**2. Indication to revascularize a CTO**

In more than 50% left ventricular (LV) function is still preserved in the territory of supply of the CTO artery [9], whereas the maintaining supply by collateral connections (CCs) is sufficient for only 20% of CTO patients while preventing exercise-induced myocardial ischemia [10, 11]. The fractional flow reserve (FFR) distally of the CTO lesion is usually less than 0.5 reflecting an insufficient collateral circulation [12]. Accordingly, exercise-testing oftentimes reveals an exercise-induced myocardial ischemia in the territory of supply of the chronically occluded coronary artery.

No prospective randomized controlled studies have been published yet evaluating clinical endpoints in patients with CTO-PCI compared to patients being treated conservatively by optimal medical therapy. However, there are numerous observational studies comparing a successful with unsuccessful CTO-PCI. A meta-analysis of these retrospective registry data show an improvement of angina pectoris and a decrease of consecutive need for CABG surgery after successful CTO-PCI [2].

Although symptoms' relief instead of prognostic benefit represents the primary indication for an elective CTO-PCI, the prognostic aspect is debated increasingly as a potential indication. Accordingly, there are still only retrospective cohort studies available suggesting a potential prognostic benefit after successful CTO-PCI [13]. The largest CTO registry from the UK database demonstrated a 30% improvement of long-term survival both for patients with successful PCI of at least one CTO as well as for those with complete coronary revascularization in 13,433 CTO patients [14].

Sub-analyses of the New York State Registry including more than 21,000 patients with elective coronary stent implantation showed that a complete revascularization was associated with an improved adjusted long-term survival compared to incomplete revascularization including CTOs [8]. These data support the concept targeting the complete revascularization including the revascularization of coronary CTOs.

**Figure 1** shows own data from a recent monocentric analysis including 1,642 CTO-patients. The prognostic benefit of a CTO-PCI depends on the extend of coronary artery disease and is most prominent in patients with a coronary three-vessel disease [15].

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

In more than 50% left ventricular (LV) function is still preserved in the territory of supply of the CTO artery [9], whereas the maintaining supply by collateral connections (CCs) is sufficient for only 20% of CTO patients while preventing exercise-induced myocardial ischemia [10, 11]. The fractional flow reserve (FFR) distally of the CTO lesion is usually less than 0.5 reflecting an insufficient collateral circulation [12]. Accordingly, exercise-testing oftentimes reveals an exercise-induced myocardial ischemia in the territory of supply of the chronically

No prospective randomized controlled studies have been published yet evaluating clinical endpoints in patients with CTO-PCI compared to patients being treated conservatively by optimal medical therapy. However, there are numerous observational studies comparing a successful with unsuccessful CTO-PCI. A meta-analysis of these retrospective registry data show an improvement of angina pectoris and a decrease of consecutive need for CABG sur-

Although symptoms' relief instead of prognostic benefit represents the primary indication for an elective CTO-PCI, the prognostic aspect is debated increasingly as a potential indication. Accordingly, there are still only retrospective cohort studies available suggesting a potential prognostic benefit after successful CTO-PCI [13]. The largest CTO registry from the UK database demonstrated a 30% improvement of long-term survival both for patients with successful PCI of at least one CTO as well as for those with complete coronary revascularization in

Sub-analyses of the New York State Registry including more than 21,000 patients with elective coronary stent implantation showed that a complete revascularization was associated with an improved adjusted long-term survival compared to incomplete revascularization including CTOs [8]. These data support the concept targeting the complete revascularization including

**Figure 1** shows own data from a recent monocentric analysis including 1,642 CTO-patients. The prognostic benefit of a CTO-PCI depends on the extend of coronary artery disease and is

most prominent in patients with a coronary three-vessel disease [15].

CTO-PCIs into the spotlight of modern interventional cardiology.

**2. Indication to revascularize a CTO**

occluded coronary artery.

86 Interventional Cardiology

13,433 CTO patients [14].

the revascularization of coronary CTOs.

gery after successful CTO-PCI [2].

**Figure 1.** Adjusted 3-year mortality of 1,642 CTO patients presenting at the University Heart Centre Bad Krozingen, Germany. A clear prognostic benefit is shown for complete coronary revascularization, especially in patients with a coronary three-vessel disease including a CTO (HR, hazard ratio; CI, confidence interval) a CTO (HR, hazard ratio; CI, confidence interval) [15].

A main mechanism for a beneficial prognostic influence of a successful CTO-PCI may consist in an improved tolerance for future acute coronary syndromes. A sub-analysis from the HORIZONS-AMI-study showed that patients with an ST segment elevation myocardial infarction (STEMI) and a concomitant CTO revealed a significantly increased mortality both in the acute phase and within long-term follow-up, especially in the presence of a coronary three-vessel disease [16]. Another registry database demonstrated that the presence of a CTO was associated with the future development of malignant ventricular arrhythmias in patients with an ischemia-related LV dysfunction [17].

The so-called EURO-CTO-study has just finished the recruiting phase. It represents the first prospective and randomized CTO-study comparing CTO-PCIs with optimal medical treatment focusing on the improvement of predefined clinical endpoints (i.e., quality of live at 1 year, death or myocardial infarction at 3 years). Furthermore, the prospective DECISION-PCI-study from Korea randomizes CTO patients either to PCI or optimal medical treatment in order to evaluate the influence of CTO-PCI on cardiovascular mortality and future myocardial infarction at 5 years.

Whether LV function being assessed by cardiovascular magnetic resonance imaging (cMRI) might be improved is currently being evaluated within the REVASC-study, in which 200 patients with CTOs are randomized to PCI or optimal medical treatment. Within a prior smaller cMRI study, regional LV function depended on the extend of transmural scarring after myocardial infarction [18], whereas a further meta-analysis of registry data demonstrated an improvement of global LV ejection fraction (LVEF) of 4.7% [19].
