THE DRAWINGS
FIG. 1 is a schematic longitudinal section of a prior art device, the Jarvik 2000 heart, implanted into the apex of the left ventricle.
FIG. 2 is a schematic illustration of a prior art hybrid blood pump implanted into the apex of the left ventricle.
FIG. 3 is a schematic illustration of a prior art partially magnetically suspended blood pump implanted into the apex of the left ventricle.
FIG. 4 is a schematic longitudinal section of a prior art device, having a magnetically and hydrodynamically supported rotor, which is implanted at the apex of the left ventricle in essentially the same way as the pump illustrated in FIG. 2.
FIG. 5 is an illustration of a Jarvik 2000 heart with a smooth outer surface showing the formation of thick thrombus surrounding it.
FIG. 6 is a longitudinal section of the wall structure and coating of the preferred embodiment of the present invention also shown in FIG. 8.
FIG. 7 is an enlarged detail of a portion of the device of FIG. 6.
FIG. 8 is an illustration of the device of the present invention fitted in place over the housing of an intraventricular blood pump.
FIG. 9 is an illustration of the textured conforming shell affixed onto a Jarvik 2000 heart and implanted into the apex of the heart.
FIG. 10 is a sectional view of the blank which is used to fabricate preferred embodiment of the present invention showing the material that is removed by machining and the material remaining which comprises the wall of the finished shell.
FIG. 11 is an enlarged longitudinal section of a portion of the end of the blank of FIG. 10, after coating with microspheres.
FIG. 11A is a section of a portion of the finished textured conforming shell after final machining.
FIG. 12 is an illustration showing the material of the blank that is removed by machining to obtain the finished textured shell.
SPECIFIC DESCRIPTION OF THE INVENTION
The present invention provides a thin wall “shell” which surrounds a ventricular assist device implanted in the heart. The assist device may be implanted into any of the four chambers of the natural heart. The most common position used in present clinical practice is the left ventricle, as illustrated in FIG. 1, from the prior art. An intraventricular axial flow pump 2 is positioned in the left ventricle and is implanted through a hole in the wall of the left ventricle 4, typically cut with a special instrument called a coring knife. The axial pump includes a rotor 6, supported on bearings 8, 10. The rotor supports impeller blades 12, 14. The armature of a motor, 16, receives electric power via a cable, 18. Properly timed power pulses induce magnetic fields in the motor armature which apply magnetic force to magnets within the rotor. The blood pumping device may be substantially implanted inside the heart, as in the prior art embodiment of FIG. 1, or it may utilize some elements within the heart and some outside the heart, as illustrated in the prior art invention of FIGS. 2 and 4, where part of the bearing and rotor structure is located within the heart, and part of the pump structure, such as a centrifugal diffuser 20, or a centrifigual pump impeller 22, is located just outside the natural heart.
Referring to the prior art inventions shown in FIGS. 1-4, note that in each case the structure within the ventricular chamber and the structure within the ventricular wall contains precision heat sensitive components, such as motor windings 26, magnets 28, 30, bearing components 8, 10, 32 and thin walled metal housing components 36, 38, which would be subject to warping if placed in a very hot furnace.
Blood pumps of this general configuration can be manufactured to high precision using standard machining methods with proper coolant. FIG. 5 illustrates a problem which may occur in some patients with devices having a smooth highly polished surface. The intraventricular housing of an axial blood pump 42, is in contact with the cut wall of the ventricle 46, at position 44, which represents the circumference of a hole cut through the ventricle, into which the pump has been inserted, and affixed via sewing cuff 48, using sutures 50, 52. The inner lining of the heart, called the endocardium, is generally indicated by dotted lines 54, 56. A large circumferential thrombus, 58, 60, surrounds the blood pump housing 42. Typically, this type of thrombus can first form in the crevice at the cut junction of the myocardium 44, where the freshly cut heart tissue acts as a stimulus to clotting, due to release of substances known as tissue thromboplastins. After initial formation of the thrombus in the crevice it may enlarge to become a large thrombus, as shown at 58, 60. Motion of the heart causes motion of the device relative to the thrombus which stimulates it to enlarge.
FIG. 6 illustrates the device of the present invention, in a cylindrical configuration. The thin wall “shell” 74 is a simple tube coated with sintered titanium microspheres, 76. This is better seen in the enlarged illustration FIG. 7, where the wall of blood pump housing, 42, has also been shown in longitudinal section. At the end of the textured shell that makes the junction to the smooth surface of the blood pump housing 66, the thin wall of the shell has a radius on the edge which is coated with microspheres. This is better seen in FIG. 11 where the radius 78 on the end of the tube is enlarged. Refering to FIG. 8, the textured microsphere coating 62, extends directly against the smooth polished surface 42 of the blood pump housing.
FIG. 9 illustrates a blood pump surrounded by a textured “shell” 62 after implantation into a heart and formation of a layer of neo-intima 64, over the textured portion of the “shell”. This neo-intima contains cells which grow into the spaces within the textured surface, and attach a surface layer of living tissue firmly to the device. The neo-intima makes contact with the endocardium at the cellular level and this living lining develops an endothelial cell surface which prevents blood clots from forming and growing to a large mass as shown in FIG. 5, at 58, 60. In the preferred embodiment, the textured shell does not cover the entire outer surface of the device, but ends at a position generally indicated at 66, in FIGS. 8 and 9. The exposed end of the blood pump housing 42, as seen in FIG. 8, is a smooth highly polished surface. The neointemal tissue which grows into the textured surface covers only the textured surface. It stops at the junction of the textured to the smooth surface 66.
The portion of the myocardium in contact with the textured surface 72, in FIG. 9, forms connective tissue in growth into the spaces within the surface that further helps anchor the device to the natural heart tissue.
FIG. 10 illustrates the method of manufacture of the preferred embodiment of the invention. A titanium alloy blank, 82, is machined with an outer diameter approximately 0.010-0.015″ greater than the outer diameter of the blood pump housing, over which it will be fitted. A pilot hole 84 may be used in the blank to facilitate machining after coating and sintering of the microspheres. The edge of the blank has a machined radius, approximately equal to the wall thickness of the completed “shell”. The dotted line 86, in FIGS. 10 & 11 indicates the final amount of material which will comprise the “shell” thickness after finish machining. FIG. 11A shows a longitudinal section of the finished shell. FIG. 12 shows the portion of the blank (in dotted lines 88) which must be removed by machining to obtain the finished device.
Typically, the blank has a thick wall section or is solid, so when this is placed in the furnace at high temperature to sinter the microspheres, negligible warping occurs. The final machining is done with a very clean filtered coolant, so that the pores between the microspheres remain extremely clean. The machining process is also carefully controlled to prevent heating sufficient to warp the finished part. Even if slight warping occurs, when the shell is placed over the pump housing, as seen in FIG. 8, it conforms to the cylindrical shape of the blood pump housing. The textured “shell” is manufactured with a tight slip fit if it is to be welded to the pump housing. This may be accomplished without damage to the pump motor inside the pump housing, by heat sinking, and by using small spot laser welds. By making the surface coating on the blank (82) relatively thick, such as 0.015-0.025″ thick, it becomes strong enough that the machining process may remove the entire blank in which case the entire “textured shell” is comprised only of sintered microspheres.
The structure of the present invention described above is feasible to manufacture by the method described, and when affixed to the surface of a ventricular assist device, by welding or by another suitable method, produces a blood pump substantially similar to the device that could be obtained if a very low temperature sintering method existed, which allowed the finished precision blood pump to be coated directly. Since no sufficiently low temperature sintering process exists, it can be seen that the present invention discloses an original and important structure to improve the performance of mechanical cardiac assist devices.
The information disclosed in the description of the present invention is intended to be representative of the principles I have described. It will thus be seen that the objects of the invention set forth above and those made apparent from the preceding description are efficiently obtained and that certain changes may be made in the above articles and constructions without departing from the scope of the invention. It is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative but not in a limiting sense. It is also understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall there between.
Patent Application
20070299297
