Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Heart valve – Having rigid or semirigid pivoting occluder
Reexamination Certificate
1998-10-02
2001-02-06
Milano, Michael J. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Heart valve
Having rigid or semirigid pivoting occluder
Reexamination Certificate
active
06183511
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to bileaflet hemodynamic heart valve prostheses of the type permitting translational and rotational movement of the leaflets, and particularly to a low-excursion prosthetic heart valve suitable for mitral valve replacement involving preservation of the papillary muscle and chordal structure wherein the valve may be oriented in either an anatomical or anti-anatomical configuration.
BACKGROUND OF THE INVENTION
The replacement of defective heart valves with hemodynamic prostheses is the most prevalent course of treatment for certain types of heart disease and dysfunction affecting the atrioventricular valves—namely the right AV (tricuspid) and the left AV (bicuspid) valves. Although a variety of tissue and prosthetic heart valve mechanisms have been developed, monoleaflet (tilting disc) and bileaflet valves currently hold the greatest measure of acceptance among practitioners. These valves include one or two pivoting leaflets or occluders retained within a seating collar or suture ring that is implanted in place of the physiological valve.
Replacement of a bicuspid (mitral) valve using a procedure that preserves portions of the papillary muscle and chordal apparatus is discussed herein for exemplary purposes. In that procedure, the anterior leaflet is bisected and detached from the annulus, and the two halves are groomed and then sutured to the posterior mitral annulus with the papillary muscle and chordal apparatus substantially intact. Such a procedure and its benefits are described in significant detail by H. Feikes, et al.,
Preservation of All Chordae Tendineae and Papillary Muscle During Mitral Valve Replacement with a Titling Disc Valve,
5 J. Cardiac Surg., No. 2 pp. 81-85 (1990). The authors conclude that this mitral valve replacement procedure can be practical using both monoleaflet and bileaflet valves. However, it is readily apparent to those skilled in reconstructive cardiac surgery that selection of a suitable valve type and proper orientation of the prosthesis can be important factors impacting the long term success of this procedure for a given patient. In particular, due to the position at which the valve tissue is sutured to the posterior mitral annulus, care must be taken to ensure that the peripheral edge of a leaflet does not contact the tissue during normal operation of the valve. Such contact can result in the intermittent, partial, or complete malfunction of the valve, as well as damage to or dislodgement of the valve tissue.
Four primary combinations of valve types and orientation are considered, as diagramed in
FIGS. 25-28
herein. The four combinations ranked by ascending level of risk include: (1) monoleaflet valve M with anterior orientation (FIG.
25
); (2) bileaflet valve with anti-anatomical orientation (FIG.
26
); (3) bileaflet valve with anatomical orientation (FIG.
27
); and (4) monoleaflet valve M with posterior orientation (FIG.
28
). While the monoleaflet with posterior orientation is generally regarded as a high risk configuration and the monoleaflet with anterior orientation is considered to have little or no risk, the degree of risk associated with a bileaflet valve oriented in either the anatomical or anti-anatomical configuration depends upon the particular type of valve selected (particularly its range of excursions, radial exposure, and lateral exposure), the post-procedure anatomical characteristics of the annuls, and the patient's requirement for certain operational parameters associate with the valve.
While a monoleaflet valve may be preferred in order to achieve the lowest risk level with an anterior orientation, a physician may prefer to implant a bileaflet valve to obtain specific functional benefits associated with or unique to the particular bileaflet valve structure.
The bileaflet valve has been extensively developed and refined. However, there is still room for further improvement. Problems associated with the weakening or structural failure of critical components in the valve are linked both to dynamic mechanical stresses and cavitation. It is noted that a certain amount of antegrade and retrograde leakage is generally anticipated. However, the amount of leakage is preferably maintained within acceptable limits corresponding roughly to normal anatomical valves. In addition, minimizing the physical size of the valve prosthesis, particularly the longitudinal dimensions of the annular base, produces greater excursion along the peripheral edges of the leaflets, while simultaneously increasing the difficulty in raising the heights of the pivot axis. Furthermore, recesses, crevices, corners, and obstructions required to restrain the leaflets within the annular base and maintain pivotal movement also interfere with circulation, create turbulence, and produce zones of stagnation, each potentially providing a thrombogenic nidus that may eventually lead to an embolism. Although bileaflet valves are hemodynamic, spacing the fixed axis of rotation of the leaflets significantly apart from the secondary natural axis of rotation limits the maximum speed or angular rate which the leaflets may attain during opening and closing.
In regard to the selection of suitable materials, there is an inherent balancing between the selection of materials for ease of fabrication, biocompatibility, strength, and weight versus selection with respect to the acceptable level of fragility of the resulting components, particularly those involving delicate structures such as wire guides, cages, and pins that bear significant loads. In addition, the structure of many pivot mechanisms requires the annular bases to have opposing flat sides rather than a substantially or completely circular bore, thereby restricting the maximum flow volume and increasing the valve's nominal fluid pressure.
U.S. Pat. No. 4,276,658 to Hanson provides a representative example of a conventional bileaflet heart valve. That valve utilizes a pair of semicircular pivot “ears” disposes on opposing sides of each leaflet received within “hourglass-shaped” slots to control the pivotal movement of the leaflets—including the angular sweep between the open and closed positions, the tiling of the valve away from its restrained pivotal axis, and the translational movement of the leaflet both parallel with its normal plane and along the linear flow path through the bore of the annular base. The Hanson '658 patent also describes the use of a pyrolytic carbon coating over a metallic or synthetic substrate for fabrication of the valve's components.
For comparison, U.S. Pat. Nos. 4,240,161 to Huffstutler and 3,859,668 to Anderson provide representative examples of the features, structure, and operation of monoleaflet or “titling disc” heart valves.
Various improvements directed toward correcting the deficiencies described above have been developed, each achieving varying degrees of success and accompanied by inherent tradeoffs with other beneficial features.
U.S. Pat. No. 3,903,548 to Nakib discloses an effort to utilize the beneficial features of the monoleaflet principle in a bileaflet valve that similarly omits fixed pivotal axis, however the resulting cage structure produces an unacceptably small effective bore and correspondingly high pressure gradient across the valve.
In a bileaflet valve structure such as disclosed in the Hanson '658 patent, the leaflets may each pivot filly between the open and closed portions on the order of 80,000-120,000 times per day given a standard pulse of 60-80 beats per minute. Movement of the leaflets through a viscous aerated fluid such as blood may produce significant cavitation —the formation of partial vacuums caused by sudden movement of the flowing fluid away from the surface of the leaflets as a result of mechanical forces exerted by the leaflets. These partial vacuums produce “micro bubbles” on or near the surface of the leaflets, and when the pressure is released, vacuums change into positive pressure regions which lead to implosion of bubbles which can cause pitting o
Mikhail Adel A.
Patke Nandkishor G.
Stobbs Gene E.
CV Dynamics, Inc.
Milano Michael J.
Moore & Hansen
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