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21. Wires, Sheaths, and Catheters
Endovascular procedures include vessel access, obtaining diagnostic images, navigating and crossing the lesion, treating the lesion, and vessel closure. To accomplish these tasks, the operator needs to have a continuous platform between the vascular access site and the true lumen of the vessel distal to the lesion. Devices used to establish that platform are guidewires, catheters, guiding catheters, and sheaths.
Interrelation of endovascular procedures platforms. From top to bottom: 0.35 glide wire, torque device, Tuohy-Borst, 5 Fr Bernstein catheter, and 5 Fr sheath
Guidewires
Guidewires are the innermost and leading devices of endovascular interventions. They are used to maintain access, insert sheaths, and deliver catheters and therapeutic devices.
Tip Design
Angled-tip glide wire (left), J-wire (center), and Rosen wire (right)
Length
Wires come in different lengths to cover the cumulative distance from the access to beyond the targeted lesion. The length of wires varies between 15 cm and 480 cm. Short wires of 15 to 45 cm are usually used for initial vessel access. Longer wires of 260 to 300 cm are mainly used in coaxial systems to allow the insertion and exchange of catheters, sheaths, and therapeutic devices. Intermediate wires, 145 to 180 cm, are used with monorail system or for target lesions close to the access, such as diagnostic studies or iliac artery or anterograde tibial interventions.
Thickness
Wire thickness is measured in inches. Available thicknesses are 0.014, 0.018, 0.025, 0.035, and 0.038 inches. Selection of the size is based on the diameter of the smallest target vessel. Thicker wires are used for larger vessels like the aorta or iliac, femoral, and popliteal vessels. Similarly, thinner wires are used for tibial, carotid, or visceral artery work. Wire size selection determines the platform for the size of catheters, sheaths, and therapeutic devices that can be inserted after crossing the lesion.
Stiffness
Soft wires are usually used for maneuvering through lesions and crossing tortuous vessels. These are often exchanged for stiffer wires before starting the intervention.
Stiffer wires are used to straighten tortuous vessels or to provide a stable platform for the delivery of sheaths and devices, especially large sheaths and devices like those used for aortic interventions.
Hydrophilic Coating
Some wires have a hydrophilic coating (Teflon, polytetrafluoroethylene, or silicone), which make it slippery when wet. The coating decreases the friction between the vessel walls, catheter, and sheaths, thereby improving the crossing ability of the wire. Hydrophilic wires can get sticky when dry, however, so they can be accidentally withdrawn during exchanges. For that reason, the wire should be wet-wiped during exchanges.
Hydrophilic wires are used for maneuvering through smaller vessels and tight lesions, but because of their high crossing ability, hydrophilic wires may cause undesired subintimal dissection. On the other hand, that can become useful in crossing total occlusive lesions by creating a subintimal plane with the goal of re-entry into the vessel past the lesion.
Non-coated wires are easier to grip but may encounter increased resistance during passage through narrow areas. They are better exchanged over a catheter.
Selection
Wire selection should be based on vessel anatomy and lesion characteristics. A combination of wires is usually needed to accomplish the task. Access should be performed using a wire with non-hydrophilic coating, to avoid needle shearing, and a long floppy tip or J-shaped tip to avoid vessel trauma. For maneuvering through vessels or crossing lesions, hydrophilic, soft wires with an angled or straight tip can be used.
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