Introduction
When bileaflet mechanical mitral valves (MMVs) were first introduced in
the 1970s, it seemed intuitive to position them in an anatomical
orientation in an attempt to imitate nature1. However,
in the early 1980s, cases of early valve thrombosis were
observed1. Imaging studies suggested that these
thrombotic complications were due to a restricted excursion of the
posterior occluder and resultant stagnation of blood
flow2,3. This phenomenon, coined as the “lazy”
leaflet1, was found to be avoided with anti-anatomical
implantation1. This historical observation shaped the
standard implantation technique, but practice variation in leaflet
orientation persists. Some new-generation MMVs, such as the On-X valve
(On-X Life Technologies, Austin, Texas), benefit from a rotatable cuff
design, but it is unclear if they are susceptible to asymmetric occluder
mobility in the anatomical plane. Valve manufacturers typically endorse
anti-anatomical implantation, although it is not formulated as a strong
recommendation.