Comment
This case illustrates that the phenomenon of the “lazy” posterior leaflet, originally described in the 1980s, still occurs with new-generation MMVs, revealing the importance of maintaining anti-anatomical orientation. One of the characteristics of the On-X valves is the ability to rotate the sewing ring in situ during implantation. While this feature can be used more arbitrarily in the aortic position, it creates the risk of overlooking careful anti-anatomical orientation in the mitral position.
Two observations suggest that the phenomenon of the “lazy” leaflet is intrinsically related to the heterogeneous distribution of the blood flow dynamics in the left ventricular cavity. First, this phenomenon typically involves the posterior leaflet1. Second, as seen in our case, it can occur with newer MMV models, despite their improved physical profiles and features. Under physiological conditions, the diastolic flow acquires a laminar pattern and enters the left ventricle mostly through the posterior portion of the mitral inflow tract4. However, in systole, the twisting motion of the contracting heart produces a spiral ejection flow that travels preferentially in the anterior area, corresponding to the anterior leaflet4. This, perhaps, underlines one of the roles of the asymmetrical structure of the native mitral valve, which is lost with the symmetrical design of bileaflet MMVs. Furthermore, in our patient, the restricted excursion of the posterior leaflet only became apparent later, probably from the changes of the flow states after weaning from CPB. This observation is in keeping with prior studies that reported further exacerbation of the posterior leaflet restriction in low cardiac output states2.
Mitral valve replacement comes with several technical challenges. The main one centers on finding the right balance between preservation and debridement. Maintaining the subvalvular apparatus helps retain left ventricular geometry, but leaving excess native tissue risks inadequate fitting of the prosthesis into the annulus and leaflet immobilization. It should also be kept in mind that any prosthetic valve orientation comes with inherent risks of impingement. Because of the geometry of the left ventricle, the closest structure to the valve annulus is usually the posterior left ventricular wall. In bileaflet MMVs, since the leaflets arc into the ventricle, their excursion becomes limited at different points of the arc depending on the valve orientation. In the anatomic orientation, the greatest risk for interference is at the leading edge of the leaflet when it is nearly closed5. With the valve oriented in anti-anatomical orientation, the interference occurs with the leaflet fully open5.
This case also highlights how careful evaluation of leaflet mobility is key to identify the presence of prosthetic dysfunction. Repeated careful TEE examinations, effective team communication and interdisciplinary collaboration are all essential components of the safety culture in cardiac surgery.