Critical lesions refer to lesions with coronary angiographic assessment of coronary luminal diameter stenosis ≥ 50% and ≤ 70%.
Although coronary angiography is the "gold standard" for coronary anatomy assessment, there are still great limitations in judging the severity of lesions and identifying the vulnerable nature of plaques.
Considering the anatomical diversity of borderline lesions, there is little evidence in evidence-based medicine, and clinical treatment tends to be empirical. At the same time, coronary intervention is invasive and risky.
Therefore, how to define the borderline lesion, how to evaluate the borderline lesion and its significance, and whether to intervene with the borderline lesion is one of the difficult problems that plague interventional doctors.
At present, the evaluation methods of clinical decision-making for the treatment of borderline coronary lesions are divided into non-invasive and invasive examinations. Non-invasive examinations mainly include treadmill exercise test, coronary CTA, and stress myocardial perfusion imaging. Invasive examinations include FFR, IVUS, and OCT.
1. Non-invasive inspection
Treadmill exercise test is a simple, economical, and relatively safe non-invasive examination method. It is widely used in the diagnosis and prognosis evaluation of coronary heart disease and other cardiovascular diseases, but it is relatively prone to false negatives and false positives, which requires comprehensive evaluation by clinicians .
Therefore, the birth of stress radionuclide myocardial perfusion imaging has made up for the insufficiency of treadmill exercise test. Interventional intervention should be carried out for patients whose stress test suggests large-area myocardial ischemia.
Coronary artery CTA is a common method for clinical examination of coronary artery disease, and it is of great significance for the diagnosis of coronary artery disease. The composition of the plaque can be reflected by the CT value: the calcification component has the highest CT value, followed by the fiber component, and the lipid component has the lowest CT value.
Therefore, a low CT value needs to be paid attention to by clinicians. In general studies, ＜30 HU is defined as a low-attenuation plaque (referring to the lipid component plaque with the lowest CT value and the easiest to rupture).
However, the CT value of plaque is affected by many factors, such as contrast agent, plaque volume, layer thickness, tube voltage and so on. In addition, the CT values of lipid plaques and fibrous plaques overlap, and it is difficult to distinguish using CT values alone. Therefore, the current research mainly relies on special procedures to identify which plaques are low-attenuation plaques.
2. Invasive inspection
The fractional coronary blood flow reserve (FFR) is the ratio of the maximum blood flow provided to the myocardium in the innervated area by the coronary artery of epicardial stenosis and the maximum blood flow provided to the myocardium when the same coronary artery is normal. The ratio of the mean pressure in the coronary artery distal to the stenosis to the mean pressure in the aorta at the orifice of the coronary artery.
• If the lesion is in the left main trunk, the cut-off point value is ≤ 0.8, it can be considered that intervention is needed;
• If the lesion is in the distal or middle part of the main trunk, the FFR cut point value ≤ 0.75 requires intervention;
• If the lesion is proximal to the anterior descending artery, intervention is required when the FFR may be 0.76 or 0.78.
Intravascular ultrasound (IVUS) can provide real-time cross-sectional images of the lumen and tube wall, accurately measure the diameter and cross-sectional area of the blood vessel, and can identify the degree of stenosis and plaque properties of critical lesions seen on coronary angiography. In particular, it can clearly show the characteristics of lesions at openings and bifurcations that are difficult to display by coronary angiography.
The "Chinese Expert Consensus on the Application of Intravascular Ultrasound in Coronary Artery Diseases (2018)" pointed out: Early research suggests that for non-left main trunks, including left anterior descending artery, left circumflex artery, right coronary artery and its main branch proximal lesions, interventional treatment The threshold values for IVUS are area stenosis> 70%, minimum lumen diameter ≤ 1.8 mm, and MLA ≤ 4.0 mm².
The results of meta-analysis in recent years have shown that the IVUS cut-off value for interventional therapy is MLA <2.8 mm² for lesions other than the left main trunk and reference vessel diameter> 3 mm; for lesions with a reference vessel diameter <3 mm, the IVUS cut-off value for interventional therapy For MLA <2.4 mm².
For the left main disease, it is generally believed that the MLA> 6.0 mm² in the left main disease can be used as the limit value for delaying interventional therapy.
Current clinical studies in Asia suggest that MLA 4.5 mm² can be used as a threshold for judging whether there is ischemia, but more data are needed to prove it. For patients with an MLA of 4.5 to 6.0 mm², FFR is recommended to assess ischemia.
Optical coherence tomography (OCT) can obtain a spatial resolution of 4-16 μm, which has a higher intravascular spatial resolution than IVUS. In the identification of vulnerable plaques, OCT has important clinical value in identifying the thickness of the diseased fiber cap and the size of the lipid core.
In 2020, a study published in ACC Cardiovascular Imaging used OCT to perform retracement imaging of three epicardial coronary arteries (RCA, LAD, LCX). Analyzing the type and distribution of plaque, it is proposed that when the tube wall loses the normal three-layer structure, it is defined as plaque formation, and the minimum lumen area (MLA) <3.5 mm² is defined as stenosis.
According to OCT image characteristics, plaques are divided into three categories: fibrous plaques (FP), calcified plaques (FCP), and atherosclerotic plaques (FA). Among them, FA takes the thickness of the fiber cap of 80 μm as the boundary value, and can be subdivided into thick fiber cap atherosclerotic plaque (ThCFA) and thin fiber cap atherosclerotic plaque (TCFA).
When multiple types of plaques appear in the same frame of image, the plaque type with higher vulnerability (FP <FCP <ThCFA <TCFA) is the main plaque type.
In the diagnosis and treatment of borderline lesions, the advantage of OCT lies in the accurate identification of thrombus, vulnerable plaques, and minor lesions such as intimal erosion and intimal tears.
To sum up, in the current situation where evidence-based medicine is not yet sufficient, Lepu suggests that we should focus on the comprehensive evaluation of patients' clinical manifestations, combine immediate interventional effects with long-term benefits, and pass various non-invasive and invasive examinations. A comprehensive and systematic evaluation of borderline lesions is carried out, and patients with borderline lesions that are necessary for interventional intervention and may have long-term benefits are screened out, and then more targeted and reasonable interventions are carried out.
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