Stent expansion system using a pulsated fluid medium

Abstract: The stent expansion system comprises a balloon catheter (1), which has a portion (8) of its tubular shaft (2) sequentially squeezed between a ram (30) reciprocating in a box (18) and a saddle (36) arranged in a cover (19) closely fitting on the box (18). The pressurised fluid medium supplied to the balloon is pulsated by the squeeze and release action of the ram and saddle arrangement.

Description: This invention relates to a stent expansion system comprising an expandable stent and a balloon catheter to at least help completing expansion of the stent in a body vessel, said balloon catheter with a tubular shaft having proximal and distal portions, a dilatation balloon mounted on the distal portion of the shaft, a fluid supply lumen extending throughout the shaft for ballon inflation, and a pressure source for dispensing to and withdrawing a fluid medium from said ballon via said supply lumen. Balloon catheters are quite currently used for dilating vessels or other body cavities. To this end, the balloon is positioned at the area to be dilated and then fed with a fluid medium to achieve dilatation and thereby expand the vessel. During the treatment, the vessel is occluded by the balloon and the blood supply to the upstream organs is interrupted. A further problem is that some occlusions cannot be dilated because the vessel has achieved a rigidity resisting the dilating pressure executed by the balloon. US Patent 4,439,186 describes a dilatation catheter with an expandable balloon in communication with an inflation lumen extending along the length of the catheter. The balloon has a pressure-volume relationship which is not linear, and a pressure source is provided which supplies a pulsating pressure to the balloon for alternating expansion and contraction thereof. The source of fluctuating pressure comprises a pump supplying a fluid to a container filled with the fluid and which is provided with a flexible bottom connected to the magnetic core of an electromagnet. The container is connected to the dilatation balloon and energizing of the electromagnet causes the magnetic core to move the flexible bottom of the container, thus producing a corresponding pressure pulse or a series of pressure pulses in the fluid within the container. By alternating expansion and contraction of the balloon the blood may circulate during the periods of time during which the vessel is not under action of the balloon. Connection of the container of pressure fluid to the core of an electromagnet requires serious insulation measures in order to avoid any risk of having the patient or other attendant materials in contact with electric current. US Patent 5,152,776 shows a dilatation balloon catheter fed by a pump controlled by a drive mechanism. The actual fluid conditions present in the balloon are identified by a monitor and communicated to a microprocessor sending orders to the drive mechanism in accordance with a predetermined pattern in order to prevent prolonged cessation of blood flow to sites distal from the action. This structure does not allow the feed of any pulsating pressure to the balloon. US 4,446,867 shows a fluid driven balloon catheter comprising a catheter with a through going lumen, a fluid supply inflation device attached to one end of the catheter, and a balloon attached to the other end. A pulse generator is provided for generating pressure pulses in the fluid through the lumen to sharply expand and contract the balloon at intervals. This pulse generator comprises a pulse inflation device communicating with the catheter lumen via a T joint and valve, a spring driven ram to bump upon the piston of the pulse inflation device, and a cam rotor to move the ram away from the piston of the pulse inflation device, whereby when the cam moves the ram away from the piston of the pulse inflation device, the spring of the ram is compressed until the cam rotates further and releases the ram to strike the piston of the pulse inflation device. By this pulse action, it is said that the occlusive material in the vessel, which is more brittle than the surrounding vessel wall will crack. However, the friction of the piston in the pulse inflation device of the pulse generator will substantially damp down the pulse action. Furthermore, the hammer operation of the spring loaded ram may cause non negligible stresses on both the piston and pulse inflation device. The balloon catheter is also an instrument of common use as a mechanism for transporting and applying by expansion a balloon expandable prosthesis, called a stent, for maintaining the patency of a vessel. It is also used for completing the expansion of self-expandable stents which are not transported and applied by a balloon catheter but by a specially devised hollow catheter. Expansion of a stent requires however a relatively high pressure in the balloon, at least for the last stage force needed to seat or press the stent against the vessel wall. High balloon pressures may induce the risk of overpressure causing trauma to the vessel wall; they also induce the risk of bursting the balloon and further wounding the patient. Furthermore, it is difficult to modulate the pressure in the balloon to precisely control the stent expansion and its embedding into the vessel wall. These difficult conditions need a lot of attention for the expansion manipulation, which is an added load for the practitioner. US Patent 5,409,495, which is used as basis for the preamble of claim 1, describes an apparatus for uniformly implanting a stent. This document outlines (col. 1, l. 58 to col. 2, l. 14) that the effectiveness of a stent can be diminished if the stent is not uniformly implanted within a body vessel. And it further explains that balloons having a stent placed upon them tend to have non-uniform radial expansion due to the increased restriction the stent imposes on the working length of the balloon, whereby the balloon expands first at the proximal and distal ends along the path of least resistance, i.e., towards the distal and proximal ends of the balloon, which expands the balloon in a "dog-bone" fashion lacking uniform expansion. Thus, when the balloon expands in this "dog-bone" fashion, the proximal and distal regions of the balloon overexpand, the stent is not expanded uniformly and it may be improperly implanted. Accordingly, to Improve the radial expansion of a catheter balloon used to deliver a stent, there is provided for elastic restraining bands surrounding each of the proximal and distal segments of the balloon to exert a restriction force in response to the resistive force created by the addition of the stent on the balloon. And in order to further control the radial expansion of the balloon, a coaxial elastic sheath or sleeve surrounds and is in contact with the balloon and the restraining bands. There is no suggestion in the documents referred to hereinabove that pulsation of the fluid medium feeding a balloon catheter could be envisaged as a help for stent expansion. Moreover, it has always been considered that a sharp highblow is the way to properly expand and seat a stent in the vessel wall. It is an object of this invention to propose a stent expansion system which is highly versatile, simple to manufacture, and easy to use. A further object of the invention is to propose pulsating means for the fluid medium inflating the balloon of the balloon catheter of the system which are highly versatile and very easy to operate, which are simple to manufacture, and which afford a high degree of safety for the patient. To this effect, the invention complies with the definitions given in the claims. Accordingly, by use of means for pulsating the fluid medium dispensed to the balloon for the stepwise expansion of an expandable stent, the expansion of the stent is achieved by a vibrating strength which causes a succession of very small increments in the radial size of the stent; a better, more uniform and less brutal embedding of the stent in the vessel wall is obtained; the trauma to the vessel wall is reduced and the fluid pressure may be substantially lower than usual. With the means for pulsating the fluid medium squeezing the squeeze region of the tubular shaft of the balloon catheter, the pulsation is obtained by action external to the fluid medium, there is no damping of the pulse action, and there is no need for additional fluid containers to be acted upon by electrical equipment. And the means pulsating the fluid medium sequentially squeeze and release the tubular shaft without affecting or being affected by the undamped pulse action. The squeeze region of the tubular shaft of the balloon catheter in the vicinity of its proximal portion may be a first region having a first softness. The tubular shaft may then comprise a second region distal of said first region and having a second softness, with the first softness being greater than the second softness. The means for pulsating the fluid medium squeezes the tubular shaft in said first region. A squeeze region is thus created in the tubular shaft which has characteristics different from those of the other portions of the tubular shaft which may thus retain its original characteristics of flexibility, pushability and resistance to kinking. Where the tubular shaft of the balloon catheter comprises a third region proximal of said first region and having a softness smaller than that of the first region, the system may be made on the basis of standard catheter elements in which only the first portion has the required softer condition. To further take advantage of standard catheter elements, the second and third regions may have the same softness. And when the first region of the tubular shaft is detachable, the system may be achieved on the basis of a standard catheter shaft with a squeeze portion which may be selected at will, in view of the pulsating conditions which are sought. Where the system comprises saddle means for bearing a portion of the catheter shaft and ram means for squeezing said portion of the tubular shaft against the saddle means, such a system constitutes a fully independent pulsating equipment for the fluid medium feeding the balloon catheter. There are no stresses on equipment components and no added fluid containers to obtain the pulsation. The balloon catheter may be handled separately for sterilisation purposes and the person manipulating the catheter may proceed with sterilised gloves, without handling the squeezing means which may be operated by another person. Where the system comprises means for reciprocating the ram means towards and away from the saddle means, a very simple mechanisation may be achieved, preferably by means of motor driven cam means. The latter allows easy and rapid change of the pulsation by mere variation of the motor speed or change of the cam means. The system may comprise groove means for positioning the shaft with respect to the ram and saddle means, whereby a very simple and fail proof locating of the shaft. The system may comprise box means containing one of said saddle means and ram means, cover means for containing the other of said saddle and ram means, and means for positioning said cover means on said box means, with the possibility of having means for locking the cover means on the box means. This results in a closed, self-contained, error proof unit which can be permanently placed in an appropriate location of the operating room or which can be brought in any convenient place in the operating room to be available upon need of pulsating the fluid medium in a balloon catheter. These and other objects of the invention will become readily apparent from the following detailed description with reference to the accompanying drawings which show, diagrammatically and by way of example only, one embodiment illustrating the invention. Figure 1 is a partly cut upper plan view of a stent expansion system and pulsating machine. Figure 2 is a part section according to line II-II of Figure 1. Figure 3 is a part section according to line III-III of Figure 1. The stent expansion system shown in Figures 1 to 3 comprises a balloon catheter 1 with a tubular shaft 2 having proximal and distal portions 3 and 4 respectively. A dilatation balloon 5 is mounted on the distal portion 4 of shaft 2, i.a. for expanding an expandable stent 6. A fluid supply lumen 7, visible on Figure 3, extends throughout the shaft 2 and this fluid supply lumen is fed by a pressure source (inflation device 14) for dispensing to and withdrawing from the balloon a fluid medium. In the vicinity of its proximal portion 3, the catheter shaft 2 comprises a first region 8 having a first softness and a second region 9 distal of first region 8 and having a second softness, with the softness of first region 8 being greater than the softness of second region 9. The first region 8 is formed by a piece of catheter shaft 10 detachably connected, via standard shaft connectors 11, between the second region 9 of the catheter shaft and a third region 12 of the catheter shaft proximal of the first region 8, said third region 12 having, preferably, a softness smaller than the softness of first region 8. In order to be made of the same catheter material, the second and third regions 9 and 12 may have the same softness. The proximal end 13 of the tubular shaft 2 is connected to the inflation device 14 for feeding the balloon 5 with a fluid medium under pressure. The first region 8 of the tubular shaft 2 and the connectors 11 are respectively located in the positioning grooves 15 and 16 of a machine 17 for pulsating the fluid medium inflating the balloon 5 of balloon catheter 1. This machine comprises a box 18 in which are arranged the grooves 15 and 16 and a cover 19 pivotally mounted as shown by pivots 20. The cover comprises two pivotal handles 21 having each a lock 22 adapted to fit in a catch 23 devised in box 18 for rapid and precise closure of cover 19 over box 18. Inside the box 18 is arranged an electrical rotary motor 24 connected to a source of power such as, for instance, a rechargeable battery 25 also located inside the box 18. Rotation of the motor 24 is controlled by a regulator 33 the control knob 34 of which is located on a lateral wall of box 18. Motor 24 drives a shaft 26 the end of which comprises a flat portion 27 for driving an eccentric-wheel or cam 28 mounted thereon and secured by a nut 29 screwed on the end of shaft 26. Eccentric wheel 28 drives a ram 30 mounted for reciprocal motion in a vertical groove 31 arranged in the upper wall 32 of box 18. Vertical groove 31 opens into an enlargement 35 in which extends the top 35 of ram 30. The enlargement 35 of vertical groove 31 opens into groove 15. The cover 19 comprises positioning grooves 36 and 37 respectively corresponding to and facing positioning grooves 15 and 16 devised in box 18 for positioning the first region 8 and connectors 11 of the tubular shaft 2. By this arrangement, top 35 of ram 30 faces groove 36 of cover 19 which may act as a saddle for the first region 8 of tubular shaft 2 when the latter is positioned into grooves 15 and 36 of box 18 and cover 19, with cover 19 abated on box 18 and locked thereon by locks and catches 22 and 23. Operation of this material may be as follows : the balloon catheter 1 with its shaft 2 and the inflation device 14, which are totally independant from the machine 17, may be sterilized and handled by an operator wearing sterilised gloves, whereas the machine 17, including handling of cover 19 and control of motor 24, may be handled by another operator. When the catheter shaft is positioned into grooves 15 and 36, respectively 16 and 37, of box 18 and cover 19, the motor 24 may be energized to rotate the cam or eccentric-wheel 28 which reciprocates ram 30 the top 35 of which consequently squeezes and relaxes the first region 8 of tubular shaft 2 against and from the saddle or groove 36. When the inflation device 14 feeds the balloon 5 with fluid under pressure, there is a base pressure within the tubular shaft 2 and balloon 5. Hence, squeeze and release of the catheter shaft by ram 30 and saddle 36 create an overpressure in the catheter shaft followed by a return to base pressure, thereby pulsating the fluid medium. Frequency of the pulsating condition may be adjusted by varying the speed of rotation of motor 24 via regulator 33. Variants can be envisaged : for example, the two handle locking of cover 19 on box 18 may be replaced by a one handle locking. The motor 24 may be energised by direct connection to the mains. The inflation device 14 may be replaced by a motorised pump. The system may be used for vessel dilatation, i.e., without stent expansion; similarly, the machine 17 may be used for pulsating the fluid medium inflating the balloon for stenosis dilatation, not necessarily followed by a stent deployment. Depending on the characteristics of the tubular shaft 2, it may be possible to avoid the three region arrangement described; similarly, the first region 8 may be extended up to the inflation device 14, thereby avoiding use of the third region 12. Of course, the technology herein described also fully applies to self-expandable stents which are not delivered by a balloon catheter but by a specifically devised hollow catheter from which the stent is extruded for self-expansion; with such a kind of stents, an additional balloon expansion is currently performed to complete or help completing the embedding of the stent in the vessel.

Claims: A stent expansion system comprising an expandable stent (6) and a balloon catheter (1) to at least help completing expansion of the stent in a body vessel, said balloon catheter with a tubular shaft (2) having proximal and distal portions (3,4), a dilatation balloon (5) mounted on the distal portion of the shaft, a fluid supply lumen (7) extending throughout the shaft for ballon inflation, and a pressure source (14) for dispensing to and withdrawing a fluid medium from said ballon via said fluid supply lumen, characterized by a squeeze region (8) in the vicinity of said proximal portion (3) of the shaft (2), and squeeze means (30, 36) to sequentially squeeze and release said squeeze region (8) for pulsating the fluid medium dispensed to the balloon to stepwise expand the stent. A system according to claim 1, wherein the squeeze region (8) of the tubular shaft (2) in the vicinity of its proximal portion (3) is a first region having a first softness and wherein the tubular shaft (2) comprises a second region (9) distal of said first region and having a second softness, wherein said first softness is greater than said second softness. A system according to claim 2, wherein the tubular shaft (2) comprises a third region (12) proximal of said first region (8) and said third region has a softness smaller than that of the first region. A system according to claim 3, wherein the second and third regions (9, 12) have the same softness. A system according to any of claims 1 to 4, wherein the first region (8) of the catheter shaft (2) is detachable. A system according to any of claims 1 to 5, wherein the squeeze means comprises saddle means (36) for bearing said first region (8) of said shaft (2) and ram means (30) for squeezing said first region (8) of the shaft (2) against the saddle means (36). A system according to claim 6, further comprising means for reciprocating said ram means (30) towards and away from said saddle means (36). A system according to claim 7, said reciprocating means comprising motor (24) driven cam means (28). A system according to any of claims 6 to 8, further comprising groove means (15, 16) for positioning said first region (8) of the shaft (2) with respect to the ram means (30) and saddle means (36). A system according to any of claims 6 to 9, further comprising box means (18) for containing said saddle means (36) or ram means (30), cover means (19) for containing said ram means (30) or said saddle means (36) respectively, and means (20) for positioning said cover means (19) on said box means (18). A system according to claim 10, further comprising means (22, 23) for locking said cover means (19) on said box means (18).

Inventors: ANDREA MARTIN, PERRINS JOHN DR MED, ANDREA, MARTIN, PERRINS, JOHN, DR. MED.
Applicants: SCHNEIDER EUROP GMBH, SCHNEIDER (EUROPE) GMBH
Application year: 1995
Main classification: A61F2
IPC codes: A61M25, A61F2