Appropriate selection and manipulation of equipment is critical to successful percutaneous coronary intervention (PCI) outcomes and low complication rates. The guidewire is the first piece of interventional equipment to contact the lesion to be treated. Proper intraluminal advancement of the guidewire through the lesion and into the distal vessel allows the coronary guidewire to serve as the backbone for the safe delivery of diagnostic and therapeutic devices while maintaining secure and safe access to the vessel lumen. Although the current standard 0.014-inch wires are suitable for the majority of interventions, operator familiarity and facility with guidewire selection and manipulation are still paramount. The advent of specialty guidewires, such as those designed for chronic total occlusions (CTOs), has furthered our ability to successfully treat more complex lesions, but the use of these wires requires an understanding of specific wire performance features and the possible complications that can result from their use. Given the wide variety of guidewires that are available, knowledge of their design, materials and structure aids the operator in understanding unique differences in performance and ultimately in making the proper selection for an individual patient or lesion.

In this chapter, we will review specific characteristics of coronary guidewires including their construction and properties that favor different clinical situations. In order to optimize guidewire selection, we have developed a general classification scheme based on wire performance features. We will discuss techniques for guidewire manipulation in selected subsets of coronary lesions with the caveat that minimal comparative literature is available. As with other aspects of interventional cardiology, there are multiple guidewires that can be used for each lesion, and operator selection may change with experience or as technologic advances are made.

More than 30 years have passed since the introduction of a catheter system allowing an independently movable, flexible-tipped guidewire for coronary intervention. Unlike the initial balloon catheters with fixed-wire tips, the 2 component balloons and independent, steerable guidewire systems greatly enhanced coronary artery and lesion accessibility.^1-3 Guidewires are designed to allow the tip to be shaped or curved so that the wire could be purposefully directed into the desired artery and across the target lesion using rotation and advancement. The independent catheter–guidewire system also brought increased safety with the ability to exchange devices without recrossing the coronary lesion.^4,5

The first guidewire for angioplasty, available from 1979 to 1982, was a 0.018-inch standard wire (Cook Group Inc.). This wire had a safety wire at its tip— a precursor to the shaping ribbon—that allowed it to be shaped but resulted in added tip stiff ness. The next wire to be developed (ACS) was a standard wire that replaced the safety wire with a metal ribbon. This change made the tip more flexible while retaining the ability for shaping. Further advances included construction of a floppier wire, which lacked a shaping ribbon, and had greater flexibility and safety but sacrificed some directional control. Thus the objective was to develop wires that combined flexible and safe tips while maintaining shapability and torsional control.⁶ Currently, as no guidewire meets all needs or preferences, several manufacturers offer a line of coronary guidewires, many with subtle variations, to allow artery- or lesion-specific guidewire selection.

Knowledge of the underlying construction of a guidewire provides an understanding of the expected performance features including steerability and trackability. Steerability relates to the ability to direct the wire to a desired location within an artery or lesion. Trackability is the ability of a wire to follow the course of an artery during advancement with minimal resistance or buckling. Multiple characteristics including flexibility, radiopacity, torquability and kink resistance, and the frictional resistance of the guidewire within the system it is used, all contribute to the fundamental properties that result in maneuverability of guidewires (Fig. 27-1). Torquability is a term that describes the relationship between rotational movement of the proximal wire (the site where the operator grasps the wire) to the tip. Torquability that is 1:1 means that for every degree rotation by the operator, a similar rotation will occur at the tip.

Coronary guidewires are composed of 3 main components, a central core that tapers distally, a flexible tip which includes a spring, and the external surface or coating (Fig. 27-2). These components all influence the ability of a wire to reach and cross a lesion and also to support the delivery of balloon catheters and other devices to the lesion. For example, the core provides the support for device advancement but is also integrally related to trackability, steerability, and torque transmission.

The core may be constructed as a single continuous unit or have more than one segment. As the core extends distally, the diameter tapers and the degree of tapering and the location of tapering vary. These variations in core diameter, length and degree of tapering affect performance. Cores that extend to the distal wire tip provide extra support and torque transmission but are stiff. Cores that do not extent to the distal tip and that gradually taper are more flexible and retain more trackability than wire cores that abruptly end.⁷ For this reason, wires that have a single core construction have the smoothest transition into the flexible preshaped tip and provide a high degree of steerability and trackability. The core strength also varies with the core material and diameter, and as stiffness increases, flexibility may be compromised, but vessel straightening and device delivery improve. The core wire is commonly composed of stainless steel or alternative alloys such as nitinol. The nitinol core increases wire trackability, including the ability to traverse acute artery angulations without wire prolapse. Nitinol wires, therefore, might be more capable of entering a retroflexed circumflex takeoff than a stainless steel core wire.

The tip of the wire is composed of a coil or spring that provides a flexible leading tip that enhances safety and steerability. The ability to shape the tip into a retainable and variably shaped curve is accomplished with a shaping ribbon. This thin metallic strip that runs parallel to the longitudinal axis of the wire allows the tip to retain a curved shape or “J” configuration that provides directionality to the guidewire. The degree to which the tip retains its shape during use relates to the properties of the shaping ribbon, the material of the distal tapered core, and, additionally, to the coatings, which are discussed below. Wires with straight tips and shaping ribbons can be shaped to more acute angles, or sequential bends can be placed to negotiate unusual or severe (<90°) instances of vessel tortuosity. Wires that have preshaped tips are also available. These wires lack a shaping ribbon, which results in less ability to alter the tip shape.

The wire tip also varies in stiffness. Highly flexible tips are termed floppy or soft and these wires are particularly safe and atraumatic in that the likelihood of subintimal dissection or vessel perforation is very low. Commonly such wires include a core of moderate flexibility and support and are accordingly used as “workhorse wires.” Because of enhanced tip flexibility, they can prolapse or form a large “J” configuration when advanced. Such a configuration, if it occurs after the wire crosses the lesion to be treated, is an advantage in that the wire can be readily and safely advanced into the distal artery without the need for steering.

Other potential features of the wire tip that may be manipulated include the distal diameter and weight of force, or tip load. Guidewire tips can have a tapered coil from the shaft of 0.014-inch down to 0.009-inch. There are also lines of wires that are designed with incremental tip loads, or grams of force at the wire tip. These wires with reduced profile or increased tip load, discussed below, are designed to improve crossing of subtotally or totally occluded arteries. Caution must be exercised with these wires to avoid coronary dissection or perforation.

The distal coil segment is constructed of platinum, tungsten, or an alternative radiopaque material. Radiopacity is critical for monitoring fine wire manipulation and advancement. The standard wire has a radiopaque tip of 2 to 3 cm in length, and although the entire wire is visible with fluoroscopy, the entire length of the wire may be difficult to follow. Problems with the wire such as kinks or the development of loops, particularly outside the guiding catheter and within the aorta, may be difficult to detect. These situations, however, are usually recognized by accompanying clues such as loss of 1:1 torque, pushability, guide stability, or the ability to deliver devices. The benefit of a short radiopaque tip is that it can be advanced past the target lesion so as not to influence the identification of devices or evaluation of the targeted lesion. The radiopaque segment may also interfere with the ability to perform quantitative coronary angiography. Certain wires have longer radiopaque tips of 11 to 40 cm. This “high radiopacity” feature is found on more aggressive wires where more force may be applied to wire advancement, and intense monitoring of the entire length of the wire in the coronary and guiding sheath is needed for safety. Besides the safety issue, the longer radiopaque tip does not offer additional benefits.

The third component of the coronary wire is the coating, which can be silicone, Teflon, polytetrafluoroethylene (PTFE), or a hydrophilic polymer. The coating decreases the friction, making the surface lubricious within the device lumen and across lesions, and improves wire and device tracking in tortuous vessels. The hydrophilic wires are well suited for severe stenoses and total occlusions, but they may create vessel dissections or perforations if not manipulated cautiously. As with other aspects of wire construction, each feature may improve one or more clinical aspects of the wire, but at the expense of another.

The majority of coronary wires are 0.014-inch diameter for compatibility with low-profile coronary balloon and stent systems. Larger diameter specialty wires such as the Glidewire® Gold 0.016 to 0.018 inch (Boston Scientific Corporation) and the Magnum wire (Schneider) 0.021 previously used for recanalization of chronic total occlusions (CTOs), have been replaced by 0.014 wires engineered specifically for CTOs. Wires come in 2 general lengths. Standard length guidewires are 175 to 190 cm and exchange length wires are 270 to 300 cm. Longer wires, 335 to 350 cm, are available for specific procedures that require guidewire externalization such as retrograde CTO interventions. The choice of wire length depends largely on operator preference and the balloon catheter system chosen, single operator or rapid exchange (RX) versus over the wire (OTW). Details of these techniques are discussed in the next section. Importantly, most, but not all, standard length guidewires can be extended with compatible extension wires if conversion to an OTW technique is required. If a standard length wire is not compatible with an extension wire, there are techniques, discussed below, that can be used to remove OTW devices or to exchange the wire without uncrossing the target lesion or losing access to the distal vessel. Additional features on some wires include marker bands that can reduce fluoroscopy time. These bands are generally placed at 90 and/or 100 cm, the length of a guiding catheter, to allow passage of the wire through the guide or balloon to the appropriate distance without fluoroscopy, ensuring that the wire has not exited from the guide catheter. Wires can also be designed with radiopaque markers at the distal tip that are a known distance, apart allowing for estimation of lesion length. These wires are termed marker wires.

OTW Systems

In an OTW system the wire traverses the entire length of the balloon catheter lumen, which is generally 135 to 150 cm. Standard coronary balloon and stent catheters are designed for 0.014-inch wires. Often the tolerances of the balloon catheter lumens and the guidewires overlap such that there is little clearance between lumen and wire. There are 2 approaches to using an OTW system. In the more common approach, the operator first places the guide wire through the balloon lumen and then the guidewire-loaded device is advanced into the guiding catheter to the coronary ostium. The guidewire is manipulated through the vessel across the target lesion, and, with the wire fixed in place, the balloon can be advanced across the lesion for dilation. The advantage of this technique is that the balloon catheter can be advanced over the wire into the coronary for more precise guidewire manipulation. Additionally, if the operator requires a different guidewire, the balloon catheter can be left in place within the coronary to maintain access. For example, OTW balloon catheters are of special value when attempting difficult anatomy including calcified, tortuous, or highly stenotic vessels and especially chronic total occlusions. The greatest challenge for successfully treating such lesions is to cross the lesion with a guidewire, and, accordingly, an assortment of different guidewires is often necessary in these cases. The OTW catheter can be positioned directly proximal to a total occlusion to facilitate guidewire exchanges.

Either a standard length wire (175-100 cm) or an exchange length wire (300 cm) can be used to cross the lesion with the OTW system. If a standard wire successfully crosses the target lesion, the wire can be extended with an extension wire to remove the balloon catheter or the balloon can be advanced distal to the lesion and the wire can be exchanged through the balloon for an exchange-length wire prior to balloon withdrawal. Another method for removing an OTW device from a standard length wire is to use a trapping balloon. This method is commonly used in CTO interventions, where meticulous care is required to prevent vessel injury or perforation from unintended migration of stiff or polymer coated wires. To perform this technique, a rapid exchange balloon is advanced to the distal tip of the guiding catheter on its own, not over a wire. For an 8-French (Fr) guiding catheter, a 3.0-mm balloon is used, and, for 7-Fr or smaller, a 2.5-mm balloon is recommended. The OTW device is retracted proximal to the trapping balloon, then the trapping balloon is inflated to 14 atmospheres, pinning the wire against the guiding catheter to maintain position. Then, the OTW device is withdrawn from the guide, followed by deflation and removal of the trapping balloon. During the trapping, the guidewire pressure will be damped, and, following device removal, the system should be cleared of potential trapped air. Another advantage of this method is that fluoroscopy can be minimized and radiation exposure reduced. An alternative technique to preloading the guidewire in the OTW device is one where the operator advances a guidewire alone into the guiding catheter and across the target lesion. In this “bare-wire technique,” the balloon or stent is then advanced over the wire into the lesion. This approach allows better visualization in smaller diameter guiding catheters, but given the low profile of current OTW balloons, the advantage of this approach is minimized. Passage and removal of OTW balloon catheters over standard length wires has been reported using other techniques, such as the hydro-glide method. This method uses hydrostatic pressure applied to the central lumen of the balloon catheter with a saline-filled syringe or inflation device.^8,9 Loss of wire position is the main drawback of this approach. Since this situation can lead to loss of vessel access it should be avoided, and a rapid-exchange catheter or trapping balloon should be used in these situations.

Rapid Exchange Systems (RX)

The RX system is commonly referred to as a single-operator exchange system. The coronary balloon and stent catheters are labeled RX (for rapid exchange) or Monorail and are compatible with 0.014-inch wires. The catheters were modified from the OTW type and the distal portion is similar, with the guidewire traversing through the balloon lumen. The OTW segment, however, is short, and the remainder of the wire tracks outside the catheter adjacent to the balloon lumen. The RX system is ideal for the single operator and can reduce fluoroscopy time. A standard length guidewire can be used for all RX intracoronary catheters. Initially, the bare wire technique is used to cross the lesion, and then the balloon catheter is loaded on the distal end of the guidewire. The catheter is advanced until the wire exits the catheter lumen and the wire is then fixed in place as the remainder of the catheter is advanced across the lesion. Although the RX catheters may have less pushability and trackability and cannot act as a device for exchanging wires, the current balloon catheters are low profile, easy to deliver, and can be used in the majority of cases.

When using an RX system, the operator must be prepared change to an OTW system when necessary. In certain situations, such as inability to cross a lesion with a wire or balloon or an unanticipated non-dilatable lesion, the wire may need to be exchanged for a specialty wire, such as an extra support wire or rotational atherectomy wire. If balloon inflations have been performed, and, in particular, if a dissection in the vessel is present, maintenance of distal wire position is essential. Normally these situations pose no problem, as the majority or standard length wires can be extended to exchange length with extension wires, and a microcatheter or OTW balloon catheter can be used to secure position during the wire exchange. Another option is to use a dual lumen catheter such as the Twin-Pass (Vascular Solutions, Minneapolis, MN) which has both an RX and OTW lumen. The Twin-Pass can be placed on the standard length wire through the RX lumen and advanced distal to the lesion, then a long wire can be placed in the OTW lumen of the catheter.

There may be many appropriate guidewire choices for each coronary intervention. Categorizing the guidewires into groups according to their general performance features and becoming familiar with a few wires from each group is a sound initial approach. Subsequently, each operator may find subtle differences among the guidewires in each group and develop a personal preference for a specific guidewire. Most operators will choose an “all-purpose” guidewire for the majority of cases and then have preferred wires for circumstances where “extra support” is needed or for specific lesion subsets. A guidewire classification grouping according to the general performance features is given in Table 27-1.

Specialty Wires for Total Occlusions

There are many wires that have been developed to cross severely narrowed or totally occluded coronary stenosis. These wires are generally classified by the coating and tip characteristics such as style and stiffness (Table 27-2). This section will review examples of these types of wires.