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Recanalization of Chronic
Total Occlusions: Basic Techniques
and New Guide Wires

J. Kähler, MD; R. Köster, MD; C. W. Hamm MD

Dept. of Cardiology, University Hospital Hamburg, Hamburg, Germany

   Chronic total coronary occlusions (CTO´s) still are a challenge to the interventional cardiologist. Up to one third of angioplasty procedures are attempted in chronic total occlusions, but less than 60 percent of chronic occlusions can be recanalized. The use of a laser guidewire, as documented in the TOTAL study, only slightly improves success rates although it is a cost-intensive technique that is limited to a few high-volume angioplasty centers, figure 1. However, during the last years, several new "conventional" wires have been developed specially for the recanalization of chronic total occlusion and thereby facilitated this procedure. Whether their use increases success rates remains to be determined.

Figure 1

   The purpose of this presentation is to refresh some basic technical aspects of the recanalization of CTO´s and present a selection of new wires.

BASICS: PREDICTORS OF SUCCESS
   Prior to the procedure, the operator should estimate the potential clinical benefit the patient may achieve in order to determine how much risk and time he is willing to invest. He also needs to determine what the chances of success are. Predictors of success and failure are depicted in figures 2 and 3.

Figure 2

Figure 3

BASICS: CHOICE OF WIRE
   Modern guidewires feature excellent handling characteristics and are manufactured in a large variety, so that only experienced operators may reach their technical limits. On the other hand, for the inexperienced operator the choice of the adequate wire is difficult, but will crucially determine his success. It is therefore recommended to work with only a few products in order to get experience with those rather than to use all wires that are on the market at the same time.

   The usual approach is to start with a floppy wire in order to follow the path of least resistance, i.e. the "latent true lumen" without causing dissection or perforation. However, once a floppy wire was used without success, intermediate, standard or special recanalization wires may be used.

   Stiffer wires offer more push but carry the risk, to loose track and thereby miss the chance to recanalize the true lumen. Once a false lumen has been created, the chance to recanalize the true lumen approaches zero. Details of wires will be discussed and depicted below in the "New wires" section.

BASICS: RECANALIZATION
   Once adequate backup has been achieved using an appropriate guiding catheter, the wire is slowly advanced over the lesion. Turning the wire tip left and right may help advance the wire. When a floppy wire can not be advanced, a stiffer wire may be employed. In order to increase support, the wire also may be enforced by the use of a small balloon that is inflated in the proximal vessel. Further, the use of an "over the wire" balloon may improve backup.

   When conventional wires fail, special recanalization wires may be used, but their use increases the risk of perforation, particularly with forceful advancement.

   When no significant progress has been made with more than 3-4 different wires, the procedure should terminated. The attempt usually should not last more than 30 minutes fluoroscopy time, unless any promising progress has been made in the meantime.

BASICS: POTENTIAL COMPLICATIONS
    The major risk of any coronary intervention, complete vessel occlusion, is for obvious reasons a lesser problem in chronic total occlusions. However, in cases with TIMI I flow, perfusion may actually be worsened. Usually this does not aggravate clinical symptoms or cause infarction, but postprocedural monitoring may be indicated in patients with TIMI O flow following the procedure.

   A frequent complication, particularly with the use of stiff or hydrophilic-coated wires, is vessel perforation. Unless a balloon is advanced or coagulation and platelet aggregation are excessively inhibited, perforations usually do not lead to significant pericardial hemorrhage. Repeated echocardiographic exclusion of pericardial tamponade however, is mandatory in these cases.

   Potential complications while attempting the recanalization of CTO´s are listed in figure 4.

Figure 4

BASICS: ONCE THE WIRE PASSED THE LESION
    Once the guidewire has been passed into the distal vessel, the lesion usually can be crossed with a balloon catheter and dilated in the usual manner. This should only be done, when it is perfectly clear, that the wire has distally reached the true lumen. In cases of doubt, this can be verified by contralateral contrast injection through a second catheter.

   If an adequately sized balloon does not pass the lesion not readily, a smaller one may be used for predilatation.

   The use of GP 2b/3a antagonists following recanalization is not recommended, since it carries the risk that vessel perforations continue to bleed and may cause significant pericardial hemorrhage.

   However, perhaps because of competitive flow through collaterals or other lesion characteristics, successfully dilated chronic occlusions have higher restenosis and reocclusion rates than do subtotal stenoses. Long-term success rates can be improved by using stents.

NEW WIRES: REQUIREMENTS
   Modern wires have become highly complex devices in order to fulfill the needs of the operator.

   Major requirements for guidewires are:

Push transmission:          Allows advancement of the distal wire
Torque transmission:       Allows turning the tip
Body support:                  Allows placement of a balloon
Tip support:                     Allows moving the tip to search for the true lumen
Elasticity:                         Prevents bending of the wire
Visibility:                          Wire alloys are not necessarily radiopaque

NEW WIRES: WIRE ANATOMY
   Guidewires typically feature three components, shaft, core and tip. The tip is usually constructed as a metal coil in order to allow atraumatic advancement of the wire. The "core to tip" design leads to a stiff tip, while the "shaping ribbon is more flexible, figures 5 and 6. The anatomy of a modern wire is depicted in figure 7.

Figure 5

Figure 6

Figure 7

   Floppy wires feature long tip coils and have no continuity between core and distal tip for maximum flexibility at the cost of support.

   Supportive wires have thicker cores and shorter tip coils. They also may have a continuos core that is tapered but continues all the way to the tip. Supportive wires are therefore less flexible and can more easily penetrate the vessel wall. Characteristics of floppy and supportive wires are depicted in figure 8.

Figure 8

   The use of different alloys allows to separately influence the characteristics of the wire over its entire length, leading a large variety of possible wire constructions, figure 9.

Figure 9

NEW WIRES: WIRE MATERIALS
   Wires are contemporarily made from steel alloys. Among the recent developments are Nitinol and Elastinite, the latter being particularly flexible thus preventing any bending of the wire.

   The tip of the wires is usually made from platin/iridium alloys in order to achieve flexibility and assure x-ray visibility. Lately, polymer tips have been developed that are supposed to more readily pass complex lesions.

NEW WIRES: COATINGS
   Wires are traditionally coated with silicone or Teflon, in order to allow easy advancement. A recent development is the hydrophilic coating. It consists of a polymer, layered onto the wire, that keeps a steady lubricous film on the surface thereby reducing thrombus adhesion, figure 10.

Figure 10

   Once moistened, this coating is extremely slippery and facilitates the advancement of the wire within the lesion. The slippery surface requires the use of a torquer and sufficient moistening prior to its use. Because of the very low friction within the vessel, it is important to apply only a low but constant pressure on the wire since it tends to advance by the movements of the beating heart. Fluoroscopic control of the distal tip even after passage of the occlusion is necessary to avoid subsequent vessel perforation. An option to prevent perforation advocated by some operators is to exchange the wire for a conventional wire once the lesion has been passed. Recent data suggest that this coating improves recanalization rates, figure 11.

Figure 11

NEW WIRES: CROSS-IT (GUIDANT)
   This wire in manufactured in four grades, rather representing a family of wires. They feature a core that runs all the way to the tip and make them rather stiff. The tip is tapered from 0.014" to 0.01" to facilitate the passage of microfissures, which supposedly line the previous true lumen. Ranging von Cross-It 100 to 400, torque transmission and support increase while flexibility decreases. The wires are all hydrophilic coated, figure 12.

Figure 12

NEW WIRES: CROSSWIRE NT (TERUMO)
   The Crosswire NT was developed from the Crosswire and has several new features: The hydrophilic coating only covers the 40 distal cm of the wire, so the handling of the proximal wire is facilitated. While the very tip (1 cm) is made from gold and a little stiffer than before, the wire per se is a slightly more flexible to improve handling characteristics, figure 13.

Figure 13

NEW WIRES: CHOICE PT (BOSTON SCIENTIFIC/SCIMED)
   The Choice PT and the Choice PT extra support are made from a metal core distally covered with a polymer sleeve ("Unibody core"); the tip is made from polymer as well.

   The polymer component is used in order to create a "soft" surface to ease the passage of complex lesions. The wires are additionally equipped with a hydrophilic coating to further facilitate the advancement. The distal 35 cm of the wires are radiopaque, figure 14.

Figure 14

NEW WIRES: SHINOBI (CORDIS)
    The Shinobi wire is manufactured with a 0.007 or 0.01 core and a 3 cm radiopaque tip. Particular emphasis was put into the development of a smooth and stable transition between core and tip, to prevent bending in this area. The wire is covered with Teflon, figure 15.

Figure 15

 

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2nd Virtual Congress of Cardiology

Dr. Florencio Garófalo
Steering Committee
President
Dr. Raúl Bretal
Scientific Committee
President
Dr. Armando Pacher
Technical Committee - CETIFAC
President
fgaro@fac.org.ar
fgaro@satlink.com
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