**1. Introduction**

Chronic total occlusions (CTO) of coronary arteries are defined as a complete coronary arterial occlusion (thrombolysis in myocardial infarction, TIMI grade 0) being present for more than 3 months. About 20% of patients undergoing percutaneous coronary interventions (PCI) reveal a CTO, whereas in patients with prior coronary artery bypass grafting (CABG), CTOs are even more common in more than 50% [1]. Although registry data demonstrate an improvement of the patients' symptoms such as angina pectoris or dyspnea [2] and a reduction of

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adverse cardiac events [3, 4] after successful revascularization of a CTO, the overall clinical benefit is still under controversial debate, since prospective randomized controlled studies are still lacking [5, 6]. This is due partly to the greater complexity of catheter-based interventional techniques and the higher demand for materials compared to PCIs of nonchronically occlusive coronary lesions. In contrast, over the last decade, modern and novel developments of special techniques and materials increased the success rates of CTO revascularization in specialized centers toward more than 85% alongside acceptable low complication rates. This technical advance and the growing scientific evidence envisaging potential complete coronary revascularization in patients suffering from coronary multivessel disease [7, 8] have pushed CTO-PCIs into the spotlight of modern interventional cardiology.
