What are the properties of each generation of cardiac stent?

Properties of Each Generation of Cardiac Stents

Bare-Metal Stents (BMS)

Bare-metal stents, composed of stainless steel or cobalt-chromium alloys, effectively prevent acute vessel closure but carry a 20-30% restenosis rate within 6-9 months due to neointimal hyperplasia, making them inferior to drug-eluting stents for most clinical scenarios. 1

Material Properties

• Stainless steel (316L) provides strength, ductility, and corrosion resistance as the original stent material 2
• Cobalt-chromium alloys offer improved radial strength and allow thinner strut design while maintaining mechanical properties 2
• All metallic platforms require minimum 30 days of dual antiplatelet therapy (DAPT) 2

Clinical Performance

• Restenosis occurs in 20-30% of cases within 6-9 months post-implantation 1
• Lower rates of late stent thrombosis compared to first-generation drug-eluting stents 1
• Current role limited to patients requiring extremely short-duration DAPT (<1 month) or those unable to tolerate/comply with prolonged antiplatelet therapy 1, 3

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First-Generation Drug-Eluting Stents (DES)

First-generation DES (sirolimus-eluting and paclitaxel-eluting stents) significantly reduced restenosis compared to bare-metal stents but demonstrated increased propensity for late and very late stent thrombosis due to delayed endothelialization from durable polymer coatings and potent antiproliferative drugs. 1, 4, 5, 6

Design Components

• Stainless steel platforms with thicker struts 4, 5
• Durable polymer coatings (non-bioabsorbable) that persist indefinitely and trigger chronic inflammation 4, 5, 6
• Antiproliferative drugs: sirolimus or paclitaxel 1

Clinical Performance

• Dramatically reduced angiographic restenosis and ischemia-driven target vessel revascularization compared to BMS 1
• Sirolimus-eluting stents (SES) showed superior angiographic metrics and further reduction in reintervention rates compared to paclitaxel-eluting stents (PES) 1
• Long-term follow-up (≥5 years) available for SES, PES, and zotarolimus-eluting stents (ZES) 1
• Critical limitation: Increased late (>30 days) and very late (>1 year) stent thrombosis due to delayed healing, persistent polymer-induced inflammation, and incomplete endothelialization 1, 4, 5, 6
• Require minimum 12 months of DAPT 3

Pathophysiologic Issues

• Delayed arterial healing with persistent fibrin deposition 6
• Local hypersensitivity reactions to polymer coatings 6
• Neoatherosclerosis development within stented segments 6

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Second-Generation Drug-Eluting Stents

Second-generation DES (everolimus-eluting and zotarolimus-eluting stents) demonstrate superior clinical outcomes to first-generation DES through thinner cobalt-chromium struts, more biocompatible durable polymers, and more potent limus-family drugs, with significantly lower rates of target lesion failure, myocardial infarction, and stent thrombosis. 1, 4, 5, 6

Design Improvements

• Thinner struts using cobalt-chromium alloy platforms (reducing strut thickness from 130-140μm to 80-90μm) 4, 5, 6
• Enhanced biocompatible durable polymers with reduced inflammatory response 4, 5, 6
• More potent antiproliferative agents: everolimus and zotarolimus (limus-family drugs with improved pharmacokinetics) 4, 5

Clinical Performance

• SPIRIT-IV trial: Xience V (everolimus-eluting) showed significantly lower target lesion failure at 1 year compared to Taxus-Express (4.2% vs 6.8%) 1
• COMPARE trial: Xience V demonstrated lower ischemia-driven target vessel revascularization compared to Taxus-Liberté (6% vs 9%) 1
• Reduced myocardial infarction and stent thrombosis compared to BMS, with trend toward lower cardiac mortality 1
• Safety ranking from meta-analyses: durable-polymer DES > biodegradable-polymer DES > BMS 1

Current Guideline Recommendations

• Class I, Level A recommendation: DES should be used in preference to BMS to prevent restenosis, MI, and acute stent thrombosis 1
• Preferred for high-risk lesion subsets including left main disease, small vessels (≤2.5mm), bifurcations, diabetes, and long lesions 1, 3
• Require minimum 12 months DAPT, though shorter durations (3-6 months) may be considered in high bleeding risk patients 3

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Newer-Generation Innovations

Biodegradable Polymer DES

• Bioabsorbable polymer coatings eliminate long-term polymer presence while maintaining controlled drug delivery 2, 4, 5
• Theoretical advantage of reduced chronic inflammation after polymer resorption 4, 5, 6
• May allow shorter DAPT duration, though clinical data still evolving 6

Bioresorbable Scaffolds (Third-Generation Concept)

• Polymer-based (polylactic acid) and metal-based (magnesium, iron, zinc) fully biodegradable platforms 7, 8
• Provide temporary scaffolding (6-24 months) then completely resorb, theoretically restoring vessel vasomotion 7, 8
• Current status: Early polymer-based bioresorbable scaffolds showed increased thrombosis rates and have been withdrawn from most markets; newer iterations and metal-based platforms under investigation 7, 8
• Require optimization of degradation kinetics, mechanical properties, and biocompatibility before widespread clinical adoption 7, 8

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Clinical Decision Algorithm

For stent selection, assess in this order:

1. DAPT tolerance/compliance: If patient cannot safely take or afford aspirin + P2Y12 inhibitor for 12 months, use BMS 3

2. Bleeding risk assessment: If HAS-BLED ≥3 or requiring oral anticoagulation, consider BMS or shortened DAPT with newer-generation DES 3

3. Restenosis risk evaluation: If high-risk features present (diabetes, small vessels, long lesions, bifurcations, left main), strongly favor second-generation DES 1, 3

4. Default choice: Second-generation DES for all other patients undergoing PCI 1, 3

Common Pitfalls

• Avoid first-generation DES given inferior outcomes compared to newer-generation devices 1
• Do not use BMS in high restenosis-risk lesions unless absolute contraindication to prolonged DAPT exists 3
• Premature DAPT discontinuation catastrophically increases stent thrombosis risk regardless of stent type 2