Thoracic Endovascular Aortic Repair (TEVAR) Guidewires

Introduction

Whether diagnostic or interventional, catheters and other endovascular devices are rarely sufficiently maneuverable to be used without guidewires. The purpose of guidewires is to create a pathway in the vascular system through which the endoluminal practitioner may act. In most endovascular procedures guidewires achieve and maintain the critical access across the target lesion, making them particularly significant.

Guidewire Construction & Materials

Standard guidewires are constructed of an inner core wire, also called a mandrel, and outer coil wrap. The stiff inner wire is tapered distally and does not extend to the tip of the guidewire, allowing for a more flexible (and ideally, atraumatic to vessel walls) distal coil tip. There is typically a safety wire connecting the mandrel to the tip of the outer coil, but this may not be the case in movable core wires. The tip of the outer coil of the guidewires may be preformed by the manufacturer into a J-curved, angled, or straight tip, but most are able to be formed by the physician into the shape deemed most suitable. A “floppy” tip denotes one that is adaptable in the vessel and is not designed to retain a formed shape. Currently, the components of guidewires are most often composed of stainless steel or nitinol, a nickel-titanium alloy. With a fixed diameter, stainless steel guidewires are traditionally several times stiffer than nitinol wires. Newer nitinol alloys are said to be a super-elastic material which resists kinking and maintains its shape throughout a procedure. Guidewire outer coils may also be plated with a heavy metal such as gold or platinum for enhanced radiopacity under fluoroscopy. Nearly all guidewires have some form of antifriction coating, and some may have antithrombogenic/heparin coating. A tetrafluoroethylene (TFE) coating has been shown to reduce the coefficient of friction for stainless steel wires to 1/2 the uncoated value, and a silicone coating can reduce it to 1/6 the uncoated value. Many newer wires are coated with a hydrophilic polymer similar to silicone; when wet, it has a slipperiness that facilitates passage through vessels and catheter exchanges. External torque devices (e.g. Terumo Torque Device) are employed to increase control of these wires. Hydrophilic-coated wires must be meticulously cleaned and moistened in order to avoid drying out and becoming tacky. Because passage through entry needles can shear off the hydrophilic coating, these wires are not used for initial vascular access.

Initial Access & Lesion Crossing

Traditionally, soft J-tipped wires (e.g. Safe T-J; Cook, Inc.) have been used for initial access because of their association with the lowest risk of dissection or other vessel injury. Our preferred guidewire for initial arterial access using the Seldinger technique is a non-hydrophilic-coated bentson-type wire (Bentson Starter; Boston Scientific Corp. or Bentson; Cook, Inc.). We find the Bentson Starter wire especially useful because its straight floppy tip forms an atraumatic “functional J-tip” when advanced through a vessel, yet the wire is able to cross tight stenoses because the J is not fixed. The steerable Wholey wire (Mallinckrodt, Inc.) has some similarities to the Bentson Starter and may be favored by some practitioners for this task.

The hydrophilic-coated Glidewire manufactured by Terumo Medical Corporation features a nitinol mandrel with a polyurethane outer coating instead of a metal coil. The polyurethane material contains tungsten for radiopacity, and this surface is further coated with a hydrophilic polymer; most manufacturers now offer similarly constructed wires. This wire is well-known for its ability to track in tortuous areas and stenoses. However, care must be taken when using this or any hydrophilic-coated wire, as there is greater risk of dissection or perforation due to the little resistance offered by these wires when advanced through vessels (“best friend and greatest enemy!”). An alternative is the hydrophilic-coated Magic Torque wire (Boston Scientific Corp.), designed to provide directional control without use of an external torque device. This wire also features 1 cm radiopaque markings to measure vessel segments or lesions.

Guidewire Length & Diameter

The previously mentioned guidewires are intended for access to a specific place in a vessel, catheterization of a branch vessel, and/or crossing a lesion. For these functions, a standard guidewire length of 145 to 180 cm is usually adequate. However, to facilitate exchange of catheters while maintaining a lesion crossing, exchange-length guidewires (260 cm to 300 cm) are used. These longer wires will generally also have more support (i.e. are stiffer) than those used to cross lesions. The standard guidewire diameter for peripheral interventions, especially those involving large vessels, is 0.035 inches. All the wires mentioned here fall into that group. However, due to improved guidewire construction, an increasing number of endoluminal procedures can be performed using 0.014 or 0.018 inch wires.

Catheter & Device Tracking

Exchange-length guidewires function to provide support and tracking ability to various catheters introduced over them, and their characteristics often reflect the task they are enlisted to help accomplish. For example, in TEVAR, a relatively stiff guidewire is needed to accommodate the 8.2F IVUS catheter for inspection of the thoracic aorta. The guidewire also needs a soft tip so that when it is “anchored” by reflecting off the aortic valve, injury to the valve is avoided. For this purpose we prefer the Nitrex wire (ev3, Inc.), Platinum Plus wire (Boston Scientific Corp.), or Meier wire (Boston Scientific Corp.). These wires provide enough support to track most large catheters or devices. The Nitrex wire has become a favorite because it routinely reflects off the valve without any difficulty. The Platinum Plus is often used for peripheral stent placement, and the Meier wire is intended for (T)EVAR. However, a very stiff guidewire may be needed to further straighten vessel tortuosity and to provide the tracking capability needed when delivering large devices such as endograft systems. For this we choose either an Amplatz Super Stiff wire (Boston Scientific Corp.) or a Lunderquist Extra Stiff wire (Cook, Inc.). The most flexible and safest guidewire that can accommodate the intended action should be used first. Because Lunderquist wire is the stiffest guidewire in our supply, the action is first attempted with the Amplatz Super Stiff wire. Both the Lunderquist and Amplatz stiff wires feature a short, straight tip. Alternatively, a stiff guidewire with a preformed J-tip, such as a Rosen wire (Cook, Inc.), could be used. This wire is often employed for exchange of angioplasty catheters.

Conclusion

Ultimately, the choice of guidewire for a specific task will depend, to a large extent, on physician preference. Adequate experience in the proposed procedure should be acquired in order to determine which guidewires will accomplish individual tasks most efficiently. If questions or problems arise, consultation with an experienced interventional specialist or endovascular surgeon is recommended.

References

1. Schneider PA. Endovascular Skills, 3rd Ed. New York: Informa 2009.
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3. Casserly IP, Sacher R, Yadav JS, eds. Manual of Peripheral Vascular Intervention. Philadelphia: Lippincott Williams and Wilkins, 2005.
4. Moore WS. Vascular and Endovascular Surgery: A Comprehensive Review, 7th Ed. Philadelphia: Elsevier Saunders, 2006.
5. White RA, Fogarty, TJ, eds. Peripheral Endovascular Interventions, 2nd Ed. New York: Springer-Verlag, 1999.