CT coronary angiography of chronic total occlusions of the coronary arteries: how to recognize and evaluate and usefulness for planning percutaneous coronary interventions.

Chronic total occlusions (CTO) of the coronary arteries are a common finding. A CTO can be underdiagnosed on CT coronary angiography (CTCA) as a high grade stenosis, because of the presence of retrograde collaterals which allow opacification of the vessel distal to the stenosis, or can be missed completely, especially if another adjacent opacified artery is mistaken for occluded artery. CTOs are considered as Type C or high risk lesions with a higher restenosis rate and increased technical failure rate by percutaneous coronary intervention (PCI). CTCA can help identify features that most influence current success rates of PCI such as marked calcifications at the stump, severe tortuosity of the proximal vessel, long length of the occluded segment as well location of the vessel distal to the occlusion, which often may not be well seen on conventional angiography. Identification of these features and displaying the 3D information as the best angiographic projection that demonstrates the length and orientation of the CTO, either as hard copy images or transmitted direct to the angiographic catheter lab for data fusion, allows strategic preprocedural planning and scheduling of the PCI. Myocardial viability of the affected area of the occluded segment is a major factor that influences whether PCI for CTO is attempted but is not currently readily available by cardiac CT. Contrast enhanced cardiac MR imaging is still the gold standard for this and may need to be performed prior to PCI.