Multi-modality intra-coronary plaque characterization: A pilot study

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Abstract

Background

The risk of rupture and subsequent thrombosis of the atherosclerotic coronary plaques is related to the presence of necrotic core with high lipid content.

We conducted an exploratory pilot trial to compare the capability for lipid tissue detection using four intra-coronary diagnostic techniques: greyscale intravascular ultrasound (GS IVUS), IVUS radiofrequency data (IVUS RFD) analysis, optical coherence tomography (OCT) and intravascular magnetic resonance spectroscopy (IVMR).

Methods

Twenty-four matched target plaques were analyzed with the 4 techniques in non-culprit lesions in five patients with stable angina. Following IVUS pullback, OCT and IVMR was performed. Plaque composition was assessed using established criteria of each technology.

Results

Atherosclerotic plaques classified as soft by GS IVUS were mainly composed by fibro-fatty (80%) or necrotic core (20%) by IVUS RFD. These soft plaques were classified as “lipid-rich” by OCT in the majority of cases (80%). IVMR confirmed the presence of lipid with a lipid fraction index ranging between 36 and 79 in these soft plaques. Besides this good agreement for soft plaques, GS IVUS, IVUS RFD and OCT had 100% agreement in the identification of calcified plaques.

Conclusion

The present study explored multi-modality imaging of atherosclerotic plaque in-vivo. Assessing specifically lipid-rich plaques, there was generally good agreement for plaque components identified as soft by traditional GS IVUS with RFD and OCT whereas IVMR showed a varying amount of lipid in these regions. Nevertheless there continues to remain inherent variation, namely as a result of the different imaging resolutions and the lack of common nomenclature and classification.

Introduction

Acute coronary syndromes (ACS) are common initial manifestations of coronary atherosclerosis. The propensity of atherosclerotic lesions to destabilize is highly dependent on their composition, with autopsy studies of sudden cardiac death victims showing that the most frequent cause of the coronary occlusion is rupture of a thin cap fibroatheroma (TCFA) plaque [1]. Such lesions are characterized by a large necrotic core (tissue with lipid-rich necrotic areas containing remnants of foam cells, lymphocytes, cholesterol clefts and microcalcification) with a thin, fibrous cap, usually < 65 μm in thickness [2]. Since the necrotic core is a tissue with high lipid content, discrimination of lipid-rich tissue may have an important impact on the detection of lesions prone to rupture.

Greyscale (GS) intravascular ultrasound (IVUS) is the most often employed diagnostic technique for the evaluation of extent and distribution of coronary atherosclerotic plaque [3], however, its specificity and sensitivity for tissue identification are limited [4], [5]. Spectral analysis of IVUS radiofrequency data (RFD) is a tool developed in the last few years for more reliable analysis of plaque composition [6]. Optical coherence tomography (OCT) is a high-resolution imaging modality that uses reflected near-infrared light to visualize vascular microstructures and it has been successfully applied for the characterization of coronary atherosclerotic plaques in-vivo[7]. Intravascular magnetic resonance spectroscopy (IVMR) is a new technique developed to identify specifically the lipid component of plaques based on the self-diffusion of water molecules that is translated into a lipid fraction index (LFI) [8].

These four imaging modalities have in common the ability to give a detailed assessment of the composition of atherosclerotic plaques but do differ in the means of achieving this. Currently, it is unclear to what extent these techniques, with different physical properties and varying resolution, are able to give comparable results. We conducted this exploratory pilot trial to compare the capability for lipid tissue detection using these four intra-coronary diagnostic modalities (GS IVUS, IVUS RFD analysis, OCT and IVMR) while comparing these findings to each other and to GS IVUS, the most widely used and standardized method for plaque characterization.

Section snippets

Study population

Patients with stable angina undergoing percutaneous coronary intervention (PCI) were included in this pilot study. Following treatment of the culprit vessel, an IVUS pullback was performed in a non-culprit vessel containing a non-flow limiting stenosis (defined as less than 50% diameter stenosis by online quantitative coronary angiography, QCA). Following the IVUS pullback, OCT and IVMR acquisitions were performed. Heavily calcified and tortuous vessels and those with a minimal lumen diameter < 

Patient and procedural characteristics

Twenty-four matched target plaques were collected from five patients. The intra-coronary diagnostic devices were successfully advanced to the area of interest in all the patients. There were no cases of coronary spasm, dissection, acute closure or perforation. During OCT and IVMR pullbacks transient signs of ischemia with ST segment changes were documented. Following the procedure, all patients remained symptom-free with no detected elevation in the creatinine kinase-MB or Troponin-T enzymes.

GS

Discussion

A body of various clinical, post-mortem and experimental observations suggest that the composition of atherosclerotic plaque is an important determinant for subsequent clinical outcome. This knowledge triggered the development of a variety of new technological approaches for the analysis of plaque structure and chemical composition. It is however challenging to estimate the accuracy of a given diagnostic method in vivo due to the fact that no ‘gold standard’ method is available. A pragmatic way

Limitations

The main limitations of the present study are: 1) the small sample size 2) lack of histological correlation 3) the localization of the sector scanned by IVMR was difficult to precisely assess due to the simplified spatial representation associated with the technique; however specifically designed rotation markers, meticulous inspection and exclusion of doubtful rotations were used to optimize data analysis. The multi-modality plaque characterization described in this study is at present limited

Conclusions

The present study explored multi-modality imaging of atherosclerotic plaque in-vivo. Assessing specifically lipid-rich plaques, there was generally good agreement for plaque components identified as soft by traditional GS IVUS with RFD and OCT whereas IVMR showed a varying amount of lipid in these regions. Nevertheless there continues to remain inherent variation, namely as a result of the different imaging resolutions and the lack of common nomenclature and classification.

Acknowledgement

The authors of this manuscript have certified that they comply with the Principles of Ethical Publishing in the International Journal of Cardiology [26].

References (26)

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All authors have approved the final manuscript, which has not been published and is not under consideration elsewhere. We declare that there is no conflict of interest for any author. Dr Gonzalo has received a Research Grant from the Spanish Society of Cardiology.

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