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 (Figure 1). 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.
Click here to get more.
Deciding which device attributes are needed in individual cases requires knowledge of engineering concepts that create those attributes. In certain cases, one wire may be needed for crossing and then exchanged in order to achieve better or safer device delivery. Intraluminal crossing requires different techniques and device attributes than subintimal crossing. With proper wire choice and manipulation, the overwhelming majority of occlusions can be crossed and treated interventionally without the need for more expensive dedicated crossing tools. This article breaks down the basic building blocks of guidewires and how to select and optimize use of the right type.
The core diameter is the functional diameter of the guidewire. In peripheral intervention cases, the most widely utilized sizes are 0.014, 0.018, and 0.035 inch. Larger-diameter wires have greater rail support, as the strength is related to the radius4 (Figure 2). A larger diameter improves torque and can be used to straighten vessels (eg, sheath placement in a tight iliac bifurcation). Smaller diameters have increased flexibility and trackability through the vessel.1 Device compatibility and requisite sheath size often dictate the choice of core diameter. Clinical needs such as tortuosity (increased flexibility), crossing a tight stenosis, as well as device compatibility and support (for example, 0.014-inch size for most atherectomy procedures, plus the need for column strength), should also be considered in the device selection process.
The core material of a guidewire affects flexibility, support, steering, and tracking. In general, stainless steel is easier to torque and is more rigid, providing better columnar support (Figure 3A and 3B). Nitinol is more flexible and kink resistant (Figure 3C and 3D). Developments such as high-tensile-strength stainless steel and combinations of stainless steel with nitinol have been utilized.2 High-tensile-strength stainless steel provides more column strength and torquability than original stainless steel. The use of hybrid wires incorporates high-tensile stainless steel shafts with nitinol tips to impart high torquability and columnar shaft strength with kink-resistance tips.
Broad, gradual, or long tapers offer acute vessel access and improved tracking (Figure 4A). Additionally, the wire follows itself well around bends. Devices with abrupt or short tapers create support in shorter distances and have a greater tendency to prolapse (Figure 4B). The core grind is a core with constant diameter (stated wire size), and the core tapers are areas where the core of the wire changes over a set distance. There may be several tapers in a wire (Figure 4C). Long, gradual tapers track well around bends, but do not provide as much support in short distances. Guidewire support charts are affected by core material, core diameter, and tapers (Figure 5).
Guidewire tip design affects steering and durability. A core that extends to the tip of the wire increases the transmission of force, is more durable and steerable, improves tactile feedback, and is ideal for use in peripheral vessels (Figure 6A). A core that does not extend to the tip (ie, the shaping ribbon design) is delicate, flexible, and soft (Figure 6B). This kind of tip is also easier to shape, can be easily prolapsed, and is less likely to inadvertently injure distal vessels. The tip penetration is a function of the tip stiffness and cross-sectional area of the tip.1 Different levels of tip penetration provide the guidewire with more or less push force or “tip load” to cross challenging lesions (Figure 7).
Goto Hainwise to know more.
Furthermore, guidewire tip coils affect support, tracking, shapeability, and radiopacity (Figure 8). Each of these attributes is positively affected by coils. The coils, however, also add to drag by increasing frictional elements.
Guidewire covers are sleeves of polymer or plastic placed over the wire core to enhance lubricity (Figure 9). This results in less drag, enhanced lesion crossing, and smooth tracking in tortuous vessels. Hybrid wires with tip coils and covers are utilized to achieve a combination of desired effects. Hydrophobic coatings reduce friction and improve device trackability by repelling water to create a smooth, “wax-like” surface, with no water actuation required.1 Hydrophilic coatings attract water to create a slippery, “gel-like” surface.1 There is an inverse relationship between lubricity and tactile feedback.
Visibility is directly related to wire diameter and the density of the materials used. Materials such as platinum and palladium are more radiopaque. The density of the material determines radiopacity. Visibility is an important component for wire visualization under fluoroscopy, as it confirms access in the target vessel and may aid in sizing the lesion for proper selection of device size (Figure 10).
Longer wires allow distal device delivery and catheter exchange without losing distal wire position. As a general rule, however, there is a loss of torque response as the wire tip is farther from the torque site. Torque control is also diminished by tortuosity. Straight tips or small angles increase tip penetration (Figure 11). Adding a secondary bend may allow a better angle for navigation of tortuous segments. J tips are ideal for subintimal crossing and provide an atraumatic distal end, reducing the potential of perforating the vessel.1
Understanding wire characteristics is crucial to choosing the ideal wire or wires for a particular case. The ability to steer, cross, deliver therapy, avoid distal wire injury, straighten vessels, not induce kinks, and resist deformation or kinks is a function of wire design. Wire performance can also be affected by tortuosity, external support catheters, and proximity of the torque site to the treatment site. Advancements in guidewire design and a better understanding of how to use these wires results in improved procedural success.
Craig Walker, MD, is Clinical Professor of Medicine at Tulane Medical School in New Orleans, and an interventional cardiologist at the Cardiovascular Institute of the South in Houma, Louisiana. He has disclosed that he has no financial interests related to this article. Dr. Walker may be reached at (800) 445-; .
Want more information on Peripheral Guidewires? Feel free to contact us.