Stents - Types and Mechanism of Action

What Is a Stent?

1. Prevent elastic recoil - the plaque and vessel wall would spring back inward without scaffolding
2. Tack up dissection flaps - balloon inflation creates small intimal tears; the stent holds these against the vessel wall, preventing acute thrombotic closure
3. Scaffold the lumen - provides a rigid, permanent conduit

Types of Coronary Stents

1. Bare Metal Stent (BMS)

• Plain metallic mesh; no drug coating
• Material: stainless steel or cobalt-chromium alloys
• MOA: Pure mechanical scaffolding - prevents recoil and seals dissection planes
• Limitation: In-stent restenosis (ISR) in 20-30% of patients within 6-9 months, due to neointimal smooth muscle cell proliferation stimulated by the injury of balloon/stent deployment
• Requires DAPT for minimum 1 month post-implantation
• Now rarely used; largely superseded by DES

2. Drug-Eluting Stent (DES) - First Generation

• Metal scaffold coated with a permanent polymer that releases antiproliferative drugs over 1-3 months
• Drugs used:
  • Sirolimus (rapamycin) - a hydrophobic macrolide; binds the cytosolic immunophilin FKBP12; the FKBP12-sirolimus complex inhibits mTOR (mammalian target of rapamycin), blocking the G1-to-S cell cycle progression in smooth muscle cells, thereby inhibiting neointimal proliferation
  • Paclitaxel - a tricyclic diterpene; inhibits cellular proliferation by binding to and stabilizing polymerized microtubules, preventing mitotic spindle disassembly and thus arresting cell division
• Result: DES reduces clinical restenosis by 50% vs BMS, bringing symptomatic ISR down to 5-10% in uncomplicated lesions
• Limitation of first-generation DES: Permanent polymers associated with chronic inflammation, delayed endothelialization, and increased risk of late/very late stent thrombosis
• Requires DAPT for minimum 6-12 months

3. Drug-Eluting Stent (DES) - Second Generation

• Uses newer antiproliferative agents on improved polymer platforms
• Drugs used:
  • Everolimus - sirolimus derivative; same mTOR inhibition mechanism
  • Zotarolimus - another sirolimus derivative; same mechanism
  • Biolimus - highly lipophilic sirolimus analogue
• Advantages over first generation: More effective restenosis prevention + fewer complications (especially reduced early and late stent thrombosis)
• Some use biodegradable polymers that dissolve after drug elution is complete, theoretically reducing late inflammation and thrombosis risk
• Nearly 100% of stents placed today are second-generation DES

4. Bioresorbable Vascular Scaffold (BVS) / Biodegradable Stent

• Made of polylactic acid or similar biodegradable material; designed to dissolve over 2-3 years
• First-generation everolimus-eluting BVS showed reasonable short-term safety
• Theoretical advantage: After scaffold resorbs, the vessel can regain vasomotion and normal physiology; eliminates the permanent foreign body
• Clinical setback: Concerns about late and very late stent thrombosis prevented widespread adoption in the US
• Additional next-generation bioresorbable stents are still under investigation

5. Drug-Coated Balloon (DCB)

• Not a stent per se, but a balloon catheter coated with an antiproliferative drug (usually paclitaxel)
• Mechanism: Drug transfers from balloon surface to vessel wall during brief inflation (30-60 seconds); achieves local drug delivery without leaving a permanent implant
• Primary use: Treatment of in-stent restenosis (ISR) within a previously placed stent; also used in small vessels or bifurcations where stent placement is difficult
• No permanent scaffold remains; no DAPT requirement beyond the short healing period

MOA Summary Table

Key Complications

• Result of neointimal hyperplasia (SMC proliferation + matrix deposition in response to injury)
• Occurs more in BMS, diabetics, long stented segments, small arteries
• Presents as recurrence of angina within 12 months
• Histology: fibrocellular occlusion narrowing the lumen (see image below)

Neointimal hyperplasia causing restenosis - Harrison's 22e

• Acute (<24 h): mechanical/procedural complications + inadequate anticoagulation
• Subacute (24 h - 30 days): inadequate platelet inhibition; stopping P2Y12 inhibitor in this window causes 30-100x increased risk
• Late (30 days - 1 year) / Very late (>1 year): principally with DES; associated with delayed endothelialization, neoatherosclerosis

Non-Coronary Stent Contexts (Brief)

• Biliary/GI stents: Self-expanding metal stents (SEMS) or plastic stents to relieve obstructive jaundice, esophageal strictures, or colonic obstruction - purely mechanical
• Ureteral stents: Double-J (pigtail) design; maintains ureteral patency after ureteroscopy or in obstruction
• Airway stents: Silicon or metal; used for tracheal/bronchial stenosis; biodegradable steroid-eluting stents (e.g., mometasone-releasing) available for post-FESS sinonasal surgery
• Vascular/Aortic stents: Nitinol or stainless steel self-expanding or balloon-expandable; used in carotid, renal, iliac, and aortic disease - ISR pattern similar to coronary stents

Landmark Stent Trials

ERA 1 - BMS vs Balloon Angioplasty (1990s)

BENESTENT-I (1994) [PMID: 8041413]

• Journal: NEJM | Authors: Serruys PW et al.
• Design: RCT, 520 patients, stable angina with single de novo lesion
• Intervention: Palmaz-Schatz BMS vs balloon angioplasty (PTCA)
• Key Result: Stent reduced angiographic restenosis (22% vs 32%) and event-free survival was better at 7 months
• Significance: One of the two landmark trials (alongside STRESS) that established BMS as superior to PTCA alone and led to routine stent use. 5-year follow-up confirmed continued benefit [PMID: 11345371]

STRESS Trial (1994) - Parallel to BENESTENT

• Stent Restenosis Study; similar design to BENESTENT
• Showed BMS reduced restenosis rate vs balloon angioplasty (31.6% vs 42.1%)
• Together with BENESTENT, changed practice to routine stenting in coronary interventions

ERA 2 - First-Generation DES (2000s)

SIRIUS Trial (2003) [PMID: 14769686]

• Journal: Circulation (1-yr outcomes), JACC (5-yr follow-up PMID: 19389558)
• Design: RCT, 1058 patients, complex de novo native coronary lesions
• Intervention: Sirolimus-eluting stent (Cypher) vs BMS
• Key Results:
  • Target lesion revascularization (TLR): 4.1% vs 16.6% at 9 months
  • In-stent restenosis: 3.2% vs 35.4%
  • No difference in death/MI at 1 year
• 5-year follow-up: Durable benefit in TLR maintained; no excess late mortality
• Significance: Established first-generation sirolimus-eluting DES; FDA approval for Cypher stent followed

TAXUS-IV Trial (2004)

• Design: RCT, 1314 patients
• Intervention: Paclitaxel-eluting stent (TAXUS Express) vs BMS
• Key Results: TLR 3% vs 11.3%; restenosis 5.5% vs 24.4% at 9 months
• Significance: Established paclitaxel-eluting stent; FDA approval for TAXUS stent. Concern later emerged about higher very late stent thrombosis vs sirolimus stent

ERA 3 - Second-Generation DES (2007-2013)

SPIRIT III Trial [PMID: 24239202]

• Design: RCT, XIENCE V everolimus-eluting stent (EES) vs TAXUS paclitaxel stent
• Key Results (5-year): EES showed significantly lower MACE (major adverse cardiac events) and stent thrombosis vs paclitaxel stent
• Significance: Demonstrated second-gen DES superiority over first-gen; everolimus-eluting stents (XIENCE/PROMUS) became global standard

RESOLUTE All-Comers / RESOLUTE China [PMID: 23523240]

• Intervention: Zotarolimus-eluting stent (Resolute Integrity) vs paclitaxel stent
• Key Result: Non-inferior outcomes; established zotarolimus DES as another safe second-generation platform

DES vs BMS Meta-Analysis (Lancet 2019) [PMID: 31056295]

• Individual patient data meta-analysis, 26 RCTs, ~20,000 patients
• Key Finding: DES reduced repeat revascularization and MI vs BMS with no increase in mortality or stent thrombosis at 5-10 years
• Significance: Definitively settled DES vs BMS debate; confirmed DES superiority across all patient subgroups

ERA 4 - PCI vs Surgery / Medical Therapy

COURAGE Trial (2007) [PMID: 17387127]

• Journal: NEJM | Design: RCT, 2287 patients, stable coronary artery disease
• Intervention: PCI + optimal medical therapy (OMT) vs OMT alone
• Key Result: No significant difference in death or non-fatal MI at median 4.6 years (19.0% vs 18.5%)
• Significance: Showed PCI does not reduce hard cardiac events over OMT in stable CAD; however, PCI did improve angina relief and quality of life

ISCHEMIA Trial (2020) [PMID: 32227755]

• Journal: NEJM | Design: RCT, 5179 patients, stable CAD with moderate-severe ischemia
• Intervention: Invasive strategy (PCI/CABG) + OMT vs OMT alone
• Key Result: No significant difference in primary composite outcome (CV death, MI, hospitalization for unstable angina/heart failure/resuscitated cardiac arrest) at median 3.2 years
• Caveat: Invasive strategy showed early hazard (periprocedural MI) but late benefit; superior for angina relief
• Significance: Confirmed COURAGE - routine revascularization for stable CAD does not reduce mortality; OMT is the cornerstone

REVIVED-BCIS2 Trial (2022) [PMID: 36027563]

• Journal: NEJM | Design: RCT, 700 patients, ischemic LV dysfunction (EF ≤35%)
• Intervention: PCI + OMT vs OMT alone
• Key Result: No difference in death or hospitalization for heart failure at 3.4 years
• Significance: Even in patients with viable myocardium and reduced EF, PCI provided no mortality benefit

SYNTAX Trial (2009-2019) [PMIDs: 19228612, 23439102, 31488373]

• Journal: NEJM (initial), Lancet (5-yr and 10-yr follow-up)
• Design: RCT, 1800 patients, 3-vessel or left main CAD
• Intervention: PCI (paclitaxel DES) vs CABG
• Key Results:
  • At 1 year: CABG better for MACCE (12.4% vs 17.8%)
  • At 5 years: CABG better for repeat revascularization and MI; similar mortality in left main subgroup
  • At 10 years: CABG superior in 3-vessel disease (death, MI, stroke); left main outcomes similar
• SYNTAX Score: Angiographic complexity score developed from this trial; high SYNTAX score (>33) = favor CABG
• Significance: Defined role of PCI vs CABG; established that complex 3-vessel disease benefits from surgical revascularization

ERA 5 - Bioresorbable Scaffolds and Novel Devices

ABSORB III Trial (2015) and Meta-Analysis [PMID: 28408454]

• Design: RCT + subsequent meta-analysis, everolimus-eluting BVS (Absorb) vs XIENCE EES
• Key Result: Non-inferior at 1 year, but at 2-3 years BVS showed significantly higher device-oriented failure and stent thrombosis (2-3x higher)
• Significance: Led to withdrawal of Absorb BVS from the US market in 2017; set back the bioresorbable stent field

REC-CAGEFREE I Trial (2026) [PMID: 41194754]

• Journal: JACC | Design: RCT, drug-coated balloon (DCB) vs upfront DES stenting for de novo CAD
• Key Result (3-year follow-up): DCB non-inferior to DES for MACE in de novo lesions
• Significance: First major RCT supporting DCB as an alternative to stenting in de novo lesions (not just ISR) - potentially allowing "leave nothing behind" strategy

INFINITY-SWEDEHEART Trial (2024) [PMID: 39481425]

• Journal: Lancet | Design: Registry-based RCT, bioadaptor stent vs contemporary DES
• Intervention: DynamX bioadaptor (uncages after 4 months to restore vessel motion) vs DES
• Key Result: Non-inferior at 12 months; promising safety profile
• Significance: Emerging evidence for next-generation "adaptive" stent technology

Summary Table

DAPT Guidelines: By Stent Type and Clinical Scenario

The Purpose of DAPT After Stenting

The P2Y12 Inhibitors Used in DAPT

DAPT Duration by Stent Type

Bare Metal Stent (BMS)

• Minimum DAPT: 1 month (ACC/AHA 2016)
• After 1 month, aspirin monotherapy indefinitely
• ESC 2022 guidelines make no specific BMS recommendations (largely obsolete)
• Rationale: BMS re-endothelializes faster than DES; 1 month is sufficient to bridge the thrombotic risk window

First-Generation DES (Cypher/TAXUS)

• DAPT: 12 months minimum
• Permanent polymer causes delayed endothelialization and chronic inflammation, extending the vulnerable period for late/very late stent thrombosis
• Largely replaced; rarely implanted today

Second-Generation DES (Current Standard)

• Stable CAD (elective PCI): 6 months (ACC/AHA 2016; ESC 2022)
• ACS (STEMI or NSTEMI/UA): 12 months from index event
• Evidence suggests extended DAPT (up to 30 months) provides additional anti-ischemic benefit but at the cost of more bleeding - the trade-off must be individualized
• High bleeding risk with second-gen DES: As short as 1 month DAPT is acceptable based on accumulating evidence, because stent thrombosis is now much less common with modern polymer-free or biodegradable polymer platforms

DAPT by Clinical Scenario

1. Stable CAD / Elective PCI

• Standard: Aspirin + clopidogrel for 6 months, then aspirin alone indefinitely
• Preferred P2Y12: clopidogrel (ticagrelor/prasugrel offer no proven mortality benefit in stable CAD)
• Evidence from COURAGE: OMT is primary; PCI does not reduce death/MI in stable CAD but does relieve angina

2. NSTEMI / Unstable Angina (UA)

• DAPT for 12 months regardless of whether PCI performed or managed medically
• Loading dose of ASA 162-325 mg immediately, then 81 mg/day
• Preferred P2Y12: ticagrelor (mortality advantage; Washington Manual: "preferred P2Y12 inhibitor of choice") or prasugrel (only after coronary anatomy known and PCI planned)
• Clopidogrel: used when ticagrelor/prasugrel are contraindicated or unavailable
• Prasugrel: NOT for pre-treatment before knowing coronary anatomy; contraindicated if prior stroke/TIA; only use after PCI decision is made

3. STEMI (Primary PCI)

• DAPT for 12 months minimum
• Loading doses at first medical contact: ASA 162-325 mg + P2Y12 (ticagrelor 180 mg OR prasugrel 60 mg preferred; clopidogrel 600 mg if others unavailable)
• Anticoagulation during procedure: UFH, enoxaparin, or bivalirudin (direct thrombin inhibitor)
• GpIIb/IIIa inhibitors (eptifibatide, tirofiban) reserved for large thrombus burden or bailout; not routine
• ESC 2022: Ideal interval before non-cardiac surgery after PCI for ACS = 12 months on DAPT; can be reduced to 3 months with newer-gen DES if time-sensitive surgery is needed

4. High Bleeding Risk (HBR)

• Shortened DAPT: 1-3 months
• ARC-HBR criteria define high bleeding risk (e.g., recent major bleeding, anticoagulation need, severe CKD, thrombocytopenia, advanced age)
• After short DAPT, transition to P2Y12 inhibitor monotherapy (preferably high-potency: ticagrelor) rather than aspirin alone
• JAMA Cardiology 2024 network meta-analysis [PMID: 39382876] (35,326 ACS patients, 15 RCTs):
  • 1 month DAPT followed by P2Y12 monotherapy reduced major bleeding by 53% (RR 0.47) vs 12-month DAPT with no difference in MACCE
  • 3-month DAPT followed by P2Y12 monotherapy ranked best for reducing MACCE (RR 0.85)
  • Note: evidence mainly applies when potent P2Y12 (ticagrelor) is used for monotherapy phase
• Catheter Cardiovasc Interv 2025 meta-analysis [PMID: 40963197] (53,421 patients, 13 RCTs):
  • Short DAPT (≤3 months) significantly decreased net adverse clinical events (NACE) (RR 0.80) without impacting MACE
  • 3-month duration outperformed 1-month; monotherapy with high-potency P2Y12 preferred over aspirin

5. High Ischemic Risk / Extended DAPT (>12 months)

• Patients with prior MI + complex anatomy (multivessel, bifurcation, left main, long stents, diabetes, CKD)
• DAPT Score (calculates benefit vs bleeding of extended therapy): score ≥2 = benefit from extended DAPT; score <2 = excess bleeding harm
• Extended DAPT up to 30 months: additional reduction in MI and stent thrombosis but increased major bleeding - individualize based on bleeding and ischemic risk profile
• DAPT Trial (2014): 30 months vs 12 months - MI reduction but more bleeding and all-cause mortality (mainly non-cardiac)

6. Concurrent Oral Anticoagulation (AF + PCI) - "Triple Therapy"

• Patients with AF on OAC who need DAPT post-stent present the highest bleeding risk
• Triple therapy (OAC + aspirin + P2Y12): Recommended for only 1 month regardless of stent type
• ESC recommendation (Class IIa): After 1 month, transition to dual therapy: OAC + clopidogrel (drop aspirin) for up to 12 months
• After 12 months: OAC monotherapy
• Prefer NOAC over VKA (lower bleeding risk in AF-PCI setting; PIONEER-AF, RE-DUAL PCI, AUGUSTUS trials)
• Prefer clopidogrel over ticagrelor/prasugrel during dual/triple therapy (lower bleeding)

7. Perioperative / Surgery After PCI

Key Algorithmic Framework

Post-PCI Stent
       |
       ├── Stable CAD + DES → DAPT 6 months → Aspirin indefinitely
       |
       ├── ACS + DES → DAPT 12 months → Aspirin indefinitely
       |        |
       |        └── High ischemic risk → Consider extended DAPT (up to 30 months)
       |
       ├── High Bleeding Risk → Shorten DAPT to 1-3 months → P2Y12 monotherapy (ticagrelor preferred)
       |
       ├── AF + Anticoagulation → Triple therapy 1 month → OAC + clopidogrel up to 12 months → OAC alone
       |
       └── BMS → DAPT 1 month minimum → Aspirin indefinitely

De-escalation Strategies (Emerging Evidence)

1. Early aspirin dropout - Drop aspirin after 1-3 months; continue P2Y12 inhibitor alone (TWILIGHT, TICO, STOPDAPT-2 trials)
2. P2Y12 de-escalation - Switch from potent P2Y12 (ticagrelor/prasugrel) to clopidogrel after 1 month; validated by TROPICAL-ACS (PFT-guided) and TALOS-AMI trials (Class IIb, LOE A in ESC guidelines)
3. Dual pathway inhibition - Replace DAPT with antiplatelet (aspirin) + low-dose DOAC (rivaroxaban 2.5 mg BD; from COMPASS trial); for post-ACS patients at low bleeding risk