantly, no atrial changes were detected in relation to cardiopulmonary bypass exposure in the conventional coronary artery bypass grafting group. Atrial histology showed degenerative changes that correlated with advanced age and left atrial enlargement.

CONCLUSIONS: Our study supports the contention that atrial fibrillation after coronary surgery is associated with pre-existing histopathologic changes of the right atrium. Patients randomly allocated to off-pump coronary artery bypass grafting procedures showed a similar rate of atrial fibrillation and a similar relationship to atrial histology as did those exposed to cardiopulmonary bypass. Cardiopulmonary bypass did not cause additional changes in tested histology variables.

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