Mitral coaptation index

The mitral coaptation index is a dimensionless normalization of the mitral valve's coaptation area. In the primary method of Frederick C. Cobey and colleagues, it is the three-dimensional end-systolic coaptation-zone area divided by the three-dimensional mitral-valve area used in that protocol:The denominator and surface-reconstruction convention are part of the definition.^[ref]

The study used intraoperative transesophageal echocardiography in 25 patients with functional mitral regurgitation, followed by offline analysis of the end-systolic geometry.^[ref] This supplies an experimental acquisition context for the ratio; it does not make every area called annular area interchangeable with the protocol's valve-area measurement.

An original normalization example uses $A_{\mathrm{coaptation}}=1.5$ cm${}^2$ and $A_{\mathrm{MV}}=10$ cm${}^2$, giving $I_c=0.15$. A second constructed valve with areas 3 and 20 cm${}^2$ has the same index despite twice the absolute contact area. Conversely, keeping contact area 1.5 cm${}^2$ while changing the denominator to 15 cm${}^2$ gives $I_c=0.10$. Absolute area and normalized coverage answer different questions.

Uniformly scaling every length by a positive factor $s$ multiplies both areas by $s^2$, leaving $I_c$ unchanged. Inconsistent surface conventions do not cancel: counting two apposed faces in the numerator while counting their interface once in another reconstruction can change the ratio without a biological change.

Finally, the index does not describe the connectivity of any remaining gaps. Two contact patches with equal coaptation area and equal denominator can have different shapes and positions, as illustrated under coaptation area. The mitral coaptation index is a geometric descriptor to interpret alongside the reconstructed valve and blood flow, rather than a complete description of valve sealing.