Chronic Total Occlusion Of The Coronary Artery

A coronary chronic total occlusion (CTO) is defined as 100% occlusion of a coronary artery for a duration of greater than or equal to 3 months based on angiographic evidence. The TIMI (thrombolysis in myocardial infarction) flow grading system is a scoring classification from 0-3 referring to the levels of coronary blood flow assessed during coronary angiography. The TIMI flow grading system is as below: TIMI 0 flow (no perfusion-complete occlusion) - the absence of any forward flow beyond a coronary occlusion. TIMI 1 flow (penetration without perfusion) - faint forward flow beyond the occlusion, associated with an incomplete filling of the distal coronary bed. TIMI 2 flow (partial reperfusion) - delayed forward flow with complete filling of the distal coronary bed. TIMI 3 flow (full perfusion) - normal flow, which fills the distal coronary bed. A true CTO is defined as 100% occlusion of a coronary artery with TIMI 0 flow; whereas a functional CTO is defined as severely stenotic, yet, less than a 100% occlusion of the coronary artery with TIMI 1 flow for a duration of greater than or equal to 3 months based on angiographic evidence. Moreover, it is difficult to identify the exact period over which a CTO lesion is present in the absence of serial angiograms. Therefore, it is mostly estimated based on available clinical information related to the timing of the event that caused the occlusion, for example, prior myocardial infarction or sudden change in anginal symptoms with electrocardiogram changes consistent with the location of the occlusion. However, in many patients, the age of the CTO cannot be determined with confidence.