Coronary CT Angiography: Evaluation of Stenosis and Occlusion

Once an atherosclerotic plaque has been identified and properly characterized by means of coronary CT angiography (CTA), the next step is to define the extent of atherosclerotic involvement, i.e., significant reduction of the lumen by stenosis or complete occlusion of the vessel. A reduction in the caliber of the vessel lumen is associated with a reduction in blood flow and may have significant hemodynamic consequences; however, an important and clearly evident parietal atherosclerotic plaque may be present without significantly reducing lumen caliber. Thus, an exact definition of the extent of lumen reduction by means of coronary CTA is very important from a clinical point of view. In most cases, this diagnostic procedure is employed in not highly symptomatic patients (in patients in whom there is strong clinical suspicion of coronary disease, catheter angiography is directly performed); then, depending on the results of the clinical examination, a decision is made as to whether a more invasive approach (catheter angiographsy) is required. This decision depends at least in part on the significance of the vessel stenosis. Both the aim and the key role of coronary CTA are to differentiate patients with normal coronary vessels from those with limited atherosclerotic involvement without evidence of stenosis (who may benefit from supportive drug therapy) and from those with significant stenosis. In this latter group, catheter coronary angiography may confirm the significance of the disease and define the therapeutic approach. The direct evidence of arterial stenosis provided by coronary CTA yields additional information. For example, a stenosis > 70% causes a significant hemodynamic reduction of vascular flow. Completely asymptomatic patients, with negative treadmill tests, may present with important and significant stenosis of one or more coronary arteries but with an overall reduction in flow that is less than the 70% threshold. In clinical practice, a stenosis is considered significant when the vessel caliber is reduced by > 50%. Thus, the goal is to interpret coronary CTA images such that the level of stenotic vascular involvement is precisely determined.