The Role of Multiple Imaging Modalities to Disclose the Mechanism of ACS Angioscopy in Comparison to Other Imaging Modalities Including OCT, IVUS and CTA

Aims: Whilst pathological and optical coherence tomography (OCT) studies have indicated that ACS lesions have either ruptured fibrous (RFC-ACS) or intact (IFC-ACS) fibrous caps, CT angiographic (CTA) characteristics of RFC-ACS include low-attenuation plaques and positive plaque remodelling. However, features associated with IFC-ACS have not been previously described. The aim of this study was to assess the CTA characteristics of IFC-ACS lesions. Methods and Results: Of the 66 patients with ACS or stable angina that consented to multiple imaging procedures, 57 culprit lesions in 57 patients were evaluated with sufficient image quality of angioscopy, OCT, IVUS and CTA. Whilst intraluminal thrombus was assessed by OCT or angioscopy, culprit lesions were classified further by OCT-based demonstration of fibrous cap integrity. Of 35 culprit lesions with ACS, OCT revealed IFC with thrombus in 10 (29 %) and RFC in the remaining 25 (71 %); all 22 lesions with stable angina had intact fibrous caps. Fibrous caps were significantly thinner in RFC-ACS than in IFC-ACS and stable angina (45 ± 12 µm, 131 ± 57 µm, 321 ± 146 µm, respectively; p = 0.001). CT-verified low-attenuation plaques were more frequently observed in RFC-ACS than in IFC-ACS and stable angina (88 %, 40 %, 18 %; p = 0.001) lesions. Similarly, positiveremodelling was more predominantly seen in RFC-ACS than in IFC-ACS and stable angina (96 %, 20 %, 14 %; p = 0.001). However, none of the specific CT angiography features clearly distinguished IFC-ACS from stable lesions. Conclusion: This report is derived from our previous study proposing for the first time that nondisrupted culprit lesions (IFC-ACS) would represent pathological plaque erosions. IFC-ACS lesions based on OCT and angioscopy features demonstrated less low-attenuation plaque and less positive remodelling than RFC-ACS by CT angiography. Since there are no unique CT features of IFC-ACS lesions to enable their clear distinction from stable lesions, it will be difficult to develop CT-based non-invasive imaging techniques to allow the clear identification of subjects at high risk of developing ACS due to IFC.