History and evolution of coronary stenting



by M. E. Bertrand, France

Michel E. BERTRAND, MD, FESC, FRCP, FACC Hôpital Universitaire Cardiologique, Lille FRANCE

Coronary stenting represents a major step in the history of percutaneous coronary angioplasty. Jacques Puel performed the first stent implantation in man in 1986, and research in the area took off immediately. The primary concern about balloon angioplasty procedures was safety, as there is a risk of abrupt occlusion during the procedure. This risk and the subsequent need for emergency bypass surgery were dramatically reduced with stent implantation. Nevertheless, investigators then faced another problem: the risk of stent thrombosis. However, such risk is suppressed by the use of a dual antiplatelet treatment. Coronary stenting has now played a major role in the fight against restenosis, with drug-eluting stents considerably reducing this risk, even in high-risk patients (diabetics). With coronary stenting, coronary interventional procedures have become the primary approach to myocardial revascularization.

The first coronary angioplasty in man was performed by Andreas Gruentzig from Zurich (Switzerland) in September 1977.1 This new, noninvasive approach for myocardial revascularization would have an immediate and great success. In the years that followed, significant technical improvements were proposed. The over-the-wire technique, designed by John Simpson,2 and the monorail system3 were rapidly adopted by the interventional cardiology community. However, new problems were observed: the most important pertained to the safety of the procedure. During or immediately after angioplasty, an abrupt occlusion of the vessel was observed in 3% to 5% of cases. This accident was related to an occlusive dissection or an occlusive thrombosis of the vessel. Thus, when use of coronary angioplasty was beginning, it was recommended to perform the procedure with a surgical backup, enabling immediate emergency bypass surgery if needed. In most cases, this emergency operation was followed by limited myocardial necrosis. Aside from this immediate problem, 30% to 45% of cases experienced later restenosis in a process such as the following: the mechanism of initial enlargement of the lumen was through dissection of the vessel; and this dissection was followed by a process of healing, which involved migration and proliferation of smooth muscle cells into a loose extracellular matrix; thus, intimal hyperplasia occurred, contributing to the renarrowing of the dilated vessel. Later, it was discovered that another important phenomenon was occurring— negative remodeling of the vessel, leading to shrinkage of the dilated segment. It is within this context that coronary stenting arose and solved, at least partially, the two major problems of coronary angioplasty, namely abrupt occlusion and restenosis.

History of stenting

It has been said that the Egyptians tried to cure the narrowing of urethra by introducing a small reed in the urinary canal in order to reestablish a more fluid relationship between the internal and external milieu.

In September 1912, the French surgeon, Alexis Carrel made a prophetic statement following the publication of his work on permanent intubation of the thoracic aorta in dogs4:

The permanent intubation of a large vessel is a simple operation. It may become practical, if the shape and the nature of the tube be modified as to avoid lacerations (…). The question of the application of this method to human surgery may then, possibly, be considered.

It took more than 70 years to verify this assumption.

The first stent was conceived from the progress in therapeutic intervention initiated by Charles Dotter5; he was a true inventor and a pioneer in the interventional cardiovascular world. He opened the way for interventional cardiology, and he started to design the first vascular stent at the end of the 1980s with insertion of plastic tubes and collapsible stainless-steel prostheses into the femoral or popliteal arteries of dogs.

In 1978, a young fellow who had recently arrived from Argentina attended a lecture by Andreas Gruentzig at a meeting of the Society of Cardiovascular and Interventional Radiology. His name was Julio Palmaz, and he thought that “the problems that doctor Gruentzig had with his balloon could be avoided by inserting some sort of a scaffold at the time of dilatation.” 6 The chairman of the department said that it could be a nice research project. After writing a report and making drawings, he started to build a prototype in his garage with copper wire and solder materials.

The wire was woven in a crisscross mesh around a pencil with two rows of pins. Solder was used to fix the cross points to allow the mesh to retain its shape. Once built, the mesh diameter was decreased by compressing it on progressively smaller wooden dowels and then was crimped by hand on a folded balloon. However, the material was excessively rigid, and the slots and the spaces between were inadequate. Julio Palmaz searched for a manufacturer, but several companies refused to consider this device.

In Switzerland, the story of stenting started during a party: two Swedish persons met—one, Hans Wallstén, was the designer of a revolutionary machine intended to manufacture paper; the other, Ake Senning, was a well-known cardiovascular surgeon. During the meeting, Senning explained that aortic dissection was a very serious acute disease and went on to detail his concept of a mechanical scaffolding of the arterial wall by a latticed metallic tube. Wallstén, very excited, decided to take up the problem of metallic endoprostheses. He created the Wallstent but had some difficulties finding a solution for a percutaneous approach; the solution was found by the engineer Christian Imbert. The self-expandable stent, which could be implanted via a percutaneous femoral approach, was thus created. Looking for centers to experiment with his device, Christian Imbert met Ulrich Sigwart in Lausanne and the group of Jacques Puel in Toulouse.

In cooperation with radiologists from Toulouse, Jacques Puel conducted experiments in sheep and dogs. These experiments quickly (probably too quickly) met with success and showed, at least at first glance, that it was easy (possibly too easy) to implant the endocoronary prosthesis percutaneously and that rapid endothelialization of the struts occurred. However, these animal experiments did not reveal the high risk of subsequent thrombosis. Later, Puel confessed that he had probably underestimated this risk. Simultaneously in Lausanne, Ulrich Sigwart was conducting experimental implantation in dogs.

The first stent implantation in man was performed on March 28, 1986 by Puel using the Wallstent.7 The medical history of this first patient is quite simple: the patient was a 63-year-old male with arterial hypertension and symptomatic restenosis 6 months after treatment of a mid–left anterior descending artery lesion (Figure 1).

Figure 1. First stent implantation in man. Stent implantation in a 63-year-old male with arterial hypertension and symptomatic hypertension 6 months after treatment of a mid–left anterior descending artery lesion. The procedure was carried out by Jacques Puel in 1986. A. Angiogram showing high-grade stenosis of the proximal left anterior descending artery (yellow arrow) before the procedure. B. The bare metal stent used in the procedure. C. Angiogram showing the stent in place (yellow arrow). All rights reserved.

Figure 2. Impact of stenting on acute occlusion and emergency surgical bailout procedures. Abbreviation: Emerg CABG, emergency coronary artery bypass graft surgery. All rights reserved.

In 1986, with evidence-based medicine still in its infancy, the patient received no antiplatelet drugs or statins in preparation for stent implantation; rather, he received only subcutaneous heparin during the procedure and within the next 6 weeks. By chance, he had no stent thrombosis or in-stent restenosis within that time span; however, he did not escape progression of the atherosclerotic process and has had recurrent episodes of angina pectoris related to a new lesion on the ostium of the left anterior descending artery and another one on the circumflex artery, which was treated in 2004 by a new stent implantation. In the weeks after that first implant, seven other patients received a self-expandable Wallstent without any complications.

In Lausanne, the results obtained from 9 months of animal experiments were convincing enough to persuade the Institutional Review Board to give approval in April 1986 for the use of stent implants for three indications: abrupt vessel closure after balloon angioplasty, restenosis after balloon angioplasty, and stenosis of saphenous vein bypass grafts.8 After a number of deployments in human femoral and iliac arteries, the self-expanding mesh stent was first deployed after balloon dilatation of a tight stenosis in a vein bypass procedure.

Although initial results were promising, they were misleading— the next four patients to undergo the stent procedure experienced a subacute stent thrombosis. With a single antithrombotic treatment using full-dose heparin, the risk of thrombosis was very high.

Later, Ulrich Sigwart would perform the stent implantation procedure under full anticoagulation treatment with heparin followed by oral anticoagulation with warfarin.8 This medical treatment slightly decreased the risk of stent thrombosis, though it remained very high (occurring in 5% to 10% of cases).

These two clinical trials, conducted initially in Toulouse and later in Lausanne, proved the feasibility of the stent implantation method. However, they also demonstrated the high potential thrombogenic risk posed by introduction of this foreign body; nevertheless, stents markedly reduced the risk of acute or subacute occlusion. As a result, the need for emergency surgical bailout procedures was drastically reduced (Figure 2).

The evolution of coronary stenting over the years that followed can be divided into three different parts—technical improvement, safety improvement, and restenosis prevention and treatment. These will be discussed in turn.

Technical improvements in stenting

A number of variations of the stent have been proposed over the years. The first stent implanted in the coronary arteries in man was the Wallstent (Medinvent) (Figure 3A). It was a selfexpanding stent composed of 20 strands of 0.06 to 0.09 mm diameter arranged into a self-expanding mesh design. It was flexible; its length ranging from 15 to 30 mm; and its diameter between 3.0 to 6.0 mm. The mesh was compressed and elongatedon thedelivery catheter owing to a double wall sleeve membrane. Retraction of this membrane allowed the progressive release into the vessel. The aforementioned work of Julio Palmaz led to creation of a tubular slotted stent; together with Richard Schatz, it was implanted in coronary arteries for the first time in December 1987 (Figure 3B).9 This was a balloon- expandable stent crimped on the delivery catheter, and it became very popular. The Gianturco Roubin stent10 (approved in the United States in 1993) (Figure 3C) had a poor radial strength, which was responsible for an increased rate of restenosis and stent thrombosis. Later, Medtronic proposed a coil stent or Wiktor stent (Figure 3D). Finally, stents covered by a membrane of polytetrafluoroethylene were proposed and used in saphenous vein graft stenoses to avoid the embolization of the friable materials characteristic of these lesions. It was also used for the emergency treatment of coronary perforations.

Figure 3. Four types of stents: the precursors. A number of variations of the stent have been proposed. Shown here are the (A) Wallstent, (B) Schatz-Palmaz, (C) Gianturco- Roubin, and (D) Wiktor stents. All rights reserved.

Drug-eluting stents were introduced in 2000. They are composed of two parts: the polymer coating the strut (one or several layers) and the drug delivered into the vessel wall. The drugs act on the cell cycle (Figure 4) and are able to suppress smooth muscle cell proliferation without toxicity and with a low inflammatory risk. Most drug-eluting stents use an analog of sirolimus (drugs used from the limus group include sirolimus, everolimus, zotarolimus, biolimus, the sirolimus metabolite novolimus, and myolimus, a macrocyclic lactone close to the rapamycin family).

Figure 4. Impact of the drugs delivered by drug-eluting stents on the cell cycle. Abbreviations: G0 phase, resting phase of the cell cycle; G1, G2 phases, interphases of the cell cycle; M phase, mitotic phase of the cell cycle; mTOR, mammalian target of rapamycin. All rights reserved.

The first drug-eluting stent of this group was the Cypher (Cordis Corporation). Almost simultaneously proposed was paclitaxel, which inhibits cell replication and is the drug delivered by the Taxus stents (Boston Scientific). Cypher and Taxus stents were the first-generation drug-eluting stents. These were followed by second-generation (followed by a second generation (Xience, Endeavor stents) and third-generation drug-eluting stents, the latter being fully bioresorbable vascular scaffolds (BVS), including: (Igaki-Tamai (Igaki Medical Planning), BVS 1.0 (Abbott Vascular), DESolve (Elxir Medical Corporation), REVA (Reva Medical), ART 18AZ (Arterial Remodeling Technologies), and Amaranth stents.

Safety improvements in stenting: the fight against acute or subacute stent thrombosis (first revolution in coronary stenting)

It would take nearly 10 years to eliminate the frightening risk of acute or subacute stent thrombosis. A number of strategies were proposed; these included use of full-dose unfractionated heparin, low-molecular-weight heparin, dextran, sulfinpyrazone, aspirin, and antivitamin K. The combination of these drugs was ineffective and led to significant bleeding at the puncture site resulting in big hematomas that required vascular repair. In this context, although stenting was recognized to be effective for the treatment of abrupt periprocedural occlusion and to help avoid emergency bypass operations, many investigators were ready to abandon this technique for the treatment of restenosis. However, coronary stenting would be resuscitated by two new findings by

Antonio Colombo from Italy and Paul Barragan from Marseille. Antonio Colombo, through extensive use of intravascular ultrasound, demonstrated that in many cases, stent implantation was far from perfect, with malapposition and insufficient deployment. From these observations, he recommended inflation of the balloon at a higher level of pressure to improve embedding of the stent inside the wall. With a larger lumen and a better flow, stent thrombosis might be avoided.

Figure 5. Rate of stent thrombosis in patients taking a dual antiplatelet treatment (aspirin + ticlopidine) compared with patients taking aspirin + a vitamin K antagonist. Abbreviations: ASA, acetylsalicylic acid; FANTASTIC, Full ANTicoagulation versus ASpirin and TIClopidine (study); ISAR, Intracoronary Stenting and Antithrombotic Regimen; STARS, STent Anticoagulation Restenosis Study; Vit, vitamin. Based on data from references 13-15. All rights reserved.

Almost simultaneously, Paul Barragan reported that a dual antiplatelet treatment with aspirin and ticlopidine was successful. 11 Barragan participated in a trial launched by Bertrand et al (The TACT trial [Ticlopidine Angioplasty Coronary Trial]). The goal of this trial was to verify if an antiplatelet drug (ticlopidine) could prevent restenosis. This study presented at the American Heart Association meeting in 1992 had negative results but was able to demonstrate the benefits of ticlopidine + aspirin in preventing acute periprocedural complications of balloon angioplasty. Thus, Barragan continued to use this dual anti-platelet treatment after completion of the study. In performing stent implantations, he was the only investigator to have no (or rare) cases of stent thrombosis. Finally, on the basis of a French registry collecting data on the usual strategies, it was observed that the combination of aspirin and ticlopidine was markedly effective for reductions in stent thrombosis and vascular complications.12 Three randomized studies performed initially in Europe13,14 and later in the United States15 demonstrated the benefit of this dual antiplatelet treatment (Figure 5). Subsequently, Bertrand et al showed that another thienopyridine (clopidogrel) was superior to ticlopidine (the CLASSIC trial [CLopidogrelAspirinStent InternationalCooperative study]).16 The danger of acute/subacute thrombosis having been overcome, the so-called “stentomania” began, with an increasing number of stent implantation procedures taking place.

The fight against restenosis

The role of stenting

In 1991, Serruys et al published in the New England Journal of Medicine the results from the first 105 patients in the world treated with the Wallstent.17 This report essentially addressed the problem of subacute thrombosis, but few readers overlooked the fact that the rate of restenosis after stenting was only 14%. In this context, Dutch investigators began a multicenter registry, and several investigators (Serruys, Bertrand, Rutsch) launched a randomized study assessing the role of coronary stenting in the treatment of restenosis. Although initially impossible to find support from industry for such a trial, the tenacity of Serruys, de Jaegere, Kiemeneij and colleagues led to the launch of the BENESTENT I trial (BElgian-NEtherlands STENT) in Belgium and the Netherlands. This pilot study included only 60 patients and took almost 1 year to complete in four centers with a total number of almost 4000 interventions, demonstrating the skepticism of the interventional cardiology community for stenting.18 This landmark study demonstrated the benefit of coronary stenting for the treatment of restenosis. The results were confirmed by an American trial (STRESS [STent REStenosis Study]).19 Later, the results were complemented by the BENESTENT II study, which was performed with a heparin-coated stent and showed that bleeding complications almost completely disappeared.20

However, over time, it appeared that in-stent restenosis was a true matter of concern. It was discovered that though the scaffolding role of stenting prevented negative remodeling— the shrinkage of the artery—as a reaction to the metallic foreign body, the vascular wall generated a new, intense hyperplasia. Solinas et al21 showed the different aspects of in-stent restenosis, as follows: in-stent restenosis was focal (margin or mid-stent) in 42%, diffuse in 22%, proliferative (ie, with extension beyond the stent) in 30%, and even occlusive in 6%. Several techniques were used to address this new problem; these included redilatation by balloon (mainly for focal in-stent restenosis), by the stent-in-stent technique, by Rotablator therapy, and even by brachytherapy. At first glance, brachytherapy seemed promising but was subject to numerous regulations due to the rules of radioprotection. This method was never well accepted, was limited to a small number of centers, and was finally abandoned with the emergence of drug-eluting stents.

Drug-eluting stents (the second revolution in coronary stenting)

Giessen—attempted to coat the struts of the metallic stents with different substances, the goal being to coat the struts with a polymer as a drug-carrier vehicle; these drugs sought to inhibit the cell cycle. In July 1999, Cordis Corporation studied a stent coated with a polymer releasing the drug rapamycin. The company conducted a pilot study in Rotterdam, the Netherlands with Patrick Serruys and in Sao Paulo, Brazil with Eduardo Souza, in which 15 patients were studied with angiographic and intravascular ultrasound follow-up. The two principal investigators were surprised to discover that at 4 and 12 months’ follow-up there was no evidence of neointimal hyperplasia. These results led to a randomized clinical trial conducted in 237 patients treated by bare-metal stent or the Cypher, the first drug-eluting stent—the RAVEL study (RAndomized study with the sirolimus-eluting VElocity balloon-expandable stent in the treatment of patients with de novo native coronary artery Lesions).22 This study, presented at the European Society of Cardiology congress in Vienna (September 2001) by Marie-Claude Morice, was a new “turning point in coronary interventional cardiology,” as there was zero restenosis.

Subsequently, two major trials confirmed these excellent results: the SIRIUS trial (SIRolImus-elUting Stent in coronary lesions),23 as well as the TAXUS trial (Treatment of de novo coronAry disease using a single paclitaXel-elUting Stent),24 which used another eluting drug, paclitaxel. Later, the course of drug-eluting stents was disturbed by a frightening issue—at the 2006 European Society of Cardiology congress in Vienna, results suggesting late stent thrombosis were presented. Fortunately, these scary results were not confirmed,25 but they led to a still ongoing debate about the duration of dual antiplatelet treatment: 6 months, 12 months, or more? Nevertheless, the development of drug-eluting stents continued and with the new drug-eluting stents using a different drug-carrier vehicle, all of them have been shown to offer efficacy and safety.

Thus, the challenges were overcome: the cage prevents negative remodeling and the eluted drug prevents cell proliferation and migration (Figure 6). A final step was the development of stents that used biodegradable polymers and bioresorbable scaffolds: drug-eluting stents with biodegradable polymers provide the benefit of drug-eluting stents in the early days/months and of the bare-metal stents later. A number of prostheses were studied: AXXESS (Biosensors),Orsiro (Biotronik), DESyne (Elixir), Infinium (Sahajanand), Biomine (Meril Life).

As the polymer may induce side effects, polymer-free drugeluting stents have been proposed. The eluting drug may be introduced into a microporous surface on metallic stents. Examples include the Yukon stent (Translumina), BioFreedom (Biosensors), VESTAsync (MIV Therapeutics), Nano (Xience), and Bicare (Lepu Medical). In other examples, the Optima stent (CID Vascular) proposes small reservoirs of tacrolimus covered with carbofilm, and the Amazonia PAX stent (MINVASYS) is a cobalt-chromium stent coated with paclitaxel.

Figure 6. Summary of the relationship between restenosis and stenting. Whereas balloon angioplasty often results in negative remodeling and sometimes in restenosis, the use of stents prevents negative remodeling. Drug-eluting stents can provide this benefit and also prevent cell proliferation and migration. Abbreviation: BMS, bare-metal stent. All rights reserved.

Bioresorbable stents are very promising: they offer the vascular scaffold for a certain amount of time and then the implanted materials are progressively resorbed. This offers a number of advantages, including the elimination of foreign bodies inside the wall, restoration of endothelial coverage, and possibly restoration of vasomotion. These biodegradable stents can be divided into two categories: metallic stents that are magnesium based and those that are polymeric resorbable— more than 10 stents of this type have been studied, made of poly-L-lactic acid (PLLA) and poly-D,L-lactic acid. Absorb BVS (Abbott Vascular) is a fully resorbable stent which has obtained the CE mark (Conformité Européenne [European conformity]); the ABSORB II trial published in the Lancet in 2014 compared Absorb BVS vs the Xience metallic drugeluting stent in a cohort of 501 patients.27-29 At follow-up, there was no significant difference in terms of safety and efficacy between the two devices. Currently, there is great interest for these new bioresorbable stents, but it is obvious that a longer follow-up is needed in order to reach final conclusions. There are currently a number of studies underway evaluating these new devices.

Conclusion

Coronary stenting represents one the most important advances in the field of coronary angioplasty. With this technique, percutaneous coronary interventions are safe in most cases and the risk for patients to be sent for surgery for emergency bailout procedures has become minimal. Additionally, the risk of reintervention after angioplasty is markedly reduced after drug-eluting stent implantation. With coronary stenting, coronary interventional procedures, as minimally invasive techniques, have become the primary method of myocardial revascularization in man.

Reference

1. Gruntzig A. Transluminal dilatation of coronary-artery stenosis. Lancet.1978;1 (8058):263. 
2. Simpson JB, Baim DS, Robert EW, Harrison DC. A new catheter system for coronary angioplasty. Am J Cardiol. 1982;49(5):1216-1222. 
3. Bonzel T, Wollschlager H, Just H. A new catheter system for the mechanical dilatation of coronary stenoses with exchangeable intracoronary catheters, fast flow of the contrast agent and improved control [in German]. Biomed Tech (Berl). 1986;31(9):195-200. 
4. Carrel A. Permanent intubation of the thoracic aorta. J Exp Med.1912;16(1): 17-24. 
5. Dotter CT, Judkins MP. Transluminal treatment of arteriosclerotic obstruction. Description of a new technic and a preliminary report of its application. Circulation. 1964;30:654-670. 
6. Palmaz JC, Sibbitt RR, Reuter SR, Tio FO, Rice WJ. Expandable intraluminal graft: a preliminary study. Work in progress. Radiology. 1985;156(1):73-77. 
7. Puel J, Joffre F, Rousseau H, et al. Self-expanding coronary endoprosthesis in the prevention of restenosis following transluminal angioplasty. Preliminary clinical study [in French]. Arch Mal Coeur Vaiss. 1987;80(8):1311-1312. 
8. Sigwart U, Puel J, Mirkovitch V, et al. Intravascular stents to prevent occlusion and restenosis after transluminal angioplasty. N Engl J Med. 1987;316(12):701- 706. 
9. Palmaz JC, Richter GM, Nöldge G, et al. Intraluminal Palmaz stent implantation. The first clinical case report on a balloon-expanded vascular prosthesis [in German]. Radiologe. 1987;27(12):560-563. 
10. Macander PJ, Agrawal SK, Roubin GS. The Gianturco-Roubin balloon-expandable intracoronary flexible coil stent. J Invasive Cardiol. 1991;3(2):85-94. 
11. Barragan P, Pietri P, Villain P, Silvestri M, Roquebert PO. Antiplatelet therapy during coronary endoprosthesis placement [in French]. Arch Mal Coeur Vaiss. 1996;89(11 suppl):1515-1520. 
12. Karrillon GJ, Morice MC, Benveniste E, et al. Intracoronary stent implantation without ultrasound guidance and with replacement of conventional anticoagulation by antiplatelet therapy. 30-Day clinical outcome of the French multicenter registry. Circulation. 1996;94(7):1519-1527. 
13. Schömig A, Neumann FJ, Kastrati A, et al. A randomized comparison of antiplatelet and anticoagulant therapy after the placement of coronary-artery stents. N Engl J Med.1996;25;334(17):1084-1089. 
14. Bertrand ME, Legrand V, Boland J, et al. Randomized multicenter comparison of conventional anticoagulation versus antiplatelet therapy in unplanned and elective coronary stenting. The Full Anticoagulation Versus Aspirin and Ticlopidine (FANTASTIC) study. Circulation. 1998;98(16):1597-1603. 
15. Leon MB, Baim DS, Popma JJ, et al. A clinical trial comparing three antithrombotic- drug regimens after coronary-artery stenting. Stent Anticoagulation Restenosis Study Investigators. N Engl J Med.1998;339(23):1665-1671. 
16. Bertrand ME, Rupprecht HJ, Urban P, Gershlick AH; CLASSICS Investigators. Double-blind study of the safety of clopidogrel with and without a loading dose in combination with aspirin compared with ticlopidine in combination with aspirin after coronary stenting: the clopidogrel aspirin stent international cooperative study (CLASSICS). Circulation. 2000;102(6):624-629. 
17. Serruys, PW, Strauss BH, Beatt KJ, et al. Angiographic follow-up after placement of a self-expanding coronary-artery stent. N Engl J Med. 1991;324(1): 13-17. 
18. Serruys PW, de Jaegere P, Kiemeneij F, et al. A comparison of balloon-expandable- stent implantation with balloon angioplasty in patients with coronary artery disease. Benestent Study Group. N Engl J Med.1994;331(8):489-495. 
19. Fischman DL, Leon MB, Baim DS, et al. A randomized comparison of coronarystent placement and balloon angioplasty in the treatment of coronary artery disease. Stent Restenosis Study Investigators. N Engl J Med. 1994;331(8): 496-501. 
20. Serruys PW, van Hout B, Bonnier H, et al. Randomised comparison of implantation of heparin-coated stents with balloon angioplasty in selected patients with coronary artery disease (BENESTENT II). Lancet.1998;352(9129):673-681. 
21. Solinas E, Dangas G, Kirtane AJ, et al. Angiographic patterns of drug-eluting stent restenosis and one-year outcomes after treatment with repeated percutaneous coronary intervention. Am J Cardiol. 2008;102(3):311-315. 
22. Morice MC, Serruys PW, Sousa JE, et al; RAVEL study group. A randomized comparison of a sirolimus-eluting stent with a standard stent for coronary revascularization. N Engl J Med. 2002;346(23):1773-1780. 
23. Stone GW, Moses JW, Ellis SG, et al. Safety and efficacy of sirolimus- and paclitaxel-eluting coronary stents. N Engl J Med. 2007;356(10):998-1008. 
24. Stone GW, Ellis SG, Cox DA, et al; TAXUS-IV Investigators. A polymer-based, paclitaxel-eluting stent in patients with coronary artery disease. N Engl J Med. 2004;350(3):221-231. 
25. Kastrati A, Mehilli J, Pache J, et al. Analysis of 14 trials comparing sirolimuseluting stents with bare-metal stents. N Engl J Med. 2007;356(10):1030-1039. 
26. Windecker S, Remondino A, Eberli FR, et al. Sirolimus-eluting and paclitaxeleluting stents for coronary revascularization. N Engl J Med. 2005;353(7):653- 662. 
27. Diletti R, Farooq V, Girasis C, et al. Clinical and intravascular imaging outcomes at 1 and 2 years after implantation of ABSORB everolimus eluting bioresorbable vascular scaffolds in small vessels. Late lumen enlargement: does bioresorption matter with small vessel size? Insight from the ABSORB cohort B trial. Heart. 2013;99(2):98-105. 
28. Diletti R, Serruys PW, Farooq V, et al. ABSORB II randomized controlled trial: a clinical evaluation to compare the safety, efficacy, and performance of the Absorb everolimus-eluting bioresorbable vascular scaffold system against the XIENCE everolimus-eluting coronary stent system in the treatment of subjects with ischemic heart disease caused by de novo native coronary artery lesions: rationale and study design. Am Heart J. 2012;164(5):654-663. 
29. Dudek D, Onuma Y, Ormiston JA, Thuesen L, Miquel-Hebert K, Serruys PW. Four-year clinical follow-up of the ABSORB everolimus-eluting bioresorbable vascular scaffold in patients with de novo coronary artery disease: the ABSORB trial. EuroIntervention. 2012;7(9):1060-1061.