Patent Application
20070225757
The present invention relates generally to a medical device for closing an opening or defect in an organ within a living body, e.g. a septal defect in a heart or a percutaneous puncture in a vessel wall, and in particular to an expandable and repositionable closure device, which can be remotely maneuvered from an initial positioning configuration to a final configuration in which the opening or defect is closed.
The closing of an opening in an organ of a patient is a medical procedure that frequently has to be practised by doctors or other trained medical personnel. The opening may be a hole created by the doctor for a specific and usually temporary purpose, or the opening can be a congenital or acquired defect. An example of the former would be a puncture hole created in a patient's femoral artery to obtain access to the coronary system, while an example of the latter is a septal defect in a patient's heart. For descriptive and illustrative purposes the present invention will be described with reference to such a septal defect, although such techniques can be applied to other fields of application, such as walls in arteries or other blood vessels.
As is well-known, the human heart is divided into four chambers: the left atrium, the right atrium, the left ventricle, and the right ventricle. The atria are separated from each other by the interatrial septum, and the ventricles are separated by the interventricular septum.
Either congenitally or by acquisition, abnormal openings or holes can form between the chambers of the heart, causing shunting of blood through the opening or hole. For example, with an atrial septal defect, blood is shunted from the left atrium to the right atrium, which produces an over-load of the right side of the heart. In addition to left-to-right shunts such as occur in patent ductus arteriosus from the aorta to the pulmonary artery, the left side of the heart has to work harder because some of the blood will recirculate through the lungs instead of going to the rest of the body. The ill effects of such lesions usually cause added strain on the heart with ultimate failure if not corrected.
One way to cure a septal defect in the septum of a heart is to position and anchor a specially designed closure device at the septum such that both sides of the septal defect are spanned by the closure device to thereby close the defect. Examples of such septal defect closure devices are known from the U.S. Pat. Nos. 5,853,422; 6,024,756; 6,117,159 and 6,312,446 to Huebsch et al., which disclose a closure device comprising a cylindrical shaft of metal or polymeric material with concentric parallel cuts through the wall of the device to thereby create flattened support struts. The centers of the support struts are intended to move radially away from the longitudinal axis of the device in a hinge like fashion in response to movements of the proximal and distal ends of the device towards the centre thereof. A special feature of the known septal defect closure device is that it is of a unitary construction.
A similar septal defect closure device is also disclosed in the international application WO 2005/006990 A2.
One general object of the present invention is to improve a closure device of the aforementioned type in such a way that a more reliable and versatile device is obtained, which more easily can be adapted to the special characteristics of individual patients as well as individual openings, e.g. septal defects or puncture holes.
According to the present invention, a septal defect closure device comprises an elongated tubular member in which a first set of longitudinal slits or cuts has been made on a first side of a shorter uncut central portion and a second set of longitudinal slits or cuts has been made on the opposite side of the central portion. On each side of the central portion, the slits extend towards the ends of the tubular member to terminate a short distance before the respective end, such that uncut proximal and distal end portions are formed. The tubular member, which is made from a flexible and preferably resorbable material, has thereby been provided with proximal and distal sets of struts or ribs. The distal ends of the distal struts are flexibly connected to the distal end portion of the tubular member, while the proximal ends of the distal struts are flexibly connected to the central portion. Similarly, the proximal ends of the proximal struts are flexibly connected to the proximal end portion of the tubular member, while the distal ends of the proximal struts are flexibly connected to the central portion. The struts are further each provided with a weakened section, which can act as a hinge, such that each strut in effect is divided into two articulated arms.
When the septal defect closure device during use is compressed such that the distal and proximal end portions are forced towards each other, the weakened sections of the struts move radially out from the longitudinal central axis of the closure device, and the respective arms of the struts assume an essentially perpendicular angle to the central axis of the closure device. According to the invention, the septal defect closure device comprises further a central cylindrical locking member, which is separate from the tubular member and which over its length comprises several portions with different diameters. In use, the cylindrical locking member is inserted into the tubular member such that the distal end portion of the tubular member abuts a distal end rim of the locking member, and the proximal end portion of the tubular member is then pushed over a proximal end rim of the locking member. In the compressed state, the central, proximal and distal portions of the tubular member fit snugly over respective portions of the central locking member, and the closure device is held in the compressed state by the enlarged distal and proximal rim portions of the locking member, which prevents the closure device from resuming its original tubular shape.
In an alternative embodiment of the invention, the septal defect closure device comprises two separate slit tubular members, which can slide on a common, separate locking member. In practice, these two separate slit tubular members would thereby correspond to a closure device as already described above, which at its central portion is cut into two separate halves. A three-piece closure device will give a doctor enhanced possibilities to adapt a closure device to a patient's specific requirements.
By providing a locking member which is separate from the slit elongated tubular members, a doctor can easily adapt a septal defect closure device to different septa having different thicknesses by simply selecting a locking member of a suitable length. With a separate locking member a closure device can be easier and cheaper to manufacture. A separate locking member can also be made from a different material than the rest of the closure device, to thereby, for example, match the resorption time of a locking member to the resorption time of a tubular member despite their different dimensions and shapes. In other words, a separate locking member can be regarded as a prerequisite for a more reliable and versatile closure device, which also is easier and cheaper to manufacture and which also allows separate modifications of the tubular member without changing the design of the locking member.
A schematic cross-sectional view of a human heart 1 is shown in
In conjunction with FIGS. 2 to 5, a medical procedure will be briefly described, in which a septal defect closure device according to one embodiment of the present invention is employed to close a septal defect in the septum of a heart; and thereafter different positions and parts of the closure device itself will be described in detail in conjunction with FIGS. 6 to 9.
To ascertain correct positioning of the closure device 10 with respect to the septal defect 12, the distal set of struts can be moved radially outwards from the central axis of the closure device 10, such that a partly expanded configuration is obtained. The radial movements of the distal struts are effectuated by partially compressing the closure device 10 through the maneuvering of a mechanical actuator (not shown in the figures). In this semi-expanded locating configuration, the closure device 10 is retracted until the distal struts abut the distal side of the atrial septum 13 surrounding the septal defect 12. The septal defect 12 can thereby be located by a doctor, who in this phase of the medical procedure will feel a marked increase in resistance against further retraction. This intermediate step of the medical procedure is depicted in
As an alternative or complement, the proximal set of struts can be moved radially outwards from the central axis of the closure device 10, such that another partly expanded configuration is obtained. As before, the radial movements of the proximal struts are accomplished by partially compressing the closure device 10 through the maneuvering of the mechanical actuator mentioned above. In this second semi-expanded locating configuration, the closure device 10 is advanced out of the catheter 11 until the proximal struts abut the proximal side of the atrial septum 13 surrounding the septal defect 12. The septal defect 12 can thereby be located by a doctor who in this phase of the medical procedure will feel a marked increase in resistance against further advancement. This intermediate step of the medical procedure is depicted in
When the atrial septum 13 and thereby the septal defect 12 have been correctly located, either by the step shown in
An embodiment of a septal defect closure device 20 according to the present invention is illustrated in
Here it should be emphasized that the term “tubular” is merely intended to indicate the general shape of an elongated, cylindrical member, which comprises a number of struts, the ends of which are connected to shorter ring-shaped members, and which in a first positioning configuration assumes a tubular shape. In other words, a tubular member, like tubular member 21, does not actually have to be cut or slit in order to create distal and proximal struts. On the contrary, a tubular member, having struts with weakened hinge-sections as well as ring-shaped central, distal and proximal end portions, can advantageously be directly produced in this form, e.g. by injection molding. It can therefore be appreciated that a separate locking member simplifies the manufacture of a closure device of the present type, because, for example, the injection mold can be given a much less elaborated shape.
In
As can be seen in
In
In
Another way to facilitate the adaptation of a septal defect closure device to septa having different thicknesses is to arrange the distal set of struts and the proximal set of struts as two separate members. Such an arrangement would effectively correspond to cutting a tubular member like the tubular member 21 of
The septal defect closure device has been shown with proximal and distal struts having equal lengths. It is, however, possible to provide a closure device having proximal struts with one length and distal struts with a different length. It may, for example, be desirable to arrange a closure device in such a way that the left part of the closure device, i.e. the part that is implanted into the left atrium of a heart, is smaller than the right part of the closure device, to thereby reduce the amount of artificial material introduced into the left atrium, which in turn may reduce the formation of thrombogenic material therein. In this context, it should be recognized that it is not mandatory that a heart is accessed via the venous system, as is shown in FIGS. 2 to 5, but the heart could be accessed via the arterial side. This implies that if a doctor wishes to place a smaller part of a closure device at the left side of a heart than at the right side of the heart, then this smaller part (i.e. the shorter struts) will constitute the distal set of struts if the heart is accessed via the venous system, whereas the smaller part will constitute the proximal set of struts if the heart is accessed through the arterial system. It can therefore be appreciated that it can be advantageous to provide a closure device in the form of two separate tubular members (and a separate locking member) as this would provide a doctor with the possibility to tailor a septal defect closure device to the specific medical situation at hand, without the necessity of producing an excessive large number of closure devices with different dimensions. For example, with only three different strut lengths for a distal tubular member, three different strut lengths for a proximal tubular member, and three different lengths for a locking member, it is possible to obtain twenty-seven (27) different combinations and thereby twenty-seven (27) different closure devices, each suited for a specific medical situation.
It has already been mentioned that the length of the distal struts can differ from the length of the proximal struts; and it is also possible to have different lengths of the articulated arms within a strut set, such that, for example, the distal arms are longer than the proximal arms, or vice versa. The arms that actually contact a septum or a vessel wall can, for example, be shorter than the arms that do not contact the septum or the vessel wall, to thereby ensure a reliable closing of a septal defect in the septum or a puncture hole in the vessel wall.
As already has been stated, a closure device comprising a central locking member that is separate from a tubular member can be regarded as a prerequisite for other advantageous effects. A two-piece closure device is generally easier and thereby cheaper to manufacture. If, for example, the closure device is produced by injection moulding, the moulds—i.e. one mould for the locking member and one mould for the tubular member—can be given comparatively less complicated shapes than if the closure device was to be moulded in a single mould.
It is in particular anticipated that a locking member is made from a first material and that a tubular member is made from a second material, something which in practice may require that the locking member is separate from the tubular member. With different materials some specific advantages can be achieved. If, for example, the closure device is a resorbable closure device, then the resorption time of the material in the locking member can be different from the resorption time of the material in the tubular member, such that the locking force between the two members during the degradation of the closure device is reduced and ultimately lost in a controllable and predictable way. In this respect it may be advantageous if the material of the tubular member has a shorter resorption time than the material of the locking member. Further, whether or not the materials are resorbable materials, different requirements are put on the different pieces. For example, the material in the hinge portions of a tubular member must be flexible and have a high tenacity, whereas the locking member must have a rather high stiffness. Also in a resorbable closure device it can be necessary to have one material in a locking member and another material in a tubular member, because of the different dimensions involved. It can, for example, be necessary to have a material with a relatively long resorption time in the thin hinge portions of the tubular member in order to match the resorption time of the material in a thick-walled locking member.
Examples of resorbable materials for the tubular member and the locking member may include, but are not limited to, those materials made from aliphatic polyesters, polyether esters, and polycarbonates. More specifically, synthetic resorbable polymers such as homopolymers and copolymers made from any of the monomers lactide, glycolide, epsilon-caprolactone, trimethylene carbonate, and paradioxanone are advantageous because of their long clinical use.
The tubular member could preferably be made from a semi-crystalline material with a lower tensile modulus than the locking member. As previously stated, the device could, e.g. because of the hinge portions, have a more flexible material in the tubular member. Such material is preferably made from a block copolymer characterized by having a soft middle part characterized by having a glass transition temperature below room temperature and a semi-crystalline part at each end of the soft middle part. The semi-crystalline part could be polymerized from any of the monomers glycolide, lactide, or paradioxanone. Since polyparadioxanone is a relatively soft and pliable material compared to polyglycolide and polylactide, the tubular member can be made from pure polyparadioxanone itself.
The locking member can be made from any of the above materials, but to secure the locking mechanism it is advantageous if the material is stiffer than the material used in the tubular member. The material should also preferably resorb at a somewhat slower pace than the tubular member. The locking member could also be made from amorphous or semi-crystalline material, and preferably from homopolymers or copolymers where the main monomer component is lactide, caprolactone, or paradioxanone.
A particular advantage of the groups of synthetic resorbable polymers mentioned above is that various mechanical properties can be accomplished by simply changing the monomer composition in the homopolymer or copolymer. Further, in contrast to natural biopolymers, these materials can be molded and machined into complex structures, and by varying the monomer composition large time spans can be achieved for their resorption times.
It may be appreciated that it can be advantageous to provide a radiopaque closure device which is visible in an X-ray machine. When the closure device is made from a synthetic resorbable polymer, a radiopaque closure device can conveniently be produced by mixing the polymer with a suitable radiopaque agent. A suitable radiopaque agent is barium sulfate, which can be blended into the polymer or copolymer in an amount between 5% and 50%, and more preferably in an amount of 15% to 30%, to obtain the opacity needed in order to locate the closure device during an X-ray observation. Radiopaque materials can be used in a tubular member of the closure device, but is preferably used in the locking member, which marks the centre of the device. The radiopaque agent, e.g. barium sulfate, can—instead of being mixed with the polymer—be introduced into preformed holes in the closure device, which are then sealed by a synthetic resorbable material. As an alternative, preformed holes can be plugged with a resorbable material containing a large amount of a radiopaque agent, e.g. barium sulfate.
Other aspects, features, variations, and ways of using the present invention are described in the U.S. Patent Applications and filed under attorney docket numbers 030481/0250 (entitle “Closure Device”); 030481/0254 (entitled “Closure Device”); and 030481/0258 (“Closure Device and Insertion Assembly”) concurrently herewith. The entire contents of these related applications are incorporated herein by reference. Features in these different applications may be combined with each other
Although the present invention has been described with reference to specific embodiments, also shown in the appended drawings, it will be apparent for those skilled in the art that many variations and modifications can be done within the scope of the invention as described in the specification and defined with reference to the claims below. It is possible to have different lengths of the articulated arms within a strut set, such that, for example, the distal arms are longer than the proximal arms, or vice versa. The weakened strut sections discussed above can be replaced with other designs that provide the desired hinge-like action. The hinge action could, for example, be accomplished by real hinges arranged along the struts.
