Guidewires are an integral part of vascular intervention. They are utilized to access target vessels, cross lesions, and deliver definitive interventional therapy. There are many choices in guidewires, as different clinical presentations require different device attributes. Selection of an appropriate guidewire can improve crossing success (particularly in total occlusions), improve device delivery, limit cost, and limit the risk of vascular injury either from the distal wire tip or wire shaft buckling.
Guide wire features:
Trackability: this is the ability of the wire to follow the tip down a vessel, especially through curves of tortuous vessels. Less stiff, floppy wires can navigate sharp bends much easier than stiff wires. Trackability is affected by how the tip is designed and the material of the core wire.
Torqueability: He described this as the ability to apply rotational force at the proximal end of the guidewire and have that force transmitted efficiently to achieve proper control at the distal end.
Flexibility: This is the ability of a wire to flex on its longitudinal axis while maintaining torque and trackability. This is important when reaching a tortuous lesion. The core of wires are either made of very flexible nitinol or stiff stainless steel, which dictates a guidewire’s flexibility.
Crossability: Ability to cross a lesion with little or no resistance. Stiffer wires can usually cross significant lesions.
Supportability: Ability of a guidewire to support the passage of another device or system over it.
The performance of a guidewire in any of these areas is determined by the composition materials and design.
Core Diameter: This is not the overall size of the wire, but the one element that usually tapers near the tip. Diameter helps determine overall flexibility (smaller diameters) or increased support and torqueability (larger diameters).
Core Taper: This is the pattern of the wire as it goes from core diameter to the tip. The ability to transmit torque is dependent on taper length, with shorter tapers tending to prolapse (fold in on themselves) and longer offering greater torque. The taper affects traceability and the ability of the wire to follow the tip around bends. Tip taper also determines if the tip is blunt or more pointed like a needle. The pointed tips have the ability to better penetrate and push through CTOs.
Core Type: Usually made of either stainless steel or nitinol. Stainless is good for support, push and torque, but is less flexible. Nitinol is super-elastic, offers good flexibility and torque in tortuous anatomy, and is more durable.
Tip Style: Guidewires have a core wire that either tapers down to the tip of the wire for added support, or stops short of the tip, with shaping ribbons used at the tip to make the tip more flexible. The way this is designed helps control torqueability.
Tip Coils: The end of the wire tip is wrapped in a ribbon of flexible metal to make the tips more flexible and atraumatic. On nitinol wires, the shaping ribbon is required to help retain the shape of the tip. The design of the coils helps determine a wire’s torque and crossability. The use of spring coils can provide more tactile feedback to the operator, but these tips increase the amount of friction, making them more difficult to navigate in tortuous vessels.
Coatings: Wires can be coated in polymers to make them more hydrophilic or hydrophobic. Hydrophobic coatings are usually made of silicone and repel water to reduce friction, increase trackability and offer good tactile feedback. Hydrophilic coatings attract water and the coating becomes a gel when wet. This makes the wires more slippery and reduces friction, helping increase trackability. However, hydrophilic wires are not recommended as a first choice because the slippery tip can slide between plaque and create a dissection during insertion. These wires also can cause perforation and because they have less tactile feedback for tissue resistance.
Support: This is the level of support a wire provides. Floppy/light wires were originally designed for balloon angioplasty and provide improved trackability and flexibility. Moderate support wires are used for stenting, offering the needed support to deliver and deploy a stent. Extra support wires are often used for stenting or to support buddy wires.
Tip Load: This is a value of the tip stiffness and a measure of strength based on how many grams of pressure are needed to deflect/buckle the tip.
Support Catheters: These travel over the guide wire like a sheath to strengthen the guide wire. It can go over a floppy workhorse wire to effectively give the tip of the guide wire enough support to become a CTO wire.
Wire Length: Most wires are about 180 cm in length, which is long enough for use in both femoral and radial artery access. Some wires are between 330-350 cm, which are designed for retrograde CTO lesion access.