ABC | Volume 110, Nº5, May 2018

Review Article Percutaneous Coronary Intervention in Chronic Total Occlusion Luiz Fernando Ybarra, 1 Marcelo J. C. Cantarelli, 2,3 Viviana M. G. Lemke, 2,4,5 Alexandre Schaan de Quadros 2,6 McGill University Health Centre, 1 Montreal - Canadá Sociedade Brasileira de Hemodinâmica e Cardiologia Intervencionista, 2 São Paulo, SP - Brazil Hospitais Leforte, São Paulo, 3 SP - Brazil Hospital das Nações, Curitiba, 4 PR – Brazil Hospital do Rocio, Campo Largo, 5 PR – Brazil Instituto de Cardiologia / Fundação Universitária de Cardiologia – IC/FUC, 6 Porto Alegre, RS - Brazil Keywords Coronary Artery Disease / complications; Coronary Occlusion; Percutaneous Coronary Intervention. Mailing Address: Luiz Fernando Ybarra • 101 - 11 Hillside Av., Montreal – Canada E-mail: lfybarra@gmail.com Manuscript received October 03, 2017, revised manuscript February 23, 2018, accepted March 07, 2018 DOI: 10.5935/abc.20180077 Abstract Percutaneous coronary intervention in chronic total occlusion is a rapidly evolving area, being considered the last frontier of interventional cardiology. In recent years, the development of new techniques and equipment, as well as the training of specialized personnel, increased their success rates, making it the most predictable procedure available. Although the number of randomized and controlled studies is still limited, results from large multicentered registries allow us to safely offer this intervention to patients, as another treatment option along with the optimized drug treatment and myocardial revascularization surgery. This review summarizes the last and most relevant publications in the subject in order to provide an overall view of the field’s current status. Introduction Percutaneous coronary intervention (PCI) in chronic total occlusion (CTO) has expressed great expansion and evolution with the development of new techniques and equipment, as well as with the training of specialized personnel. These factors have significantly raised success rates, making these procedures more effective and predictable. The aim of this manuscript is to present an update regarding indications, the aspects of the procedure, their results and clinical applicability of PCIs in CTO. Definition and epidemiology CTO are defined as coronary obstructions which produce total occlusion of vessel lumen with TIMI 0 flow and duration longer than 3 months. Occlusions with minimal passage of contrast without opacification of the distal vessel are considered “functional CTO”. CTOs are present in 18-52% of patients submitted to coronary angiography and who have coronary heart disease. 1-3 More recent registries showed a prevalence between 16 and 20%. 4,5 In these studies, the percentage of patients with CTO submitted to PCI was low. In two Canadian studies, only 9-10% of patients underwent PCI, while 57 to 64% of them remained in clinical treatment and 26 to 34%were referred for surgery. 2,4 Histopathological aspects Understanding the histopathology of CTOs is an essential step to define the best percutaneous therapeutic strategy. The CTOs are consisted of a proximal and a distal cap, with an occluded segment between them. Histological analysis of these lesions showed that, in the proximal cap, more fibrous and calcified components are more predominant than in the distal one and which, despite complete angiographic occlusion, may have intravascular microchannels which cross the occluded segment. 6-8 Blunt caps present histopathological differences when compared to tapered ones, with less frequent intravascular microchannels. 7 The viability of the myocardium irrigated by the occluded artery is maintained by collateral circulation, which may be developed by angiogenesis or by the action of circulating endothelial progenitor cells. 9 It is difficult to assess the ability of collateral vessels to maintain coronary perfusion, and the angiography is not the most accurate method to predict the functionality of collaterals. The traditional knowledge that the occluded vessel has ‘adequate and sufficient collaterals’ for CTO ischemia prevention is challenged by physiological evidence with fractional flow reserve (FFR) analysis. 10 Selection of patients European guidelines for myocardial revascularization recommend that CTO PCI should be considered for ischemia reduction in the corresponding myocardial territory and/or for reduction of angina (class IIa, level of evidence B). 11 According to the guidelines for the management of stable coronary disease, indications for CTO revascularization should be the same as one for a subtotal stenosis, provided that viability, ischemia of a sufficiently large territory and/or angina symptoms are present. 12 With the current techniques, equipment, success and complication rate, patient selection should not depend on the type of lesion (total, subtotal or severely obstructive), but rather on symptoms and on the findings in complementary tests. 13 Although it is essential to ensure the viability of the myocardial territory supplied by a chronically occluded vessel, the presence of collateral circulation does not prevent the occurrence of ischemia in this area. 10 Thus, the size of the collateral circulation should not be used as a criterion to contraindicate revascularization. 476