When was stent invented

He tackled the problem of menorrhagia, heavy menstrual bleeding that affects one in ten women and requires surgery and hospitalisation. He recently applied for a new medical patent. Several variations of the stent have been developed since my invention in the s. Today, an estimated two million stents are implanted worldwide every year. Toggle navigation. Agenda Contact Twitter issuu. These properties have enabled stent struts to become thinner and still have the same ability to resist deformation as a thicker strut with a lower elastic modulus [ 13 ].

Thinner struts are advantageous as they improve flexibility, increase the inner diameter of the stent, and reduce the amount of vascular injury during implant [ 13 , 14 , 16 ]. Platinum chromium platforms are also available and have an even higher density than cobalt-chromium, which makes them more radio-opaque.

The other physical characteristics are similar to cobalt-chromium [ 13 ]. Graphic representation of the clinical correlates of the stent characteristics. Metallic choice influences the strut thickness which in turn affects radial strength, radio-opacity, and inflammation. The cell size and design open versus closed cell affects the ability to access the side branches and scaffold the artery, while distributing the antiproliferative agent to the vessel wall.

In addition to the metallic backbone, the construction method and scaffold structure affect deliverability, ability to scaffold, radial strength, and side branch access [ 12 , 14 , 16 ]. Stents are classified as coil or slotted tube, or modular.

The coil stents are made of wires that are formed into a circular coil to form the stent scaffold, while the slotted tube stents are constructed from a metallic tube and then laser etching is used to cut out the design [ 12 , 16 ]. Modular ring stents are the final category of metallic stents [ 12 , 16 ].

Coil stents are flexible but exhibit poor radial force and have high rates of restenosis, and they were replaced by slotted tube stents [ 12 , 16 ]. The slotted tube stents have more radial force, but at the expense of less flexibility and deliverability [ 12 , 16 ].

The modular stent design therefore, has replaced the coil and slotted tube stents. They are constructed using multiple repeat modules that are fused together to construct a stent tube.

This improvement in the design provides flexibility and side branch access Figure 2 [ 12 ]. Modular stents can either have open or closed cell designs. Open cell stents are not connected on all of the sides, whereas closed cells are connected [ 12 ].

The closed cell stents reduce the plaque prolapse and increase the radial when compared with the open cell stents at the expense of flexibility, conformability, metal to artery ratio, and ability to access the side branches that are covered by the stent [ 12 , 14 , 16 ].

While effective in preventing abrupt closure, early recoil, and reducing the risk of restenosis when compared with balloon angioplasty alone, BMS had unacceptably high rates of restenosis [ 7 , 22 ].

Changes in the metallic composition and stent structure as well as the addition of various coatings failed to reduce the rates of restenosis to a clinically acceptable rate. Heparin coatings lower the risk of stent thrombosis but not restenosis [ 2 , 18 ]. Pathophysiologically, neointimal hyperplasia as a result of vascular injury, leads to lumen loss from smooth muscle cell proliferation [ 7 ].

Thus, if the stents possessed a method of inhibiting neointimal hyperplasia, the restenosis rates would be reduced.

Anti-proliferative drugs are used in the suppression of rejection in transplant recipients and inhibit the cell growth by various mechanisms of action. Rapamycin derivatives block the transition from G1 to S phase in the cell cycle, while paclitaxel stabilizes the microtubule polymer and prevents it from disassembling and, thus, inhibits cell division [ 2 , 7 ].

The half-life of these drugs is very short, but the length of antiproliferative effect that is necessary to prevent restenosis is long. Therefore, for a DES to prevent restenosis, there must be a long, controlled elution of the anti-proliferative drug from the metallic backbone so as to ensure its presence over an extended period of time [ 22 , 23 ].

This mission is accomplished using a carrier vehicle like a polymer. An ideal polymer must be biocompatible, not interact with the active restenotic drug, release the drug at the proper rate, and be biologically inert and mechanically stable over the long term [ 23 ]. Durable, non-degradable polymers have been used historically and, more recently, polymer free elution methods and biodegradable polymers have been developed [ 23 ].

The polymers have become more biocompatible over the years. Initially polyethylene- co -vinyl-acetate PEVA and poly- n -butyl-methacrylate were used in the Cypher stent, and poly styrene-b-isobutylene-b-styrene was used in the Taxus stent [ 23 ].

The current drug eluting stents have more biocompatible polymers, such as poly-vinylidene fluoride, hexofluropropylene, and polyvinyl pyrollidone [ 23 ]. Despite the improved bio-compatibility, the persistence of polymers has been linked to inflammation and early neoatherosclerosis with DES [ 23 ].

As a result, biodegradable polymers have been proposed as a solution to this problem. Clinical studies have failed to demonstrate a difference in safety or efficacy outcomes in the durable polymer compared to the bioresorbable polymer DES [ 23 ].

While balloon expandable stents comprise the share of the coronary stent market, a review of coronary stent technology should include self-expanding stents. As mentioned previously, balloon expandable stents can be precisely placed, while self-expanding stents are more difficult to position because of the foreshortening during expansion and longitudinal motion with deployment [ 15 ].

Unlike balloon expandable stents, which achieve their maximal diameter by the inflation of the balloon that they are mounted on, self-expanding stents are manufactured at their set diameter and are then constrained to a lower diameter by a sheath. The stent is then expanded by removing the constraining element and allowing the stent to expand [ 15 ]. The majority of these stents are constructed from a nickel titanium alloy [ 15 ].

Balloon expandable stents are susceptible to permanent deformation when they are compressed extrinsically, which is not an issue in the coronary tree. Self-expanding stents do not have this limitation. Furthermore, self-expanding stents have less axial stiffness and are thus more flexible and will conform to the shape of the vessel rather than the vessel conforming to the shape of the stent [ 15 ].

Balloon expandable stents, by virtue of their design, resist expansion by the balloon, but they have less acute recoil when they are placed in a poorly compliant lesion [ 15 ]. However, after the initial deployment, the stent is at its maximal diameter and cannot get larger, whereas a self-expanding stent that is appropriately oversized for the vessel will exhibit a chronic outward force on the lesion and may lead to a larger lumen over time [ 15 ].

For the reasons above, there are some coronary lesions where balloon expandable stents are not ideal, such as aneurysmal, ectatic vessels, thrombus laden vessels, and vessels that are tapering with a large size mismatch between distal reference and proximal reference vessels [ 24 ].

Self-expanding coronary stents might be beneficial in this scenario. The stent is available in both drug eluting and bare metal varieties [ 25 ]. While, theoretically, it is promising that there a paucity of long term outcome data for the stent [ 24 ]. Source: manufacturers websites www. While the current drug eluting stents have reduced the rate of restenosis and thrombosis, there is still room for improvement. Once implanted, the metallic stents and their polymer coating are a permanent fixture in the artery where they were placed, leading to the possibility of late stent failure along with impaired vasomotor function [ 26 ].

Additionally, the permanent presence of metal in the artery limits the luminal gain, with subsequent stenting inside the same stent in case of stent failure, and also limiting the options for coronary artery bypass surgery in the future, should the stent fail [ 26 ]. Bioresorbable scaffolds are being developed to combat these problems, while hopefully avoiding the problems that the current generation of drug eluting stents have already solved.

Bioresorbable devices share the components of DES, consisting of a scaffold, a polymer, and an antiproliferative drug [ 26 ]. The bioresorbable vascular scaffold BVS is formed by either a polymer or a biodegradable metal, rather than a durable metal. On this platform, a polymer for antiproliferative drug elution is added, along with the antiproliferative drug [ 26 ].

Poly- l -lactic acid PLLA , polytyrosine derived polycarbonate, and magnesium alloys have been used thus far to construct the backbone of these devices [ 26 , 27 ]. The polymers are broken down via hydrolysis, followed by the metabolism of the monomeric pieces into pyruvate, which enters the Krebs cycle and is broken down into carbon dioxide and water, whereas the magnesium eventually becomes hydroxyapatite, which is digested by macrophages [ 26 , 27 ]. These BVSs must be able to fulfill the same mission as metallic scaffolds that are mentioned above.

The polymeric BVS are inherently different than their metallic counterparts, because they are made of organic material and they are prone to fracture with over-expansion and their strut thickness is larger, making them more bulky and difficult to deliver [ 26 ].

Furthermore, they are more prone to recoil than their metallic counterparts. Bioresorbable metallic scaffolds have a higher radial strength than the polymeric scaffolds and thus can have thinner struts [ 27 ]. This also corresponds with the improved deliverability and lower profile over the polymeric scaffolds.

Of the multiple types of bioresorbable devices that were tested, only the Absorb BVS was ever commercially available. Unfortunately, the clinical performance was underwhelming with a signal towards increased target lesion failure from late scaffold thrombosis, leading to its withdrawal from the market [ 26 ].

At this point, advances are being made in technology so as to improve the deliverability and enhance the clinical result and safety. The field of percutaneous coronary intervention has demonstrated several technological advances since the days of primitive balloon dilation catheter. We effectively resolved the problem of the acute vessel closure with BMS, and later developed DES to minimize restenosis.

Although the current generation of DES has excellent safety and efficacy, there are still individuals with stent failure. Improvements have been made in the stent design that have improved deliverability and radiopacity, while maintaining radial strength, however, lower profile devices would still be welcomed to improve procedural safety and success.

Despite the theoretical advantages of bioresorbable scaffolds, the fist BVS to reach the market in the U. With history serving as a preview of things to come, we will likely see both an improvement in current metallic stent technology along with an improvement in the bioresorbable scaffold technology in the future, and possibly further development of self-expanding coronary stents.

Plastic, more durable, changes can be achieved with plaque dissection, but this mechanism carries potential risks of acute vessel closure. Abrupt occlusion obliged the pioneers of coronary angioplasty to have an active surgical stand-by during these procedures. The balloon induced intimal denudation and medial tearing exposed subendothelial matrix to blood, promoting platelet aggregation and thrombosis in the acute phase and chronic negative vascular remodeling late recoil and neointimal hyperplasia.

These limitations required further technological advancement, resulting in the introduction of coronary artery stents. Pathophysiology of in-stent restenosis and stent thrombosis. BMS and DES may prevent some of these negative processes, but also serve as a stimulus to inflammation and fibrosis. In-stent restenosis and stent thrombosis may also be determined by patient risk factors ie, diabetes, smoking , anatomical features of the treated vessel such as heavy calcified lesions, diameter of the vessel, the presence of side branches or inadequate stenting strut thickness, stent malapposition, inadequate stent diameter.

Coronary stents were developed to prevent arterial recoil and restenosis after balloon dilatation. An ideal metallic stent should have good flexibility and deliverability, low thrombogenicity, strong radial force, good radio-opacity under fluoroscopy, and good biocompatibility to ensure low rates of neointimal hyperplasia and stent thrombosis during long-term follow-up Figure 2.

Platinum-chromium, cobalt-chromium or other alloys have largely substituted stainless steel to provide sufficient strength and visibility with thinner struts. Stent structure and design. A, B, C: Struts, rings, cells, crowns and connectors form the backbone of a stent. Strut: single element that forms larger structural entities cells, rings and crowns.

Cell: small but regularly repetitive structure of a stent, delimited by 2 layers of rings and the connectors and might be open or closed. Connectors: attach the adjacent rings and can be straight or curved or can be direct welds that link the rings directly. D: Orientation of the stent in-phase or out-of-phase and connectors offset peak-to-peak; mid-shaft; peak-to-peak—out-of-phase; peak-to-valley—in-phase. Design and geometry of these components define the mechanical performance of a stent: crowns and rings determine radial support and expansion capacity; the number of connectors is responsible for the longitudinal stability, flexibility, deliverability, side branch access and longitudinal integrity.

Open cell designs with a reduced number of connectors provide greater stent flexibility with reduced arterial injury and decreased neointimal response. A drug-eluting stent has a more complex structure, in general wrapping a polymer coating containing an antiproliferative drug around the stent struts.

The polymer may be durable or bioresorbable and some recent stents elute the drug directly. A BRS consists of a platform made of bioresorbable material, either magnesium or poly-L-lactic acid PLLA , coated with a polymer and an antiproliferative drug.

There was still an obstacle against their universal adoption, the high incidence of acute and subacute stent thrombosis, obliging implanters to use high doses of anticoagulant drugs, leading to unacceptable rates of bleeding. This problem was overcome by the observation with intravascular ultrasound that stents required high pressure for complete expansion and the introduction of dual antiplatelet therapy DAPT combining ticlopidine or clopidogrel with aspirin.

Since the identification of neointimal hyperplasia as the major determinant of ISR, the application of antiproliferative agents was the logical answer. Subsequently, in addition to acting as permanent vascular scaffolds, stents soon evolved to become efficient local drug delivery platforms. In , Sousa implanted the first DES in Brazil, signaling the third revolutionary paradigm shift in the history of interventional cardiology.

Very late ST, although now recognized as a possible complication of first-generation DES, is a rare entity and numerous meta-analyses and data registries have provided reassurance about the use of such devices. In second-generation DES, the platform was changed to metal alloys ie, cobalt-chromium or platinum-chromium , which allowed for a reduction in strut thickness and more flexibility Table 2.

Polymers were made of new, more biocompatible molecules such as zotarolimus, everolimus and novolimus the limus-family drugs , with faster drug elution and subsequent earlier endothelial coverage.

The polymer coat is involved in the pathogenesis of long-term stent failure by triggering a potential chronic inflammatory stimulus responsible for delayed endothelial coverage and ST. Therefore, a new strategy to eliminate polymer-mediated complications has been the development of polymer-free DES, which can theoretically avoid these long-term negative effects, decreasing the rate of ST and allowing a shorter duration of DAPT.

However, since the polymer not only acts as a drug carrier, but also modulates the controlled release of the drug over time, the development of polymer-free DES required a new technology to maintain an adequate level of antiproliferative drug over time without the polymer vehicle Table 2. Thus, the metallic stent surface was modified to be porous pores of nm and the antiproliferative drug was then directly loaded onto these pores during the DES manufacturing process.

However, the drug release was difficult to control and some minor RCTs showed noninferiority but no improvement in clinical outcomes when compared with second-generation DES.

To date, few RCTs have evaluated the performances of polymer-free DES and larger trials are needed on long-term efficacy and safety. Degradation of the bioresorbable polymer occurs simultaneously with controlled release of the antiproliferative drug in the early phase after implantation.

Following complete elution of the drug and biodegradation of the polymer, only the metallic platform remains in the coronary artery Table 2. Several bioresorbable polymers are currently used and they differ in biocompatibility, degradation time, and in their different impact on endothelial function, smooth muscle cells growth, and thrombogenicity. Despite theoretical advantages and encouraging early results, showing lower rates of very late ST than first-generation DESs and noninferiority in terms of efficacy and safety compared with second-generation DESs, long-term results are needed.

Concerns over late adverse events related to the persistence of the metallic platforms in the coronary vessel have led to interest in fully bioresorbable stent technology in the past decade, potentially representing the fourth revolution in interventional cardiology.

The rationale behind their use is to create a temporary mechanical support in the vessel in order to prevent immediate restenosis and vascular recoil, then allowing it to degrade over time, eliminating the long-term risk associated with the presence of a metallic scaffold.

Referred to as a BRS, these devices provide the local drug delivery and mechanical support of permanent metallic DES in the first 12 months and reabsorb completely after 24 to 36 months, allowing restoration of normal luminal diameter and vasomotor function over the years, removing any nidus for late unfavorable events, potentially reducing the need for long-term DAPT and allowing surgical revascularization if needed. Bioresorbable scaffolds could be either a metallic alloy magnesium or iron alloy or an L-isomer of PLLA polymeric platform, covered with a polymer and an antiproliferative drug.

When an angioplasty is performed with a BRS, the technique used for implantation, the selection of suitable lesions and patients, the pre- and postdilatation technique and the choice of a tailored DAPT are considered crucial to reduce the incidence of ST.

The radial force of a BVS is weaker than the force of DES, so recoil can be a problem because of the rapid absorption. To overcome this problem, stent design requires thick struts to maintain radial strength and they might result in incomplete expansion and reduced lumen diameter after deployment.

These data were confirmed by meta-analyses and clinical registries 27 and mainly referred to the Absorb BVS, which is so far the most widely used scaffold and the only one with CE mark and FDA approval. Due to the higher incidence of ST observed with Absorb, Abbott has recently restricted its use to controlled clinical trials or registries. Indeed, there is still a long road ahead before BRS can be routinely used in clinical practice. Drug-eluting stents clearly offer an advantage over BMS with regard to restenosis.

Randomized trials and registries have consistently shown the superiority of second-generation DES over BMS regarding clinical and angiographic restenosis Table 1 , with reduced rates of repeat revascularization and ST events, but comparable clinical outcomes in terms of death and spontaneous MI , as recently shown by the NORSTENT trial. In these clinical scenarios, the small anticipated benefit to be gained from reduced restenosis may be balanced by the need to withhold the antiplatelet regimen.

It should be stressed that the use of BMS requires careful patient selection, with the exclusion of particular coronary anatomy bifurcation lesions requiring a 2-stent strategy, long lesions, left main disease, or small vessel diameter mm and clinical situation treatment of chronic total occlusion, occlusion of saphenous vein graft, ST-segment elevation MI , in which the use of BMS is considered unadvisable.

The recent availability of polymer-free DES in some countries has further narrowed the area where a BMS may be needed. Metallic stents with a thin biodegradable abluminal polymer layer or isolated dots may represent a safer alternative. There is no way we could have foreseen the impact of our work so many years ago. Coronary artery stenting is the treatment of choice for CAD.

With the advent of stents, the mechanical contribution to restenosis and acute recoil have been solved, making emergency bypass surgery a thing of the past. A large body of evidence has demonstrated a significant improvement in coronary stent safety and efficacy with device evolution, making second-generation DES the treatment of choice for patients requiring coronary angioplasty.

BMS, which have dominated our cath labs for 15 years, remain an option for selected patients, especially those who cannot complete the recommended duration of DAPT. Now the challenge is to develop the right cocktail of drugs, platforms and coatings to entirely eliminate, not just reduce, thrombosis and restenosis. Home Articles in press Current Issue Archive. ISSN: Previous article Next article. Issue 5. Pages May More article options.

Breve historia de los stents coronarios. Download PDF. Corresponding author. This item has received. Article information. Show more Show less. Table 1.