Atrial Functional vs Ventricular Secondary Mitral Regurgitation: Differential Ultrasound Diagnostics
Regurgitation is defined as pathological blood return through a closed valve (Blagodir B.V., 2024). In functional (secondary) mitral regurgitation, the leaflets themselves are structurally intact, and leaflet coaptation failure is due to remodeling of the atrium or ventricle.
Pathophysiological Differences
According to source materials, functional regurgitation of atrioventricular valves is pathophysiologically associated with atrial fibrillation (Muraru D. et al., JASE 2020)—this association is described as requiring further investigation. Restoration of sinus rhythm can reverse chamber remodeling and reduce valve regurgitation in patients with atrial fibrillation (Soulat-Dufour L. et al., JACC 2022). This confirms the role of atrial dilation and annular enlargement in the genesis of the atrial variant.
For the tricuspid valve, the concept of "atrial secondary regurgitation" with a separate definition, pathophysiology, diagnostics, and treatment has been formalized (Muraru D. et al., Eur Heart J 2024; Schlotter F. et al., Circ Cardiovasc Interv 2022). By analogy, atrial functional mitral regurgitation is caused by atrial dilation and mitral annulus enlargement; ventricular regurgitation is caused by LV dilation and dysfunction. Exact echocardiographic criteria for differentiation are not provided in the available fragments [clarification needed].
What to Assess on Echocardiography
When examining the mitral valve from the parasternal short axis (SAX), the anterior (AML) and posterior (PML) leaflets are visualized; their motion resembles a "fish mouth" (Blagodir B.V., 2024). It is necessary to exclude:
— leaflet prolapse/elongation;
— myxomatous change/thickening/calcification with or without restriction of excursion;
— flail leaflet, chordae, papillary muscles;
— mitral annular calcification.
Absence of these structural changes in the presence of regurgitation indicates a functional (secondary) mechanism. Further differentiation between atrial and ventricular variants requires assessment of LV and LA size and function, as well as rhythm status (presence of atrial fibrillation)—specific threshold values are not presented in the sources [clarification needed].
Special Mechanism in HCM
In hypertrophic cardiomyopathy, mitral regurgitation is associated with systolic anterior motion (SAM) of the leaflet and LVOT obstruction; the mechanism is a mismatch in length and mobility of the posterior and anterior leaflets (Schwammenthal E. et al., Circulation 1998). Regurgitation in obstructive HCM is related to obstruction and decreases after myectomy (Yu EH et al., JACC 2000). Doppler jet direction helps establish the etiology of regurgitation in obstructive HCM.
Frequently asked questions
How does atrial functional MR differ from ventricular MR by mechanism?
The atrial variant is caused by left atrial dilation and mitral annulus enlargement, often in the setting of atrial fibrillation; the ventricular variant is caused by LV remodeling and dysfunction. The leaflets are structurally intact in both cases. Exact echocardiographic criteria for differentiation are not provided in the sources [clarification needed].
How to differentiate functional MR from organic MR on echocardiography?
In functional MR, the leaflets are structurally unchanged. On SAX, prolapse/elongation, myxomatous change, thickening, calcification with restriction of excursion, flail leaflet, and mitral annular calcification are excluded (Blagodir B.V., 2024).
Can rhythm restoration affect functional MR?
Yes. Restoration of sinus rhythm reverses chamber remodeling and reduces valve regurgitation in patients with atrial fibrillation (Soulat-Dufour L. et al., JACC 2022).
What is the mechanism of MR in hypertrophic cardiomyopathy?
Regurgitation is associated with SAM and LVOT obstruction due to mismatch in length and mobility of the posterior and anterior leaflets; it decreases after myectomy (Schwammenthal E., Circulation 1998; Yu EH, JACC 2000).