Is Mitral Valve Hinge Motion Important for Leaflet Closure?
Akinobu Itoh1, Daniel B. Ennis1, Wolfgang Bothe1, Julia C. Swanson1, Gaurav Krishnamurthy1, Tom C. Nguyen1, Neil B. Ingels2, D. Craig Miller1; 1Cardiothoracic Surgery, Stanford University, Stanford, CA; 2Palo Alto Medical Foundation, Palo Alto, CA
Comment on this Abstract
Objective: The mitral annulus (MA) is composed of 2 different structures: The fibrous annulus contiguous with the aortic root, and the muscular annulus subtending the commissures and posterior leaflet. 3-D echocardiographic studies have demonstrated that the MA is saddle-shaped and becomes flattened and dilated in humans with functional mitral regurgitation (FMR). The contribution of saddle-shape configuration change to leaflet closure and coaptation throughout the cardiac cycle, however, is unknown.
Methods: Five sheep had a dense array of 18 radiopaque markers implanted(16 around the MA and 2 on the middle of the anterior and posterior leaflet free edges). 4-D marker coordinates were acquired with biplane videofluoroscopy at 60Hz. The mitral “hinge angle”(Φ) was calculated as the angle between the best fit planes through the fibrous and muscular annular markers (Fig). MA area (MAA) and coaptation distance between mid-edge markers (D) were computed at early-filling (E, 50 msec after end-isovolumic relaxation), end-diastole (ED), end-isovolumic contraction (EndIVC) and end-systole (ES), and reported as mean±SD.
Results: Minimum Φ(annulus flattest) occurred during late-diastole (47±11o), but increased abruptly (more saddle-shaped) during early-systole (ED vs. EndIVC, 46±11o vs. 61±14o, P=0.003), where it remained during ejection (EndIVC vs. ES, 61±14o vs. 63±14o, P=0.1). After ES, Φ decreased again (e.g. a flatter annulus). Paralleling the changes in Φ, maxima during diastole and minima during early-systole were observed for both MAA (E vs. EndIVC, 9.1±1.5 vs. 7.8±1.0cm2, P=0.01) and D (1.5±0.6 vs. 0.4±0.2cm, P=0.04). During ejection, MAA (EndIVC vs. ES, 7.8±1.0 vs. 7.6±1.1cm2, P=0.1) and D (0.4±0.2 vs. 0.3±0.2cm, P=0.2) did not change, but increased rapidly during early-diastole (Fig).
Conclusion: The mitral hinge angle (Φ) changes more than 14o during the cardiac cycle in concert temporally with changes in MAA and D. The hinge angle reflects the interactions between the muscular annulus, fibrous annulus, and aortic root. A steeper hinge angle may contribute to pre-systolic annular area reduction and rapid leaflet closure, which enhance valve competency. Rigid, complete annuloplasty rings would abolish any such hinge angle motion. Further quantification of hinge angle dynamics in patients with mitral valve prolapse and FMR both before and after repair will shed light on how important this intrinsic motion is and aid in the design of new annuloplasty devices.
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