Atrial Infarction and Ischemic Mitral Regurgitation Contribute to Post-MI Remodeling of the Left Atrium.

BACKGROUND: Left atrial (LA) remodeling after an acute myocardial infarction (MI) is poorly characterized regarding its determinants or its effect on ischemic mitral regurgitation (MR) development.
OBJECTIVES: The purpose of this study was: 1) to compare LA structural remodeling in experimental MI swine models recapitulating the effects of left ventricular (LV) dysfunction, ischemic MR, and left atrial infarction (LAI); and 2) to analyze how LA remodeling influences ischemic MR development.
METHODS: Three models of MI were generated: 1) proximal left circumflex (LCx) coronary artery occlusion involving the LA branch (LAI group); 2) proximal LCx occlusion not involving the LA branch (LCx group); and 3) left anterior descending (LAD) occlusion (LAD group). Serial cardiac magnetic resonance scans were performed to define LA and LV remodeling and ischemic MR, and were correlated with histology.
RESULTS: Occlusion of the LA branch (LAI group) induced a greater degree of LA dilation at 1 and 8 weeks post-MI than the LCx and LAD groups, along with early and severe impairment of LA function. In the LCx and LAD groups, LA dysfunction was less pronounced and not consistent. Development of ischemic MR was more pronounced in the LAI group than in the LCx group. Histology confirmed atrial infarction with extensive fibrosis in the LAI group and interstitial fibrosis in the LCx group. In the LAD group, LA remodeling was not observed by cardiac magnetic resonance or histology.
CONCLUSIONS: We provide the first experimental evidence of the deleterious effect of acute LAI on atrial structural remodeling, characterized by early LA dilation, dysfunction, and fibrosis, and early occurrence of ischemic MR.