Bioabsorbable Vascular Scaffolds

Introduction:

Percutaneous coronary intervention (PCI) is an optimal medical procedure for managing coronary artery disease (CAD), where the blood vessels supplying the heart muscles undergo narrowing or blockage. This intervention employs a catheter with a balloon at the tip to expand the constricted blood vessels. In certain instances, stents or mesh tubes may be utilized to maintain the openness of the blood vessel. On the other hand, bioresorbable vascular scaffolds (BVS) represent a distinct category of stents designed to be assimilated by the body. The innovative concept of bioabsorbable scaffolds fosters a natural healing process within the arterial walls.

What Are Bioabsorbable Vascular Scaffolds?

Bioresorbable vascular scaffolds represent a category of stents capable of being assimilated by the body, aiding blood vessels in reclaiming their natural function and state while reducing device-related blood clots. These scaffolds are crafted from biodegradable materials and offer temporary support, gradually degrading over time, thereby facilitating the restoration of the arteries' natural state. In their early stages, these scaffolds emulate the function of drug-eluting stents (DES)—small mesh tubes that aid in reopening and maintaining the arteries, coupled with the slow release of medications to prevent blood clot formation. Subsequently, these bioresorbable vascular scaffolds undergo dissolution.

The initial iteration of bioabsorbable vascular scaffolds featured ABSORB and DESolve scaffolds, incorporating poly-L-lactic acid (PLLA), while DREAMS 1G utilized magnesium alloy. However, these designs exhibited higher strut thickness. The second-generation advancements introduced Magmaris (DREAM 2G) with a magnesium alloy, Fantom with Tyrosine polycarbonate, and ART (absorbable magnesium scaffold) with a poly-D, L-lactic (PDLLA) coating. Notably, these innovations boasted enhanced properties and reduced the strut thickness in the scaffold's support structures. The latest BVS models provide increased resistance to fractures during post-implantation dilation. Of particular interest, Fantom, featuring iodinated Tyrosine, is visible on X-ray images without additional markers.

What Are the Advantages of Bioabsorbable Vascular Scaffolds?

The advantages of bioabsorbable vascular scaffolds are:

1. Restoration of Endothelial Function: When bioabsorbable vascular scaffolds dissolve, they restore average artery properties by reducing inflammation and fostering a more conducive healing environment. This distinctive phenomenon sets them apart from solid metal stents.

2. Reduction of Atherosclerotic Plaques: Bioabsorbable vascular scaffolds are pivotal in addressing atherosclerotic plaque concerns by diminishing plaque accumulation and reinstating normal physiological functions, including systolic and diastolic activities.

3. Advantage in Younger Patients: Specifically beneficial for younger patients facing acute coronary issues, these biodegradable materials offer positive outcomes compared to traditional metal stents.

4. Prevention of Side Branch Issues: Bioabsorbable vascular scaffolds are anticipated to avert complications with side branches post-resorption. This advantageous feature distinguishes them from metal stents and eliminates the potential impact of a 'full metal coat,' allowing for early restenosis treatment without additional metal stents.

5. Possibility of Surgical Revascularization: Introducing the potential for a surgical revascularization procedure, bioabsorbable vascular scaffolds facilitate the restoration of blood flow to blocked arteries or veins, providing a unique treatment avenue.

6. Avoidance of Permanent Foreign Body: Unlike permanent stents, bioabsorbable vascular scaffolds do not leave a lasting foreign body, ensuring longer-term outcomes. They are placed temporarily, minimizing the presence of a permanent implant.

7. Risk Reduction of Late Complications: Bioabsorbable vascular scaffolds decrease the risk of late complications associated with metallic stents, such as the need for repeated interventions, offering a distinct advantage in long-term patient care.

8. Enhanced Flexibility in Future Interventions: The absorption of the scaffold enhances flexibility for future interventions, allowing adjustments as needed, a characteristic not found in traditional stents.

9. Lower Allergic Reaction Risk: Bioabsorbable vascular scaffolds, typically crafted from materials less prone to causing allergic reactions compared to metals in permanent stents, uniquely prioritize patient safety.

How Do Bioresorbable Vascular Scaffolds Work?

Biocompatible polymer materials are commonly used in the construction of BVS. Specific bioresorbable scaffolds are treated with an anti-proliferative drug, aiding in the prevention of smooth muscle cell growth within the arterial wall and lowering the likelihood of restenosis (recurrence of narrowing or blockage in a previously treated blood vessel). As time passes, the scaffold's polymer material's gradual degradation occurs, typically unfolding over several months to a few years. Following the implantation of bioabsorbable vascular scaffolds, the initial three months witnessed its crucial role in drug elution, releasing medications to prevent blood clots and vessel re-narrowing while supporting the vessel walls. The support to the artery wall persists for up to 12 months. Bioabsorbable vascular scaffolds begin resorption at six months, extending up to 36 months. As the scaffold gradually absorbs, the artery reverts to a more natural state, restoring its ability to constrict and dilate as necessary. Between 38 to 46 months, the scaffolds become undetectable and non-viable through optical coherence tomography which is a non-invasive medical imaging technique that uses light waves to capture high-resolution, cross-sectional images of biological tissues.

What Are the Outcomes Of Bioresorbable Vascular Scaffolds Performance?

Presently, there exists a lack of conclusive proof demonstrating the superiority of bioresorbable vascular scaffolds over drug-eluting stents in randomized trials. The extended efficacy of BVS is subject to various factors, including:

1. Device Design: The thickness of the stent structure may result in vessel narrowing.

2. Procedural Details: Malposition during the procedure can lead to incomplete lesion coverage, potentially causing later-stage scaffold fractures. The 'PSP technique' (preparing the lesion, sizing it adequately, and post-dilatation) is a specific implantation approach crucial for success.

3. Characteristics of Blood Vessels: BVS implantation is linked to a less symmetric vessel shape in the long term. Improper implantation can induce increased asymmetry, consequently elevating the occurrence of target lesion failure (TLF).

4. Implantation Site Characteristics: Lesions over 28 mm are unsuitable for bioresorbable scaffolds.

Conclusion:

Bioresorbable vascular scaffolds have introduced a groundbreaking approach to interventional cardiology, offering a potential solution to the drawbacks associated with permanent metallic stents. Initially, people were hopeful about these devices and expected them to bring about a new era where stents would become less visible or even disappear. However, as clinical trials progressed, it became clear that expectations still had to be tempered, highlighting the necessity for significant advancements. Traditional drug-eluting stents currently maintain their status as the preferred choice in most scenarios. Nevertheless, ongoing advancements in the design and materials of bioresorbable vascular scaffolds aim to overcome limitations and enhance clinical outcomes through the development of newer generations.