Coronary Artery Stents

Function

Stent Types

There are multiple stents' models (at least 16) approved by FAD from multiple different manufactures. Types of coronary artery stents which are currently approved in the USA include:[5]

• Bare-metal stents
• Durable polymer drug-eluting stents
  • These use cobalt-chromium or platinum chromium for stent platform and everolimus or zotarolimus as antiproliferative agents.
• Drug-eluting stents
• Bioabsorbable polymer drug-eluting stents

Coronary guidewires are designed to navigate blood vessels to reach the segment of a vessel or the lesion in the vessel. Coronary wires are generally 0.014 mm in diameter and introduced to the coronary tree via a guiding catheter. Multiple different coronary wires exist described as "workhorse," "extra supportive," or "hydrophilic."

Issues of Concern

Newer generation drug-eluting stents have a great safety and efficacy profile. Specific subgroups of patients with markedly complex anatomical and clinical characteristics present a higher risk of complications. These are the characteristics for which further margins of improvement are indicated:

1. Diabetes Mellitus: Diabetes mellitus has been associated with highly accelerated atherosclerosis due to its highly thrombotic and inflammatory state. These patients usually present with narrow coronaries, multivessel involvement, and long lesions, which are challenging for coronary revascularization. Novel drug-eluting stents with higher antiresorptive activities might help negate these problems associated with diabetic patients in the future.[6]
2. Acute Myocardial Infarction (MI): Percutaneous intervention with drug-eluting stent placement plays a central role in the management of acute myocardial infarction. Still, the rate of stent-related complications is higher compared to stable patients. Stent malapposition is one of the complications among patients with myocardial infarction due to the presence of vasoconstriction and thrombus between the stent and arterial wall. To overcome this issue, newer technologies are under study. Specifically, self-expandable stents that are designed to adjust to arterial size over time. Secondary, mesh-covered stents are developed to overcome distal embolization. These new advancements that may improve clinical outcomes in patients with myocardial infarction are under extensive studies.[7][8]
3. Restoration of Vascular Pathology: Most of the metallic drug-eluting stents are permanent in nature, which limits the restoration of normal vessel physiology of the coronary artery. Fully bioresorbable stents in the future seem to negate this limitation in the future.[9]
4. Calcified Lesions: Heavily calcified lesions continue to present challenges to PCI and stent thrombosis. Future development of novel devices is warranted for better outcomes.
5. Bifurcation Lesions: Coronary bifurcation possess a higher rate of complications. There are several approaches and novel stents developed. The need for dedicated devices for bifurcation lesions is still under study.

Clinical Significance

Bare-metal Stent: Circumstances in which bare-metal stent (BMS) may be reasonable have considerably decreased since the advent of drug-eluting stents.[10] Some experts recommend BMS in situations like: 

• Patients who require noncardiac surgery within 4 to 6 weeks of PCI. 
• Patients with active bleeding at the time of PCI or those who are at a very high risk of bleeding while taking Dual antiplatelet therapy. 
• If a patient is unlikely to comply with antiplatelet therapy for more than 1 month.

Drug-eluting Stent: First-generation drug-eluting stents (DES) are no longer used in the USA, Europe, and Canada since advancements in stent platforms and polymer biocompatibility found in newer DES listed above. For most patients undergoing coronary artery intervention with stent placement, current-generation DES are used.

Primary percutaneous coronary intervention with drug-eluting stent implantation is indicated to patients with acute MI according to the recent clinical guidelines. Evidence showed improved outcomes with new-generation DES as compared to early-generation DES and bare-metal stents.[11] The risk of stent-related complications is relatively still higher than patients with stable coronaries. 

There are several advancements in drug-eluting stents. Vessel size among patients with acute MI is either underestimated or overestimated due to vessel wall correction or pressure of thrombus between the vessel wall and stent platform. To negate this issue, self-expanding stents that adapt to the size of the artery were developed. The role of fully biodegradable stents is under extensive study. Further studies are indicated to improve clinical outcomes in diabetic patients with a diffuse disease requiring DES either introducing novel DES with higher restenotic activity or fully bioresorbable scaffolds. For coronary bifurcation disease, these are several techniques, but in 2019 meta-analysis showed DK crush technique to reduce stent-related events compared to others. 

Revascularization with percutaneous coronary intervention as opposed to coronary artery bypass graft surgery:

• Single-vessel disease
• Two-vessel disease involving the right coronary artery and circumflex coronary artery

There are several other determining factors that are taken into account to determine percutaneous coronary intervention as opposed to coronary artery bypass graft (CABG).

Other Issues

Complications

Procedural Complications

A percutaneous angioplasty with coronary artery stent placement has several procedural/stent-related complications and late complications.

1. Coronary Perforation: It is an immediate procedure-related complication. It is associated with a 5-fold increase in the mortality rate within 30 days of the procedure. Coronary perforation is most commonly caused by a balloon or stent to the arterial wall mismatch. Less commonly, perforation can occur in the presence of arterial calcifications, use of atherectomy devices, advanced age, history of CABG, or female sex.[12]
2. Device Embolization: It is a rare PCI complication, but there have been several incidences reported. This complication results from a loss of a device during the procedure. Stents are the most commonly embolized devices. Other devices that are reported are guidewires and catheter fragments
3. Longitudinal Stent Deformity (LSD): The newer generation chromium or platinum stents are thinner. These stents have good radial strength and radio-opacity but lack longitudinal strength because of a reduction in the number of fixed links between cells and the alteration of their geometry. LSD can lead to stent strut protrusion into the lumen and extensive strut mal-apposition, which causes flow disruption and increased risk of stent thrombosis.[12]

There are several other procedural complications like coronary artery dissections, intramural hematoma, myocardial ischemia, myocardial infarction, access site bleeding, retroperitoneal hematoma, atheroembolism, acute kidney injuries, strokes, hypersensitive reactions, arrhythmia. All the complications in detail are explained in the percutaneous coronary intervention procedure section.[12]

Coronary Artery Stent-related Complications

Failure of stent deployment is a serious problem associated usually with first-generation stents. It occurs in 2.0 to 8.3 percent of the procedures performed. Failure of stent deployment with dislodgment from the balloon tip leads to serious complications. Several studies have shown second, and third-generation stents have a higher rate of successful deployment.[13]

Stent Thrombosis: Stent thrombosis is a serious complication that leads to myocardial infarction or death. This is a medical emergency and should be managed per protocol. Stent thrombosis is classified into acute, subacute, or late. If the thrombosis occurs during the PCI or within a few hours of the procedure, it is termed "acute". Subacute thrombosis is when it occurs within 30 days of stent placement. Late thrombosis is defined as thrombosis that occurs 1 year or later and is often associated with a drug-eluting stent. Stent thrombosis has been associated with premature cessation of dual antiplatelet therapy.[14]

Stent Infection: Coronary artery stent Infections are rare but are potentially catastrophic complications. These infections can lead to coronary perforations and mycotic aneurysms.[15]

Coronary artery aneurysm is a very rare complication mostly associated with drug-eluting stents.

Enhancing Healthcare Team Outcomes

A large meta-analysis of several randomized control trials was done comparing short-term and long-term outcomes of drug-eluting stents and bare-metal stents, which reported a reduction in myocardial infarction rate and stent thrombosis with DES compared to BMS. The study reported a rate ratio, 0.51 with a 95% credibility interval of 0.35 to 0.73.[16] [CEBM Level 1]

Nursing, Allied Health, and Interprofessional Team Interventions

An interprofessional team compromising of nursing staff, home health caregivers, and primary care physicians should have an integrated postoperative care plan from the operating cardiologist. In all patients, dual antiplatelet therapy is indicated to prevent stent thrombosis. Medication compliance is of utmost importance. 

Patients with bare-metal stent need at least 1 month of dual antiplatelet therapy (DAPT)) versus drug-eluting stent need 6 to 12 months and in patients with a low risk of bleeding complications 18 to 24 months is recommended. In a recently published study, 1 to 3 months of use of DAPT did not increase odds of postoperative stent-related complications but reduced odds of any bleeding by 30%. The risk of stent thrombosis is a lethal complication of coronary artery stent placement. A major adverse cardiac event such as cardiac death, MI, or stroke diminishes with the use of DAPT. 

Pharmacy consultation–medication safety directions, educating the importance of patient compliance, and home health care counseling on diet and exercise modification. 

Primary care physicians should be updated, performing accurate medication reconciliation on discharge, medical records, and plan of care should be sent over to primary care physician for continuity of care. Schedule the patient for follow-up within 3 days. Cardiology follow-up in 1 to 2 weeks.