ABC | Volume 110, Nº5, May 2018

Review Article Ybarra et al CTO PCI Review Arq Bras Cardiol. 2018; 110(5):476-483 Ischemia and myocardial viability In addition to symptoms, evaluating the presence of ischemia and myocardial viability are fundamental steps. In asymptomatic patients, the evaluation of ischemia before CTO PCI is considered. The analysis of the receiver operating characteristic (ROC) curve of a cohort involving 301 patients showed 12.5% as the optimal amount of ischemia pre‑procedure in order to identify patients who have benefited from the intervention in terms of ischemia reduction. 14 The presence of myocardial viability is important to identify patients who would benefit from CTO recanalization. A combination of viability parameters may predict better and more accurate myocardial function than the use of a single parameter, such as transmural extension of the infarction, evaluation of the contractile reserve with dobutamine and thickening of the normal myocardial wall in cardiac magnetic resonance, especially in segments with intermediate extension of infarction. 15 The procedure Planning the procedure The use of angiographic scores to estimate the probability of success and the type of approach is essential in the planning of the procedure. The J-CTO score is the oldest and most widespread one (Figure 1). 16 Patients with higher J-CTO scores have significantly lower success rates, longer procedures, greater use of contrast, and more frequent use of the retrograde approach. 17,18 Other relevant scores are the PROGRESS-CTO score and the Clinical and Lesion (CL) score. 19,20 These three scoring systems present similar predictive abilities for technical success, being more accurate in anterograde cases. 21 Overall technical aspects The performance of ad hoc CTO PCI to the diagnostic procedure is widely discouraged, in order to allow a careful and appropriate review of angiography, obtaining informed consent and limiting the use of contrast and procedure. Contrast injection in the occlusion vessel simultaneously with injection into the donor vessel of the collateral circulation (simultaneous contralateral injection) is indispensable for the determination of CTO characteristics, including lesion length, proximal and distal cap morphology, lateral branches and the extension and morphology of the collateral branches. Anterograde injection should be avoided from the moment that subintimal dissection occurs in the anterograde space, since the hydraulic pressure of the contrast injection may increase the dissection plane, increasing the subintimal bruise. The use of combinations of bi-femoral, femoral-radial or bi-radial accesses will depend on the staff's preference, the availability of the necessary materials, the patient's characteristics, the procedure and the anatomy. 22 In order to have better planning of treatments of CTOs, the so-called hybrid algorithm has been developed, which has allowed to maximize success and reduce the time of the procedure, radiation and the use of contrast, enabling the teaching and dissemination of techniques and reducing inter‑and intra-operator approach variability and success rates. The core of this algorithm is the rapid identification of the failure of each strategy followed by immediate exchange for another type of technique. The algorithm or hybrid approach consists of two paths (anterograde and retrograde) and two ways of crossing CTO: through true lumen or through the subintimal space (with dissection and then re-entry to the true lumen). The definition of which path to use and how to cross the occlusion is determined by 4 main anatomical factors: proximal cap anatomy, occlusion length, presence of a disease‑free zone for reentry in the distal vessel and presence of usable septal or epicardial collaterals (Figure 2). Even by using modern techniques in centers of excellence, failure can still occur, which does not make a new attempt unfeasible. 23 Unsuccessful cases in which the lesion is “modified” – especially the proximal cap, whether with multiple dissections made by wire-specific guides or micro catheters, whether through balloon angioplasty or even subintimal approach – are called “investment procedures”, which aim to facilitate a future attempt at recanalization. 23 Anterograde technique with wire scaling Staggering of anterograde wires is the most commonly used approach. A micro catheter is advanced to the proximal cap, followed by attempts to cross CTO using specific guidewires according to the morphology of the cap. Generally, it starts with a soft and fine-tipped guidewire (1.0 g), coated with polymer. If the crossing is unsuccessful, a slightly heavier wire (4.0 g), also polymer coated, or a sharp, tapered 12-gauge wire is used. The recent introduction of rigid composite core guidewires seems to further enhance the success of anterograde crossover by allowing better torque control and transmission. Understanding the guidewire path is critical both to increase the likelihood of success and to minimize the risk of complications. If the guidewire enters the true distal lumen (confirmed in two orthogonal projections), the micro catheter is advanced through the occlusion and the guidewire is replaced by a traditional one, followed by balloon angioplasty and stent implantation. If the guidewire comes out of the vessel architecture, it must be retracted and redirected. If the guidewire crosses the occlusion but enters the subintimal space, reentry into the true lumen can be achieved by the “parallel wires” technique (less commonly used today) or the use of a dedicated re-entry system. Anterograde dissection and reentry technique Dissection and reentry are related to the intentional use of the subintimal space to cross the occlusion, a strategy that should be considered when the CTO extension is greater than 20 mm. Strategies to induce limited and controlled dissections seem to have better short- and long-term results when compared to those that cause extensive dissections. 24-26 Controlled dissection can be achieved with dedicated micro catheters that create a limited dissection plane. The reentry is obtained with the help of a specific balloon for this purpose. A recent study demonstrated that the use of 477