**5. Retrograde recanalization techniques**

In about 50% of CTOs, very complex occlusions are present being characterized by a straight nontapered proximal cap, long length or torturous course of the lesion, diffuse alterations of the distal vessel, or prior failures of recanalization attempts [20]. Retrograde recanalization techniques were introduced by Japanese CTO experts and have increased significantly the success rates of these complex CTOs without increasing peri-interventional complication rates [30–32]. The main goal of all retrograde techniques is to advance successfully a coronary wire to the distal end of the CTO lesion using collateral connections originating from the contra-lateral coronary artery. Additionally, ipsilateral retrograde techniques without using contra-lateral collaterals can be applied [33, 34]. **Figure 3** shows schematically an occlusion of the right coronary artery (RCA) and wire positioning using epi-myocardial collateral connections to the distal end of the CTO (**Figure 3A**, **B**). This retrograde wire marks exactly the distal end of the occlusion and can afterwards be targeted precisely by an antegrade wire, which will be able to be advanced antegradely and parallel to the retrograde "marker" wire into the distal vessel lumen (so-called "marker wire" technique, **Figure 3C**, **D**).

**Figure 3.** "Marker-wire" technique (CTO, chronic total occlusion) [34].

Occasionally, more complex retrograde techniques may be performed, such as the "reverse-CART" ("controlled antegrade and retrograde tracking")-technique [35, 36]. Here, balloon inflation over the antegrade wire creates space within the CTO lesion, which alleviates the entry of the retrograde wire, which may then advance parallel to the antegrade wire into the antegrade guiding catheter (**Figure 4A**, **B**). A consecutively introduced microcatheter protects

**5. Retrograde recanalization techniques**

90 Interventional Cardiology

In about 50% of CTOs, very complex occlusions are present being characterized by a straight nontapered proximal cap, long length or torturous course of the lesion, diffuse alterations of the distal vessel, or prior failures of recanalization attempts [20]. Retrograde recanalization techniques were introduced by Japanese CTO experts and have increased significantly the success rates of these complex CTOs without increasing peri-interventional complication rates [30–32]. The main goal of all retrograde techniques is to advance successfully a coronary wire to the distal end of the CTO lesion using collateral connections originating from the contra-lateral coronary artery. Additionally, ipsilateral retrograde techniques without using contra-lateral collaterals can be applied [33, 34]. **Figure 3** shows schematically an occlusion of the right coronary artery (RCA) and wire positioning using epi-myocardial collateral connections to the distal end of the CTO (**Figure 3A**, **B**). This retrograde wire marks exactly the distal end of the occlusion and can afterwards be targeted precisely by an antegrade wire, which will be able to be advanced antegradely and parallel to the retrograde "marker" wire into the

distal vessel lumen (so-called "marker wire" technique, **Figure 3C**, **D**).

**Figure 3.** "Marker-wire" technique (CTO, chronic total occlusion) [34].

**Figure 4.** "Reverse-CART" ("controlled antegrade and retrograde tracking") technique [36].

coronary circulation, and within the microcatheter, a 330-cm long special externalization wire can be advanced from retrogradely and outside of the body (so-called "externalization"). After wire externalization, balloon dilation and stent implantation will then be performed antegradely using the externalization wire.
