Dilatation balloons and stents are widely used for the treatment of vascular disorders where partial occlusion of a vein or artery has occurred, for example, from a buildup of plaque or other deposits on an inner wall of a blood vessel. Typically a catheter is moved through the blood vessel from a convenient external entry point to the affected region of the vessel. A guide wire and dilatation balloon are inserted in the catheter and advanced through the catheter and blood vessels to the site. Once in position, the flexible, expandable, preformed dilatation balloon is inflated to a predetermined size with a liquid or gas at relatively high pressures (e.g. about eight to twelve atmospheres) to radially compress the arthrosclerotic plaque in the lesion against the inside of the artery wall and thereby dilate the lumen of the artery. The balloon is then deflated to a small profile so that the dilatation balloon, guide-wire and catheter may be withdrawn from the patient's vasculature and blood flow resumed through the dilated artery.
In order to prevent or reduce restenosis; i.e., a natural re-narrowing of the treated artery, an intravascular prosthesis generally referred to as a stent can be implanted in the affected region. The stent often takes the form of a cylindrically shaped, radially expandable mesh fabricated of, for example, stainless steel or other suitable alloy. The stent is inserted by mounting it in collapsed form over a dilatation balloon, advancing the balloon-stent combination along a guide-wire to the site, and then expanded the balloon and the stent so that the stent is pressed into the inner wall of the blood vessel. The stent overcomes the natural tendency of the vessel walls of some patients to close back down. In this way, normal flow of blood is maintained through the vessel that would not be possible if the stent was not in place. Such procedures and stents are generally known in the art.
A particularly difficult problem arises when the blood vessel region to be treated involves a bifurcation, that is, where a single blood vessel divides into two branches. It is much more difficult in this situation to position the dilatation balloon and the stent. Further, where both branches of the bifurcation have plaque deposits, great care must be taken to compress the deposits in both branches as simultaneously as possible to prevent narrowing or closing of one branch while treating the other.
FIG. 1 shows bifurcated blood vessel region 10 with main vessel portion 12 and branches 14, 16. A balloon catheter (not shown) has previously been used to compress plaque 18 present in the bifurcation region against inner walls 20, 22, 24 of vessels 12, 14, 16 respectively. Stent 26 has been brought to the bifurcation region and expanded against compressed plaque 18 on the inner wall of vessels 12, 14, 16. Stent 26 is bifurcated, that is having portion 28 located in main vessel 12, portion 30 located in branch vessel 14 and portion 32 located in branch vessel 16. Thus, stent 26 can reduce or delay restenosis.
A number of catheter assemblies, methods and stents for treating stenosis in bifurcated regions have been described, for example, in U.S. Pat. No. 6,086,611 to Duffy et al; U.S. Pat. No. 6,129,738 to Lashinski et al; U.S. Pat. No. 6,428,567 to Wilson et al; and U.S. Pat. No. 6,475,208 to Mauch. FIGS. 2-3 illustrate prior art dilatation balloon-stent assemblies 40, 80 used in the prior art to place bifurcated stents. In FIGS. 2-3, balloon-stent assemblies 40, 80 have dilatation balloon 42 with main vessel portion 44 and branch portions 46, 48. Dilatation balloon 42 is shown un-inflated with stent 50 mounted thereon, ready for insertion. Stent 50 has main vessel portion 52 and branch portions 54, 56 located, respectively on balloon portions 44 and 46, 48. Running through dilatation balloon 42 are guide-wires 58, 60 where guide-wire 58 passes through dilatation balloon branch 46 and guide-wire 60 passes through dilatation balloon branch 48. One or both of rounded tips 62, 64 on guide-wires 58, 60 are often placed at a slight angle to the guide-wire to facilitate penetration into the branch vessel.
Assembly 80 of FIG. 3 differs from assembly 40 of FIG. 2 in that balloon branch 48 has extension portion 66 attached to distal end 49 thereof and clip 68 provided thereon. Portion 58-1 of guide-wire 58 is initially bent down and placed in clip 68 before insertion of assembly 80 through the catheter (not shown) into the affected region of the blood vessel. This aids in keeping branches 46, 48 of balloon catheter 42 together during insertion, reducing the chance that tip 62 will snag on an interior wall of the vessel or go into a branch ahead of the site being treated. Once assembly 80 is just in front of the bifurcation, guide-wire 58 is withdrawn slightly until it pops out of clip 68, so that assembly 80 now takes on an orientation much like assembly 40 in FIG. 2 as far as tips 62, 64 are concerned. Guide-wires 58, 60 are then advanced respectively into the bifurcated vessel branches. Then balloon catheter portions 46, 48 with stent portions 54, 56 are advanced along guide-wires 58, 60 to place the balloons and respective stent portions into the vessel branches. Balloon 42 is inflated to expand stent 50 and place it against the inner walls of the vessels. Balloon 42 is then deflated and withdrawn. Stent 50 remains in place.
While the above-described apparatus and methods are useful, they suffer from a number of disadvantages. For example, it is often very difficult to advance the dilatation balloon along the guide-wires when the guide-wires become twisted or tangled during insertion. When this happens it is often necessary to withdraw the guide-wires partially or completely and re-insert them. The more the guide-wires and/or balloon assembly are inserted, withdrawn and re-inserted before or after balloon dilatation, the greater the likelihood of damaging the interior wall of the vessel. Damage can occur when one or both of tips 62, 64 and/or stent 50 snag on the vessel wall and/or go into a dissection, that is, a fissure in the vessel wall that can arise from the dilatation process. Further, the need to partially withdraw and advance one or more guide-wires to release tips 62, 64, as for example, with the arrangement of FIG. 3, can exacerbate this situation. In addition, the very large ratio of length L to diameter D of the guide-wires (typically L/D=103 to 104) means they have very low stiffness, which makes it to difficult to insert them, to control their orientation and to avoid tangling. An increase in stiffness without loss of flexibility is desirable.
Accordingly, there continues to be a need for improved means and methods for dilatation balloons and stents to treat vascular stenosis. In particular, there is an ongoing need for means and methods that reduce the need for withdrawing and re-inserting guide-wires, dilatation balloons and/or stents. Further, there is a need for improved means and methods for treating bifurcated regions so that the guide-wire tips can be maintained in fixed relationship to each other during insertion without requiring one or both to be partially withdrawn in order to be released. In addition, there is an ongoing need for means and methods that reduce twisting and/or tangling of the guide-wires during insertion and manipulation of the dilatation balloon and stent. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.