As a result, Case 1, Case 2 and Case 3 received stenting of coronary artery.
Case 296
【Progress】
Three cases of Case 1, Case 2 and Case3 whose FFR were 0. 78, 0.75 and 0.77 received stenting for coronary artery stenosis.
Meanwhile, three cases of Case 4, Case 5 and Case 6 whose FFR were 0. 78, 0.75 and 0.77 did not receive stenting.
【Discussion】
Identification of high-risk plaque on CT coronary arteriography is one of the imperative radiologic interpretations (1). Histologic and radiologic correlation reveals the vulnerable plaque with low attenuation less than 30HU is surrounded by fibrous mural with mild high attenuation around 60HU (1-4). This pattern is called napkin ring sigh; ring means fibrous mural indicative of absorbed thrombus and napkin means vulnerable plaque.
Further, other morphologic figures as high-risk plaque are characteristic of spotty calcification, low attenuation plaque and remodeling (1-4). These findings reflect composition of absorbed and/or unabsorbed thrombus (5). Namely, fatty deposition such as low-weight cholesterol in vessel mural is first, phagocyted as foreign body by macrophages. Phagocytes phagocyting much cholesterol die and adhere vessel mural, other viable macrophages phagocyte cadaver of macrophages and unprocessed cholesterol. This process is repeated many times because of ingesting much cholesterol. At last, the accumulation of cholesterol surpasses its process function by macrophages, inducing accumulation of cholesterol at vessel mural. Fibrocytes coming from smooth muscle layer work to absorb the lipid plaque by surrounding cholesterol mass and making organization with minute new vessels, calling atheromatous plaque (5). Fibrous mural is formed in the process of absorbing cholesterol accumulation and hyaline fibrous tissue becomes to contain calcification (5). If this process were well completed, no damages would happen. However, when the overwhelming cholesterol accumulation beyond the process by macrophages and fibrocytes occur, the vulnerable plaque or high-risk plaque called napkin ring sign with remodeling emerge. It causes hemorrhage into the vulnerable plaque and occlusion of the vessel lumen, inducing myocardial infarction (5).
Slab maximum intensity projection (MIP) is useful to detect lumen of cardiac vessels and evaluate mural calcification and low attenuation plaque. Slab MIP indicates that maximum attenuation values are taken out in certain thickness (slab) of sliced images, leading to select coronary artery with lumen and mural three-dimensionally (6, 7). Then, slab MIP is appropriate to evaluate occlusive coronary artery with calcification. Multiplanar imaging is useful to check low-attenuation plaque and stenosis ratio. Cross sectional image is also useful to detect low-attenuation plaque outlined with high-attenuation plaque, namely napkin-ring sign.
Fractional flow reserve (FFR) is calculated based on blood pressure at peripheral site after occlusive lesion and at proximal site before occlusive lesion using microcatheter with pressure sensor: FFR = pressure at distal / pressure at proximal. FFR measurement is conducted under intravenous injection of medicines of adenosine or nicorandil because auto-reserve function of peripheral vessel dilatation works in case of stenosis emergence (6, 7). Then, it is necessary to measure FFR under the situation of maximum dilatation of coronary artery whether to check real coronary ischemia is present or absent. As a result of several studies, FFR less than 0.8 under coronary artery dilatation is reported to be a reliable indicator for myocardial ischemia beyond auto-reserve (6, 7).
As FFR is calculated by data of invasive diagnostic measurement, one of the roles of CT angiography is to check whether most stenosis ratio exceeds 50% or greater in which case, it is possibly corresponded to FFR less than 0.8 (6, 7).
【Summary】
We presented six cases with coronary artery occlusive diseases: FTR less than 0.8 in three cases while that more than 0.8 or more in three cases.
It is borne in mind that high-risk plaques on coronary CT include spotty calcification, low-attenuation plaque, remodeling and its combination called napkin ring sign that composes of relatively high attenuation fibrous ring of CT values more than 60 HU corresponded to organized or fibrous thickness of vessel mural, and sequent low-attenuation thrombus less than 30 HU protruded into vessel lumen corresponded to napkin-ring decoration. The occlusive lesion in coronary artery with stenosis ratio more than 50% or greater can be corresponded to FFR less than 0.8. Then, on interpretation of coronary CT, it is imperative to find out the lesion with stenosis ratio of 50% or greater, and/or high-risk plaques of low-attenuation plaque, spotty calcification, remodeling and napkin-ring sign.
【References】
1.Maurovich-Horvat P et al. The Napkin-Ring Sign: CT Signature of High-Risk Coronary Plaques?J Am Coll Cardiol Img. 2010 Apr, 3 (4) 440–444
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5.Seifarth H, Schlett CL, Nakano M et-al. Histopathological correlates of the napkin-ring sign plaque in coronary CT angiography. Atherosclerosis. 2012;224 (1): 90-6.
6.Cury, R. C., et al. CAD-RADS™ 2.0 - 2022 Coronary Artery Disease-Reporting and Data System: An Expert Consensus Document of the Society of Cardiovascular Computed Tomography (SCCT), the American College of Cardiology (ACC), the American College of Radiology (ACR), and the North America Society of Cardiovascular Imaging (NASCI). J Am Coll Radiol Available online 8 July 2022
7.Cury, R. C., et al. (2016). “CAD-RADS: Coronary Artery Disease – Reporting and Data System.: An Expert Consensus Document of the Society of Cardiovascular Computed Tomography (SCCT), the American College of Radiology (ACR) and the North American Society for Cardiovascular Imaging (NASCI). Endorsed by the American College of Cardiology.” J Am Coll Radiol 13(2 Pt A): 1458 – 1466.
2023.4.25