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Mitral annular excursion is displacement of the mitral annulus over a specified part of the cardiac cycle. A commonly used longitudinal observation follows an annular landmark along the cardiac long axis during ventricular systole. The reference position, direction and endpoints are part of the measurement; displacement is distinct from annular area or leaflet coaptation.

The measurement question can be written explicitly. For a fixed unit axis $\hat{\mathbf{e}}$ and landmark position $\mathbf{x}(t)$, defineAn original 10 mm displacement viewed along an axis tilted by $30^{\circ }$ projects to $10\cos 30^{\circ }\simeq 8.66$ mm. Thus changing the observation direction changes the reported excursion even for the same motion. A single landmark also need not represent every part of a deforming mitral annulus.

A primary human study used cine magnetic resonance imaging, measuring longitudinal displacement in long-axis views and stroke volume in short-axis views. Its model combined displacement with a ventricular short-axis area.^[ref] In an original rigid-piston approximation, area $A$ moving axially by $\Delta s$ sweeps volume $A\Delta s$. Areas 20 and 40 cm${}^2$ paired with displacements 1 and 0.5 cm both give 20 mL. Smaller excursion need not imply a smaller geometric swept volume when area differs; this model area is not automatically the mitral opening area.

A complementary experiment by C. Carlhäll and colleagues implanted markers around the mitral annulus and ventricular wall in six sheep. Biplane fluoroscopy reconstructed three-dimensional marker motion, and tetrahedron-based estimates assessed annular contributions to filling while loading and contraction were varied.^[ref] This connects a displacement measurement to moving-chamber geometry. The changing boundary, surrounding deformation and blood flow must be distinguished when relating mitral annular excursion to filling or ejection.

The mitral annulus is the supporting attachment region around the mitral valve between the left atrium and left ventricle. It supplies a reference for the valve leaflets but is not adequately described as a rigid, flat circle. Its spatial shape and motion form part of the coupled valve apparatus.

A primary left-heart simulator study compared flat and saddle-shaped annular configurations in eleven human valve specimens. The investigators measured chordae tendineae forces in selected experiments and found a redistribution of those forces with annular shape.^[ref] This tests a geometrical variable directly rather than assuming that one diameter captures the complete attachment boundary.

An original circular approximation illustrates why fractional diameter and area changes differ. If a hypothetical ring's diameter changes from $D$ to $0.9D$, its planar area changes from $\pi D^2/4$ to $0.81\pi D^2/4$. A $10\%$ diameter decrease gives a $19\%$ area decrease in this model. The equation is not a claim that the native mitral annulus is circular or planar.

Motion adds another geometrical contribution. In a rigid-piston model, translation of a boundary with area $A$ by distance $\Delta z$ changes the represented volume by $\Delta V=A\Delta z$. Stipulated values 10 cm${}^2$ and 0.4 cm give 4 mL. Actual mitral annular excursion occurs in a deforming heart, so this does not assign all stroke volume to one translating plane.

Annular area, shape, position and leaflet coaptation are therefore related but distinct observations. Comparisons need consistent landmarks and phases, while models must specify which parts of the surrounding apparatus are allowed to move.