What Are Bioresorbable Vascular Scaffolds (BVS)?

What are Bioresorbable Vascular Scaffolds (BVS)?

Introduction

Coronary artery disease (CAD) remains a leading cause of morbidity and mortality worldwide. Percutaneous coronary intervention (PCI) with stent implantation has revolutionized the treatment of CAD, providing mechanical support to diseased vessels and delivering anti-proliferative drugs to prevent restenosis. While metallic drug-eluting stents (DES) have significantly improved patient outcomes, their permanent presence within the coronary artery raises concerns regarding long-term complications such as late stent thrombosis, impaired vasomotion, and the potential for future re-interventions. This has led to the development of **bioresorbable vascular scaffolds (BVS)**, an innovative technology designed to provide temporary scaffolding and drug delivery, ultimately disappearing from the vessel once their therapeutic function is complete.

Understanding Bioresorbable Vascular Scaffolds

Bioresorbable vascular scaffolds are a class of implants designed to transiently support a diseased coronary artery, deliver antiproliferative drugs, and then gradually resorb into the body. Unlike metallic stents, which remain permanently in the vessel, BVS are intended to restore the natural physiology of the coronary artery by allowing for the recovery of vasomotion, avoiding chronic inflammation, and facilitating future surgical or interventional procedures without the hindrance of a permanent metallic cage. The primary materials used in first-generation BVS were polymers, predominantly poly-L-lactic acid (PLLA), which undergo hydrolysis and are metabolized into water and carbon dioxide.

Mechanism of Action and Advantages

The mechanism of action of BVS involves several phases. Initially, the scaffold provides mechanical support to the vessel wall, similar to a metallic stent, preventing acute recoil and maintaining luminal patency. Concurrently, it releases an anti-proliferative drug to inhibit neointimal hyperplasia. Over time, typically within 2-3 years, the scaffold gradually degrades and is absorbed by the body. This bioresorption process is a key advantage, as it aims to leave behind a healed, native-like vessel, free from a permanent implant. The theoretical benefits of BVS include:

• **Restoration of Vasomotion:** The absence of a permanent metallic cage allows the treated vessel to regain its natural pulsatility and ability to dilate and constrict in response to physiological demands.
• **Elimination of Chronic Inflammation:** The permanent presence of metallic stents can lead to chronic inflammatory responses. BVS aim to mitigate this by disappearing from the vessel.
• **Facilitation of Future Interventions:** In the event of recurrent disease, the absence of a permanent scaffold simplifies future revascularization procedures, whether surgical or percutaneous.
• **Prevention of Late Stent-Related Complications:** The long-term risks associated with permanent metallic implants, such as very late stent thrombosis, are theoretically reduced with BVS.

Challenges and Lessons Learned from First-Generation BVS

Despite the promising theoretical advantages, the clinical experience with first-generation BVS, particularly the Absorb BVS (Abbott Vascular), revealed several challenges. These included higher rates of scaffold thrombosis and target lesion revascularization compared to contemporary metallic DES. The reasons for these adverse outcomes were multifactorial and attributed to:

• **Scaffold Design and Material Properties:** First-generation BVS had thicker struts and were less radially strong than metallic stents, leading to challenges in implantation and potentially incomplete apposition.
• **Implantation Technique:** The

need for meticulous implantation techniques, often referred to as the PSP (Prepare, Size, Post-dilate) strategy, was crucial but not always consistently applied.

• **Degradation Profile:** The relatively slow degradation rate of first-generation BVS meant that the scaffold remained present for an extended period, potentially contributing to adverse events during the resorption phase.

These challenges led to the withdrawal of first-generation BVS from the market. However, the lessons learned have been invaluable, driving significant advancements in the development of second and third-generation BVS with improved designs, materials, and implantation strategies.

Advancements and Future Directions

Research and development in BVS technology have continued, focusing on overcoming the limitations of first-generation devices. Key areas of advancement include:

• **Novel Materials:** Exploring new bioresorbable polymers and metallic alloys (e.g., magnesium-based scaffolds) with optimized degradation profiles and mechanical properties.
• **Thinner Strut Designs:** Developing BVS with thinner struts to improve deliverability, reduce vessel injury, and enhance re-endothelialization.
• **Improved Radial Strength and Flexibility:** Engineering scaffolds with better radial strength to maintain vessel patency and increased flexibility for easier navigation through tortuous coronary arteries.
• **Enhanced Drug Elution Kinetics:** Optimizing drug release profiles to effectively inhibit neointimal hyperplasia while minimizing adverse effects.
• **Advanced Imaging and Implantation Techniques:** Utilizing intravascular imaging modalities like optical coherence tomography (OCT) and intravascular ultrasound (IVUS) to guide precise BVS implantation and ensure optimal scaffold expansion and apposition.

The future of BVS lies in achieving a delicate balance between providing adequate mechanical support during the acute phase and ensuring complete, timely, and safe resorption. Ongoing clinical trials are evaluating the safety and efficacy of newer generation BVS, with promising early results suggesting improved outcomes compared to their predecessors.

Conclusion

Bioresorbable vascular scaffolds represent a significant paradigm shift in the treatment of coronary artery disease, offering the potential to restore vessel integrity and function without leaving a permanent implant. While first-generation devices faced considerable hurdles, the insights gained have propelled the field forward. The continuous innovation in materials science, scaffold design, and implantation techniques holds the promise of a new era where temporary scaffolding can provide long-term benefits, ultimately improving the lives of patients with CAD. It is crucial to emphasize that this information is for academic purposes only and should not be considered medical advice. Always consult with a qualified healthcare professional for any medical concerns or treatment decisions.