Coronary Computed Tomography Angiography-Specific Definitions of High-Risk Plaque Features Improve Detection of Acute Coronary Syndrome

Abstract

Background High-risk plaque (HRP) features as detected by coronary computed tomography angiography (CTA) predict acute coronary syndrome (ACS). We sought to determine whether coronary CTA-specific definitions of HRP improve discrimination of patients with ACS as compared with definitions from intravascular ultrasound (IVUS). Methods and Results In patients with suspected ACS, randomized to coronary CTA in the ROMICAT II (Rule Out Myocardial Infarction/Ischemia Using Computer Assisted Tomography II) trial, we retrospectively performed semiautomated quantitative analysis of HRP (including remodeling index, plaque burden as derived by plaque area, low computed tomography attenuation plaque volume) and degree of luminal stenosis and analyzed the performance of traditional IVUS thresholds to detect ACS. Furthermore, we derived CTA-specific thresholds in patients with ACS to detect culprit lesions and applied those to all patients to calculate the discriminatory ability to detect ACS in comparison to IVUS thresholds. Of 472 patients, 255 patients (56±7.8 years; 63% men) had coronary plaque. In 32 patients (6.8%) with ACS, culprit plaques (n=35) differed from nonculprit plaques (n=172) with significantly greater values for all HRP features except minimal luminal area (significantly lower; all P<0.01). IVUS definitions showed good performance while minimal luminal area (odds ratio: 6.82; P=0.014) and plaque burden (odds ratio: 5.71; P=0.008) were independently associated with ACS but not remodeling index (odds ratio: 0.78; P=0.673). Optimized CTA-specific thresholds for plaque burden (area under the curve: 0.832 versus 0.676) and degree of stenosis (area under the curve: 0.826 versus 0.721) showed significantly higher diagnostic performance for ACS as compared with IVUS-based thresholds (all P<0.05) with borderline significance for minimal luminal area (area under the curve: 0.817 versus 0.742; P=0.066). Conclusions CTA-specific definitions of HRP features may improve the discrimination of patients with ACS as compared with IVUS-based definitions. CLINICAL TRIAL REGISTRATION URL: https://www.clinicaltrials.gov . Unique identifier: NCT01084239.

Keywords: acute coronary syndrome; angiography; computed tomography angiography; coronary angiography; myocardial ischemia; tomography, X-ray computed; ultrasonography, intravascular.

Figure 1. Stepwise measurements for quantitative plaque assessment using (semi-) automated software

Quantitative plaque measurements using semi-automated software. In a curved multiplanar reconstruction (MPR) of the left anterior descending (LAD) coronary artery in long axis (Figure A), the reader manually selects the beginning and end of the plaque (blue lines). The yellow lines indicate sites of the vessel cross-section displayed in Figure B. The software automatically delineates inner and outer vessel wall and detects plaque components with low CT attenuation <30HU (red), 31 to 60HU (light green) and 61 to 130HU (dark green). The software then provides stenosis degree, remodeling index, minimal luminal area, plaque burden and volumes of plaque and volumes of plaque subcomponents (Figure C).

Figure 2. Probability of ACS in patients with high-risk plaque on coronary CTA using IVUS-based definitions for TCFA equivalent (plaque volume <30HU), plaque burden and minimal luminal area

Relative risks for ACS are shown according to presence of IVUS based HRP features. A MLA of 4.0 mm² or less and a plaque burden of 70% or more were pre-specified for use in this model, since they have been used frequently in previous studies. For low HU plaque, a prespecified threshold of <30 HU was used as TCFA equivalent, since it corresponds to a necrotic core in IVUS. For the volume of low HU plaque, we used a CTA-specific threshold of 1.31 mm³, as there is no equivalent definition based on IVUS.

Figure 3

Receiver operating characteristic curves (ROC) for the prediction of acute coronary syndrome by presence of IVUS based HRP characteristics as measured on coronary CTA: (A) low density plaque (TCFA equivalent), (B) low density plaque (TCFA equivalent) and plaque burden and (C) low density plaque (TCFA equivalent), minimal luminal area and plaque burden. AUC indicates area under the curve (A vs. B: p=0.0082; A vs. C: p=0.0001; B vs. C: p=0.0190)

Figure 4

Receiver operating characteristic curves (ROC) for the prediction of acute coronary syndrome by presence of HRP characteristics (low density plaque (TCFA equivalent), minimal luminal area, plaque burden) using (A) IVUS based and (B) newly derived coronary CTA-specific thresholds, and (C) using all available information from coronary CTA (low density plaque, minimal luminal area, plaque burden, remodeling index, lesion length and diameter stenosis). AUC indicates area under the curve. (A vs. B: p=0.2347; B vs. C: p=0.0752; A vs. C: p=0.0209)