Bare-Metal Versus Drug-Coated Intracoronary Stents in Clinical Practice: Are There Guidelines?
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Introduction
The development of bare-metal stents (BMS) and optimal post-procedure antiplatelet therapy in the mid 1990s resulted in marked reductions in acute and subacute stent thrombosis, bleeding complications, negative remodeling, and acute vessel recoil, and a consequent dramatic rise in procedural success. Yet, intermediate-term outcomes remained hampered by restenosis from aggressive neointimal hyperplasia. The advent of drug-coated stents, which impede the growth of neointima while maintaining the strengths of BMS, heralded their widespread utilization to approximately 90% of procedures. Recently, however, very late stent thrombosis rates in excess of those seen with BMS were noted, prompting a reduction in the penetration of drug-coated stents to approximately 65% of all procedures. To date, there are no official guidelines on choice of bare-metal versus drug-coated stents in clinical practice. This article, therefore, summarizes current opinion regarding situations where BMS might be preferable to drug-coated stents, and where one drug-coated stent might be preferable to another, in hopes of guiding the clinician on optimal stent selection.
History of Percutaneous Coronary Intervention
Although a major breakthrough in technology and patient care, balloon angioplasty was fraught with several significant limitations, including uncontrollable plaque disruption and acute elastic recoil, leading to coronary occlusion and acute procedural myocardial infarction (MI). In addition, a 20–40% incidence of restenosis within the first 6–9 months was seen, due to a combination of negative vessel remodeling and neointimal hyperplasia.1 In addition to the development of recurrent ischemic symptoms, restenosis in this setting portended a poor prognosis.2 Balloon-expandable stents were developed to address these limitations. By scaffolding the vessel at the site of lesion disruption, they mitigated acute occlusion and elastic recoil, while virtually eliminating subsequent negative remodeling. However, there was an apparent increase in neointimal hyperplasia as a reaction to vessel injury from and inflammation to the foreign body, resulting in restenosis, albeit at lower rates than seen in the balloon angioplasty era.3,4 Two landmark trials solidified these findings and the benefits of BMS. The North American STRESS trial showed lower angiographic restenosis (31.6% vs. 42.1%) and lower target vessel revascularization (TVR, 10.2% vs. 15.4%) in patients who received a BMS versus balloon angioplasty, while the European BENESTENT trial confirmed these results (restenosis, 22% vs. 32% and TVR, 13.1% vs. 22.9%).5,6
Despite the marked improvement in procedural complications and intermediate-term clinical outcome with widespread utilization of BMS, two problems remained: subacute stent thrombosis and in-stent restenosis. Subacute stent thrombosis, defined as acute vessel occlusion within 30 days of the index procedure, was eventually reduced from 15% to the current rate of < 1% through a series of studies showing that combination anti-platelet agents are superior to anticoagulant-based regimens, dual antiplatelet therapy with aspirin and clopidogrel is optimal, and high-pressure balloon expansion of the stent optimizes deployment and further reduces this complication.7–10 With the control of subacute stent thrombosis, focus shifted to the prevention of neointimal hyperplasia and its associated restenosis. Indeed, for the next 10 years, restenosis was deemed the Achilles’ heel of percutaneous coronary intervention.
The Rise of Drug-Coated Stents
Despite the significant relative reduction in restenosis provided by BMS, observed restenosis rates remained in the 20–30% range in randomized controlled trials, and as high as 50–60% in real-world experience, particularly in the high-risk subgroups of diabetics, bifurcation lesions, small caliber vessels, chronic total occlusions, long lesions, and overlapping stents.1,5,6,11
As mentioned previously, neointimal hyperplasia was the dominant contributor to in-stent restenosis in the BMS era. Indeed, due to the higher degree of vessel wall injury with stent placement compared to balloon angioplasty, a more exuberant neontimal response was evidenced.12 Endothelial and medial injury as a result of stent deployment causes inflammation, leading to recruitment of macrophages and lymphocytes to the target lesion. The subsequent release of cytokines and growth factors activate dormant vascular smooth muscle cells, which proliferate, enter the intima, and produce abundant extracellular matrix, a process that continues for 6 to 9 months.13 After multiple failed attempts to control neointima formation with pharmacotherapy and brachytherapy,1,14 polymer-coated stents that elute anti-proliferative drugs in a controlled-release fashion to coincide with the restenosis cascade emerged as the dominant treatment modality. The sirolimus-coated Cypher stent (Cordis Corporation, Johnson & Johnson, Miami Lakes, Florida) was approved by the FDA in April 2003, followed by the paclitaxel-coated Taxus stent (Boston Scientific, Natick, Massachusetts) the following year.
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