**4. Antegrade recanalization techniques**

**3. Principal approaches during CTO-PCI**

• Extend of patient's symptoms under optimal medical therapy.

*antegrade approach or as the primary approach for selected patients*.").

• Global and regional ventricular function and viability.

CTO depends on comprise the following:

• Severity of coronary artery disease.

**Figure 2.** Indications for CTO-revascularization.

• Localization and morphology of the CTO.

• Exercise testing.

88 Interventional Cardiology

As shown in **Figure 2**, the principal factors on which the indication for revascularization of a

Considering these factors before CTO-PCI allows the estimation of the potential benefit for the patient, as well as the technical severity and risk being associated with the intervention. Using the so-called J-CTO-score reveals optimal graduation of the complexity of the CTO-

The latest European guidelines for myocardial revascularization from the year 2014 [21] recommended a class IIa, with a level of evidence B ("*Percutaneous recanalization of CTOs may be considered in patients with suspected ischemia reduction in a corresponding myocardial territory and/or angina relief*."), and retrograde recanalization techniques are recommended only by a class IIB, level of evidence C ("*Retrograde recanalization of CTOs may be considered after a failed* 

lesion itself and is more commonly being applied by experienced CTO operators [20].

The close cooperation of members of national and international CTO-expert groups such as the EuroCTO-club in collaboration with Japanese CTO-specialists refined and improved specific CTO techniques for more than 10 years. As a result, their experiences consolidated and were summarized including numerous publications about technical approaches and interventional steps in the so-called expert consensus statements [9, 23, 24].

The primary aim is to advance a coronary guide wire through the CTO lesion into the distal true lumen of the coronary artery. Most interventionalists at first apply a soft, polymerjacked recanalization wire with a reduced tip diameter, which passes the CTO lesion in about 40% into the right direction usually through microchannels or soft tissue at the site of the occlusion. In the case of hard and severely calcified parts of the occlusion, a so-called "wire escalation strategy" is required using recanalization wires with increasing tip loads. Within a next step, a medium-heavy, very well guidable recanalization wire is used, when the course of the CTO lesion is unclear. In contrast, when the course of the CTO-lesion is recognizable again, a harder recanalization wire with a reduce tip diameter is used, which in turn reveals an increasing force to penetrate the CTO-tissue and is targeted actively into the true distal coronary arterial lumen. The correct distal position of the wire has to be confirmed in two different angulations by contralateral contrast injections through the contralateral coronary artery (i.e., from LCA in the case of RCA-CTO and from RCA in the case of LCA-CTO). This makes a double arterial access necessary for most CTO-PCIs. When the recanalization wire does not pass the distal end of the CTO into the true vessel lumen, the so-called "parallel-wire technique" may be applied. Here, the first wire marks the false pathway, whereas a second mostly harder wire is used additionally and usually enters then the distal lumen. A crucial technical device are microcatheters—catheters of very narrow diameters—which will be advanced over and to the tip of the recanalization wires. They secure the achieved recanalization pathway and thereby exchanging to other recanalization wires becomes possible.

After successful wire passage through the CTO-lesion, predilation with increasing balloon sizes will be performed with final implantation of drug-eluting coronary stents, which ensure valuable long-term results [25].

The success rates of the above-described antegrade recanalization techniques reach 55–80% depending of characteristics of patients and CTO lesions [26–29].
