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Imaging

Combining IVUS and NIRS improves accuracy of fibroatheroma detection

Sudden cardiac death and myocardial infarction are often caused by rupture of a lipid-rich fibroatheroma. Intravascular ultrasonography (IVUS) has been used extensively to detect and characterize unstable plaques. In the past four years, the role of intracoronary near-infrared spectroscopy (NIRS) to identify lipidic plaque has also been validated. Combining IVUS and NIRS in a single catheter allows both modalities to be acquired simultaneously. In a study published in JACC: Cardiovascular Imaging, Kang and colleagues sought to determine the accuracy of IVUS and NIRS in detecting histological fibroatheromas, and the benefit of combining NIRS and IVUS.

Greyscale IVUS and NIRS images were acquired using the same protocol. Superficial attenuated plaques measured using IVUS were defined as attenuation of deeper arterial structures that began closer to the lumen than to the adventitia. NIRS generates a chemogram—a digital colour-coded map of the location and intensity of lipid seen from the surface of the lumen, which is used to predict the probability of lipid-core plaque. A lipid-rich plaque can be identified by the presence of a yellow or tan block chemogram. After acquisition of IVUS and NIRS images, arterial segments were fixed in formalin and stained for histological analysis. Morphometric and quantitative assessments of the arc and size of the necrotic core were performed using an automatic computer-assisted technique.

Images obtained from IVUS and NIRS were compared with histopathology in 1,943 sections of 103 coronary arteries from 56 autopsied hearts. Both IVUS-superficial attenuation and NIRS-detected, lipid-rich plaques (NIRS-LRP) had a similarly high specificity of 96% and 94%, respectively, for the prediction of a histological fibroatheroma. However, IVUS-superficial attenuation showed poor sensitivity compared with NIRS-LRP (36% versus 47%; P = 0.001), and reduced accuracy for the detection of fibroatheromas at the minimal lumen site.

One of the most important findings from this study was that the accuracy of predicting a plaque containing a necrotic or lipid core was superior when both NIRS and IVUS were combined. When histopathological sections showed either IVUS-attenuation or NIRS-LRP, the sensitivity for fibroatheroma prediction was more accurate than with IVUS-attenuation alone (63% versus 36%; P <0.001) or NIRS-LRP alone (63% versus 47%; P <0.001). Furthermore, the positive predictive value improved in sections that showed both IVUS-attenuation and NIRS-LRP, compared with IVUS-attenuation alone (84% versus 66%; P <0.001) or NIRS-LRP alone (84% versus 65%; P <0.001).

The investigators explain that these findings “demonstrate the complementary use of both sound (IVUS) and light (NIRS) to characterize plaques ... the two are now available in a single catheter as the first combined intravascular imaging device.” They conclude that “combining IVUS and NIRS overcame some of the limitations of each technique and was more accurate than either IVUS or NIRS alone.”

Credit: GraficallyMinded/Alamy

In a separate study published in JACC: Cardiovascular Interventions, Madder and colleagues describe the results of the first-in-man study using NIRS in carotid arteries to detect and characterize lipid-core plaques. The investigators successfully identified large lipid-core plaques in two patients with severe carotid stenosis, which dramatically reduced after stenting. The researchers emphasize the need for future studies to “determine whether NIRS can predict procedural complications during carotid stenting”.

References

  1. Kang, S.-J. et al. Combined IVUS and NIRS detection of fibroatheromas: histopathological validation in human coronary arteries. JACC Cardiovasc. Imaging 10.1016/j.jcmg.2014.09.021

  2. Madder, R. D. et al. First-in-man use of intravascular near-infrared spectroscopy in the carotid arteries to characterize atherosclerotic plaque prior to carotid stenting. JACC Cardiovasc. Interv. 10.1016/j.jcin.2013.11.029

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Huynh, K. Combining IVUS and NIRS improves accuracy of fibroatheroma detection. Nat Rev Cardiol 12, 130 (2015). https://doi.org/10.1038/nrcardio.2015.3

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  • DOI: https://doi.org/10.1038/nrcardio.2015.3

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