SPECIAL SECTIONS
ACC expert consensus document on coronary artery stents
Document of the American College of Cardiology1
David R. Holmes, Jr., MD, FACC, Lead Author,
John Hirshfeld, Jr., MD, FACC, Lead Author,
David Faxon, MD, FACC, Lead Author,
RonaldE Vlietstra, MD, FACC, Lead Author,
Alice Jacobs, MD, FACC, Lead Author,
Spencer B. King, III, MD, FACC, Lead Author,
Thomas M. Bashore, MD, FACC, Co-author,
Nancy D. Bridges, MD, FACC, Co-author,
Charles B. Higgins, MD, FACC, Co-author,
Loren F. Hiratzka, MD, FACC, Co-author,
William C. Little, MD, FACC, Co-author,
Raymond D. Magorien, MD, FACC, Co-author,
Michael A. Nocero, Jr., MD, FACC, Co-author,
Stephen Oesterle, MD, FACC, Co-author,
Robert A. Vogel, MD, FACC, Co-author,
James S. Forrester, MD, FACC, Chair Technology Practice Executive Committee,
Pamela S. Douglas, MD, FACC, Technology Practice Executive Committee,
David P. Faxon, MD, FACC, Technology Practice Executive Committee,
John D. Fisher, MD, FACC, Technology Practice Executive Committee,
Raymond J. Gibbons, MD, FACC, Technology Practice Executive Committee,
Jonathan L. Halperin, MD, FACC, Technology Practice Executive Committee,
Adolph M. Hutter, Jr., MD, MACC, Technology Practice Executive Committee,
Judith S. Hochman, MD, FACC, Technology Practice Executive Committee,
Sanjiv Kaul, MD, FACC, Technology Practice Executive Committee,
William S. Weintraub, MD, FACC, Technology Practice Executive Committee,
William L. Winters, Jr., MD, MACC, Technology Practice Executive Committee and
Michael J. Wolk, MD, FACC, Technology Practice Executive Committee
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Contents
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- Executive Summary 1472
- Preamble 1473
- Introduction 1473
- Description and Analysis of Technology 1473
- Basic Technology 1473
- Balloon Expandable 1473
- Self-Expanding 1473
- Stents as Local Delivery Devices 1473
- Method of Data Collection 1473
- Potential Indications for Stenting 1474
- Prevention of Restenosis 1474
- Summary 1474
- Issues in Evaluating Stent Restenosis Trials 1474
- Chronic Total Occlusion 1475
- Summary 1475
- Saphenous Vein Graft (SVG) Disease 1475
- Summary 1475
- Acute Myocardial Infarction 1476
- Summary 1476
- Treatment of Restenotic Lesions 1476
- Summary 1476
- Small Vessels 1476
- Summary 1477
- Long Lesions and Diffuse Disease 1477
- Summary 1477
- Treatment of Acute or Threatened Closure 1477
- Summary 1477
- Other Unfavorable Lesions 1477
- Bifurcation Lesions 1477
- Ostial Lesions 1477
- Left Main Coronary Artery Disease (LMCA) 1477
- Generalizability of Current Knowledge 1478
- Which Patients/Lesions Should Be Stented? 1478
- Adjunctive Approaches: High Pressure Deployment and Adjunctive Therapy 1478
- Summary 1479
- IIb/IIIa Drugs 1479
- Combined Therapies 1479
- Stents and Radiation 1479
- Intravascular Ultrasounds (IVUS) 1479
- Summary 1480
- Physiologic Assessment 1480
- Cost Implications for Stenting 1480
- Conclusions 1480
- References 1480
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Executive summary
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This Expert Consensus document updates the initial document published in 1996.
In summary.
- Stenting, particularly with high pressure postdeployment balloon inflation and adjunctive therapy with acetyl salicylic acid (ASA) and ticlopidine have been proven to reduce angiographic and clinical restenosis compared to conventional dilatation. In several areas, widespread clinical practice patterns have occurred in advance of rigid controlled scientific data. The consensus recommendations are based upon scientifically controlled trials, single and multicenter experience and clinical practice.
- In selected patients with focal stenosis in native coronary arteries, stent implantation with high pressure postdeployment inflation and adjunctive therapy with ASA and ticlopidine have been definitively proven to reduce angiographic and clinical restenosis compared to conventional dilatation.
- Stenting can improve the longer-term outcome of selected patients being treated for chronic total occlusion and can result in improved restenosis rates in selected patients.
- Vein graft disease remains a significant problem because of the often diffuse nature of the process and the underlying severe coronary artery disease. In selected patients and lesions, stents have resulted in improved initial success rates and larger acute angiographic gain. Restenosis rates and longer-term morbidity remain increased.
- Stenting is a promising approach to optimize the results of catheter-based therapy and to treat complications of primary angioplasty. Whether stenting should be used only to treat suboptimal results or should be recommended as a primary therapy is still under study. Randomized trials within the next 2 years should resolve these issues.
- Stenting results in improved outcome in selected patients with restenosis following conventional percutaneous transluminal coronary angioplasty (PTCA). In contrast, the role of stenting for instent restenosis is uncertain. It may be useful for focal stenoses, and when conventional dilatation does not result in an excellent angiographic outcome. For diffuse instent restenosis, there are insufficient data upon which to base a recommendation.
- The currently available data on treatment of small vessels indicate that it is safe but that it does not result in improved longer-term outcome compared with conventional PTCA provided that dilatation gave a satisfactory initial result. Stents remain useful in this setting if the results of conventional PTCA are suboptimal with persistent significant residual obstruction.
- The treatment of long lesions or diffuse disease remains problematic. Long stents or multiple stents may play an important role when the result of conventional dilatation is suboptimal. Restenosis rates appear to be increased but may be improved compared with conventional PTCA.
- Intravascular ultrasound provides substantial information as an adjunctive approach to guide stent placement. Accumulating data indicate that it can be used to optimize early and longer-term outcome in selected patients.
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I. Preamble
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Topics chosen for coverage by Expert Consensus documents are designated because the evidence base and experience with the technology or clinical practice are not sufficiently well developed to be evaluated by the formal American College of Cardiology/American Heart Association (ACC/AHA) Practice Guidelines process. The Expert Consensus document represents the ACC’s best attempt to guide clinical practice in areas where rigorous evidence is not fully mature. Such documents require frequent revision. Ever since the initial Expert Consensus on Coronary Stents (1), the knowledge base has increased significantly. In many institutions, stents are the most commonly performed interventional cardiology procedure (2).
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II. Introduction
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More than 500,000 Americans and 1,000,000 patients worldwide undergo a nonsurgical coronary artery interventional procedure yearly. In many laboratories, stents are now used in over 50% of cases (2). The first Expert Consensus document (3) included two completed trials using a single type of stent (Palmaz-SchatzTM) (3–5) and the approval process that culminated in Food and Drug Administration (FDA) approval of two stents: 1) the Gianturco-RoubinTM (G-R) approval for acute or threatened closure during coronary intervention (6–9) and 2) the Palmaz-SchatzTM (P-S) for selected patients eligible for balloon angioplasty with discrete, de novo native coronary artery lesions in large-millimeter vessels.
Only a small percentage of patients undergoing percutaneous coronary revascularization are candidates for stents based upon the initial FDA-approved selection criteria. The greatly expanded practice of stenting for other indications was the result of widespread operator experience, significant changes in implantation procedures with high pressure balloon inflation, changes in adjunctive medications including ASA and ticlopidine, documentation of continued improved early and long-term results, and continued insights from complementary techniques such as Intravascular ultrasound (IVUS) and coronary flow or gradient measurements.
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Description and analysis of technology
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Basic technology.
There are two broad groups of stent devices: 1) balloon expandable and 2) self-expanding. Within these groups, there is substantial variability, which has led to approximately 500 issued stent-related patents using a variety of delivery systems, metals, architecture, length and design. In addition, new stent designs allow delivery of drugs, radiation or other biological material to help further reduce stent thrombosis and possibly restenosis.
Balloon expandable.
At the time of the initial consensus document, there were only two FDA-approved stents (i.e., G-R and P-S) both of which are balloon expandable. During 1998, it is anticipated that approximately nine balloon-expandable stents will be available in the United States. The structure of balloon-expandable stents ranges from metallic coils arranged in different patterns to slotted tubular designs to hybrids. Device performance, deliverability, flexibility, radial strength, accessibility to side branches, and radio-opacity vary. The method of delivery also varies (i.e., sheathed stents vs. bare metal stents). Clinically important differences in performance parameters between different stents are difficult to assess.
Self-expanding.
This group includes the initial stent used in coronary arteries, the Wallstent (Medinvent-Schneider, Lausanne, Switzerland) (10–12). Although this initial stent has been modified, its fundamental properties remain unchanged (13). There are also other newer devices in this group with some unique metals. Nitinol, for example, can expand to a predetermined size. This feature may foster continued local arterial enlargement over time (14). Self-expanding devices require some type of sheath; this may limit some devices because of the added bulk and external diameter of the sheath.
Stents as local delivery devices.
Various local drug delivery devices are currently available. These have not used a stent platform. At the present time, heparin has been used to coat stents. In the future, other coatings will be available that have the potential to improve early and longer-term outcome.
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Method of data collection
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The rapid evolution of stent design, deployment approaches, and adjunctive therapy have led to changes in clinical practice patterns that precede rigidly controlled supporting scientific data. This Expert Consensus document uses data from both randomized clinical trials and observational studies. Recently completed but not yet published clinical trials are also included. Multicenter randomized trials were given more weight in recommendations than were single-center observational experiences.
Currently, several randomized trials are comparing one stent versus another (15), which will allow evaluation of some aspects of device performance (e.g., procedural success, need for device crossover and clinical outcome). These trials are designed as equivalency trials (16–18) rather than the traditional superiority trial design used in STRESS (4) and BENESTENT (5). As a greater variety of stent designs becomes available, there will be increasing emphasis on matching the specific device to the angiographic anatomy. This will become increasingly important as stents are used in less ideal lesions (e.g., calcified small vessels, ostial stenoses, vein graft disease, and long lesions).
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Potential indications for stenting
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Potential indications for stents include 1) prevention of restenosis, 2) optimizing the initial result of treatment in lesions felt to be high risk because of adverse angiographic characteristics, 3) optimizing the result of conventional PTCA, and 4) treatment of acute or threatened closure.
Prevention of restenosis.
In the STRESS-I (4) and BENESTENT-I (5) trials, reduction in restenosis was the result of achieving a larger initial lesion minimal lumen diameter. Although stenting resulted in more late loss of diameter than did PTCA, the loss was more than compensated by the greater initial acute gain.
The subsequent randomized BENESTENT-II trial of stent implantation using current deployment techniques versus conventional PTCA included 827 patients with selection criteria similar to that in BENESTENT-I (19,20). Angiographic restenosis rates were significantly less in patients randomized to the heparin-coated stent (17.0% vs. 31.0%), a reduction of 45% (p < 0.01). Angiographic restenosis rates were similar to the low rates seen in BENESTENT-II pilot (21) and slightly less than in BENESTENT-I. The results of conventional dilatation were also markedly improved compared to historical controls.
Assessment of stents for reducing restenosis is, in part, dependent on the definition of restenosis. Although angiographic documentation of restenosis is an objective end point, from the patient’s standpoint, clinical restenosis is more important. Assessment of clinical restenosis is less rigorous, because it can be affected by the presence of untreated lesions, medication use, the disparity between symptoms and angiographic findings, and the lack of patient and physician blinding. Target lesion or target vessel revascularization (TLR) has been used as a surrogate for angiographic restenosis, although with multiple lesions that may be problematic. In BENESTENT-I, there was a significant reduction in need for repeat revascularization (10.0% vs. 20.6%, p = .001) at 1 year (21). In BENESTENT-II, the magnitude of the benefit was somewhat less. The TLR in the stented group was 13%, compared to 15.7% for the PTCA group. In the Multicenter Ultrasound Stenting in Coronaries Study (MUSIC) (22), 161 patients with stable angina and a de novo native coronary artery lesion were treated with a second-generation P-S stent using IVUS guidance. When predetermined IVUS criteria were met, patients were treated only with ASA. Subacute stent thrombosis was documented in two patients (1.3%). Repeat angiography was performed at 6 months in 140 patients (89%). Restenosis (diameter stenosis >50% at follow-up) was documented in only 11 patients (8%), and target lesion revascularization was required in only 7 patients (4.5%).
It must be kept in mind that when conventional dilatation results in an excellent angiographic result with a residual stenosis <20% or when normal physiologic flow reserve has been restored, restenosis rates have also been found to be decreased compared with historical cohorts of patients undergoing PTCA.
Longer-term follow-up data for stents is now available. Kimura et al. (23) performed serial angiography at 6, 12 and 36 months after P-S stent placement in 143 patients. They confirmed that the major loss in minimum lumen diameter (MLD) occurred within the first 6 months: 2.55 ± 0.46 mm immediately following implantation to 1.94 ± 0.48 at 6 months, 1.95 ± 0.46 at 1 year and 2.09 ± 0.48 at 3 years (p < 0.001).
Although much of the published benefit in restenosis reduction with stent implantation has been confined to analysis of P-S stents, a current group of randomized trials indicates that restenosis rates with newer-generation devices (e.g., ACS MultilinkTM, AVE, and Sci Med NIRTM stents are similar). An exception to this appears to be the Gianturco-Roubin (G-R) IITM stent, which has higher restenosis rates (24) that may relate to stent design or implantation techniques.
Summary.
In selected patients with focal stenosis in native coronary arteries, stent implantation with high pressure postdeployment inflation and adjunctive therapy with ASA and ticlopidine have been definitively proven to reduce angiographic and clinical restenosis compared to conventional dilatation.
Issues in evaluating stent restenosis trials.
Current stent trials utilize clinical events including TLR as primary end points with an angiographic or IVUS substudy to examine mechanisms. An important consideration in use of TLR is that after routine follow-up angiography, there is often a "flurry" of additional revascularization procedures. In the BENESTENT-II trial of conventional PTCA versus stent implantation, one-half of each group had angiographic follow-up, and one-half had clinical follow-up alone (25). In those patients undergoing angiographic follow-up, the incidence of repeat TLR was significantly greater (14.4% vs. 9.1%). Thus, the results of follow-up angiography may affect subsequent clinical decisions irrespective of patient symptoms. The rates of revascularization are higher in studies with mandated routine angiographic follow-up.
Another important issue is that the randomized trials of stent implantation compared with conventional PTCA involve highly selected patient and lesion subsets. Recent data indicate that lesions and patients meeting STRESS/BENESTENT criteria account for only about 25% of current stent practice. In the remainder of the patients and lesions, data are lacking as to the impact of stenting on reduction in restenosis. Restenosis rates may or may not be superior to conventional PTCA, but they are likely to be higher than those in STRESS/BENESTENT ideal lesions. Many of these other lesion/patient subsets are currently being studies in randomized trials.
Chronic total occlusion.
The treatment of chronic total occlusion (CTO) with conventional PTCA has been limited by the inability to cross the occlusion, increased restenosis rates, the size of the distal vessel, and viability of myocardium supplied by the occluded vessel. If the vessel is small and supplies only infarcted myocardium, there is no need for revascularization. In the multicenter trial MERCATOR (26), patients with successful dilatation of a CTO had a 6-month restenosis rate of 49%. One of the most important findings has been that, after successful PTCA of a CTO, the artery reoccludes in approximately 20% of patients. Stenting may affect this favorably.
There are several small reports of PTCA versus stenting for CTO. Sirnes et al. (27) evaluated the outcome of 117 patients with chronic total occlusion treated with either PTCA or a P-S stent. At the time of follow-up, there were significant differences in restenosis (32% vs. 74%, p < 0.001), target lesion revascularization (22% vs. 42%, p = 0.025), and freedom from angina (57% vs. 24%, p < 0.001) favoring patients treated with stents. In another study of 96 patients, Mori et al. (28) found a restenosis rate of 28% in patients receiving stents compared to 57% of patients treated with PTCA alone (p = 0.005). There was also a significant decrease in repeat target lesion revascularization in stented patients (p = 0.05).
Summary.
Stenting can improve the longer-term outcome of patients being treated for chronic total occlusion and can result in improved restenosis rates in selected patients.
Saphenous vein graft (SVG) disease.
Interventional treatment of SVG disease has increased the risk of both acute complications and late restenosis. As outlined in the first consensus document, observational multicenter data on both coronary P-S and biliary stent implantation appeared to show improved initial success rates and better longer-term outcome. In the most recent observational experience of 589 patients (29), the initial procedure success rate was 98.8%. At a mean follow-up of 8.1 ± 4.0 months, angiographic restenosis was 30%. However, the incidence of mortality was 5%, and 19.1% of patients had either death, Q-wave infarction or had repeat bypass surgery.
The multicenter randomized trial SAVED (Saphenous Vein Graft De Novo Study) (30) compared P-S stents to PTCA in de novo lesions, which required no more than two stents. All patients had angina and/or evidence for ischemia, preserved left ventricular function, and no contraindications to anticoagulation. The mean vein graft age was 10 years with a mean diameter of 3.19 mm. Technical success (<50% stenosis by quantitative coronary angiography [QCA] was 95% in the stent group compared with 75% for PTCA (p < 0.0001). Postprocedural MLD was 2.81 mm with the stent versus 2.16 mm (p < 0.0001) with PTCA. Clinical success was 92% for a stent and 69% for PTCA (p < 0.0001). There was a trend toward fewer non-Q-wave myocardial infarctions (MI) in stented patients (2 vs. 7 patients, p = 0.01), whereas Q-wave MI, death or need for bypass surgery occurred at similar rates in each group. At 6 months, late loss with stents was greater (1.04 mm vs. 0.68 mm, p = 0.01) but net gain remained significantly larger (0.87 mm vs. 0.52 mm) (p = 0.015). The major cardiac event rate (death, MI, need for repeat revascularization) at 6 months was 26% after stenting versus 38% for PTCA (p = 0.05). However, there was no difference in angiographic restenosis: 37% with stents, 46% with PTCA (p = 0.24).
The Palmaz Biliary stent, which has greater radial strength, a larger expanded diameter, and variable length, has been widely used for vein grafts. Single-center and multicenter experiences have documented good initial success rates (31,32), but higher follow-up mortality. Wong et al. (32) reported a single-center experience of 188 biliary stents in 124 patients with 163 vein graft lesions. In 82.8% of patients, a single stent was placed with angiographic success in 98.8% of cases. Major complications (death, emergency coronary artery bypass grafting [CABG], subacute thrombosis) occurred in 3.3% of patients and non-Q-wave infarction in 11%, and vascular complications and vascular repair in 10.1% of patients. The vascular complications reflect intense antiplatelet/anticoagulant regimens that were utilized at that time. During a mean follow-up of 142 ± 75 days in 115 patients, event-free survival was 80%.
Summary.
Vein graft disease remains a significant problem because of the often diffuse nature of the process and the underlying severe coronary artery disease. In selected patients and lesions, stents have resulted in improved initial success rates and larger acute angiographic gain. Restenosis rates and longer-term morbidity remain increased compared to stenting in large native coronary arteries.
Acute myocardial infarction.
Multiple small observational studies of stents for acute myocardial infarction (MI), either as a primary procedure or for bailout after unsuccessful direct PTCA, appear promising. In a prospective multicenter trial, Stone et al. (33) analyzed 312 patients treated with primary PTCA. Stenting was attempted in 240 patients and was successful in 98% of patients, with restoration of TIMI-3 (Thrombolysis in Myocardial Infarction trial) flow in 96%. Patients treated with stents had improved final diameter stenosis (12 ± 16% vs. 33 ± 14% for PTCA) and by 30 days required fewer subsequent revascularization procedures (3.4% vs. 12.5% for PTCA, p = 0.003). In-hospital mortality in stented patients was 0.8%, and 1.7% had recurrent ischemia.
These and other data provide the basis for the multiple current randomized trials of PTCA versus primary stenting for acute infarction (15). The FRESCO trial (34) randomized patients treated for acute infarction in whom primary angioplasty had already achieved an excellent result (defined as either a residual stenosis of <30% and TIMI-3 flow) to either adjunctive stenting or no stenting. One hundred forty-six patients were randomized. Rates of recurrent ischemia, restenosis, and reocclusion were significantly improved in the stented patients. This improvement was maintained at 6 months. Although incomplete angiographic follow-up was available, the stented patients had a 12% incidence of restenosis or reocclusion compared to 52% of the nonstented patients.
A second trial of acute infarction (ESCOBAR) (35) enrolled 204 patients randomized to either PTCA or stent. The success rate was 96% and 98%, respectively. There was a significant difference in the frequency of subacute closure and recurrent myocardial infarction, with the stented patients having improved outcome. Recurrent MI was seen in 2% in the stent group versus 7% in the PTCA group.
The large Primary Angioplasty in Myocardial Infarction Study Group (PAMI) Stent trial has recently been reported that randomized 452 patients to stent implantation and 440 to conventional PTCA. At 30 days, there was no statistically significant difference in mortality (3.5% stent; 1.8% PTCA), but there was a reduction in need for repeat target vessel intervention (0.9% for stent vs. 3.5% for PTCA). Several other trials including the 2000-patient Cadillac trial are currently being performed (15).
Summary.
Stenting is a promising approach to optimize the results of catheter-based therapy for acute MI and to treat complications of primary angioplasty. Whether stenting should be used only to treat suboptimal results or should be recommended as a primary therapy is still under study. Ongoing randomized trials should resolve these issues.
Treatment of restenotic lesions.
The restenosis rate after PTCA and other coronary interventional procedures is 30% to 50%. In all series, clinical restenosis or restenosis requiring treatment is less frequent than angiographic restenosis. The responsible mechanisms include remodeling, neointimal hyperplasia, and recoil. Restenosis following stenting usually results from neointimal hyperplasia, although, occasionally it may be the result of tissue prolapse or inadequate coverage of the initial lesion.
When restenosis occurs after PTCA, the predominant mechanisms are recoil and remodeling, both of which respond well to stent implantation. The importance of recoil after conventional PTCA was evaluated by Rodriguez et al. (36), who performed routine follow-up angiography at 24 hr after successful balloon angioplasty in 191 consecutive patients. Sixty (36%) had excessive lumen loss greater than 0.3 mm. Patients were randomized to receive either standard medical therapy or a GR stent. At a mean follow-up of 3.6 months, follow-up angiography documented restenosis in 76% of the medically treated patients compared to 21% of the stented patients (p < 0.001).
Columbo et al. (37) reported on 125 patients treated with stents for restenosis after PTCA. The acute success rate was 98%, with a late angiographic restenosis rate of 25% and clinical restenosis of 17%. The REST trial (38) (stent vs. PTCA restenosis trial) randomized 351 patients with restenosis to either a P-S stent or PTCA. There was a significant decrease in need for target vessel revascularization (10% in stented patients vs. 27% in PTCA patients, p = 0.006) and angiographic recurrent restenosis (18% stent vs. 32% PTCA).
Instent restenosis (39–44) occurs in three forms: 1) diffuse neointimal hyperplasia throughout the stent; 2) discrete lesions within the body of the stent, which may result from tissue prolapse or initial inadequate coverage; and 3) margin restenosis, which is usually discrete and may result from a dissection caused by high pressure PTCA at the time of implantation. Both of the latter two types of instent restenosis respond well to conventional dilatation (45). Many investigators favor debulking of the neointimal tissue in diffuse instent restenosis, although there is limited data on this approach (46,47).
Summary.
Stenting results in improved outcome in selected patients, with restenosis following conventional PTCA. In contrast, the role of stenting for instent restenosis is uncertain. It might be useful for focal stenoses, and when conventional dilatation does not result in an excellent angiographic outcome. For diffuse instent restenosis, there is insufficient data upon which to base a summary.
Small vessels.
Although the early randomized stent trials by protocol design required reference vessel diameter  3.0 mm, a significant number of vessels when measured by quantitative angiography were found to be <3.0 mm (48). In STRESS-I and BENESTENT-I, in vessels <3.0 mm, the immediate results were improved in patients treated with stents, but the benefit in restenosis reduction was limited and did not reach statistical significance. In a meta-analysis of BENESTENT and STRESS I and II studies, in vessels <2.6 mm and greater than >3.4 mm, there was no advantage in either clinical events or restenosis of stents versus conventional PTCA with an excellent angiographic result (15). In BENESTENT for vessels <3 mm, there was no difference in the combined end point of death, infarction, coronary bypass or re-PTCA between PTCA (17.4) and stent (18.5). Although one of the concerns with stenting of small vessels has been the potential for an increase in subacute closure, this does not appear to be the case. An increasing number of observational studies in this group document safety and early efficacy. A randomized trial is currently underway.
Summary.
The currently available data on treatment of small vessels indicate that it is safe but that it does not result in improved longer-term outcome compared with conventional PTCA provided that dilatation gives a satisfactory initial result. Stents remain useful in this setting if the results of conventional PTCA are suboptimal with persistent significant residual obstruction.
Long lesions and diffuse disease.
Long lesions or diffusely diseased vessels are often calcified, and distal runoff may be compromised. Conventional PTCA is associated with increased acute complications (i.e., dissection, acute closure) and increased restenosis. Placement of multiple stents has been associated with increased rates of stent thrombosis (49). With changes in implantation techniques, including high pressure dilatation, aspirin/ticlopidine, intravascular ultrasound, and IIb/IIIa receptor inhibitors, overall complication rates have decreased. These advances, combined with the availability of longer, smaller and more flexible stents, make stenting more attractive. Although there are a number of observational series, there are no controlled trials. Kastrati et al. (50) reported 1,084 patients with 1,399 stented lesions undergoing follow-up angiography. The three factors associated with increased restenosis were placement of multiple stents, diabetes mellitus, and minimal lumen diameter (MLD) immediately after stent implantation. Although long lesions (51) and diffuse disease subsets may have increased restenosis rates with stenting, they may still be improved compared with conventional PTCA. This area needs further study.
Summary.
The treatment of long lesions or diffuse disease remains problematic. Long stents or multiple stents may play an important role when the result of conventional dilatation is suboptimal. Restenosis rates appear to be increased but may be improved compared with conventional PTCA.
Treatment of acute or threatened closure.
Ever since preparation of the initial Expert Consensus document, there is increasing data on the importance of treating acute or threatened closure with stent implantation (5,7,8,50,52–54). The incidence of acute or threatened closure has been decreasing in current interventional practice. In STRESS the incidence of abrupt closure rate was 1.5% in patients treated with PTCA. This may be the result of early stent deployment when dissections are first identified but before the onset of acute or threatened closure. In EPILOG, BOAT, and BENESTENT-II, provisional stenting (i.e., stenting to treat suboptimal results with PTCA or atherectomy) was used in 14% of patients (55).
Summary.
Stenting is the treatment of choice of either acute or threatened closure complicating PTCA and for treatment of dissection. The goal should be to restore full TIMI-3 flow. Emergency surgery may still be required in some cases—for example, a dissection involving the left main or significant bifurcations, refractory thrombosis, loss of guide wire access, or inability to deliver a stent to the target site.
Other unfavorable lesions.
There are other lesion subsets for which there are only observational reports but no randomized data.
Bifurcation lesions.
Treatment of bifurcation lesions is associated with increased early complications including compromise of either the branch vessel or the target lesion, and increased potential for restenosis because of inadequate initial result. Stenting has an additional potential problem in that it may impair access to the side branch. Newer stent approaches including bifurcation stents, T stents, and protective guide wires may improve outcome, but further study is needed. Prior to stenting, the size of the branch, target lesion, presence and severity of ostial stenosis, and angle of the branch must be taken into account.
Ostial lesions.
Ostial lesions respond poorly to conventional PTCA, with inadequate dilation and elastic recoil. In addition, a major branch may arise from the ostium. Stents can be an excellent treatment for elastic recoil. Whether debulking is also required is uncertain. Stent implantation must be precise—if positioned too proximally, the device may protrude into the aorta and make repeat catheterization difficult, or may compromise a branch vessel.
Left main coronary artery disease (LMCA).
Stenting of the LMCA is being performed relatively infrequently, primarily in patients who have had prior coronary bypass surgery (56). Debulking is frequently performed with rotational atherectomy because of calcification. Stenting can result in improved initial and longer-term outcomes compared with balloon angioplasty.
Stenting is also being performed in patients who have not undergone prior CABG. The outcome in these patients depends upon the baseline characteristics. In patients who are excellent surgical candidates, the results may be superior to those obtained in patients who are poor operative candidates. No long-term comparison study with surgical results has been performed.
Generalizability of current knowledge.
Stents differ substantially in design and material. These differences may affect outcomes. Current randomized trials may allow detection of differences between stents, and between lesions under treatment (57).
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Which patients/lesions should be stented?
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Philosophies regarding which patients and/or lesions should be treated with a stent as opposed to conventional PTCA still differ substantially. In the United States, 40% to 50% of angioplasty patients receive at least one stent. However, there are operators who use them more often and others who use them less. At one extreme is the position that every patient undergoing dilatation should receive a stent if it can be placed. With such an unrestricted strategy, stenting is performed prophylactically. Inherent in this approach is the fact that some stents would not have been necessary. This is important because instent restenosis is more difficult to manage than restenosis after conventional PTCA.
The other approach is provisional stenting. Randomized trials and observational series have documented that when an ideal result is achieved with conventional PTCA, measured either with quatitative coronary angiography or with physiologic assessment, stenting is not required to achieve an excellent longer-term result (58). With provisional stenting, the operator chooses initial conventional dilatation equipment estimated to achieve an excellent or ideal result with PTCA. If such an excellent or ideal result is obtained with PTCA then stenting is not performed. If results of PTCA are suboptimal, stenting is performed.
The percentage of patients in which "ideal" PTCA result is achieved is about 25% to 50%. These patients would avoid the need for stenting. The cost-effectiveness of provisional stenting has not yet been established.
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Adjunctive approaches: high pressure deployment and adjunctive therapy
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The major factors responsible for the dramatic increase in stent implantation have been the changes in deployment technique:
Stent deployment.
During initial experience with stenting, low pressure deployment was felt to be adequate. However, IVUS examination documented that, with low pressure, although the stent appeared to be fully deployed by angiography, there was not full apposition to the arterial surface, creating a risk for subacute closure. With this fundamental insight, investigators changed deployment techniques to incorporate a "high pressure" approach, to expand the stent fully and appose it to the vessel wall. Currently, balloons accommodate inflation pressures as high as 25 atmospheres (atm). At the present time, stents usually are dilated following initial deployment with a higher pressure balloon to 12–16 atm. If the angiographic or IVUS results are not satisfactory, then either higher pressure or a larger balloon (e.g., an increase by 0.25 to 0.50 mm) or both are used. Newer stent delivery systems incorporate high pressure balloons so that the stent can be delivered, deployed and dilated with relatively high pressure using the same balloon.
The exact definition of high pressure inflation has yet to be determined. The French Multicenter Registry (59) has reported a consecutive, prospectively enrolled group of 2,900 patients utilizing high pressure stent deployment (mean of 12.4 ± 3.05 atm) without IVUS guidance. A 1-month event-free outcome was achieved in 97.1% of patients. Stent-related cardiac events were subacute closure (1.8%), death (0.5%), acute infarction (0.6%) and coronary bypass surgery (0.3%). Whether these excellent results reflect the need to use only lower pressure, patient selection, or operator experience is unclear.
There is debate as to whether excessively high pressure and stent oversizing may be deleterious. In some patients, high pressure may cause margin dissection at the junction of the stent with the adjacent artery. Short of performing routine IVUS after each inflation, routine high pressure (>12–16 atm) yields excellent results and is now relatively standard. Recently, the Can Routine Ultrasound Influence Stent Expansion Study (CRUISE) (60) has reported results. Two hundred and twenty-nine patients had IVUS performed during stent implantation to document final lumen; 270 patients had stent deployment with IVUS guidance. Investigators found that average minimal stent area was larger in the IVUS-guided limb as well as the angiographic MLD posttreatment. This resulted in a reduction in TLR (8.5% for IVUS guided vs. 15.3% p = 0.019). This study may change the utilization patterns of IVUS.
Pharmacotherapy.
In the ISAR (61,62) trial, patients who had successful P-S stent placement were randomized to either aspirin plus ticlopidine or anticoagulant therapy with heparin, warfarin and aspirin. At 30 days, the antiplatelet therapy group had a significant reduction in the risk of infarction, need for a repeat intervention, peripheral vascular events, and subacute closure. Consequently, many operators in the United States eliminated Coumadin in selected patients at low risk for stent thrombosis (63). Heparin is given only during the procedure, and access sheaths are removed as soon as the activated clotting time (ACT) returns to approximately 160 s, which is usually within 4 hr. Aspirin, 325 mg per day, is used routinely, and ticlopidine, 250 mg twice a day, is also added.
The STARS (64) trial has now been completed and should act as the reference document for adjunctive therapy. This study enrolled 1,961 patients and randomized 1,652 patients in a three-arm comparison-blinded evaluation of aspirin alone, aspirin plus warfarin, and aspirin plus ticlopidine. The prespecified primary end point was a composite 30-day ischemic end point that included death, Q-wave infarction, emergency bypass surgery and subacute closure. To be eligible for randomization, patients had to have no angiographic evidence of thrombus at the end of the procedure, less than 10% residual stenosis by visual estimate, no significant dissections following stent implantation, TIMI-3 flow into a target vessel without large side branch vessel occlusion and  two stents.
High pressures were used throughout the study with a mean maximum pressure of 16.8 atm. The primary end point results confirmed the ISAR data. In the aspirin group, the composite adverse end point occurred at 30 days in 3.6% of patients; in the aspirin plus warfarin group, the end point at 30 days occurred in 2.4%; and in the aspirin and ticlopidine group, the adverse end point was seen in only 3 days (0.6%). In this trial, ticlopidine was started the day of the procedure, usually in a dose of 500 mg; it was then continued at 250 mg twice a day.
Current deployment techniques combined with aspirin and ticlopidine have significantly decreased subacute closure rates. When it occurs, however, it still results in a major increase in severe complications (65,66). Hasdai et al. (65) reported on 29 patients with early coronary stent thrombosis over a 5-year period. The mean time from implantation to stent thrombosis was 6.1 ± 5 days. Various techniques were used to treat the stent thrombosis including angioplasty, angioplasty plus urokinase and intracoronary urokinase. Of the patients treated with a catheter-based approach, flow was restored without residual thrombus in 11 patients (48%). Despite restoration of flow, 90% of the patients developed acute MI and there were two deaths.
Although subacute closure rates are low with optimal stent deployment, if the outcome of stent deployment is suboptimal, subacute closure rates are increased. The STARS study included a registry of 310 patients who did not meet entry criteria because of suboptimal deployment. The combined end point of death, emergency surgery, Q-wave infarction, and subacute closure occurred in 7.8% of patients. Risks for subacute closure included multiple stents, persistent thrombus and decreased TIMI flow. In patients with suboptimal deployment, low molecular weight heparin is currently being tested in a randomized trial.
Ticlopidine has been an essential component to optimizing initial outcome. Neutropenia occurs in 1% to 3% of patients, but is rare prior to 14 days of treatment. Accordingly, an increasing number of centers use ticlopidine 250 mg bid for only 2 weeks (67). Ticlopidine may be started on the day of the procedure in combination with the aspirin rather than two to three days before stent implantation (54). An unanswered question relates to the need for ticlopidine if IVUS is used to guide deployment. In the MUSIC study (22), the subacute closure rate was only 1.3% with monotherapy with ASA. Recently, thrombotic thrombocytopenic purpura after ticlopidine has received considerable attention because it markedly increases morbidity and mortality (68).
Clopidogrel, similar to ticlopidine but with fewer side effects, particularly less bone marrow suppression, has been approved for use. Although it has not been tested with stent implantation, it is now used relatively frequently. It may reduce the adverse effects currently seen with ticlopidine without increasing the incidence of subacute closure.
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Summary
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Stents should be deployed with a high pressure technique utilizing 12–16 atm in combination with soluble aspirin 325 mg qd given indefinitely and ticlopidine 250 mg bid for 2 to 4 weeks. On the day of the procedure the ticlopidine can be initiated with a dose of 500 mg. Clopidogrel may replace ticlopidine in the future. Care should be taken to prevent or treat suboptimal deployment because it increases the risk of subacute closure.
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IIb/IIIa drugs
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There is only limited data available on the use of IIb/IIIa drugs (69–72). In three clinical trials with ReoProTM, the EPILOG trial, the EPIC trial, and the CAPTURE trial, 529 patients received stents, the majority on a provisional basis. The abciximab was given prospectively at the beginning of the case independent of the subsequent decision to use a stent. Administered after the development of complications, the agent may not be as effective. A preliminary analysis in these three trials indicates that the 30-day end point of death or MI or urgent revascularization was reduced at 30 days. The 6-month outcome data are limited in these patients.
The use of combined stenting plus IIb/IIIa drugs (73) increases the cost of the procedure and raises safety concerns. The safety concerns appear to have been addressed in these initial patients by weight-adjusting heparin and early sheath removal and discontinuing heparin after the procedure. The EPISTENT trial has now been reported, although full details are not available. A total of 2,399 patients were randomized to 1) stent plus abciximab, 2) PTCA plus abciximab, or 3) stents alone. Thirty-day events were markedly improved in the stent plus abciximab mainly by a reduction in non-Q-wave infarction reflected by creatine kinase, MB fraction (CK-MB) elevation. Whether abciximab or a similar drug is indicated in all stent patients is not yet clear.
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Combined therapies
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Debulking followed by stenting to optimize initial and final outcome has been tested with rotational atherectomy, directional coronary atherectomy, and also with transluminal extraction atherectomy (TEC). A small number of reports appear to show some advantage. Multicenter studies are currently in early stages of development and performance.
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Stents and radiation
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There is intense interest in local radiation to prevent restenosis—both with gamma as well as two with beta radiation. One small randomized trial evaluated gamma radiation in a high risk group of 55 patients with restenosis (74). Both statistically and clinically significant improvement was shown in angiographic, ultrasound and clinical end points. Currently, a large number of trials are underway in a variety of patients and lesion subsets, and with a variety of approaches.
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Intravascular ultrasounds (IVUS)
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The tomographic orientation of IVUS enables visualization of the full 360° circumference of the vessel wall and permits direct measurements of lumen dimensions including minimum and maximum diameter and cross-sectional area (75–79). Information from IVUS is additive to that obtained from angiography. Because of the lattice characteristics of stents, radiographic contrast material can surround the stent, producing an angiographic appearance of a large lumen even when the stent struts are not in full contact with the vessel wall. Several studies document the importance of full apposition of the stent struts to the vessel wall. A large observational IVUS study (76) following angiographically guided stent deployment revealed an average residual plaque area of 51% comparing minimum stent diameter to the reference segment diameter, and incomplete wall apposition was frequent. In this cohort, additional balloon inflations resulted in a final average residual plaque area of 34%, even though the final angiographic percentage stenosis was negative (–0.7%). Employing ultrasound to guide deployment, these same authors reported a subacute thrombosis rate of 0.3% using antiplatelet agents.
In the era of higher stent deployment pressures with aspirin and ticlopidine therapy, the added value of IVUS is uncertain. In the French registry study of 2,900 patients treated without warfarin and without IVUS, subacute closure rate was 1.8% (59). In the randomized STARS trial (64), which did not require IVUS, a subacute closure rate in ideal implantation outcome patients was 0.6%. At present, IVUS remains very important in studying newer stent designs, and in evaluating the results of higher risk procedures—those with multiple stents, decreased TIMI flow and residual and marginal dissections. Whether IVUS-guided stent implantation will be able to improve long-term outcome is currently being evaluated in several randomized trials. The MUSIC trial (22) evaluated 161 patients in whom stent deployment was guided by ultrasound. Optimal stent expansion was evaluated according to predefined IVUS criteria; in 75% of patients, all three criteria were met. In the remaining 25%, at least one IVUS criterion was not met. In the group with optimal deployment, the subacute closure rate was 1.3% even though monotherapy with ASA was used in 86% of patients, angiographic restenosis was documented in only 8%, and target vessel revascularization was required in only 4.5% of patients. As previously mentioned, the CRUISE study (60) documented decreased TLR when stent deployment was guided by ultrasound.
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Summary
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Intravascular ultrasound provides substantial information as an adjunctive approach to guide stent placement. The accumulating data indicate that it can be used to optimize early and longer-term outcome in selected patients.
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Physiologic assessment
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Assessment of the physiology of coronary stenosis has been used to assay whether conventional PTCA has achieved a satisfactory result (77,80,81). The DEBATE trial (58) suggests that an ideal anatomic and physiologic result with conventional PTCA results in an intermediate-term clinical result comparable to stents. Widespread adoption of this approach may decrease stent usage. Physiologic assessment can also be used to assess the adequacy of stent implantation. Following satisfactory stent implantation, the coronary flow reserve should be normalized. The measurement of distal pressure under conditions of maximal flow may also be effective in assessing adequacy of deployment (81).
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Cost implications for stenting
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Evaluation of cost includes both direct and indirect costs of the initial procedures and follow-up costs of medical care (82–85). These evaluations must take into account the fact that conventional PTCA with a bailout stent option (provisional stenting) is improving long-term outcome. Routine stent implantation is more expensive initially than conventional PTCA, particularly when multiple stents are used. With the decreased need for subsequent TLR in selected patients to treat restenosis, as well as decreased subsequent hospital admissions for recurrent angina, longer-term costs of stenting may be more equal to balloon angioplasty. New adjunctive therapy such as IIb/IIIa drugs can change the cost/benefit ratio substantially.
Conclusions.
Stent implantation improves both short- and long-term outcome in selected patients. Multiple challenges still remain, including diffuse instent restenosis, treatment of bifurcation lesions, diffuse disease and small vessels. Resolution of these issues will further define the role of stenting in optimizing percutaneous approaches to treatment of coronary artery disease.
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ACC staff
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Christine W. McEntee, Executive Vice President
David P. Bodycombe, ScD, Director, Research and Information Management
Chrystal V. Calloway, Coordinator/Committee Liaison, Clinical Practice & Guidelines
Renée L. Hemsley, Research and Information Management Department
Gwen P. Pigman, MLS, Assistant Director, Griffith Resource Library
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Footnotes
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1 Address for reprints: American College of Cardiology, 9111 Old Georgetown Road, Bethesda, Maryland 20814-1699. 
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References
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