A heart stent is a small, specialized tube placed inside a coronary artery to restore blood flow to the heart muscle. This device acts as a scaffold, providing structural support to a vessel that has narrowed due to the buildup of plaque, a condition known as atherosclerosis. Its purpose is to keep the artery open, preventing the vessel from collapsing or re-narrowing after an angioplasty procedure. The implant is designed to be a permanent fixture, ensuring a consistent supply of oxygenated blood reaches the heart.
The Basic Structure and Expanded Form
Once implanted and fully expanded, a heart stent resembles a miniature, cylindrical cage or a delicate piece of wire mesh. Common models measure between 8 and 48 millimeters in length and 2 to 5 millimeters in diameter to fit the average coronary artery. The structure is composed of interconnected metal struts that form a lattice pattern, providing the necessary radial strength to resist the inward pressure of the artery wall.
These struts are extremely thin, often measuring between 80 and 150 micrometers in thickness, comparable to the diameter of a human hair. The metallic material exhibits a subtle sheen and is designed to be flexible enough to navigate the winding coronary arteries. The open-cell mesh design minimizes the amount of foreign material introduced while maximizing coverage to prevent tissue from prolapsing through the gaps.
Variations in Design and Function
The visual characteristics of a stent can vary significantly based on its functional design, primarily whether it is a Bare Metal Stent (BMS), a Drug-Eluting Stent (DES), or a Bioresorbable Scaffold (BRS).
Bare Metal Stents (BMS)
Bare metal stents are the simplest form, consisting only of the metallic lattice structure. They have a uniform, uncoated metallic appearance and rely solely on their physical structure to keep the artery open.
Drug-Eluting Stents (DES)
Drug-eluting stents are the current standard and feature an additional layer that alters their surface composition. The metallic platform is coated with a polymer that holds and slowly releases medication into the arterial wall. This coating may give the stent a slightly thicker or more textured appearance compared to a BMS. The drug-polymer combination suppresses the formation of scar tissue that could cause the artery to narrow again.
Bioresorbable Scaffolds (BRS)
Bioresorbable Scaffolds are made from biodegradable polymers, such as polylactide, giving them a distinct appearance. These scaffolds are noticeably thicker than metallic stents due to the weaker mechanical properties of the polymer material. BRS devices often incorporate small platinum markers at the ends to make them visible during the procedure. The defining characteristic of a BRS is its eventual disappearance, as the polymer is designed to fully dissolve and be absorbed by the body over two to four years.
The Stent During Delivery
The visual appearance of a stent changes dramatically from its compressed state during insertion to its final expanded form. Before deployment, the stent is tightly crimped onto a small balloon located at the tip of a catheter. In this state, the stent is nearly invisible, appearing only as a compressed, thin sleeve. The catheter is inserted through an artery in the wrist or groin and guided under X-ray imaging to the site of the blockage.
Once positioned correctly, the physician inflates the balloon using high pressure, forcing the crimped stent to expand outward. This mechanical expansion permanently deforms the metal lattice, pressing it against the artery wall. The balloon is then deflated and withdrawn, leaving the expanded metal mesh locked into place to maintain the widened path for blood flow.
Materials and Long-Term Integration
The permanent metal structure of most modern stents is composed of specialized medical-grade alloys, most commonly Cobalt-Chromium (CoCr) or Platinum-Chromium (PtCr). These materials are selected for their high radial strength and excellent biocompatibility, ensuring they do not provoke a strong immune reaction. Using these alloys allows manufacturers to create stents with thinner struts compared to older stainless steel versions, improving flexibility.
Over time, the body begins a natural healing process where cells grow over the implanted scaffold, known as endothelialization. This involves the formation of a thin, smooth layer of tissue that covers the metallic struts. After several months, this tissue growth integrates the stent into the artery wall and hides the metallic look from the bloodstream. In drug-eluting stents, the polymer coating either degrades or becomes fully incorporated beneath this new tissue layer.