Coronary artery stents

Published on 07/02/2015 by admin

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Last modified 22/04/2025

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Coronary artery stents

Amy G. Voet, DO, MS and James A. Giacalone, BS, MEd

Coronary artery stents were first developed in the 1980s and are now placed in most percutaneous coronary interventions (PCIs). Interventional cardiologists have a wide choice of stents for implantation. The choices range from bare-metal stents (BMSs) and drug-eluting stents (DESs) (Table 144-1) that are widely used in contemporary practice to new stents, such as DESs with novel coatings, biodegradable stents, DESs with biodegradable polymers, DESs that are polymer free, dedicated bifurcation stents, and self-expanding stents. A number of DESs are currently undergoing study or are available outside the United States (Table 144-2).

Table 144-1

U.S. Food and Drug Administration–Approved Drug-Eluting Stents

Stent	Manufacturer	Drug Eluted
Cypher	J&J Cordis	Sirolimus
TAXUS Express and Liberté	Boston Scientific	Paclitaxel
Endeavor	Medtronic	Zotarolimus
Xience V	Guidant, Abbott	Everolimus

Table 144-2

Metallic Stents Available Outside the United States or Undergoing Clinical Evaluation

Stent	Drug(s) Eluted	Approved Outside U.S.	Ongoing Trials
Endeavor RESOLUTE	Zotarolimus	X
Elixir DESyne	Novolimus		X
TAXUS Element	Paclitaxel	X
PROMUS Element	Everolimus	X
Supramilus	Sirolimus		X
Excel Stent	Sirolimus		X
NEVO	Sirolimus		X
BioMatrix	Biolimus A9	X
NOBORI	Biolimus A9	X
Axxess	Biolimus A9	X
XTENT	Biolimus A9	X
SYNERGY	Everolimus		X
Combo	EPC + sirolimus		X
Elixir Myolimus	Myolimus		X
Infinnium	Paclitaxel		X
JACTAX Liberté	Paclitaxel		X
AmazoniaPax	Paclitaxel	X
BioFREEDOM	Biolimus A9		X
VESTAsync	Sirolimus		X
Tukon	Sirolimus	X
Catania stent	Polyzene F	X
TINOX stent	Titanium nitride-oxide	X
Genous stent	CD34⁺ antibody	X

Ulrich Sigwart placed the first stent in 1986. This BMS proved to be effective as a rescue device for patients who were in imminent danger of vessel closure and, thus, reduced the number of patients undergoing emergency coronary artery bypass grafting. However, the risk of subacute thrombotic coronary occlusion hindered the further development of these stents. Coronary artery stenting finally became widely accepted in 1994 after evidence showed that stenting was safe with the use of dual antiplatelet therapy (typically, aspirin and a platelet P2Y₁₂ receptor antagonist). By 1999, the placement of coronary artery stents made up more than 80% of PCIs. The risk of subacute thrombosis remained, and a new iatrogenic problem developed of in-stent neointimal hyperplasia, which resulted in 20% to 30% restenosis rates, stimulating the development of the DES. The risk of stent thrombosis after the placement of either a BMS or DES can be reduced by implementation of platelet P2Y₁₂ receptor antagonist therapy in combination with aspirin therapy. Box 144-1 lists definitions of stents, complications with their use, and related types of therapy.

Box 144-1 Definitions

Bare metal stent (BMS): Non–drug-coated vascular stent composed of various metal alloys deployed into a coronary artery or vascular conduit to restore the luminal integrity of the vessel.

Drug-eluting stent (DES): Drug-coated vascular stent that is deployed into a coronary artery or vascular conduit to restore the luminal integrity of the vessel, designed to release the coating into the vessel wall to prevent neointimal growth and restenosis.

Early stent thrombosis (EST): Stent thrombosis occurring between 0 and 30 days after implantation: acute, <24 h; subacute, 1-30 days.

Late stent thrombosis (LST): Stent thrombosis occurring between 30 days and 1 year after implantation.

Very late stent thrombosis (VLST): Stent thrombosis occurring more than 1 year after implantation.

Aspirin effect: Aspirin irreversibly acetylates platelet cyclooxygenase-1, preventing formation of thromboxane A₂ and, thus, stimulation of platelet aggregation.

P2Y₁₂ receptor antagonist: A class of drugs that induce irreversible conformational change in the P2Y₁₂ receptor for adenosine diphosphate (ADP) and inhibit platelet aggregation and limit ADP-mediated conversion of glycoprotein IIb-IIIa to its active form.

Complications

Thrombosis, hemorrhage, myocardial infarction, stroke, and contrast nephropathy

The U.S. Food and Drug Administration’s (FDA) approval for the use of DESs is currently limited to simple lesions. Sirolimus-eluting stents are approved for use in de novo lesions that are 30 mm or shorter and have a vessel diameter of 2.5 to 3.5 mm. Paclitaxel-eluting stents are approved for de novo lesions that are 28 mm or shorter and have a diameter of 2.5 to 3.75 mm. Early studies of DESs were criticized because only patients who were stable and who received a DES for an FDA-approved indication were enrolled. A much greater percentage of devices are implanted for off-label uses, although the results of studies conducted for off-label uses are equivocal. Some studies have determined that off-label use of the DES is associated with an increased risk of death, myocardial infarction (MI), and repeat revascularization, whereas other studies have demonstrated a significant improvement in outcome with the use of DESs. These differences have been attributed to the patient populations and lesion characteristics and not to a specific problem with DESs. Overall, the use of DESs significantly reduces the risk of restenosis, compared with BMSs, without increasing the overall risk of MI and death.

Stent thrombosis has surfaced as the major safety concern following the placement of coronary artery stents in practice today. A review of published data indicates no difference between DES and BMS in terms of risk of early or late stent thrombosis (0.1% and 0.9%, respectively). However, the risk for very late stent thrombosis with a DES is much higher than with a BMS (0.6-0.7% vs. 0.0-0.2%, respectively). The data also indicate that the risk of stent thrombosis is higher in patients treated with a DES for off-label use compared with patients treated for on-label use. The exact mechanism remains unclear, but several factors have been implicated. Some risk factors associated with early or late stent thrombosis include early cessation of dual antiplatelet therapy, clopidogrel unresponsiveness, complexity of lesions, multistent implantation, small lesion diameter, and lesions longer than 28 to 30 mm. Risk factors associated with very late stent thrombosis include factors such as renal failure and prior brachytherapy (Table 144-3). Other complications of PCI include hemorrhage, MI, stroke, and contrast-induced nephropathy.

Table 144-3

Risk Factors for Stent Thrombosis

Lesion-Specific Factors	Patient Risk Factors	Procedural Factors	Device Factors
Bifurcation stenting Ostial stenting Lesion/stent length Vessel/stent diameter Multiple stents/vessels Left main artery stent Bypass graft stent Calcification of vessel	Renal failure Diabetes Left ventricular impairment Prior brachytherapy Prior subacute stent thrombosis Premature cessation of dual antiplatelet therapy Clopidogrel unresponsiveness STEMI	Inadequate stent expansion Incomplete stent apposition Stent deployment in necrotic lumen	Hypersensitivity to drug coating/polymer Incomplete endothelialization Stent design

STEMI, ST-segment elevation myocardial infarction.

Hemorrhage that results in hemodynamic instability or transfusion therapy arises in approximately 0.5% to 4% of patients who have undergone PCI and is dependent on several factors, including patient characteristics, the specifics of the procedure, and patient-specific pharmacologic variables. These factors include, but are not limited to, age and sex, location of femoral arteriotomy, and level of antithrombotic therapy. The risk of stroke is relatively low (<0.2%), whereas MI complicates 5% to 38% of PCIs, with the rate depending upon the definition used for MI. New Q-wave appearance has an incidence of 1%, whereas any elevation of creatine kinase-MB occurs in up to 38% of patients. Contrast-induced nephropathy is also dependent upon multiple variables, including age, presence of congestive heart failure, preexisting renal failure, previous exposure to contrast agents, and the presence of peripheral vascular disease and is seen in about 5% to 6% patients.

Recommendations

The American College of Cardiology/American Heart Association guidelines currently recommend antiplatelet therapy for a minimum of 1 month or 4 to 6 weeks for a BMS and a minimum of 12 months and, possibly indefinitely with DES implantation, especially in patients who are at higher risk for developing thrombosis. Premature discontinuation of antiplatelet therapy has been shown to result in an increased risk of life-threatening stent thrombosis. The guidelines also recommend that nonurgent surgical procedures be postponed until after these periods of susceptibility. If the operations cannot be delayed, they may need to be performed while the patient is on dual therapy or aspirin alone because surgery itself causes a prothrombotic state. If platelet P2Y₁₂ receptor antagonist must be withheld, it should be done for, optimally, 5 days preoperatively or fewer days for patients with DESs, who are at higher risk for developing thrombosis. After the procedure, platelet P2Y₁₂ receptor antagonist therapy should be restarted as soon as possible. Some reports have shown that 6% of patients with DESs who undergo noncardiac operations within 1 year of implantation experience a major cardiac event. Therefore, patients in need of noncardiac operations within 1 year of DES implantation or within 1 month of BMS implantation should be carefully evaluated for the risk of ischemic events and bleeding. Maximizing the success of the operation requires collaboration among the cardiologist, surgeon, and anesthesiologist and sufficient lead time (2 weeks) before the procedure that will allow for implementation of a perioperative, intraoperative, and postoperative plan. Discussion with the patient of treatment options is also necessary for the patient to make an informed decision. The operation should be performed at a facility with the ability to perform emergency PCI or cardiac surgery. Stent thrombosis typically presents as acute MI, cardiogenic shock, and sudden death; thus, immediate thrombus retrieval is essential. Finally, it is imperative to educate patients about the risks of early discontinuation of dual antiplatelet therapy and encourage compliance with their prescribed regimen.

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