Abstract Aims Functional mitral regurgitation is strongly associated with dilatation of the mitral annulus. We aimed to investigate how remodelling of the left ventricle and left atrium impacts the mitral annulus size and function in patients with transmural myocardial infarction. Methods In this prospective observational study, patients with ST-elevation myocardial infarction were examined with 3D echocardiography at admission and at 1-year follow-up (n=87). Size and function of the left cardiac chambers and the mitral annulus was analysed. The cohort was divided into groups with (n=16) or without (n=71) mitral annular remodelling, defined as an area increase of 15% or more, from baseline to follow-up. Results During follow-up, the group without mitral annular remodelling had stable volumes and improved function for both the left ventricle and the left atrium. Although the group with mitral annular remodelling also exhibited improved left ventricular function, both left ventricular volume and left atrial volume increased, and no improvement was seen in left atrial emptying fraction or left atrial reservoir or contractile strain. In linear regression analysis, increased mitral annular area at follow-up was associated with change in both left atrial (β=0.025 (0.007, 0.043), p=0.006) and left ventricular volume (β=0.014 (0.003, 0.025), p=0.012). Conclusion Mitral annular remodelling after transmural myocardial infarction is associated with increased volumes of the left ventricle and the left atrium, and absence of atrial functional improvement. Both increasing left atrial and left ventricular volume are associated with mitral annular dilatation, but left atrial volume is the strongest factor.
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