Left Atrial Enlargement Induced by Pure Mitral Regurgitation: Time Frame in a New Swine Model

Background: Atrial enlargement occurs in patients with significant mitral regurgitation. However, the time frame of the development of atrial enlargement induced by mitral regurgitation remains unknown. Methods: Fourteen Lanyu miniature pigs (age = 6.6 +/- 0.9 months) were studied. Mitral regurgitation was created by placing a predefined hole on the middle scallop of the posterior mitral leaflet under cardiopulmonary bypass. The parasternal long-axis atrial dimension was measured by transthoracic echocardiographic examinations. Results: All animals exhibited grade 3 mitral regurgitation immediately after surgery. Seven pigs expired within 2 weeks after the operation [technical complications (n = 1), acute cardiac tamponade (n = 1), and acute and subacute heart failure (n = 5)]. Seven pigs remained alive at a mean follow-up of 7.7 +/- 2.1 months. The left atrial diameter indices of the 7 pigs increased significantly at 1 month (33.1 +/- 8.6 mm, p = 0.018) and 3 months (41.3 +/- 12.6 mm, p = 0.018) after surgery compared with baseline values (22.8 +/- 5.2 mm), and the left atrial diameter index increased significantly at 3 months compared to 1 month (p = 0.018). Conclusions: Left atrial enlargement develops rapidly and progresses after the creation of significant pure mitral regurgitation. Copyright (C) 2010 S. Karger AG, Basel