Definition of Chronic Total Occlusion
A chronic total occlusion (CTO) is a completely blocked coronary artery with no forward blood flow (TIMI 0 flow) that has been occluded for at least 3 months. 1, 2
Key Defining Characteristics
The two essential features that must be present are:
- Complete absence of anterograde (forward) blood flow through the coronary artery, classified as TIMI grade 0 flow 2
- Duration of occlusion ≥3 months, either documented by prior angiography or presumed based on clinical history 1, 2
Clinical Classification
CTOs are categorized into two types based on certainty of diagnosis 2:
- Definitive CTO: Has the typical angiographic appearance AND definitive evidence (such as prior angiogram) proving the occlusion has been present for ≥3 months 2
- Probable CTO: Has the typical angiographic appearance but lacks definitive documentation of the 3-month duration 2
Epidemiology and Clinical Context
CTOs are found in approximately one-third of patients undergoing diagnostic coronary angiography, making them a common finding in patients with coronary artery disease. 3, 4, 5
The most commonly affected vessels are 3:
- Right coronary artery (RCA): 52% of cases
- Left anterior descending artery (LAD): 34% of cases
- Left circumflex artery (LCX): 14% of cases
Critical Distinction from Acute Occlusion
Do not confuse a CTO with an acute thrombotic occlusion—this distinction is clinically crucial. 6 An acute occlusion causing ST-elevation myocardial infarction requires immediate intervention, whereas a CTO represents a chronic condition that requires specialized planning, equipment, and expertise for elective treatment. 1, 6
Why the 3-Month Threshold Matters
Knowing whether an occlusion is truly ≥3 months old is clinically important because occlusions <3 months have significantly higher success rates with percutaneous intervention compared to older, more organized lesions. 2 The longer an artery remains occluded, the more organized and calcified the occlusive material becomes, making it technically more challenging to cross with interventional techniques. 1
Verification Considerations
A central laboratory with CTO experience should verify that lesions are truly CTOs, as classification can be challenging. 2 This is particularly important in clinical trials and when making treatment decisions, as misclassification could lead to inappropriate management strategies.