**10. Complications**

nearly 80% and resulted in more balloon dilatations of the septal channels and a higher per-

An in-hospital analysis of procedural and long-term outcomes from the European multicenter ERCTO registry demonstrated increased numbers of safe and successful retrograde procedures with good long-term outcomes [192]. However, the retrograde approach also seems to be independently associated with increased risk of periprocedural complications [193]. IVUS, as described above, can serve as a useful tool for the detection of procedure-related vessel damage and subintimal wire tracking to help guide retrograde

The hybrid algorithm depicted in **Figure 3** represents a combined strategy comprising AWE/ RWE and ADR/RDR techniques (**Table 3**) [194, 195]. The fundamental principles in hybrid procedures require a special mindset and great flexibility in the approach with the ability to perceive failure modes early to quickly change strategy and to come back to abandoned strategies, if necessary. Experienced CTO operators aim for efficiency and look for multiple strategies with several options and different techniques. This skillset can be taught and transferred with implementation of the hybrid algorithm, ideally in a broader setting with operators of different experience levels to improve technical success while maintaining low complication rates. The adoption of only a few strategies will limit the patients who can be treated on the

foration rate [55, 191].

60 Interventional Cardiology

CTO PCI [55].

**9.3. The hybrid approach**

basis of coronary anatomy [82, 176, 186, 196, 197].

**Figure 3.** The Hybrid Algorithm. Adapted from Ref. [194].

CTO PCI has long been associated with high complication rates with one-third of failed CTO PCI attributable to periprocedural complications [96, 183]. The prognostic value of periprocedural MI in non-CTO PCI depends on the extent of irreversible myocardial injury and correlates well with the release of cardiac biomarkers [198, 199]. MI after successful CTO PCI has been associated with increased long-term mortality and is considered as one of the most common yet unrecognized complications in CTO PCI [6]. However, its prognostic value remains controversial. Most of the myocardial injuries during CTO PCI are relatively limited to absent electrocardiographic or echocardiographic changes, and the prognosis in such "asymptomatic" patients is much more dependent on the procedural success. However, techniques unique to CTO PCI add to the risk of MI compared with PCI of non-CTO lesions [6, 200–203]. Hereby, periprocedural MI may occur from shearing off the collateral circulation, obstructing or dissecting the proximal epicardial artery or sidebranch[204], collateral vessel compromise, donor artery ischemia during balloon anchoring, compression of the lumen by subintimal hematoma, thrombus formation, air embolization, or perforation [193].

Altogether, the complexity of the procedure correlates with the risk of periprocedural MI. However, its pathophysiological mechanisms are considered to be multifactorial and not fundamentally different from non-CTO PCI [201, 205–210].

Classic safety equipment should be readily available in the catheter laboratory and includes transthoracic echo, coils, pericardial drains, and stent grafts. New techniques usually provoke new complications asking for specific treatment solutions [211, 212].
