Correlation Of Pericoronary Adipose Tissue Attenuation With Plaque Characteristics And Its Value Of Clinical Prediction

Objective:Pericoronary adipose tissue（PCAT）attenuation——fat attenuation index（FAI）derived from conventional polychromatic CT could capture the existence of coronary inflammation.But conventional polychromatic CT has limitations with material component differentiation.Spectral CT can enhance the ability of discriminating tissue characteristics.On the other hand,at present the clinical studies on PCAT attenuation mainly focus on the correlation between PCAT attenuation and culprit lesions in patients with acute coronary syndrome（ACS）,and there is a lack of research on the correlation between PCAT attenuation and plaque types with different calcification degree.In addition,at present,academic field have conducted more cross-sectional researches than longitudinal studies on the clinical significance of PCAT attenuation;platelet–to-lymphocyte ratio（PLR）,a serum inflammatory marker,could reflect the inflammation of the circulatory system while no studies,so far,have combined imaging markers which reflect the local inflammation of coronary with serum inflammatory markers reflecting global inflammation of circulatory system to predict future events of acute coronary syndrome（ACS）.Hence this study aims to（1）use spectral CT to evaluate PCAT attenuation and explore the correlation between those derived indicators of PCAT attenuation and the characteristics of coronary atherosclerotic plaque;（2）analyze the correlation between PCAT attenuation and ACS events,as well as to evaluate the predictive value of PCAT attenuation,serum inflammatory marker and combination of the two for future ACS events.Methods:（1）Pericoronary adipose tissue attenuation derived from dual-layer spectral detector CT—a sensitive imaging marker of high-risk plaque:151 eligible patients presenting with acute chest pain underwent coronary CT angiography using dual-layer spectral detector computed tomography（SDCT）were included.Anatomical characteristics of each plaque were measured,including the burden,length,maximum cross-sectional area,volume of the plaque,the percentage of low-attenuation component,the percentage of medium-attenuation component,the percentage of high-attenuation component,the remodeling index of the lesion and degree of stenosis.PCAT attenuation were assessed by conventional polychromatic images,virtual mono-energetic images at40 ke V,the slope of spectral attenuation curve and effective atomic number(written as CT_poly,CT_{40ke V},λ_HUand Z_eff,respectively).According to the calcification degree,the plaques were divided into non-calcified plaques,non-calcified mixed plaques,calcified mixed plaques and calcified plaques.The high-risk plaques were determined according to the four characteristics including low-density plaques,"napkin ring"sign,positive remodeling and spotty calcification.Then we assessed the correlation between PCAT attenuation and the types of atherosclerotic plaques classified by calcification degree as well as the presence of high-risk plaques using statistical software SPSS.（2）Prediction of pericoronary adipose tissue attenuation combined with serum inflammatory marker for the occurrence of acute coronary syndrome within 2 years:We retrospectively tracked patients admitted for a first presentation of ACS with an earlier coronary CT angiography（CTA）examination before the onset of ACS who met the inclusion criteria from January 1^st,2010 to October 31^th,2020,and then collected the clinical information and image data.We recorded the value of serum PLR at the time of coronary CTA examination and calculate the time-to-ACS（TTA）which was the definition of the time elapsed from the examination of coronary CTA to the onset of ACS.The offending vessel which is the location of future culprit lesion was determined based on the examination of electrocardiogram,coronary angiography and echocardiography,and then the PCAT attenuation of offending vessel was measured.Patients were divided into ACS patients and non-ACS patients according to the onset of ACS within two weeks after the coronary CTA examination.In the cohort of non-ACS patients,patients were further divided into case group（ACS events occurred within two years after coronary CTA examination）and control group（no ACS events occurred within two years）.The difference of PCAT attenuation of the offending disease and PLR were compared between the two groups,and the predictive value of PCAT attenuation of the offending disease or PLR and their combined value for future ACS events were analyzed.Results:（1）Pericoronary adipose tissue attenuation derived from dual-layer spectral detector CT—a sensitive imaging marker of high-risk plaque:As the percentage of high-attenuation in plaque increased,the PCAT attenuation increased and indicators derived from the SDCT(especially CT_{40ke V})were more sensitive to detect the change than the indicator derived from polychromatic CT(CT_poly).Pearson correlation analysis showed that after adjusting the average attenuation of epicardial adipose tissue,CT_poly,CT_{40ke V},Z_effandλ_HUwere all correlated with the percentage of high-attenuation components in plaque（correlation coefficients were 0.298,0.513,0.413 and 0.339,especially,all P<0.001）,among which CT_40kevwas correlated the most strongly.The attenuation of PCAT surrounding high-risk plaques was higher than that surrounding non-high-risk plaques,especially CT_{40ke V}（-119.87±22.74HU vs.-153.76±24.97HU,P<0.001）.Logistic regression analysis showed that the percentage of high-attenuation components and each of the PCAT attenuation indexes were correlated with high-risk plaques（all P<0.05）.ROC curve analysis showed that higher CT_{40ke V}（≥-120.60 Hu）is helpful for identifying high-risk plaques with an accuracy of 90%（P<0.05）.（2）Prediction of pericoronary adipose tissue attenuation combined with serum inflammatory marker for the occurrence of acute coronary syndrome within 2 years:There were 104 ACS patients and 131 non-ACS patients.The degree of coronary atherosclerosis in ACS patients was severer and PCAT attenuation of the offending vessel was higher in ACS patients than in non-ACS patients（-81.30±7.29HU vs.-86.37±7.07,P<0.05）.Among the non-ACS patients,there were 50 patients in the case group and81 patients in the control group.Logistic regression analysis demonstrated that PCAT attenuation of the offending vessel,the value of PLR and the usage of antiplatelet or hypolipidemic drugs were independent risk factors of the occurrence of ACS events within 2 years（OR=1.188,95%CI:1.092～1.293;OR=1.019,95%CI:1.009～1.028;OR=0.182,95%CI:0.073～0.452,all P<0.001）.Cox regression analysis revealed that PCAT attenuation and the serum PLR were associated with the incidence of ACS events（HR=1.141,95%CI:1.092～1.192,P<0.001;HR=1.010,95%CI:1.005～1.015,P<0.001）after adjusting for the age,number of cardiovascular risk factors and the severity of coronary atherosclerosis.Stratification analysis was conducted considering the usage of antiplatelet or hypolipidemic drugs revealing that the association of PCAT attenuation with the occurrence of ACS events in patients taking medication disappeared（P=0.642）,while the association became stronger in patients who take no medication（HR=1.129,95%CI:1.081～1.180,P<0.001）.According to the analysis of receiver operating characteristic（ROC）curve,the PCAT attenuation and the serum PLR had predictive value for future ACS events（AUC were 0.737 and 0.632,respectively,P<0.05）,and the predictive efficiency was significantly improved after the two were combined（AUC=0.817,P<0.05）.Patients were divided into high-and low-PCAT attenuation population according to the cut-off of PCAT attenuation derived from ROC curve,K-M curve analysis showed that the cumulative incidence of ACS events in the population with high-PCAT attenuation was higher than that in the population with low-PCAT attenuation（P<0.01）.Conclusions:As the high-attenuation percentage in plaque increases,PCAT attenuation increases gradually;PCAT surrounding high-risk plaques showed higher attenuation,a finding that has been associated with coronary artery inflammation.The metrics derived from SDCT,especially CT_{40ke V},showed higher discriminatory power for detecting changes in PCAT attenuation than polychromatic CT.PCAT attenuation assessed by monoenergetic images of 40ke V may provide a novel imaging marker of plaque vulnerability.In addition,PCAT attenuation derived from coronary CTA and the serum PLR are helpful in the prediction of ACS events in the future two years,and the predictive efficiency were enhanced after the two were combined;the correlation between PCAT attenuation and future occurrence of ACS events is affected by the usage of antiplatelet or hypolipidemic drugs,suggesting that PCAT attenuation is of great significance in the implementation of secondary prevention measures.