Interventional medicine and cardiology rely heavily on minimally invasive techniques to diagnose and treat conditions within the body’s vessels and passageways. Two devices frequently used are the stent and the catheter, yet they serve fundamentally different roles. The catheter acts primarily as a temporary tool for access and delivery, while the stent functions as a permanent internal scaffold.
Physical Design and Composition
A catheter is a thin, flexible, hollow tube designed for navigation and fluid management. It is typically constructed from biocompatible polymers such as silicone, polyurethane, or specialized plastics, allowing it to be easily maneuvered through intricate pathways like blood vessels or the urinary tract.
Catheters are measured using the French scale, where a higher French size indicates a larger outer diameter. They often feature one or more internal channels, or lumens. A single-lumen catheter provides one channel for administration or drainage, while a multi-lumen design allows for simultaneous activities, such as injecting contrast dye or measuring internal pressure. Some catheters may also incorporate specialized tips, such as a balloon, to assist in positioning or temporarily dilate a vessel.
In contrast, a stent is a rigid, mesh-like scaffold designed to provide structural support, and it is not a hollow tube for passing substances through its core. The majority of stents are made from durable metal alloys, including cobalt-chromium, stainless steel, or nickel-titanium (Nitinol). Nitinol is particularly valued for its superelasticity and shape-memory properties, which allow a stent to be compressed for delivery and then “self-expand” to its predetermined size once released at body temperature.
Stents can also be manufactured from bioresorbable polymers, such as poly(L-lactic acid) (PLLA), which are designed to dissolve slowly over time after providing temporary scaffolding. Whether metal or polymer, the stent’s structure is laser-cut from a tube or braided wire, creating a precise pattern of struts and connectors that determine its radial strength and flexibility.
Primary Function and Purpose
The primary function of a catheter is to access internal body cavities, vessels, or ducts for diagnostic or therapeutic purposes. It acts as a conduit to deliver substances like contrast agents for imaging, medications, or even other devices, such as the stent itself.
Beyond delivery, catheters are used for specific monitoring and removal tasks, enabling the measurement of blood pressure within the heart chambers or the drainage of fluids like urine from the bladder. For instance, a cardiac catheterization uses the device to gather diagnostic data about the heart and arteries, which may or may not lead to further treatment.
The stent’s core function is to maintain the patency of an internal lumen, mechanically preventing it from collapsing or re-narrowing. This supportive role is crucial in coronary arteries, where plaque buildup can restrict blood flow and requires a continuous structural solution.
Stents are further categorized by their function, with bare-metal stents (BMS) providing purely mechanical support and drug-eluting stents (DES) offering an additional therapeutic layer. Drug-eluting stents are coated with a polymer that slowly releases anti-proliferative medications directly into the vessel wall to prevent the excessive tissue growth, known as restenosis.
Placement Procedures and Duration in the Body
A catheter is typically inserted into the body through a small puncture site, often in the groin or wrist, and is guided through the vascular system under fluoroscopic imaging. For diagnostic procedures, the catheter is used only for the duration of the test, usually minutes or a few hours, and is then completely removed.
Even when used therapeutically, such as for temporary drainage, a catheter is designed for short-term residency. This can range from a few hours to several days or weeks, depending on the need.
In contrast, the placement of a stent is a permanent or semi-permanent measure that requires the use of a catheter for delivery. The stent is first crimped tightly onto a specialized balloon catheter, which is then threaded through the body to the site of the blockage. Once positioned, the balloon is inflated, expanding the stent against the vessel wall to embed it firmly in the tissue.
The catheter is deflated and withdrawn from the body, leaving the expanded stent behind to maintain the vessel opening. Metallic stents remain in the body indefinitely, providing continuous structural support. Bioresorbable stents are designed to fully dissolve and be absorbed by the body over a period of 18 to 24 months, representing a semi-permanent solution that eventually restores the vessel to its natural state.