When discussing the anatomy of the mitral valve, many of us get a confusion regarding these A 1, 2, 3 , P 1,2,3 stuff . Is the mitral leaflet really has sub-cm clefts or interuptions , that form the popular terminology mitral scallops .If so how long , these clefts go ? If it goes deep. will it not potentially the mitral valve look a tricupid ? Yes, every thing is possible . But ,It is very important to realise AML has no scallops and indentations, while the PML has distinct sub-commisures that make the well defined three scallops. The so called A 1, 2, 3 are just corresponding segments with reference to PML. Current day cardiologists are supposed to specify , segment or scallop orieneted MR jets . 3-D echo makes it possible. Also live, online TEE( with a good interperator) in cath lab has become essential in cath lab during mitra- clip procedure
3D echo showing the well defined scallops in PML, while the AML appears as single sheet.
A brief review on this topic
The PML has scallops because it develops as three distinct segments separated by indentations (subcommissures), with chordae attaching focally at these inter‑scallops to reinforce and stabilize the scalloped architecture, whereas the anterior leaflet (AML) forms as a single, broad, continuous sheet without clefts and is pulled by chordae in a broad, basket‑like pattern that does not create scallops.
In MR the PML’s scallops are prone to malcoaptation when annular dilatation or tethering pulls them apart, often producing focal jets at P1–P2 or P2–P3, while AML‑driven MR tends to be more diffuse when the entire leaflet is involved.
During MitraClip deployment, the PML’s scallops provide a useful roadmap to target graspable segments (e.g., A2–P2), whereas the smooth AML complicates precise alignment and raises the risk of eccentric residual jets if the clip captures non‑opposite segments, making the PML’s segmental architecturea vulnerability.
Final message
Understanding these mitral leaflet segments in TTE, TEE, are crtical if you are doing a mitral valve repair or mitra clip procedure. However, we need not waste much time in delineating these complex mechansims of MR , if you contemplate a definite mitral valve replacement.
Postamble
Can AML have true scallop ?
Yes , but it is abnormal can be observed in 2 to 3 % . (Ref : Muraru D, Cattarina M, Boccalini F, Dal Lin C, Peluso D, Zoppellaro G, Bellu R, Sarais C, Xhyheri B, Iliceto S, Badano LP. Mitral valve anatomy and function: new insights from three-dimensional echocardiography. J Cardiovasc Med (Hagerstown). 2013 Feb;14(2):91-9. )
Dr.S.Venkatesan MD 