Cracking (The Code of) Coronary Artery Calcification Towin the Last Battle of Percutaneous Coronary Intervention

Still in the Middle of a Rocky Road

Norihiro Kogame; Patrick W. Serruys; Yoshinobu Onuma


Eur Heart J. 2020;41(6):797-800. 

In This Article

Is Angiography Sufficient to Diagnose Calcification and Its Distribution? What Would be the Ideal Modality of Imaging?

In a clinical setting—at variance with radiography used in this pathological study—angiography is often limited in the detection of calcification, as well as in the ability to assess its distribution. This difference stems from the setting of radiation and resolution. The radiograph is performed after explant of the coronary artery without the surrounding structures (e.g. bone) and organs (e.g. lung), so that it has a high resolution of ≤80 μm with a kilovoltage peak of 40 kVp. In clinically invasive angiography, the resolution is 200–300 μm, even with a relatively high kilovoltage peak of 80 kVp.[11,12] Historically, the presence of moderate or severe calcified lesions was detected by invasive coronary angiography according to the following definition: moderate, radiopaque densities noted only during the cardiac cycle and typically involving only one side of the vascular wall; severe, radiopaque densities noted without cardiac motion prior to contrast injection and generally involving both sides of the arterial wall.[4,6,7] Although this angiographic definition is still used in a recently conducted trial,[13] it is well known that the sensitivity of angiography to detect calcified plaque is suboptimal as is the (inter- and intra-) observer reproducibility of the assessor.[14]

Other imaging modalities such as multi-slice computed tomography (MSCT), IVUS, and OCT are clinically available for detection, quantification, and distribution of CAC (Take home figure). MSCT is able to detect calcium and its distribution, but the quantification of calcification is hampered by the blooming artefact. IVUS is the most frequently used intravascular modality of imaging; however, calcified plaque fully backscatters the ultrasound signals (the so-called shadowing effect) so that the imaging modality does not allow quantification of plaque burden behind the leading edge of the superficial calcium.[14]

Take home figure.

Multimodality assessment of coronary artery calcification. Invasive coronary angiography and coronary computed tomography angiography have a prognostic value; however, they are insufficient in guiding percutaneous coronary intervention of calcified lesions due to the limited capability of assessing the depth and distribution of calcification in relation to the lumen. Intravascular imaging such as intravascular ultrasound (IVUS), IVUS virtual histology, and optical coherence tomography (OCT) may provide a more detailed description of calcified plaque and facilitate the operator's decision-making in selecting dedicated techniques of ablation and fragmentation of calcification (e.g. atherectomy or lithotripsy). Three-dimensional optical coherence tomography (3D-OCT) has the potential to provide imaging in a fashion similar to a radiograph (green: calcification). The combined use of IVUS and OCT will facilitate the detection of calcification and the assessment of its topographical distribution. Reproduced with permission from Zeng et al.,2 Nakazawa et al.,12 and Mori et al. 1 Ca++, calcium; CT, computed tomography; H&E, haematoxylin–eosin stain; NC, necrotic core; OCT, optical coherence tomography; PCI, percutaneous coronary intervention.

Since the tissue penetration of low-coherence light used for OCT is less attenuated by the calcified matrix, the back of the calcified plaque becomes detectable, thereby OCT can visualize precisely the extent of calcium plaque (thickness, longitudinal length, deep or superficial, and arc) without the shadowing effect of calcium detected by ultrasound. An OCT-based study suggested that calcified lesions with a maximum angle >180°, maximum thickness >0.5 mm, and length >5 mm are at increased risk for stent underexpansion.[15] In addition, 3-D reconstruction of cross-sectional OCT images may display the calcium distribution and its topographic relationship with the stent strut in a fashion similar to radiographs (Take home figure). A novel catheter combining OCT and IVUS imaging may further enhance the diagnostic capability to detect calcification with precise information on its extension in circumference and depth.[16]