Combined NIRS and IVUS imaging detects vulnerable plaque using a single catheter system: a head-to-head comparison with OCT
Selected in EuroIntervention by S. Brugaletta
Roleder T, Kovacic J, Ali Z, Sharma R, Cristea E, Moreno P, Sharma S, Narula J, Kini A
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The presence of thin-cap fibroatheromas (TCFA) is associated with high risk of acute coronary syndrome, hence their early detection may identify high-risk patients. In the present study we investigated the ability of a combined imaging catheter with near-infrared spectroscopy (NIRS) plus intravascular ultrasound (IVUS) to detect TCFA in patients with stable coronary artery disease.
Methods and results
Optical coherence tomography (OCT) and combined NIRS-IVUS assessment were performed on identical coronary segments. IVUS analysis provided per-segment minimal cross-sectional area (CSA), plaque length (PL), plaque burden (PB), plaque volume (PV), and remodelling index (RI). OCT was used as the gold-standard reference to define TCFA (fibrous cap thickness <65 μm). Plaque lipid content was estimated by NIRS (lipid core burden index [LCBI]). OCT-defined TCFA was present in 18 of 76 segments. IVUS revealed that OCT-defined TCFA were positively remodelled lesions with greater PB and PV, smaller CSA, and longer PL, while NIRS revealed greater LCBI per 2 mm segment (LCBI2mm) (all p<0.001). Greatest accuracy for OCT-defined TCFA detection was achieved using LCBI2mm >315 with RI >1.046 as a combined criterion value.
OCT-defined TCFA are characterised by positive vessel remodelling, high plaque burden and greater lipid core burden as assessed by dual NIRS-IVUS imaging.
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What is known
Atherosclerotic coronary artery plaque rupture leads to intravascular thrombus formation, which may culminate in an acute coronary event with myocardial ischaemia. Rupture-prone atherosclerotic plaques are characterised by outward vessel expansion (positive remodelling), a high burden of intra-plaque lipid, macrophage infiltration and a thin fibrous cap (<65 μm). Histopathologically, these plaques are referred to as “thin-cap fibroatheromas” (TCFA).
Optical coherence tomography (OCT) is the principal imaging tool used to detect TCFA, given its high imaging resolution of OCT (10- 20 μm). However, OCT is limited by its low depth penetration into the vessel wall (2 mm), which hampers accurate assessment of necrotic core depth and vessel remodelling. On the contrary IVUS is accurate to assess vessel remodelling, but it does not have enough resolution to measure the cap thickness of coronary plaque.
The recent combination of near-infrared spectroscopy (NIRS) with greyscale IVUS in a single imaging catheter allows simultaneous assessment of plaque composition both in terms of its chemical (by NIRS) and morphologic (by IVUS) characteristics. A previous autopsy study demonstrated that NIRS is able to detect features associated with plaque vulnerability in humans. In the present study, the ability of combined NIRS-IVUS imaging to detect OCT-defined TCFA in patients with stable coronary disease was evaluated.
- Optical coherence tomography (OCT) and combined NIRS-IVUS assessment were performed on identical coronary segments.
- IVUS analysis provided per-segment minimal cross-sectional area (CSA), plaque length (PL), plaque burden (PB), plaque volume (PV), and remodelling index (RI).
- OCT was used as the gold-standard reference to define TCFA (fibrous cap thickness <65 μm). Plaque lipid content was estimated by NIRS (lipid core burden index [LCBI]).
- OCT-defined TCFA was present in 18 of 76 segments.
- IVUS revealed that OCT-defined TCFA were positively remodeled lesions with greater PB and PV, smaller CSA, and longer PL, while NIRS revealed greater LCBI per 2 mm segment (LCBI2 mm) (all p<0.001).
- Greatest accuracy for OCT-defined TCFA detection was achieved using LCBI2 mm >315 with RI >1.046 as a combined criterion value.
The present analysis showed that combined use of NIRS-IVUS in the same catheter may help interventional cardiologists to identify vulnerable plaque. Many studies are currently on going to study whether preventive treatment of such plaque may reduce future events. In this regard, the availability of a new intracoronary imaging technique is much appropriate. However, it remains still to be determined which factors should be taken into account when we choose between NIRS-IVUS and OCT in case a TCFA has to be identified. A user-friendly console, costs and clinical data will probably make the difference.