referring first to fig1 an endovascular support device 10 , referred to hereinafter more conveniently as a stent , constructed in accordance with the present invention can be seen in perspective view . the stent 10 of fig1 is shown in its expanded form , prior to compression over a suitable delivery system as discussed in detail hereinafter . in a preferred embodiment , the stent 10 comprises a single piece of material , bent to form a plurality of upper axial turns 12 and lower axial turns 14 . in the embodiment shown in fig1 four upper turns 12 are connected to the four lower turns 14 by substantially straight segments 16 . the axial turns 12 and 14 can be seen to permit the stent 10 to be compressed or expanded over a wide range while still maintaining significant mechanical force , such as required to prevent a vessel from restenosing . while a preferred embodiment comprises a single piece of material , in some instances a suitably welded wire may be acceptable . it will be appreciated that the number of turns 12 and 14 can vary over a reasonably wide range , defined as &# 34 ; n &# 34 ; numbers of turns and may in fact vary between two and ten such turns or peaks . however , it is currently believed that the optimum number of turns or peaks will range between three and five for most applications , and particularly for cardiovascular applications . the stent 10 is preferably constructed of implantable materials having good mechanical strength . an embodiment which has proven successful in preliminary testing is machined from 316lss implantable quality stainless steel bar stock . the bar stock is machined to form substantially a toroid , which is then acid etched in phosphoric and sulfuric acid at approximately 180 . to 185 . to break the edges . the etched toroid is then plated with copper to avoid galling and to provide lubricity . the copper plated toroid is then bent to the shape of the stent 10 shown in fig1 after which the copper plating is stripped from the stent . the stent is then returned to the acid bath to reduce the wire size to the desired diameter , which is in the range of 0 . 002 &# 34 ; to 0 . 025 &# 34 ;. it is presently believed that the optimum wire size for the final product is in the range of 0 . 008 &# 34 ; to 0 . 009 &# 34 ;. it will be appreciated that the strength of the stent -- that is , its ability to prevent restenosis -- is inversely proportional to the number of peaks or turns in the stent , so that stents having a greater number of turns will typically be formed of larger wire diameters . finally , although not required in all cases , the outside of the stent may be selectively plated with platinum to provide improved visibility during fluoroscopy . the cross - sectional shape of the finished stent may be circular , ellipsoidal , rectangular , hexagonal , square , or other polygon , although at present it is believed that circular or ellipsoidal may be preferable . the minimum length of the stent , or the distance between the upper turns 12 and lower turns 14 , is determined in large measure by the size of the vessel into which the stent will be implanted . the stent 10 will preferably be of sufficient length as to maintain its axial orientation within the vessel without shifting under the hydraulics of blood flow ( or other fluid flow in different types of vessels ), while also being long enough to extend across at least a significant portion of the affected area . at the same time , the stent should be short enough as to not introduce unnecessarily large amounts of material as might cause undue thrombosis . typical cardiovascular vessels into which the stent 10 might be implanted range from 1 . 5 millimeters to five millimeters in diameter , and corresponding stents may range from one millimeter to two centimeters in length . however , in most instances the stent will range in length between 3 . 5 millimeters and 6 millimeters . preliminary testing of stents having a length between 3 . 5 millimeters and 4 . 5 millimeters has been performed with good success outside the united states , and testing on animals is also ongoing . once the wire size of the stent 10 has been reduced to the desired size , the stent 10 may be crimped onto a balloon 100 , as shown in fig2 for delivery to the affected region 102 of a vessel 104 such as a coronary artery . for the sake of simplicity , the multiple layers of the vessel wall 104 are shown as a single layer , although it will be understood by those skilled in the art that the lesion typically is a plaque deposit within the intima of the vessel 104 . one suitable balloon for delivery of the stent 10 is manufactured by advanced cardiovascular systems , inc ., of santa clara , calif . (&# 34 ; acs &# 34 ;), and is eight millimeters in length with microglide ® on the shaft only . the stent - carrying balloon 100 is then advanced to the affected area and across the lesion 102 in a conventional manner , such as by use of a guide wire and a guide catheter ( not shown ). a suitable guide wire is the 0 . 014 &# 34 ; hi torque floppy manufactured by acs , and a suitable guiding catheter is the et . 076 lumen guide catheter , also manufactured by acs . once the balloon 100 is in place across the lesion 102 , as shown in fig3 the balloon 100 may be inflated , again substantially in a conventional manner . in selecting a balloon , it is helpful to ensure that the balloon will provide radially uniform inflation so that the stent 10 will expand equally along each of the peaks . the inflation of the balloon 100 , shown in fig4 causes the expansion of the stent 10 from its crimped configuration back to a shape substantially like that shown in fig1 . the amount of inflation , and commensurate amount of expansion of the stent 10 , may be varied as dictated by the lesion itself , making the stent of the present invention particularly flexible in the treatment of chronic restenosis . because of the inflation of the balloon , the lesion 102 in the vessel 104 is expanded , and causes the arterial wall of the vessel 104 to bulge radially , as simplistically depicted in fig4 . at the same time , the plaque deposited within the intima of the vessel is displaced and thinned , and the stent 10 is embedded in the plaque or other fibrotic material adhering to the intima of the vessel 104 . following inflation of the balloon 100 and expansion of the stent 10 within the vessel 104 , the balloon is deflated and removed . the exterior wall of the vessel 104 returns to its original shape through elastic recoil . the stent 10 , however , remains in its expanded form within the vessel , and prevents further restenosis of the vessel . the stent maintains an open passageway through the vessel , as shown in fig4 so long as the tendency toward restenosis is not greater than the mechanical strength of the stent 10 . because of the low mass of the support device 10 of the present invention , thrombosis is less likely to occur . ideally , the displacement of the plaque deposits and the implantation of the stent 10 will result in a smooth inside diameter of the vessel 104 , although this ideal cannot be achieved in all cases . one of the advantages of the stent 10 is that multiple stents , &# 34 ; m ,&# 34 ; may be used in the treatment of a single lesion . thus , for example , in the event the affected area shown in fig3 and 4 was longer than the stent 10 , additional stents 10 could be positioned elsewhere along the lesion to prevent restenosis . in preliminary testing , up to four stents have been used successfully along a single lesion . due to the conformability of the stent 10 , not only can varying lesion lengths be treated , but curved vessels and &# 34 ; s &# 34 ; shaped vessels may also be treated by the present invention . in instances where it is known in advance that multiple stents will be the preferred method of treatment , a plurality of such stents , &# 34 ; m &# 34 ; number of stents may be positioned along a single balloon catheter for simultaneous delivery to the affected area . as discussed above , the number of peaks or turns 12 and 14 in the stent 10 , &# 34 ; n &# 34 ; number of turns , may vary between two and ten . to this end , shown in fig6 a and 6b are two alternative configurations of the stent 10 . the alternative embodiment shown in 6a can be seen to have three upper and three lower peaks or turns , while the embodiment shown in fig6 b can be seen to have ten upper and ten lower peaks . while the primary application for the stent 10 is presently believed to be treatment of cardiovascular disease such as atherosclerosis or other forms of coronary narrowing , the stent 10 of the present invention may also be used for treatment of narrowed vessels in the kidney , leg , carotid , or elsewhere in the body . in such other vessels , the size of the stent may need to be adjusted to compensate for the differing sizes of the vessel to be treated , bearing in mind the sizing guidelines provided above . having fully described a preferred embodiment of the invention , those skilled in the art will immediately appreciate , given the teachings herein , that numerous alternatives and equivalents exist which do not depart from the present invention . it is therefore to be understood that the present invention is not to be limited by the foregoing description , but only by the appended claims .
an endovascular support device for treatment of chronic restenosis or other vascular narrowing is disclosed together with a method of manufacture and a method for delivering a plurality of such devices to an affected area of a vessel . in a preferred embodiment , the endovascular support device comprises a unitary wire - like structure configured to form a plurality of upper and lower peaks which may be compressed for delivery to an affected area of a coronary or peripheral vessel in a human , and then expanded to maintain a passageway through the vessel .