Drug-Eluting Stents - Advancements in Cardiovascular Medicine

Introduction

In the field of cardiovascular health, medical advancements have significantly improved patient outcomes, especially in the treatment of coronary artery disease (CAD). CAD is a disease of major blood vessels of the heart in which these vessels narrow or get blocked due to the buildup of plaque in the vessels, limiting the blood flow to the heart, to address this issue, stents are used to treat the narrowing of the vessels they keep the vessels open to allow normal blood flow to the heart. There are several types of stents, such as bare metal stents, drug-eluting stents, and biodegradable stents (currently unavailable in clinical practice). Drug-eluting stents (DES) are one significant invention that has transformed the treatment of coronary artery disease (CAD). Drug-eluting stents are the tiny mesh tubes inserted during angioplasty procedures that have transformed the field of cardiac care by addressing issues associated with traditional bare-metal stents (BMS). This article briefly explains drug-eluting stents, their advantages, and potential complications associated with them.

What Are Drug-Eluting Stents?

Drug-eluting stents (DES) are a type of medical device used to open up narrowed arteries in the heart. They are a significant advancement over bare-metal stents (BMS), which were introduced in the 1980s. BMS were effective at opening up arteries, but they often led to restenosis or the re-narrowing of the artery. Drug-eluting stents were introduced in the early 2000s to overcome the challenges associated with BMS. These stents are coated with a special medication, typically an antiproliferative drug, which is slowly released into the surrounding tissue over time. The purpose of this drug coating is to inhibit the growth of smooth muscle cells, which can lead to restenosis.

The development of DES has progressed through distinct generations, each addressing limitations and refining efficacy.

• First Generation: Featured stainless steel scaffolds coated with Sirolimus or Paclitaxel.

• Second Generation: Introduced cobalt-chromium scaffolds with improved polymers and drug-eluting profiles.

• Third Generation: Currently undergoing clinical testing, these DES incorporate biodegradable polymers or entirely bioabsorbable scaffolds, aiming to improve long-term outcomes further.

What Are the Advantages of Drug-Eluting Stents (DES)?

Compared to bare metal stents (BMS), DES offers several significant advantages:

1. Reduced Restenosis:

• Restenosis, or the re-narrowing of the artery after treatment, is a major issue with BMS, occurring in about 30 percent of cases.

• DES significantly reduces restenosis rates to around 5 to10 percent, thanks to the antiproliferative drugs released from the stent coating.

2. New-Generation DES for Complex Lesions: New-generation drug-eluting stents (DES) are a significant improvement over previous generations, offering benefits in treating various complex situations related to coronary artery disease (CAD).

• Diabetic Patients: Diabetes can complicate CAD treatment due to impaired wound healing and increased inflammation. New-generation DES has shown good outcomes in diabetic patients, with lower rates of restenosis and improved blood flow.

• Chronic Kidney Disease: Patients with chronic kidney disease are at higher risk of complications after PCI procedures. New-generation DES, often with thinner struts and better biocompatibility, have been shown to be safe and effective in this population.

• Acute Myocardial Infarction (AMI): New-generation DES are increasingly being used in AMI cases, which showed similar effectiveness compared to bare metal stents but with a lower risk of repeat procedures.

• Ostial Lesions or Bifurcations: These complex lesions occur at the beginning of an artery or where two arteries branch. New-generation DES with improved deliverability and flexibility are better suited for these situations, leading to better stent placement and lower complications.

• Bypass Grafts: In some cases, bypass grafts can fail or become blocked. New-generation DES can be used to reopen these grafts, offering a minimally invasive alternative to repeat surgery.

• Left Main Stem Disease: This is a serious condition where the main artery supplying blood to the heart is narrowed. New-generation DES can be used as an alternative to coronary artery bypass grafting (CABG) in some patients with left main stem disease, with comparable outcomes and lower surgical risk.

• Small Vessels or Long Lesions: Traditional stents may not be suitable for small vessels or long lesions due to their size or inflexibility. New-generation DES with smaller diameters and better flexibility can effectively treat these challenging situations.

• Chronic Occlusions: These are completely blocked arteries. New-generation DES with special features like crossing capabilities and scoring balloons can be used to open chronic occlusions, potentially avoiding bypass surgery.

3. Improved Long-Term Outcomes:

Lower restenosis rates lead to improved long-term outcomes, including a reduced risk of:

• Myocardial infarction (heart attack).

• Stroke.

• Repeat heart procedures.

• Death.

4. Potentially Improves Quality of Life: By reducing the need for repeat procedures and improving long-term outcomes, DES can contribute to a better quality of life for patients with coronary artery disease.

What Are the Potential Complications Caused By DES?

While DES has significantly improved outcomes, it can cause several complications, also:

1. Procedural Risk in Women: In contemporary coronary stenting, women may face a slightly higher procedural risk compared to men.

2. Stent Thrombosis:

• Stent thrombosis is a severe complication that can occur at different time intervals after DES placement. It may be classified as early (occurring within 30 days), late (between 61 and 365 days), or very late (exceeding 12 months).

• The incidence of early stent thrombosis is around one to two percent, with subsequent rates of approximately 0.4 percent per year.

• Individuals who are not compliant with dual antiplatelet therapy and are at increased risk of early stent thrombosis.

• Genetic factors (CYP2C19, ABCB1, and ITGB3) and certain Clopidogrel-related factors may contribute to early stent thrombosis.

• Stent thrombosis, when it occurs, is associated with a high mortality rate (40 % to 60 %), primarily due to acute myocardial infarction.

3. Hypersensitivity Reactions:

• First-generation drug-eluting stents (Sirolimus, Paclitaxel) have been associated with hypersensitivity reactions.

• Hypersensitivity may contribute to the pathophysiology of stent thrombosis.

4. Acute Interstitial Pneumonitis:

• Rare cases have been reported where the implantation of a Paclitaxel-eluting stent resulted in acute interstitial pneumonitis.

• This severe inflammatory reaction led to death within a short period after the stent implantation.

5. Coronary Artery Aneurysm:

• The occurrence of coronary artery aneurysm is a rare but serious complication, observed in approximately 1.25 % of cases after drug-eluting stent implantation.

• Risk factors for coronary artery aneurysm include stent placement during acute myocardial infarction, the use of multiple or longer stents, and the presence of residual dissection.

6. Statin Therapy and Prevention:

• Statin therapy at hospital discharge has been shown to have a preventive effect on late target lesion revascularization after stent implantation.

7. Dual Antiplatelet Therapy:

Patients receiving drug-eluting stents are typically prescribed dual antiplatelet therapy (DAPT) for an extended period to prevent thrombosis. Adherence to DAPT can be challenging, leading to increased bleeding risk.

Conclusion

Drug-eluting stents have undoubtedly transformed the landscape of interventional cardiology, offering a significant improvement over bare-metal stents in preventing restenosis. Ongoing research aims to refine the technology further, addressing challenges such as late thrombosis and enhancing customization. As the field evolves, drug-eluting stents continue to play a vital role in providing effective and sustainable solutions for patients with coronary artery disease.