The unique mechanism of functional mitral regurgitation in acute myocardial infarction: a prospective dynamic 4D quantitative echocardiographic study

Abstract

Aims Mechanisms of chronic ischaemic mitral regurgitation (IMR) are well-characterized by apically tethered leaflet caused by papillary muscles (PMs) displacement and adynamic mitral apparatus. We investigated the unique geometry and dynamics of the mitral apparatus in first acute myocardial infarction (MI) by using quantified 3D echocardiography. Methods and results We prospectively performed 3D echocardiography 2.3 ± 1.8 days after first MI, in 174 matched patients with (n = 87) and without IMR (n = 87). 3D echocardiography of left ventricular (LV) volumes and of mitral apparatus dynamics throughout cardiac cycle was quantified. Similar mitral quantification was obtained at chronic post-MI stage (n = 44). Mechanistically, acute IMR was associated with larger and flatter annulus (area 9.29 ± 1.74 cm2 vs. 8.57 ± 1.94 cm2, P = 0.002, saddle shape 12.7 ± 4.5% vs. 15.0 ± 4.6%, P = 0.001), and larger tenting (length 6.36 ± 1.78 mm vs. 5.60 ± 1.55 mm, P = 0.003) but vs. chronic MI, mitral apparatus displayed smaller alterations (all P < 0.01) and annular size, PM movement remained dynamic (all P < 0.01). Specific to acute IMR, without PM apical displacement (P > 0.70), greater separation (21.7 ± 4.9 mm vs. 20.0 ± 3.4 mm, P = 0.01), and widest angulation of PM (38.4 ± 6.2° for moderate vs. 33.5 ± 7.3° for mild vs. 31.4 ± 6.3° for no-IMR, P = 0.0009) wider vs. chronic MI (P < 0.01). Conclusions 3D echocardiography of patients with first MI provides insights into unique 4D dynamics of the mitral apparatus in acute IMR. Mitral apparatus remained dynamic in acute MI and distinct IMR mechanism in acute MI is not PM displacement seen in chronic IMR but separation and excess angulation of PM deforming the mitral valve, probably because of sudden-onset regional wall motion abnormality without apparent global LV remodelling. This specific mechanism should be considered in novel therapeutic strategies for IMR complicating acute MI.

Mitral Valve Remodeling After Acute Myocardial Infarction – A Longitudinal Three-Dimensional Echocardiography Study

“…It was demonstrated that leafl ets surface is signifi cantly larger in chronic IMR compared to acute IMR 3,4 . Chaput et al demonstrated that the mitral leafl et area increases in response to chronic tethering in patients with inferior wall-motion abnormality and dilated cardiomyopathy 7 .…”

“…Recent studies using 3D echocardiography have shown that in the setting of acute STEMI, patients with IMR have larger and fl atter mitral annulus and larger systolic tenting compared to those without IMR 3,4 . In order to diff erentiate between the MV geometrical changes in acute vs chronic MR, distinct cohorts of patients were analyzed in the previous studies 3,4 . Th ese studies have shown that chronic IMR is characterized by a fl atter annulus, larger annular area and larger tenting volume 4 .…”

“…Th e majority of studies on IMR has been focused on patients with chronic IHD and less attention was payed to acute IMR. However, recently it was demonstrated that the mechanism of IMR in the setting of acute myocardial infarction (MI) is diff erent from the mechanism of chronic IMR 3,4 .…”

“…Recent studies comparing cohorts of patients with signifi cant acute versus chronic IMR have demonstrated that in chronic IMR the MV annular surface is larger, the annular height is smaller (the annulus is fl atter) and the leafl ets surface is larger, with a larger tenting volume 3,4 . However, few little is known about the MV geometrical changes over time in the same cohort of patients.…”

Acute Ischaemic Mitral Valve Regurgitation

“…Kimura et al [ 24 ] also evaluated the physiopathology of MR in this subgroup of patients, using a 4D echocardiography dynamic model in a study conducted in Japan and the USA. Firstly, the authors reported that regardless of a comparable MI size, IMR was associated with a higher regurgitant volume (RVol), considerable changes in haemodynamic status, increased left ventricle (LV) volumes, and significantly reduced forward stroke volume, all of which are more pronounced in the presence of increasing IMR severity [ 24 ]. In addition, they noted in the acute setting of IMR that there was preservation of the annulus and functionality of the papillary muscles (PM) in contrast with loss of functionality in the chronic IMR setting [ 24 ].…”