Mitral annular excursion

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.