= Coaptation
\b[Coaptation] is the meeting and contact of opposing <valve leaflet> surfaces that helps a <heart valve> close. It is a geometrical and <contact mechanics> condition, distinct from the opening size, leaflet length or a single chordal <tension> measurement. The resulting contact region can be described by its location and <coaptation area>.
An original one-dimensional coverage model makes the role of support geometry clear. Let two opposing leaflets each reach a distance $\ell$ across an opening of width $D$. A nominal overlap margin is
$$
m=2\ell-D.
$$
With $\ell=16$ mm and $D=30$ mm, the margin is 2 mm. If the opening widens to 34 mm with unchanged reach, the margin becomes $-2$ mm, representing a gap in this simplified model. Actual leaflet contact also depends on three-dimensional orientation, deformation and loading, so positive overlap in a drawing is not sufficient proof of a seal.
A primary left-heart simulator study compared flat and saddle-shaped attachment boundaries in eleven human specimens of the <mitral valve>. Changes in <cardiac valve annulus> shape redistributed <chordae tendineae> forces; the tested shape comparison did not produce a statistically significant change in regurgitant volume.<Effects of a saddle shaped annulus on mitral valve function and chordal force distribution: an in vitro study by Jorge Hernan Jimenez and others>[Abstract, Methods and Results]{ref} Geometry, attachment forces and leakage were related but separately observed quantities.
This explains why a successful-looking contact region in one image need not specify the total backward <blood flow>. A narrow unobserved gap elsewhere may matter, while a contact outline supplies no direct measurement of its fluid transport. Conversely, measuring one chord's <tension> does not establish the contact state over every leaflet surface. A clear description of <coaptation> therefore identifies the valve, imaging phase and contact measure being discussed.
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