**6. Recanalization strategies**

Most CTO lesions can be recanalized by antegrade techniques. In about 30%, a retrograde technique is necessary due to the complex morphology of the CTO (**Figure 5**). An escalation of the recanalization strategy is valuable, because an antegrade attempt may be successful in the case of a complex morphology of the CTO. Retrograde methods reveal a high technical expertise and should only be performed independently by interventional cardiologists with sufficient training in antegrade techniques (i.e., >300 antegrade CTO-interventions, >50/year) and additional training in retrograde techniques (25 retrograde cases as second and primary operator each), as stated in a consensus document of the EuroCTO-club [9]. In the presence of high expertise in all recanalization techniques, availability of necessary specific materials and a possible widened indication up to 90% of CTOs can be recanalized. However, the high
