Self-Expanding Stents VS Balloon-Expanding Stents

Balloon-Expanding or Self-Expanding Balloon-Expanding stents are manufactured in the crimped state and expanded to the vessel diameter by inflating a balloon. Self-Expanding stents are manufactured at the vessel diameter (or slightly above) and are crimped and constrained to the smaller diameter until the intended delivery site is reached. The constraint is then removed and the stent is deployed.

Radial Strength Radial Strength is the external pressure that a stent is able to withstand without causing “clinically significant damage” Balloon-Expanding stents can collapse causing serious clinical implications. Self-Expanding stents are super elastic and will elastically recover even after complete crushing.

Radial Stiffness Radial stiffness is defined as how much the diameter of a stent is reduced by the application of external pressure. A balloon-expanding stent will be stiffer than a self-expanding stent of identical design. Typically a balloon-expanding stent will be at least three times stiffer.

Radial Compliance Radial compliance is the ability of a stent to bend. The radial compliance of a self-expanding stent is much greater than a balloon-expanding stent. A balloon-expanding stent will greatly decrease the compliance of a vessel.

Acute Recoil Acute recoil refers to the reduction in diameter immediately observed upon deflation of a balloon. A balloon-expanding stent recoils after balloon deflation. A self-expanding stent assists balloon inflation and there is no recoil.

X-Ray Visibility The x-ray visibility of stainless steel and nitonol is very similar. Both visibilities are becoming inadequate as designers learn to scaffold with less metal. Gold plated versions of both exist, but there are corrosion and clinical concerns with the use of gold. Some newer self-expanding stents use tantalum to mark the ends of the stent. This appears to be the best. At least until a reliable way is found to protect gold or platinum layers or some other method is found.

Balloon Pressure Self-expanding stents assist the balloon Balloon-expanding stents resist the balloon Balloon pressures during balloon-expanding stenting are far greater than with a self-expanding stent

Corrosion Resistance Corrosion resistance of nitinol is very slightly superior to stainless steel, but it appears unlikely that these differences are of clinical significance. Nitinol must be carefully treated by electro polishing or similar methods to make it corrosion resistant It is easier to make stainless steel corrosion-safe

Balloon-Expanding Stent

Balloon-Expanding Stent

Wallstent The Wallstent, is delivered to the obstructed site by traversing over a wire. The outer protective covering is then retracted allowing the stent to self expand to keep the artery open. A balloon is then passed over the wire to the affected site, where it is inflated for completion of the angioplasty procedure

Smart Stent A second type of self-expanding stent is the Smart Stent, made of Nitinol material. This has an advantage of allowing a very small degree of shortening so as to allow the cardiologist to exactly place it in the proper position.

Conclusion Self-expanding and balloon-expanding stents differ in many respects. Self expanding stents become part of the anatomy and act in harmony with native vessels. Balloon-expanding stents change the geometry and properties of the anatomy. Self-expanding stents assist . Balloon-expanding stents dictate. There will always be a place for both in radiology suites.