CTO in Coronary Angioplasty: Definition and Significance
In coronary angioplasty, CTO stands for Chronic Total Occlusion, which refers to a completely occluded coronary artery with TIMI flow 0 for ≥3 months duration. 1
Detailed Definition of CTO
A Chronic Total Occlusion (CTO) has two key defining characteristics:
Complete occlusion: The artery must have absent antegrade flow through the lesion (TIMI grade 0 flow). This distinguishes CTOs from functional occlusions with minimal flow (TIMI grade 1). 2
Chronicity: The occlusion must have been present for at least 3 months, either documented or presumed based on clinical presentation. 2
CTOs are classified into two categories:
- Definite CTO: Shows typical appearance with definitive evidence of occlusion duration ≥3 months
- Probable CTO: Shows typical appearance without definitive documentation of duration 2
Angiographic Characteristics
The typical angiographic appearance of a CTO includes:
- TIMI grade 0 flow (complete absence of flow)
- Angiographically visible mature collaterals
- Absence of thrombus or staining at the proximal cap 2
Bridging collaterals may fill the target vessel antegradely, but there must still be an absence of antegrade flow through the actual occlusion. 2
Clinical Significance
CTOs are frequently encountered in clinical practice:
- Present in approximately one-third of patients undergoing diagnostic coronary angiography 3
- Represent one of the most challenging lesion subsets for intervention
- Often predict referral for coronary bypass surgery 4
Technical Considerations in CTO-PCI
CTO interventions differ significantly from standard PCI:
- Lower procedural success rates
- Higher complication rates
- Greater radiation exposure
- Longer procedure times 3
Modern CTO-PCI requires specialized approaches:
- Antegrade wire escalation
- Antegrade dissection and reentry
- Retrograde wire escalation
- Retrograde dissection and reentry 1
Clinical Importance
Successfully treating CTOs can provide significant benefits:
- Reduction in symptoms (particularly angina)
- Improvement in ventricular function
- Potential survival advantage when successful 3
- Contribution to complete coronary revascularization, which is associated with improved long-term outcomes 5
Understanding the definition and implications of CTOs is essential for proper patient selection, procedural planning, and achieving optimal outcomes in this challenging subset of coronary lesions.