**8. Percutaneous intervention of CTO**

Complication rates of CTO PCI were traditionally too high to justify these procedures and success rates were based predominantly on individual operator skills and annual case volume [60, 61]. A review of the NHLBI Dynamic Registry revealed a decrease of CTO PCI attempts from 9.6% in 1997/1998 to 5.7% in 2004 [62]. With the introduction of coronary stents, procedural success rates increased substantially and became more consistent across CTO studies [63]. In-hospital MACE and 1-year target vessel, revascularization (TVR) rates have declined by approximately 50% over the years. Patients with successful recanalization of a single-vessel CTO experience a higher 10-year survival rate compared to matched patients with a single non-CTO lesion [64].

Among the patients randomized to PCI in the Synergy between PCI with Taxus and Cardiac Surgery (SYNTAX) trial, CTO lesions were present in 24% and exhibited a low success rate of only 53% [65]. Furthermore, the presence of CTO was the single most common reason for a patient to be referred to surgery, and the prevalence of CTO was almost doubled in the CABG registry.

A metaanalysis from 18,061 CTO patients treated in dedicated high-volume CTO PCI centers and expert operators reported 77% procedural success and a 3.1% risk for MACE [6], whereas an analysis from the National Cardiovascular Data Registry revealed CTO PCI in daily practice to be successful in only 59% [66].

We have recently seen dramatic improvements in outcomes from a series of single- and multiple-operator registries with procedural success of up to 98% and MACE rates as low as 1.7% [67–70]. These results were mainly achieved through constant refinement of interventional techniques and dedicated interventional tools, ongoing knowledge exchange, and the development of standardized treatment algorithms. Most of the current CTO crossing techniques were made possible by the introduction of microcatheters and specialized guidewires. Further advances in CTO PCI will be dependent on the interplay between the development of recanalization techniques and interventional armamentarium.

#### **8.1. Indications for CTO PCI**

Furthermore, the incidence of restenosis [56] or stent thrombosis after DES implantation [57] is related to minimum stent area detected by IVUS and malapposition due to aneurysm formation after subintimal DES implantation during CTO PCI, and it can be optimized with the

Although IVUS facilitates CTO PCI and has the potential to reduce periprocedural complications, the clinical benefit of IVUS-guided CTO PCI has not yet been proven, and further stud-

OCT is more sensitive than IVUS in detecting coronary dissection during PCI and improves stent deployment or detection of acute complications. Furthermore, resolution of OCT is high enough to visualize microvessels, the different layers of the vessel wall, and even collagen

In contrast to IVUS, conventional OCT, at the cost of penetration depth, has a 10-fold higher imaging resolution as the main advantage but is unable to generate images in completely occluded vessels and does not allow real-time intracoronary imaging for guidance of wire crossing. However, optical coherence reflectometry used in a combined OCT and radiofrequency ablation device might be able to minimize the risk of perforation and increase the

Complication rates of CTO PCI were traditionally too high to justify these procedures and success rates were based predominantly on individual operator skills and annual case volume [60, 61]. A review of the NHLBI Dynamic Registry revealed a decrease of CTO PCI attempts from 9.6% in 1997/1998 to 5.7% in 2004 [62]. With the introduction of coronary stents, procedural success rates increased substantially and became more consistent across CTO studies [63]. In-hospital MACE and 1-year target vessel, revascularization (TVR) rates have declined by approximately 50% over the years. Patients with successful recanalization of a single-vessel CTO experience a higher 10-year survival rate compared to matched patients

Among the patients randomized to PCI in the Synergy between PCI with Taxus and Cardiac Surgery (SYNTAX) trial, CTO lesions were present in 24% and exhibited a low success rate of only 53% [65]. Furthermore, the presence of CTO was the single most common reason for a patient to be referred to surgery, and the prevalence of CTO was almost doubled in the CABG

A metaanalysis from 18,061 CTO patients treated in dedicated high-volume CTO PCI centers and expert operators reported 77% procedural success and a 3.1% risk for MACE [6], whereas an analysis from the National Cardiovascular Data Registry revealed CTO PCI in daily prac-

help of IVUS [55].

52 Interventional Cardiology

ies are needed [52].

**7.2. Optical coherence tomography**

concentration in coronary arteries [58].

crossing potential of the guidewire in CTO PCI [59].

**8. Percutaneous intervention of CTO**

with a single non-CTO lesion [64].

tice to be successful in only 59% [66].

registry.

Indications for CTO PCI are in principle identical to the standard PCI of non-CTO lesions and are based on detailed clinical assessments (**Figure 1**). High procedural success rates in conjunction with low complication rates improve risk/benefit ratio and are paramount for the acceptance and dissemination of CTO PCI. Successful CTO recanalization has the ability to relieve angina [71], reduce ischemia [41] and the need for CABG [72], improve exercise tolerance [73], electrical stability [74], left ventricular function [44], and tolerance of future ACS [13, 75], and possibly survival [76, 77] with a similar risk compared to regular PCI of non-CTO lesions [3]. **Table 1** summarizes the rationale for CTO PCI.

Asymptomatic patients with CTO demand additional ischemia and viability testing. As described above, cardiac MRI has the ability to quantify viable myocardium and detect transmural involvement and therefore may assist in patient selection and procedural planning [78].

Based on small retrospective studies and on expert consensus, American and European guidelines recommend CTO PCI in patients with evidence for substantial ischemia in a corresponding myocardial territory when performed by an experienced operator in case of adequate clinical indications and suitable anatomy with a class-IIa, evidence level B recommendation [79, 80].


**Table 1.** Rationale for CTO PCI [226].

### **8.2. Radial access for CTO PCI**

Radial access is feasible for contralateral injections in CTO PCI but may be challenging when microcatheters and techniques with additional equipment are used [81, 82]. However, based on the availability of sheathless-guiding catheters with a larger interventional lumen, the radial approach has become more frequently used for both the antegrade and retrograde approach.

### **8.3. Procedural success in patients with CTO undergoing PCI or CABG**

In the early days of interventional cardiology, CTO PCI was associated with very low success and relatively high complication rates [83–87]. This leads to a high number of patients undergoing surgery, which was also seen in the SYNTAX and the BARI (Bypass Angioplasty Revascularization Investigation) trial, where the presence of a CTO was a strong predictor for referral to CABG [4, 88].

Procedural failures during CTO are mainly due to the incapacity to pass the lesion with a guidewire, followed by failed balloon crossing, the inability to dilate the lesion, or a vessel perforation [60, 66, 89–91]. Traditional predictors for CTO PCI failure are increasing age of the occlusion, small vessel diameter, presence of calcium or a blunt stump, proximal cap ambiguity, excessive tortuosity, long occlusion length, bridging collaterals, and absent visibility of the distal vessel [72, 89, 92–95]. Furthermore, these lesions show a higher mean Multicenter CTO Registry of Japan (J-CTO) score and have collaterals that are less likely suitable for the retrograde approach [96]. However, additional angiographic features such as multivessel disease, previous CABG, and side branch at the proximal occlusion point seem not to be predictive for procedural failure with novel guidewire techniques [97].

Over time, with the improvement of both equipment such as microcatheters and dedicated guidewires with greater torque response [98] and recanalization techniques such as retrograde procedures, safe and effective CTO PCI became possible [60] and most of the prior obstacles vanished [99].

Only limited randomized data are available on the outcomes of patients with CTO undergoing CABG [100–102]. CTOs represent a difficult lesion subset also for surgical revascularization, thus leading to incomplete revascularization with 31.9% of CTOs referred for CABG not being surgically revascularized and 7.5% with occluded bypass grafts after 1 year [103]. At least one CTO is found in more than 50% of patients with CABG [1, 104].

In SYNTAX, the presence of a CTO was the strongest independent predictor of incomplete revascularization with 51% in the PCI arm and one of the major anatomic predictors for referral to CABG [105]. Interestingly, CABG enhances the progression of atherosclerosis and increases the risk for new CTOs in native coronary arteries, which itself represents an independent predictor of death, MI, and repeat revascularization in these patients [102, 103]. Moreover, long-term patency of saphenous vein grafts (SVG) is limited and is significantly lower than for second-generation DES (70 vs 90% at 5 years, respectively) [106]. Therefore, CABG might only be considered when complete arterial revascularization can be achieved, and given the durability of LIMA-LAD grafts and superior patency of DES over SVGs to LCX or RCA, particularly in CTO cases, hybrid revascularization may represent future treatment options in selected patients [107, 108].
