**11. Interventional armamentarium**

Technical difficulties during CTO PCI with high procedural failure rates have been lately overcome by introducing a growing number of innovative devices that address a very specific problem associated within a particular recanalization algorithm [213]. In order to perform CTO PCI successfully, it is paramount to know the availability, utilization properties, and technical limitations of each individual hardware.

#### **11.1. Guidewires**

Guidewires provide the primary and most critical piece of equipment to successfully perform CTO PCI. Innovation and repetitive iteration over the last 30 years lead to a wide range of primary, secondary, and tertiary design elements that directly influence endoluminal performance, especially in occluded lesions with specific anatomical properties [214]. At this, there is an individual demand for a specific wire spectrum during CTO recanalization with specific lesion characteristics, whereas in non-CTO PCI, usually one work horse wire serves for everything.

Tip load is measured in grams and defined by the amount of force the guidewire can create at the tip, whereas penetration power is the ability to penetrate the tissue and is defined by the ratio of tip load over tip area. CTO guidewires with tapered tips exhibit higher penetration power than their nontapered counterparts with equal tip load. Additional penetration force is generated with a microcatheter, in small vessels or tight lesions proximal to the tip, and by lateral support of the coating.

The coating, generally applied to the surface of the guidewire, can be a polymer jacket, a hydrophilic or hydrophobic film, or any combination of the above, and modifies pushability, trackability, and steerability.

The introduction of composite core dual coil guidewires with a second coil layer twisted in opposite turns around the first coil dramatically improved torque transmission and steering capabilities in tortuous arteries and opened new frontiers in CTO PCI, especially in hard calcified tortuous vessels.

Flexibility defines how well a guidewire advances around a sharp corner and is characterized by the core tapering length and the coil structure at the distal end of the wire. Gradually, long-tapered wires better follow tortuous, sharp-bended vessels but provide less support to other gear following. Shorter tapers, however, provide greater support near the tip but exhibit also greater tendency to prolaps.

Spring coils generally affect not only support, trackability, and visibility but also have an impact on the guidewire diameter and provide tactile feedback.

### **11.2. Microcatheters**

most common yet unrecognized complications in CTO PCI [6]. However, its prognostic value remains controversial. Most of the myocardial injuries during CTO PCI are relatively limited to absent electrocardiographic or echocardiographic changes, and the prognosis in such "asymptomatic" patients is much more dependent on the procedural success. However, techniques unique to CTO PCI add to the risk of MI compared with PCI of non-CTO lesions [6, 200–203]. Hereby, periprocedural MI may occur from shearing off the collateral circulation, obstructing or dissecting the proximal epicardial artery or sidebranch[204], collateral vessel compromise, donor artery ischemia during balloon anchoring, compression of the lumen by

Altogether, the complexity of the procedure correlates with the risk of periprocedural MI. However, its pathophysiological mechanisms are considered to be multifactorial and not fun-

Classic safety equipment should be readily available in the catheter laboratory and includes transthoracic echo, coils, pericardial drains, and stent grafts. New techniques usually provoke

Technical difficulties during CTO PCI with high procedural failure rates have been lately overcome by introducing a growing number of innovative devices that address a very specific problem associated within a particular recanalization algorithm [213]. In order to perform CTO PCI successfully, it is paramount to know the availability, utilization properties, and

Guidewires provide the primary and most critical piece of equipment to successfully perform CTO PCI. Innovation and repetitive iteration over the last 30 years lead to a wide range of primary, secondary, and tertiary design elements that directly influence endoluminal performance, especially in occluded lesions with specific anatomical properties [214]. At this, there is an individual demand for a specific wire spectrum during CTO recanalization with specific lesion characteristics, whereas in non-CTO PCI, usually one work horse wire serves for everything.

Tip load is measured in grams and defined by the amount of force the guidewire can create at the tip, whereas penetration power is the ability to penetrate the tissue and is defined by the ratio of tip load over tip area. CTO guidewires with tapered tips exhibit higher penetration power than their nontapered counterparts with equal tip load. Additional penetration force is generated with a microcatheter, in small vessels or tight lesions proximal to the tip, and by

The coating, generally applied to the surface of the guidewire, can be a polymer jacket, a hydrophilic or hydrophobic film, or any combination of the above, and modifies pushability,

subintimal hematoma, thrombus formation, air embolization, or perforation [193].

damentally different from non-CTO PCI [201, 205–210].

**11. Interventional armamentarium**

technical limitations of each individual hardware.

**11.1. Guidewires**

62 Interventional Cardiology

lateral support of the coating.

trackability, and steerability.

new complications asking for specific treatment solutions [211, 212].

After successful crossing of the CTO lesion with a dedicated CTO guidewire, the microcatheter is advanced past the occlusion to exchange the guidewire for a work horse wire or extra support guidewire in heavily calcified lesions of tortuous vessels, followed by balloon angioplasty and stenting. Special trapping techniques for hydrophilic wires and flushing techniques for non-hydrophilic wires are used to exchange individual microcatheters. Over the years, several microcatheters have been developed to dilate microchannels, to improve back-up support and torque transmission, and to facilitate guidewire exchange or reshaping. Furthermore, wire directability and penetration capacity can be maximized with the combined use of a microcatheter and a stiff-tapered penetration wire [215].

#### **11.3. Angioplasty balloons**

Very low profile angioplasty balloons with hydrophilic coating are available to cross tight and calcified lesions. However, with increasing use of retrograde and subintimal tracking techniques, these small balloons become less crucial to successfully cross the lesion.

#### **11.4. Additional tools**

In addition to the aforementioned devices, dedicated re-entry systems such as the Stingray balloon have been invented facilitating selected cases through controlled antegrade subintimal re-entry [216, 217]. Other novel applications and techniques are constantly being developed [218]. In complex cases, adjunctive use of several sophisticated devices may be cumbersome [219].
