Coronaryarterychronictotalocclusion(CTO)isdefinedasanoccludedcoronaryarterysegmentwithoutanterogradeflowforatleastthreemonths.Itcanbeclassifiedasa“true”or“functional”CTObasedonflowcharacteristics.In“true”CTO,thereisnoanterogradeflow.In“functional”CTO,thereisminimalanterogradeflowthroughtheoccludedsegmentofthecoronaryartery.CTOisacommonfindingduringcoronaryangiographyanditsprevalencemayvarydependingonthereportedliterature.Amongpatientswithoutpreviouscoronaryarterybypassgrafting(CABG),CTOisfoundinabout20–30%ofthepatients.CTOmaydevelopinsidiouslyoveraperiodoftimeandinvolveacomplexinterplaybetweenintracellularandextracellularfactors,smoothmuscleandfoamcells,calcification,andneovascularization.ThereisagrowingbodyofevidencetosupportthatCTOrevascularizationmayimproveclinicaloutcomewhencomparedtomedicalmanagement.BoththeEuropeanandAmericancardiovascularsocietiessupportCTOrevascularizationwithaclass2arecommendation(levelofevidenceB).Historically,duetolowproceduralsuccessrate,apparentinefficientresourceutilization,potentialincreaseincomplicationratesanduncertainclinicalbenefits,onlyabout10–20%ofpatientswithCTOaretreatedwithpercutaneouscoronaryintervention(PCI).RecentadvancesusingnovelandinnovativetechniqueswithdedicatedequipmenthavesignificantlyimprovedtheproceduralsuccessrateforCTOPCItoabout90%inthehandsofexperiencedoperators.WithincreasinginterestinCTOPCIcoupledwithincreasededucationaleffort,CTOPCIlikelywillbecomemoreaccessibletopatientsinneedofCTOrevascularization.OngoingadvancementininnovativetechniquesandequipmentwillcontinuetoimproveproceduralsuccessratesandreduceproceduralcomplicationrateforCTOPCI.Furthermore,thereareanumberofprospectiveclinicaltrialsonthehorizonwhichshouldhelpdefinetheclinicalbenefitsandlimitationsofCTOPCIinthenear
