Bare Metal Stent Vs Drug Eluting Stent

The world of interventional cardiology has witnessed remarkable advancements in treating coronary artery disease, with percutaneous coronary intervention (PCI) playing a pivotal role. Among the various tools used in PCI, stents stand out as essential devices that help restore blood flow to the heart. In the early days of stent technology, bare metal stents (BMS) were the primary option. However, with continuous innovation, drug-eluting stents (DES) emerged as a significant advancement. This article delves into the detailed comparison between BMS and DES, highlighting their mechanisms, advantages, disadvantages, clinical outcomes, and future perspectives.

Introduction to Coronary Artery Disease and Stents

Coronary artery disease (CAD) is a condition characterized by the buildup of plaque inside the coronary arteries, leading to narrowing and reduced blood flow to the heart muscle. This can result in chest pain (angina), shortness of breath, and, in severe cases, heart attack (myocardial infarction). Percutaneous coronary intervention (PCI) is a minimally invasive procedure used to open blocked coronary arteries. During PCI, a catheter is inserted into an artery, typically in the groin or wrist, and guided to the blocked coronary artery. A balloon is then inflated to compress the plaque and widen the artery. To maintain the openness of the artery, a stent is deployed.

What are Stents?

Stents are small, expandable mesh-like tubes that are placed inside a coronary artery to provide structural support and prevent the artery from collapsing or re-narrowing after angioplasty. The two primary types of stents are bare metal stents (BMS) and drug-eluting stents (DES).

Bare Metal Stents (BMS)

Historical Context and Development

Bare metal stents (BMS) were the first generation of stents used in PCI. They are made of stainless steel or other metal alloys. The primary function of BMS is to provide mechanical support to the arterial wall after balloon angioplasty, preventing acute vessel recoil and improving immediate blood flow.

Mechanism of Action

BMS work by physically scaffolding the artery open. Once deployed, the stent exerts a radial force against the arterial wall, maintaining the lumen size. However, the placement of a BMS triggers a healing response in the artery, which involves the proliferation of smooth muscle cells. This proliferation can lead to neointimal hyperplasia, a process where new tissue grows inside the stent, causing the artery to re-narrow.

Advantages of BMS

• Lower Cost: BMS are generally less expensive than DES, making them a more accessible option in certain healthcare settings.
• Shorter Dual Antiplatelet Therapy (DAPT) Duration: Patients receiving BMS typically require a shorter duration of DAPT (usually 4-6 weeks) compared to those receiving DES. This reduces the risk of bleeding complications associated with prolonged antiplatelet therapy.
• Suitable for Patients at High Risk of Bleeding: In patients with a high risk of bleeding, such as those undergoing surgery or with a history of bleeding disorders, BMS may be preferred due to the shorter DAPT duration.

Disadvantages of BMS

• Higher Risk of Restenosis: The major limitation of BMS is the higher rate of restenosis compared to DES. Neointimal hyperplasia, the excessive growth of tissue within the stent, can cause the artery to re-narrow, leading to recurrent symptoms.
• Need for Repeat Procedures: Due to the higher restenosis rate, patients with BMS may require repeat revascularization procedures, such as repeat PCI or coronary artery bypass grafting (CABG).

Drug-Eluting Stents (DES)

Development and Evolution

Drug-eluting stents (DES) were developed to address the issue of restenosis associated with BMS. DES are coated with drugs that inhibit smooth muscle cell proliferation, reducing the risk of neointimal hyperplasia. The first generation of DES was introduced in the early 2000s and showed significant promise in reducing restenosis rates. Subsequent generations of DES have been developed with improved drug coatings, biocompatible polymers, and stent designs.

Mechanism of Action

DES work by combining the mechanical support of a stent with the local delivery of antiproliferative drugs. Once the stent is deployed, the drug is released gradually over a period of weeks or months, inhibiting the proliferation of smooth muscle cells. This reduces the formation of neointimal hyperplasia and lowers the risk of restenosis.

Advantages of DES

• Lower Risk of Restenosis: The primary advantage of DES is the significantly lower rate of restenosis compared to BMS. The antiproliferative drugs effectively inhibit neointimal hyperplasia, reducing the likelihood of the artery re-narrowing.
• Reduced Need for Repeat Procedures: Due to the lower restenosis rate, patients with DES are less likely to require repeat revascularization procedures.
• Improved Clinical Outcomes: Studies have shown that DES are associated with improved clinical outcomes, including reduced rates of major adverse cardiac events (MACE), such as heart attack and the need for repeat procedures.

Disadvantages of DES

• Higher Cost: DES are generally more expensive than BMS, which can be a barrier to their use in certain healthcare settings.
• Longer Dual Antiplatelet Therapy (DAPT) Duration: Patients receiving DES typically require a longer duration of DAPT (usually 6-12 months or longer) to prevent stent thrombosis, a serious complication where a blood clot forms inside the stent.
• Risk of Late Stent Thrombosis: Although rare, late stent thrombosis is a serious concern with DES. The prolonged inhibition of endothelialization (the growth of cells lining the artery) can increase the risk of clot formation within the stent.

Detailed Comparison: BMS vs. DES

To provide a comprehensive understanding, let's compare BMS and DES across several key parameters:

Restenosis Rate

• BMS: Restenosis rates with BMS range from 20% to 30% within the first year after stent placement.
• DES: Restenosis rates with DES are significantly lower, typically ranging from 5% to 10% within the first year.

Need for Repeat Revascularization

• BMS: Patients with BMS have a higher likelihood of requiring repeat revascularization procedures, such as repeat PCI or CABG, due to restenosis.
• DES: Patients with DES have a lower likelihood of requiring repeat revascularization procedures due to the reduced risk of restenosis.

Dual Antiplatelet Therapy (DAPT)

• BMS: Shorter DAPT duration (4-6 weeks) is typically recommended to balance the risk of bleeding.
• DES: Longer DAPT duration (6-12 months or longer) is necessary to prevent stent thrombosis, but it increases the risk of bleeding complications.

Cost

• BMS: Lower cost, making it more accessible in resource-constrained settings.
• DES: Higher cost, which can be a barrier to access in certain healthcare systems.

Clinical Outcomes

• BMS: May be associated with higher rates of MACE, including heart attack and the need for repeat procedures.
• DES: Generally associated with improved clinical outcomes, including reduced rates of MACE.

Risk of Stent Thrombosis

• BMS: Lower risk of late stent thrombosis due to faster endothelialization.
• DES: Potential for increased risk of late stent thrombosis, especially with first-generation DES, due to delayed endothelialization.

Clinical Evidence and Studies

Numerous clinical trials and studies have compared BMS and DES, providing valuable insights into their efficacy and safety. Some notable studies include:

• RAVEL (Randomized study with the Sirolimus-eluting Bx Velocity balloon-expandable stent in the treatment of patients with de novo native coronary artery lesions): This landmark trial demonstrated the superiority of sirolimus-eluting stents (a type of DES) over BMS in reducing restenosis rates.
• SIRIUS (Sirolimus-eluting stent in de novo native coronary lesions): The SIRIUS trial further confirmed the benefits of sirolimus-eluting stents, showing a significant reduction in restenosis and the need for repeat procedures.
• TAXUS (Paclitaxel-eluting stent): This trial evaluated the use of paclitaxel-eluting stents (another type of DES) and found that they were more effective than BMS in preventing restenosis.
• ISAR-TEST (Intracoronary stenting and antithrombotic regimen-testing): This series of trials compared different DAPT regimens after stent implantation and provided guidance on the optimal duration of antiplatelet therapy.

These studies, along with many others, have collectively shown that DES are generally more effective than BMS in reducing restenosis and improving clinical outcomes. However, the decision to use BMS or DES should be based on individual patient characteristics, risk factors, and clinical circumstances.

Factors Influencing the Choice of Stent

The selection between BMS and DES is a complex decision that involves considering several factors:

• Patient Risk Factors: Patients at high risk of bleeding may be better suited for BMS due to the shorter DAPT duration. Conversely, patients at high risk of restenosis, such as those with diabetes or complex lesions, may benefit more from DES.
• Lesion Characteristics: The complexity of the coronary artery lesion also influences the choice of stent. DES are often preferred for long lesions, small vessels, and lesions in critical locations.
• Cost Considerations: In healthcare settings with limited resources, the lower cost of BMS may be a significant factor in the decision-making process.
• Patient Compliance: Adherence to DAPT is crucial for the success of stent implantation. Patients who are unlikely to comply with prolonged DAPT may be better candidates for BMS.
• Clinical Guidelines: Current clinical guidelines generally recommend DES for most patients undergoing PCI, but they also recognize the role of BMS in specific situations.

The Role of Dual Antiplatelet Therapy (DAPT)

Dual antiplatelet therapy (DAPT) is a critical component of stent implantation. DAPT involves the use of two antiplatelet medications, typically aspirin and a P2Y12 inhibitor (such as clopidogrel, prasugrel, or ticagrelor), to prevent blood clot formation within the stent.

• Mechanism of Action: Aspirin inhibits the production of thromboxane A2, a substance that promotes platelet aggregation. P2Y12 inhibitors block the P2Y12 receptor on platelets, preventing them from activating and clumping together.
• Duration of DAPT: The duration of DAPT varies depending on the type of stent used and the patient's risk factors. As mentioned earlier, BMS typically require a shorter DAPT duration (4-6 weeks), while DES require a longer duration (6-12 months or longer).
• Risks of DAPT: The main risk of DAPT is bleeding. Prolonged use of antiplatelet medications can increase the risk of gastrointestinal bleeding, intracranial hemorrhage, and other bleeding complications.
• Balancing Risks and Benefits: The decision to use DAPT and the duration of therapy must be carefully balanced against the risk of bleeding. Factors such as age, history of bleeding, kidney function, and the use of other medications should be considered.

Newer Generation Stents and Future Directions

The field of stent technology continues to evolve, with ongoing research and development focused on improving stent designs, drug coatings, and biocompatibility. Some of the newer generation stents and future directions include:

• Biodegradable Polymer Stents: These stents are coated with polymers that dissolve over time, leaving behind a bare metal stent. The advantage of biodegradable polymer stents is that they provide the benefits of DES in terms of reducing restenosis, while also minimizing the risk of late stent thrombosis associated with permanent polymers.
• Drug-Coated Balloons (DCB): DCB are angioplasty balloons coated with antiproliferative drugs. They deliver the drug directly to the arterial wall without leaving behind a stent. DCB are particularly useful in treating in-stent restenosis (ISR), where the artery re-narrows within a previously implanted stent.
• Bioabsorbable Stents: These stents are made of materials that dissolve completely over time, leaving no foreign body in the artery. Bioabsorbable stents have the potential to restore the natural vasomotion of the artery and reduce the risk of late complications.
• Personalized Stent Therapy: Future research may focus on tailoring stent selection and DAPT regimens to individual patient characteristics and genetic profiles. This personalized approach could optimize clinical outcomes and minimize the risk of complications.

Conclusion

In summary, both bare metal stents (BMS) and drug-eluting stents (DES) have played significant roles in the treatment of coronary artery disease. BMS were the first generation of stents and provide mechanical support to the arterial wall. While they are less expensive and require shorter DAPT duration, they are associated with higher rates of restenosis. DES, on the other hand, are coated with antiproliferative drugs and have been shown to significantly reduce restenosis rates. However, they are more expensive and require longer DAPT duration, which increases the risk of bleeding complications.

The choice between BMS and DES depends on individual patient characteristics, lesion characteristics, cost considerations, and clinical guidelines. Newer generation stents, such as biodegradable polymer stents, drug-coated balloons, and bioabsorbable stents, are being developed to further improve clinical outcomes and reduce the risk of complications. As the field of interventional cardiology continues to advance, the future holds promise for even more effective and personalized approaches to treating coronary artery disease. Ultimately, the goal is to provide the best possible care for patients with CAD, improving their quality of life and reducing the risk of adverse cardiac events.