Seminar
 

Curriculum in Cath Lab: Coronary Hardware
Guidewire Selection for Coronary Angioplasty – Part 2
Sundeep Mishra, Vinay K Bahl.

Department of Cardiology, All India Institute of Medical Sciences, New Delhi

Highly Stenosed Lesions and Total Occlusion

These are one of the most challenging lesions an interventionist has to face and account for a nearly third of all interventional volume. With conventional techniques success is achieved in only about 60% cases 1, 2. While each and every component of hardware utilized in the procedure is important, the choice of guidewire is the most critical in determining success of the procedure 3. In general, the guidewires in this situation require greater tip stiffness and also should provide more support. The choice of guidewire may be influenced by the anatomy of the lesion also. If it is a relatively recent occlusion there may be a predominance of micro-channels and therefore wires with extremely low friction (invariably polymer tipped with hydrophilic coating) which are good at picking up micro-channels may be chosen (Sliding Strategy). Figure 1A In this technique a long and shallow curve is imparted to the tip with no secondary bends. This technique involves simultaneous rotation and probing of the lesion. It is mandatory to approach this strategy very cautiously as there is a high chance of entering into sub-intimal space since there is almost no tactile response. Besides recent total occlusion, sub-total occlusions and occlusions of in-stent restenosis can also be attempted with this strategy. However, if the lesion is of a longer duration, the micro-channels may be replaced by fibrotic tissue. If there is a discrete entry point a “Drilling Strategy” may be used. Figure 1A, B Here a short curve (2 mm) at 45-60º is imparted to the distal tip. Sometimes even a proximal secondary curve is also employed. The wire is advanced with a rapid rotational tip movement with gentle probing. The operator starts with a moderate stiffness tips with progressive, step-wise increase in tip stiffness. Entry into false lumen is judged by the tactile feeling while pulling back the stiff guidewire. Since success of this strategy is determined only by the “feel of wire”, it is reserved only for the most skilled and experienced operators.
In case of blunt entry point or heavily calcified or resistant lesions a Drilling Strategy may be in-effective. Here a novel “Penetrating Strategy” may be employed 4. Figure 1B This strategy employs pushing the stiff guidewire very slowly as well as gradually, using minimum amount of rotation towards the target direction. The wires utilized for this strategy may have tapered tips. The route of wiring is determined by various angiographic or even CT findings, but not by tactile feel. Therefore this strategy is not chosen for chronic total occlusions (CTOs) with tortuous and angulated lesions and bridging collaterals, because they may have higher chances of perforation. In the drilling and penetrating strategies, the chance of crossing is dependant on support provided by the guiding catheter and tip load. Increasing tip load contributes to greater chance of success, but at the same time greater risk of complications. Therefore the operator starts with softer tip guidewire, progressively using stiffer tips (greater tip load), till the lesion is crossed.

 

 

If it is still not possible to cross the CTO antegradely a “Retrograde Technique” may be used 5, 6. The logic behind this approach is that the distal fibrous cap of the CTO may be weaker than the proximal fibrous cap, resulting in easier wire crossing.  The

Figure 1A Pathology of a Total Occlusion and the Strategy Employed

Figure 1B Drilling versus Penetrating Strategy for CTO Intervention

 

correspondence:  Dr Sundeep Mishra, Associate Professor of Cardiology, All India Institute of Medical Sciences (AIIMS), New Delhi
E-mail:[email protected]

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The technique is as follows. Essentially, simultaneous bilateral coronary injections are performed to assess the CTO segment, and collateral supply to the target vessel is identified for retrograde usage. Septal branch is used in most cases, but suitable epicardial collaterals and saphenous vein grafts may also be used. First, the soft plastic jacket guide wire (Fielder, Fielder FC, or X-treme {Fielder XT}, Asahi Intec, Japan) is inserted into the target collateral artery with the aid of the micro catheter (Finecross, Terumo Inc., or Transit, Cordis Inc.). After the successful crossing of guide wire into the distal target artery, micro catheter is exchanged for small-diameter (1.25-cm) balloon to perform the collateral channel dilatation at low pressure. The guide wire is then advanced to the distal end of CTO, and CTO crossing is attempted with various guide wires ranging from soft (Fielder, Fielder FC, Fielder XT) to stiffer guide wires (Miracle series or Conquest). In some cases, the wire penetrates the CTO segment and reaches the proximal true lumen and into the guide catheter. Balloon dilatation of the entire CTO segment is then performed and thereafter ante- grade wire is passed to complete the re-canalization in standard fashion 7. The different guidewires used for re-canalization of CTO are shown in Table 1

Table 1 Guidewire Strategies for Approaching Total Occlusions
 
A) Guidewires for Approaching Micro-channels 
 
  Crosswire NT 
  - Whisper / Pilot 
  -Rinato 
  - Shinobe / Shinobe Plus 
  - ChoICE PT / ChoICE PT ES 
  - PT Graphix 
  - PT2
 
B) Guidewires for Drilling Strategy
 
  - Persuader
  - Miracle Bros  
  - Cross-It
 
C) Guidewires for Penetrating Strategy
 
  - Cross IT 
  - Conquest Pro 
   Liber 8
 
D) Guidewires for Retrograde Technique                                                                                     
 
  -Fielder/FielderFC 
  - X -treme 
  - Whisper 
  - ChoICE PT2
  - Runthrough / Runthrough Hypercoat
 

Tungsten (45%) / hydrophilic coating in the distal 40 cm accounting for extremely low friction at the tip which aids in navigating micro-channels 8. The polymer coating also enhances stiffness of the body and prevents wire from slipping out of the lesion.
Rinato™ (Asahi Intec Co.) means “reborn” in Italian. This wire is not just hydrophilic over-coated, but is designed anew from core with a very special hydrophilic coating which leaves distal 3 cm uncoated. The overall effect is not only a very good trackability of the tip but also a very good support at the range of 5-10 cm from the tip which is most often utilized to deliver interventional device.
Shinobe™ / Shinobe Plus™ (Cordis Inc.) are designed as highly steerable wire with exceptional tactile feel - “to sleek in”. Permanent PTFE sleeve (polymer coating) extends over the tip for added lubricity and much more tactile feedback as compared to hydrophilic coatings, thus ensuring optimum control. Flex-Joint Bond™ enhances distal flexibility and tip control. Flattened radio-opaque coils yield more surface area to improve tip memory and allow the wire to pass through highly stenosed lesions. Increased core- wire diameter in Shinobe Plus improves push ability and enhances the delivery of advanced interventional devices in complex cases.

ChoICE PT™ and PT Graphix™ (Boston Scientific Inc.) wires have a uni-body stainless steel core and a hydrophilic coated, polymer tip. Its distal 30 cm is radio-opaque allowing for excellent visualization of wire but impairing visibility of vessel anatomy. PT Graphix has distal 2 cm opaque tip unlike Choice PT.  PT2 ™ (Boston Scientific Inc.) wire has a similar construction like ChoICE PT, except that it has a linear elastic Nitinol core with a polymer tip increasing its flexibility.
Persuader™ (Medtronic Inc.) is another specialized wire to access and cross tight stenosis / CTOs. It has a stainless steel core-tip design with S tip for excellent torque characteristics with precise tip control and steering. Radio - opaque 3 cm tip allows better visualization during contrast injections or when using the "buddy wire" technique. Each wire is available with Pro/Pel ™ silicone coating or Hydro-track™ hydrophilic coating as required in a specific situation. It is available in three varieties of tip stiffness and support levels (Persuader 3, 6 and 9).  Figure 2
 Miracle Bros™ (Asahi Intec Co.) are a family of guidewires developed for executing the Drilling Strategy for CTO. Figure 3A They have a tip to core stainless steel body and a long (11 cm) single distal spring coil made of platinum/iridium (compared to 3 cm coil with standard wire). Figure 3B They provide for increased tip flexibility and visibility and also excellent tip shape ability and shape retention. The unique tip structure also reduces the potential for the wire to be trapped by lesions.These wires are available with increasing tip load 3, 4.5, 6, and 12.

 

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Hi-Torque CROSS – IT XT™ (Abbott Vascular Inc.) is a family of high-performance guide wires designed for accessing challenging lesions. This family offers wires that are designed with a unique tapered tip coil that allows the wire to access stenosed lesions with finesse. Unibody core runs all the way to tip so improved steer ability and torque transmission. It has a tapered tip coil from 0.014" to 0.010" at distal 3 cm for improved lesion access. A choice of wires is offered that vary in tip stiffness to address a wide variety of lesion morphologies (CROSS-IT 100, 200, 300 and 400). Hydrocoat hydrophilic coating at distal 30 cm provides low friction, smooth tracking, and enhanced crossing.

 

Figure 2 Medtronic Persuader ™ Guidewires




Figure 3A Miracle Bros ™ Family of Guidewires


Figure 3B Tip Loads of various wires. Red line indicates length of the paper, yellow circles indicate platinum/iridium coil and black circles indicate stainless steel coil.

 

Asahi Conquest™ / Conquest Pro™ (Asahi Intec Co.) guidewires are another family of guidewires designed to provide maximum penetrating power. It has a unibody steel core and a distal platinum / iridium coil which is even longer than Miracle Bros series (20cm). Also unlike Miracle Bros series it has a tapered tip, from 0.014" to 0.009". While Conquest wire is uncoated Conquest Pro is coated with hydrophilic coating except that distal most 0.1 cm remains uncoated. It is available in size Conquest 9 and 12 and Conquest Pro 12. It has much superior penetrating power as compared to comparable Miracle Bros wire. One of the reasons for its superior penetrating power is the tapered tip. The penetrating power of a guidewire is calculated as tip stiffness divided tip surface area. The hydrophilic coating in the Conquest Pro version also enhances the penetrating power. Figure 4
Liber 8™ (Brivant Medical Engineering) is an extra-stiff guidewire developed for PCI of highly stenosed lesions. Single piece core construction removes abrupt transitions and ensures that torque is transmitted along the central axis. Distal 3 cm has radio-opaque platinum alloy spring coil. It is available in tip load of 3g, 4.5g, 6g, 9g and 12g and in penetration power equals that of Conquest wire.

Figure 4 Conquest ™ Guidewire and Penetration Power of Various Guidewires

 

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Fielder™ / Fielder FC™ (Asahi Intec Co.) is a special guidewire with a distal coil coated with polymer sleeve and further coated with a hydrophilic coating. Due to its unique construction it provides advanced slip performance and trackability for highly stenosed lesion and tortuous vessels.  Additionally, it possesses very good torque performance which other competing guidewires of this polymer sleeve type have not been able to realize.  Fielder is the guidewire which combines both slide and torque performance. It is the primary wire used in the retrograde technique of recanalization of CTO. Fielder Xtreme™ (Asahi Intec Co.) is a steerable guidewire with a specially designed tip. It is intended to facilitate the use of balloon dilatation catheters (especially channel dilators in retrograde technique for CTOs) during PCI.

 

Complications with Guidewire Usage
Entrapped Guidewire
Entrapment of guidewires during cardiologic interventions is rare but can cause life-threatening complications and the need for emergency cardiac surgery 9. It may happen when guidewire is repeatedly rotated in a single direction while the distal tip is held fixed in a calcified lesion or a CTO, so that torque given at the proximal end is not transmitted to the distal tip. It may also occur when a buddy wire gets trapped between a stent and the vessel wall. Another mechanism of guidewire entrapment is during a provisional stenting approach for a bifurcation lesion. The guidewire is left in side-branch (to ensure at least some flow when this wire is removed) at the time of stenting of main branch. Figure 5 After stenting once side-branch wire is attempted to be withdrawn, it can get entrapped behind the struts of main branch stent 10. Once the guidewire gets lodged in a proximal and a patent artery there is a possibility of thrombosis, coronary spasm and stent embolization which can lead to development of myocardial infarction or even fatal arrhythmia 11, 12. This complication may be best prevented by avoiding using the same wire on multiple interventions or multiple crossing, but once it happens each case should be approached as unique and the risks should be evaluated regarding the location of the fractured piece and the condition of the patient. There are three approaches to deal with this problem.

Retrieve the wire percutaneously: If the distal tip of the wire is entrapped in a calcified CTO, the best approach is to try to rotate it in opposite direction.   Removal of fractured guidewire is however, not always that straightforward as it may uncoil and transform into razor-sharp wire.

 

    • In this situation one may need to advance a small profile balloon to the “attachment” site and use traction. Passing a small transit catheter over the wire to protect the coronary artery to free the entrapped distal end of the guidewire at operation has also been suggested 12. Coronary perforation is a potential complication of this approach. If the buddy wire gets entrapped behind the stent strut, Gentle traction may bring the wire out of the stent. The coating of the tip may “deglove” and be left behind, which could be “pushed and pasted” against the vessel wall with another stent. Sometimes the tip may completely detach and surgery may be needed to retrieve it.
    • Leave it alone: If the entrapped wire lies within small, chronically occluded coronary vessels or within a distal segment it may left alone because myocardial infarction even if it occurs will be hemodynamically insignificant 10, 12 .
    • Surgical removal: In 15-20% of failed percutaneous approach, surgical removal of the entrapped wire is always an option if the wire lies in a hemodynamically significant territory and cannot be removed percutaneously  13,14.

      Figure 5 Guidewire Entrapment after Bifurcation Stenting
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Detachment and Embolization of Guidewire Tip
Detachment and embolization of guidewire tip is an uncommon occurrence with modern generation of guidewires 15. Again there are three options. Percutaneously, it could be snared using a gooseneck or a loop snare if the fragment lies in proximal, large vessel. If the fragment lies near the ostium of a large vessel, one could even use a bioptome 16-18. If the fragment lies in distal vessel both balloon occlusion devices and filter baskets have been utilized for retrieval. A “double or triple wire technique” can also be utilized in this situation 19. An alternate strategy is to use a stent to “push and paste” it to the vessel wall. If the fragment is small and if one is unable to retrieve it, it could be left in-situ. On the other hand if a large fragment is left in a hemodynamically significant vessel, surgery is an option.

Guidewire Fracture
It is a complication with potentially devastating outcome 20, 21. It should be recognized immediately and wire first carefully withdrawn in guide catheter and then whole system carefully removed. If this is not possible, one could try to snare it if the fractured fragment lies proximally or use a “double or triple wire technique.”  Essentially this technique involves passing 2 or 3 guidewires distal to the fractured segment and rotating all of them in one direction, aiming to entangle the fractured segment of wire. Subsequently all the 2/3 wires are rotated together in one direction to further entangle the fractured wire. Subsequently the whole, entangled collection is carefully extracted into the guiding catheter 22.  Another technique is to cross beyond the fractured fragment with a balloon catheter. Once clearly beyond the distal tip of the fractured guidewire, balloon is nominally inflated and the balloon and the fractured guidewire fragment carefully withdrawn into the guiding catheter. Basket type of distal protection devices can also be employed to the same end 23. 
Accordion Effect
A mechanical alteration during maneuvering of stiff guidewires in tortuous coronary arteries frequently induces vessel wall straightening and shortening which alters the mechanical geometry and the curvature of vessel. This leads to appearance of false lesions or coronary pseudo-stenosis in the angiograms, referred as accordion phenomenon 24, 25.  Figure 6 The latter can get inappropriately identified as coronary spasm, dissection or thrombus development, which may falsely lead to unnecessary stenting at the pseudo-narrowing lesion, turning a totally reversible event into a true iatrogenic complication 26. Vasodilators like nitro-glycerin which are very useful for relieving coronary spasms are completely useless in this situation. Subtraction of the guidewires normally leads to entire resolution of the lesions. While occurrence of pseudo-lesions may by themselves be benign, other than technical difficulty posed to the operator. In some cases the inadvertent straightening of the vessel can lead to flow limiting effects and myocardial ischemia 27. Management involves immediate recognition of this problem and the removal of stiff guidewire 28. Instead a floppy guidewire with a balloon backup, or even better, a micro-catheter may be employed.  A micro-catheter nicely takes up the curves of the tortuous artery without producing the pseudo-lesions 29, 30.

Conclusions
Guidewires are an important hardware in the armamentarium of interventional cardiologist. Guidewires are composed of a central core, a spring coil and a wire coating. There are three broad categories of wire, balanced, extra-stiff and floppy besides specialized wires e.g. wires for total occlusions or tortuous lesions. Choice of guidewire is often the key to successful outcome of angioplasty procedure, therefore unique characteristics of various wires must be carefully considered before they are chosen for an individual case. Some complications may be encountered rarely with the use of modern guidewires. Guidewire entrapment, fracture, embolization and accordion effect are some of them. The operator must be able to recognize them and treat them according to the clinical situation.
Figure 6 Accordian Effect after Guidewire Insertion in a Tortuous RCA  

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