Patent Application
20080021546
Features and advantages of the present invention will become appreciated as the same become better understood with reference to the specification, claims, and appended drawings wherein:
The present invention provides an improved system and method for deploying plastically-expandable prosthetic heart valves so that they assume their intended operating shape. Expandable heart valves have outer frames or stents supporting inner flexible leaflets that provide fluid occluding surfaces. The valves are designed to expand from a compressed state for delivery into an operating shape that ensures good coaptation of the leaflets. That is, the leaflets must come together to prevent backflow or regurgitation of blood, and any misalignment of the deployed stent can compromise the efficacy of the valve. Most expandable prosthetic heart valves have stents that assume substantially the tubular operating shapes, although other final shapes are encompassed by the present invention.
The invention described herein provides a solution that ensures proper deployment of “plastically-expandable” prosthetic heart valves. This term encompasses balloon-expandable prosthetic heart valves, but should not be considered limited to those expanded only with balloons. Although balloons are the accepted method for expansion of such heart valves, other deployment mechanisms such as radially expandable mechanical fingers or other such devices could be used. In this sense, therefore, “plastically-expandable” refers to the material of the frame of the heart valve, which undergoes plastic deformation from one size to a larger size. Examples of plastically-expandable frame materials are stainless steel, Elgiloy (an alloy primarily composed of cobalt, chromium and nickel), titanium alloys, and other specialty metals. For the sake of convention, however, the term “balloon-expandable” prosthetic heart valves will be used primarily herein, but such should be considered to represent “plastically-expandable” heart valves.
The invention accommodates valves of non-constant expansion resistance. That is, the construction details of balloon-expandable prosthetic heart valves are such that one end, typically the inflow end, possesses a greater number of structural components, including stitching. The valves are mounted over an expansion balloon, delivered to the implant site, and the balloon inflated. Because of the axial constructional non-uniformity of most valves, expansion of the balloon will cause more or sooner radial expansion at whichever part of the valve presents the least expansion resistance. Typically, the inflow end presents greater resistance to expansion, resulting in the outflow end being expanded more or faster. The present invention provides a number of differently shaped balloons to accommodate this constructional non-uniformity, so that the valve expands to its designed operational shape. The final shape of the valve stent may be tubular, but it could also be slightly conical or have a non-linear profile. Those of skill in the art will understand that, given the valve properties and desired final shape, an appropriate expansion member (balloon) can be selected for any number of valves.
In the exemplary valve 20, the flexible material forming the leaflets 28 attaches to the outer stent 28 via a fabric intermediary 30 and a plurality of sutures 32. With reference to
As can appreciated by the drawings, the bulk of the attachment structure between the outer stent 26 and inner leaflets 28 is located close to the inflow end 22. Each one of the leaflets 28 desirably connects along an arcuate line between two points at the outflow end 24. This arcuate line passes close to the inflow end 22, and thus the need for more sutures and that end. As a result, the valve 20 has a nonuniform expansion profile. More particularly, the inflow end 22 of the valve 20 exerts substantially greater resistance to expansion on a balloon inflated from within than the outflow end 24. A cylindrical balloon inflated from within the valve 20 with thus expand faster or farther at the outflow end 24 that the inflow end 22, because the outflow and presents the path of least resistance.
At this point, it is important to emphasize that the exemplary heart valve 20 is representative of balloon-expandable heart valves that have non-uniform expansion resistance profiles along their axial lengths. In the illustrated embodiment, the valve 20 is stiffer near its inflow end 22 than its outflow end 24. However, other the valves might include an outer frame and an inner valve or leaflet structure which is mounted near the outflow end of the frame, so as to be accordingly stiffer near its outflow end. The term that encompasses these different constructions and other valves is “valves having non-uniform expansion resistance profiles along their axial lengths.”
A schematic illustration of this non-uniform valve expansion is seen in
At the implant location, the balloon 40 inflates to deploy the valve 20.
As mentioned above, the present invention provides differently-shaped expansion members or balloons to ensure designed expansion of prosthetic heart valves. As mentioned above, balloons are almost universally used to deploy expandable heart valves. However, is conceivable that a mechanical expansion member such as elongated fingers or hydraulically operated expanding members (i.e., not balloons) could be utilized. Therefore, the term expansion members is intended to encompass balloons and other variants.
In
It is important to note that the terms “proximal and distal” in terms of the balloon tapers is dependent on the direction of heart valve delivery into the annulus, because the heart valve leading end and thus balloon orientation on the catheter will be reversed in a heart valve replacement procedure that begins in a femoral artery as compared to a procedure that enters through the apex of the left ventricle. The balloon 50 of
For example, the expandable heart valve 20 described above is positioned in its expanded state around the deflated balloon 50. The marker bands 64 are used to position the valve axially on the balloon 54 for proper inflation. Because of the non-uniform expansion profile of the balloon 50, the axial position of the valve 20 is most important to ensure that the portions of the balloon that are capable of applying the largest initial radially outward force are in registry with the stiffer areas of the valve. In particular, the valve 20 is positioned on the balloon 50 such that its inflow end 22 is closer to the first shoulder 60, and its outflow end 24 is closer to the second shoulder 62. Subsequently, the prosthetic valve 20 is crimped around the balloon 50 so as to be ready for delivery into the body and advancement to the target implantation site. When the balloon 50 inflates, the first shoulder 60 initially expands faster and ultimately farther than the second shoulder 62, thus compensating for the increased resistance to expansion of the prosthetic heart valve 20 and its inflow end 22. By careful calculation of the non-uniform resistance of the prosthetic heart valve to expansion, the tapered balloon 50 can be chosen so that the valve expands to its full diameter and proper operational shape (typically a cylinder or a shallow frusto-conical shape).
Finally,
As will be appreciated by those of skill in the art, the specific shape of the expansion member/balloons described herein will differ depending on the valve construction. Using the exemplary prosthetic heart valve 20, the diameter of the largest part of the balloon that contacts the stiffest portion (e.g., inflow end) of the valve should be greater than the smallest part that contacts the more flexible portion (e.g., outflow end) of the valve. For example, the proximal section 92 in
The various markers or marker bands disclosed in
In a typical operational sequence, a prosthetic heart valve having biological tissue thereon is packaged in a separate sterile container from the balloon. In the operating room, the valve and balloon are conjoined for implantation. This procedure requires careful positioning of the valve in its expanded state around the balloon, and crimping of the valve onto the balloon to a predetermined maximum diameter. The marker bands described above therefore greatly facilitate the step of positioning the valve over the balloon to ensure proper expansion. The valve and balloon combination is then inserted into the body and advanced to the target implantation site. The path of delivery may be a relatively long percutaneous route, or may be substantially shorter through a direct-access port or channel in the chest. It is even contemplated that conventional open-heart surgery utilizing cardiopulmonary bypass may benefit from deploying expandable valves by reducing the procedure time.
An alternative use of the present invention is to plastically-expand a prosthetic heart valve that has been partially deployed at the target implantation site. Some self-expanding prosthetic heart valves require further balloon expansion to plastically deform their support frames and ensure proper engagement with the surrounding tissue. The invention therefore encompasses final plastic deformation of initially elastically-expandable frames. In another situation, a purely plastically-expandable heart valve may be partially expanded by a first balloon, and then a second balloon used to completely expand it into its final implant state. In this type of procedure, the marker bands described above are essential to position the non-uniform balloon within the partially deployed valve.
Conventional balloons used to deploy prosthetic heart valves are made of clear nylon. Nylon balloons have a maximum expansion diameter which is important to avoid over-inflation and rupture. In the prior art the inflation fluid consists of a mixture of saline and a contrast media, typically a viscous semi-radiopaque liquid. The inherent viscosity of this fluid increases the inflation/deflation time of the balloon, which is detrimental because the balloon can occlude the aortic annulus for long periods of time.
The present invention provides inflation balloons that are doped with a radiopaque material. The doping is typically performed prior to balloon extrusion to ensure uniform distribution of the doping agent. Consequently, because the balloon itself is radiopaque, saline can be used to inflate it without addition of a viscous contrast media. Because of the lower viscosity of saline, the inflation/deflation time is greatly reduced.
While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description and not of limitation. Therefore, changes may be made within the appended claims without departing from the true scope of the invention.
