Persistent atrial fibrillation in a goat model of chronic left atrial overload

Atrial dilatation predisposes to atrial fibrillation. Although several animal models focus on the initiating mechanisms of atrial fibrillation in dilated atria, a model of left atrial overload resulting in persistent atrial fibrillation in nonanesthetized animals has not been presented thus far.

In 24 goats a vascular shunt was implanted between the aorta and the left atrium through a left thoracotomy. In 6 animals the shunt was ligated immediately (control group). Ultrasonic crystals were implanted to monitor atrial dilatation. Bipolar electrodes were positioned epicardially on the left atrium for measurement of the atrial effective refractory period, conduction times, and atrial fibrillation duration.

Four weeks of overload resulted in an increase of left atrial pressure (23.1 +/- 6.8 mm Hg in the open-shunt group vs 7.0 +/- 1.9 mm Hg in the control group, P = .002) and a progressive dilatation of the left atrium (135% +/- 20% in the open-shunt group vs 98% +/- 8.0% in the control group, P = .002). Among the open-shunt group's long-term survivors (n = 12), 9 animals showed prolonged atrial fibrillation (>1 hour), and of these, 6 were in persistent atrial fibrillation (>1 week). The atrial effective refractory period increased during the first week and remained prolonged until death (182 +/- 11 ms in the open-shunt group vs 161 +/- 15 ms, P = .03). The conduction time did not change. An increase in collagen formation was noticed in both groups, without a significant difference between them.

A chronic aortic to left atrial shunt is a feasible model in the goat. It induces progressive left atrial dilatation with an increased atrial fibrillation duration up to hours in the majority of animals. Prolonged atrial fibrillation duration could not be explained by a shortening of atrial effective refractory period or increase in fibrosis.