Patent Application
20070073331
1. Field of the Invention
The invention relates to interventional catheters, and more particularly, a rapid exchange stent delivery catheter.
2. Brief Description of the Related Art
Stent delivery catheters are known in the art. They generally comprise an elongated tubular device having a distal portion that carries a stent for delivery to a site in a patient's vasculature. The stent may be medicated and is used to prop open and support a constricted or otherwise compromised section of the blood vessel, due for example to arterial sclerosis. The stent is delivered in a contracted state so that it can be maneuvered through the vasculature. Once it is at the desired location, it is expanded and decoupled from the catheter. The delivery catheter is then withdrawn.
The delivery catheter is provided with a balloon on which the stent is securely seated during delivery. When the stent reaches its destination, the balloon is inflated, causing the stent to expand in the lumen. The balloon is then deflated so that it disengages from the stent, allowing withdrawal of the catheter.
Stents have many different configurations and sizes, and proper selection of the stent is an integral part of the procedure. Often, the determination of whether a particular stent is suitable can only made after the stent is delivered to the lesion site. Then, if the determination is that the stent is not suitable—for example because it is of the wrong length—then before inflation the stent must be withdrawn and replaced with a different stent. Alternatively, if a stent which is too short is implanted, an additional overlapping stent may be needed. Therefore there is a long-felt need to improve the ability to pre-assess the suitability of a particular stent, before it is expanded. This task is complicated by limitations of imaging technology. In most cases, imaging or visualization of a lesion is compromised by limitations of the viewing angle because the visualization system may not be positioned to provide a direct side view of the vessel. The view in this instance is foreshortened because of the orientation of the visualization system relative to the vessel, making a determination of lesion length even more difficult. This issue is further aggravated when curved vessels are involved, making length determination even more problematic.
The rapid exchange stent delivery catheter itself is designed so that it can be quickly withdrawn and replaced if it is determined that its stent payload is of the wrong configuration for that particular application. As seen in
With reference to
An example of a device having a configuration similar to that described above is the angioplasty-type balloon catheter described in U.S. Pat. No. 5,061,273 (Yock). In the Yock patent, it was recognized that important advantages can accrue from maintaining a transition region associated with the proximal guidewire port of the balloon catheter within the guiding catheter during the angioplasty procedure. The transition region is the region from which the guidewire emerges from the balloon catheter at the proximal guidewire port, and it was found to be important to maintain this region within the guiding catheter during the procedure. Accordingly, the balloon catheter was dimensioned such that the distance between the distal end of the balloon catheter and the transition region and/or the proximal guidewire port was at least 10 cm. However, such a dimension has been found to be problematic for several reasons. For catheters which are designed for stent delivery, the distal portion of the catheter in the vicinity of the balloon and proximal thereof should be simultaneously very flexible to navigate the coronary arteries, have good column strength to provide pushability, and have good kink resistance. By comparison, the remaining, proximal portion of the catheter generally requires good column strength and less flexibility. Flexibility of the distal portion of the catheter is important for maneuverability and deliverability of the catheter. However, flexibility must be balanced so as not to compromise the ability of the catheter to track over the guidewire, or permit bowing or looping of the catheter or other movement of the catheter away from the guidewire, resulting in loss of pushability. Extending the distance between the end of the catheter and the proximal guidewire port detracts from some of these desired characteristics, for example by reducing pushability.
Another issue relating to the flexibility of the distal portion of the catheter is due to the composition of the catheter. Known rapid exchange balloon catheters and over-the-wire balloon catheters are formed by blowing a balloon from a length of suitable tubing, trimming the ends of the tubing close to the balloon and bonding the balloon onto a catheter shaft. However, the bond between the balloon and the shaft at a location close to the balloon proximal end forms a thickened and stiffer portion at a location where high flexibility and trackability are desired.
In accordance with the invention, the afore-mentioned deficiencies in the prior art are addressed by providing a stent delivery balloon catheter including a balloon leg having an extended length so that the bonding junction between the balloon and the catheter shaft is move proximally. In addition, a distance between a proximal guidewire ports and the distal end of the catheter is reduced from traditional rapid exchange catheters to achieve a move rapid termed super rapid exchange. In this manner, pushability of the distal portion of the balloon catheter and trackability over the guidewire are improved, while at the same time more rapid exchanged are possible. Improved pushability of the distal portion of the balloon catheter and trackability over the guidewire, and reduced possibilities of shaft bowing away from the guidewire, or guidewire looping can also be achieved by providing a stiffening wire, having several possible configurations, that extends at least partially along the length of the balloon leg and catheter shaft. In addition, to provide lesion dimension measurements, radiopaque marker bands are provided on the guidewire tube such that a visual frame of reference is available against which lesion measurements can be made in order to assist with proper stent or balloon selection.
The invention of the present application will now be described in more detail with reference to embodiments of the apparatus and method exemplifying principles of the invention, given only by way of example, and with reference to the accompanying drawings, in which:
As seen in
In order to control the flexibility and maneuverability of the stent delivery catheter 32, portions of the shaft of the catheter may advantageously include a structure or features that alter its structure and behavior in response to forces exerted during manipulation. According to an advantageous embodiment of the present invention, a portion of the shaft includes one or more lengths of hypotubing, one or more overlayers or exterior jackets, or both. Further, the hypotubing may include features that modify its flexibility characteristics, such as suitably-oriented (circumferential, longitudinal, helical, etc.) and pitched cuts or grooves or other modifications to its structure that commensurately change its flexibility characteristics, particularly at a distal portion of the catheter in the vicinity of the expandable portion 38, where increased flexibility may be desired.
Expandable portion 38 is depicted in an inflated or expanded state in
Balloon 50 is coupled to the remainder of catheter 32 at a connection region 62 by way of a sleeve 64 providing a strong, fluid-tight seal between balloon leg 52 and a shaft 65 of catheter 32. Sleeve 64 couples the distal opening 45 of primary lumen 40 with the proximal opening 55 of balloon leg lumen 53. This coupling provides a bonding region between the proximal leg 52, secondary tube 42 and catheter shaft 65. Sleeve 64 also provides reinforcement for the connection point of secondary guidewire tube 42 in the vicinity of proximal guidewire port 46. Secondary guidewire tube 42 extends at least partially through balloon leg portion 52. Alternatively, coupling of balloon 50 to the remainder of the balloon catheter 32 may be achieved by overlying balloon leg 52 over the shaft 65 of the balloon catheter and bonding these two components together, either by heat shrinking and/or melting, adhesive, or other expedients.
The connection region 62 includes several components, such as sleeve 64 and a proximal portion of secondary guidewire tube 42. The presence of different catheter components at this connection region 62 impacts the flexibility characteristics of this portion of the catheter. Specifically, the additional structures detract from the flexibility of the catheter 32 in that region. Moving the connection region to a distance of at least 2 cm from the balloon shoulder improves flexibility of the catheter distal end providing improved performance.
Balloon leg 52 is provided in order to distance the connection region 62 from expandable portion 38, since the flexibility of the balloon leg can be better managed than that of the multi-layer connection region.
Thus optimally, the distance from distal the end of the catheter, and specifically from distal guidewire port 48, to proximal guidewire port 46 is preferably in the range of about 5 cm to about 8 cm, and more preferably, is about 7 to about 8 cm. Selection of the materials and structure of balloon leg 52 takes into account the desired flexibility of this portion of the catheter. Typically, the flexibility of the balloon leg 52 of the catheter 32 should be greater than that of shaft 65, and even of the distal portion of shaft 65, which may be more flexible than the proximal portion of the shaft. Suitable materials for the balloon 50 and balloon leg 52, taking these flexibility requirements into account, include, but are not limited to, known balloon materials such as nylon 12.
In order to further modify or control the flexibility of the region of catheter 32 proximal to expandable portion 38, a stiffening wire may be provided. With reference to
Stiffening wire 70 is preferably free-floating at its ends, and is only attached to the catheter 32 in a region between the two ends, preferably in connection region 62. A preferred attachment method is by way of sleeve 64 to which stiffening wire 70 is bonded. Bonding can be achieved by placing a small polymer sleeve over the wire 70 and bonding the small polymer sleeve into the connection region 62. Wire 70 extends at least partially into lumen 53 of balloon leg 52, and preferably into the entire length of the lumen 53, but ends proximally of the balloon proximal shoulder. Wire 70 also extends proximally at least partially into lumen 40 of shaft 65. An advantage of stiffening wire 70 is that it improves trackability over the guidewire by providing resistance to bending to both balloon leg 52 and shaft 65 at the shaft's distal and most flexible portion. This compensates for the increased length provided by balloon leg 52 and required to maintain the connection region 62 and proximal guidewire port 46 within the guiding catheter during stent delivery. The stiffening wire 70 thus can reduce bowing of the shaft 65 of the catheter 32 away from the guidewire, kinking of the catheter or looping of the guidewire. In addition, the increase in length afforded by the balloon leg 52 is limited in order to avoid introducing too much flexibility and pushability problems.
Another advantageous feature that can be provided with catheter 32 can be referred as a radiopaque measuring stick and is described with reference to
In use, the expandable portion 38 is passed beyond the physiological feature to be measured and the measuring stick is aligned within the feature. A lesion that is 3 cm long for example would extend over three marker bands spaced 1 cm apart, enabling a physician to select a suitably dimensioned stent based on such a determination, or to determine if a selected stent is of an appropriate size.
Although the foregoing describes aspects of the present invention in the context of a rapid exchange stent delivery catheter, the present invention is not limited to such devices. Accordingly, additional embodiments exemplifying principles of the present invention include rapid exchange and non-rapid exchange catheters, balloon and non-balloon catheters including, but not limited to, infusion catheters, angioplasty catheters, angiography catheters, thermal and/or RF and/or laser ablation catheters, and fixed-wire vascular catheters.
With reference to the drawing figures, an exemplary method of stent implantation embodying further principles of the present invention will now be described. Preferably a stenosed region of a blood vessel a mammalian, preferably human, patient is first predilated with an angioplasty balloon catheter. A catheter in accordance with the present invention is then inserted into the vasculature optionally over a guidewire, and is advanced through a guide catheter to a vascular location of interest. The balloon of the catheter may then be inflated or expanded in a manner well appreciated by the skilled artisan, for example by increasing the pressure applied to an inflation fluid, and the balloon's diameter increases. When a stent is positioned on the exterior surface of the balloon, the stent is thus expanded, in a well know manner. Thus, the balloon and/or the stent can be expanded against the interior surface of the blood vessel. Due to the relative short rapid exchange length of about 8 cm or less the proximal guidewire port 46 may be positioned outside of the guide catheter during a procedure.
With reference to
While the invention has been described in detail with reference to exemplary embodiments thereof, it will be apparent to one skilled in the art that various changes can be made, and equivalents employed, without departing from the scope of the invention. Each of the aforementioned documents is incorporated by reference herein in its entirety.
