**1. Introduction**

A chronic total occlusion (CTO) of a coronary artery is defined as complete closure of the vessel lumen for at least 3 months (**Figure 1**). The true prevalence of CTOs in the general population is unknown and assumed to be around 15–20% [1–3] but varies widely (30–50%) in patients with significant coronary artery disease (CAD) [1–5].

Percutaneous coronary intervention (PCI) of CTOs is considered to be the most challenging procedure in interventional cardiology and is associated with higher periprocedural failure and complication rates. At this, the presence of a CTO influences treatment recommendations and is a strong predictor against PCI as a treatment strategy [5].

CTO PCI in specialized centers is currently performed with success rates greater than 80% and decreasing complication rates, suggesting a favorable risk/benefit ratio supporting its

**Figure 1.** Stenosis versus chronic total occlusion.

increasing selection as a treatment option [6]. However, discrepant CTO PCI quantity and success rates exist among catheterization laboratories [1] and may be explained by individual skills among operators, lesion assessment, and the absence of consensual treatment strategies. Recently, CTO PCI has become more predictable as a consequence of dedicated tools, standardized procedural techniques, and continuous educational programs.

Contemporary PCI strategies with dedicated devices significantly improved procedural success, and the introduction of drug-eluting stents (DES) led to better long-term patency with preservation of left ventricular (LV) function. Still, there is little systematic evidence that postprocedural outcomes have relevantly changed, although much retrospective data suggest CTO PCI as favorable.
