Article ID: CJ-25-0068
Background: Intravascular lithotripsy (IVL) is currently recommended for heavily calcified coronary lesions with an optical coherence tomography (OCT)- or intravascular ultrasound (IVUS)-based calcium score of 3 or 4.
Methods and Results: We retrospectively assessed both calcium scores for the same lesions, which had a heavily calcified coronary lesion requiring plaque modification. Among 52 lesions, the mean OCT-based calcium score was 3.96, whereas the mean IVUS-based calcium score was 2.15 (P<0.001).
Conclusions: This comparative study revealed a significant discrepancy between IVUS- and OCT-based calcium scores in heavily calcified coronary lesions, which may influence treatment strategies, including use of IVL.
To evaluate the severity of coronary calcium using intravascular imaging, 2 different scoring methods are used: optical coherence tomography (OCT)-based or intravascular ultrasound (IVUS)-based calcium scoring system (Supplementary Table).1,2 In both scoring systems, each calcium score correlates with stent underexpansion, and a lesion scoring 4 points (full point) is recommended for plaque modification such as orbital atherectomy (OA) or rotational atherectomy (RA). Therefore, the calcium score evaluated by either scoring system is important as the basis for the percutaneous coronary intervention (PCI) strategy for heavily calcified coronary lesions. Because the criteria for scoring differ between these systems, there could also be a diagnostic discrepancy between them, but this has not been thoroughly established.
In recent years, intravascular lithotripsy (IVL), which is a mounted emitter on the shaft of a conventional PCI balloon and can disrupt coronary calcium by diffusive circumferential pulsatile mechanical energy, is recommended for plaque modification before stenting in heavily calcified lesions.3–6 Because this simple balloon-based system has less crossability, it is mainly used for lesions that are considered as crossable by balloon or intravascular imaging catheter. Based on this, an Expert Consensus Document from the Japanese Association of Cardiovascular Intervention and Therapeutics (CVIT) suggested that a lesion with a score of ≥3 on either scoring system be considered a “severe calcified lesion” and an appropriate indication for IVL.7 However, because the method of calcium scoring is completely different between scoring systems, possible diagnostic discrepancy currently leads to some confusion among interventionalists. In this study, therefore, we compared the OCT- and IVUS-based calcium scores and any diagnostic discrepancies when evaluating heavily calcified lesions with these scoring systems.
From our single-center registry data, cases of PCI using OA, RA, and/or IVL for angiographically severe calcified coronary lesions were enrolled, and then we extracted cases of patients who underwent both OCT and IVUS imaging to evaluate coronary calcium and the efficacy of plaque modification before and/or after OA, RA, and IVL. All PCI strategies including plaque modification were essentially based on the OCT findings and stent optimization was performed using standard methods.7–10 The study protocol was based on the code of the Ethics Committee of Iwate Medical University (MH2023-101) and implemented in accordance with the Declaration of Helsinki. Additionally, it was registered with the UMIN Clinical Trials Registry (UMIN000056425). Although comprehensive informed consent was obtained from each patient at the time of admission, additional informed consent for this study was obtained through an opt-out format on the website (https://iwate-heart.jp/iwh/wp-content/uploads/2025/01/0c84864fe3fcf77be9c8155b773cc9e2.pdf).
Intravascular Imaging and Calcium ScoringPatients underwent both intravascular imaging modalities before and after the procedure, if the imaging catheter could pass the culprit lesion. For the comparison between calcium scores, we used the pre-PCI OCT and IVUS images. Either the ILUMIEN OPTISTM OCT system with a Dragonfly JPTM/Dragonfly OPTISTM imaging catheter (Abbott Vascular) or the LunawaveTM optical frequency domain imaging (OFDI) System with the FastViewTM Imaging Catheter (Terumo Corporation) was used for OCT image acquisition, For IVUS image acquisition, either the VisicubeTM 60 MHz IVUS system with the AltaViewTM imaging catheter (Terumo Corporation) or the iLabTM 60 MHz IVUS system with the OptiCross HDTM IVUS catheter (Boston Scientific Corporation) was used. In cases without pre-PCI intravascular images, the images from the first intravascular imaging undergone after ballooning or RA were used for the pre-PCI calcium scoring. Two independent reviewers (W.S. and M.I.) analyzed all images using an off-line viewer, and evaluated coronary calcium based on the previously published method.11,12 In the case of ambiguous findings, the final diagnosis was determined by consensus. The OCT-based calcium scoring system was based on the following criteria: maximum calcium angle >180°=2 points, maximum calcium thickness >0.5 mm=1 point, calcium length >5 mm=1 point.1 For the IVUS-based calcium scoring, 1 point is given for each criterion: superficial calcium angle >270° with >5.0 mm; 360° of superficial calcium; calcified nodule; vessel diameter <3.5 mm at the calcified lesion.2 In both scoring system, 3 or 4 points is considered as a “severe calcified lesion”.
Statistical AnalysisBaseline characteristics, as well as OCT and IVUS findings, are presented as absolute numbers and percentages or as median values with interquartile range (25th and 75th percentiles). Comparisons between the OCT- and IVUS-based calcium scores were performed using the Wilcoxon signed-rank test, with a P value <0.05 considered statistically significant. Statistical analyses were performed using SPSS version 21 (SPSS Inc., Chicago, IL, USA).
From March 2019 to September 2024, a total of 2,187 PCI procedures were performed at Iwate Medical University Hospital. Of them, 52 lesions from 49 patients had both imaging modalities performed during OA, RA, and/or IVL procedures. Baseline patient, lesion and procedural characteristics are shown in Table 1. Most of the patients underwent PCI because of chronic coronary syndrome, and pre-PCI images without ballooning or RA were obtained for two-thirds of the lesions. Table 2 demonstrates the detailed OCT and IVUS findings. Almost all lesions had >180° of coronary calcium, and 53.8% had ≥1 calcified nodule (CN) in the lesion. In terms of the calcium scores (Figure 1), 51 cases (98.1%) scored 4 points using the OCT assessment (with 1 case scoring 2 points), while IVUS-based calcium scores of 3 or 4 points were observed in only 21 lesions (40.1%), most of which scored 3 points. This discrepancy was also observed in lesions both with and without pre-PCI images (Supplementary Figure 1). The mean OCT- and IVUS-based calcium scores were 3.96 and 2.15, respectively, showing a statistically significant difference (Wilcoxon signed-rank test: P<0.001). In the lesions without CNs, although all lesions scored 4 points by the OCT-based scoring system, while the IVUS-based scoring system rarely diagnosed it as a “severe” (3 or 4 points) calcified lesion (OCT: 100%, IVUS: 12.5%) (Figure 2). This diagnostic discrepancy between scoring systems for “severe” calcified lesions was reduced, but remained for lesions with CNs (OCT: 96.4%, IVUS: 64.3%).
Baseline Patient, Lesion and Procedural Characteristics
| Patient characteristics | n=49 |
| Age, years | 73 (67–80) |
| Male | 37 (75.5) |
| Diabetes mellitus | 21 (42.9) |
| Hypertension | 47 (95.9) |
| Hyperlipidemia | 42 (85.7) |
| Current smoking | 6 (12.2) |
| Hemodialysis | 6 (12.2) |
| Prior PCI | 24 (49.0) |
| Prior CABG | 2 (4.1) |
| ACS / CCS | 6 (12.2) / 43 (87.8) |
| Lesion and procedural characteristics | n=52 |
| Target vessel | |
| LAD | 35 (67.3) |
| LCX | 4 (7.7) |
| RCA | 13 (25.0) |
| Minimum lumen diameter, mm | 0.56 (0.37–0.74) |
| Diameter stenosis, % | 77.6 (64.3–83.6) |
| AHA/ACC type B2/C lesion | 52 (100) |
| Bifurcation | 13 (25.0) |
| Pre-PCI intravascular imaging | 35 (67.3) |
| Cutting/scoring balloon usage | 33 (63.5) |
| Rotational atherectomy usage | 17 (32.7) |
| Orbital atherectomy usage | 17 (32.7) |
| Intravascular lithotripsy usage | 24 (46.2) |
ACC, American College of Cardiology; ACS, acute coronary syndrome; AHA, American Heart Association; CABG, coronary artery bypass graft; CCS, chronic coronary syndrome; LAD, left anterior descending coronary artery; LCX, left circumflex coronary artery; PCI, percutaneous coronary intervention; RCA, right coronary artery.
OCT and IVUS Findings
| OCT/OFDI (n=52) | IVUS (n=52) | |
|---|---|---|
| Maximum calcium angle | ||
| >180° | 51 (98.1) | 51 (98.1) |
| >270° | 45 (86.5) | 44 (84.6) |
| =360° | 28 (53.8) | 32 (61.5) |
| Calcium length, mm | 42.5 (35.0–48.6) | 45.7 (32.3–52.8) |
| Maximum calcium thickness, mm | 1.3 (1.1–1.6) | N/A |
| Presence of calcified nodule | 28 (53.8) | 28 (53.8) |
| Vessel diameter, mm | 4.2 (3.7–4.5) | 4.0 (3.7–4.4) |
IVUS, intravascular ultrasound; N/A, not available; OCT, optical coherence tomography; OFDI, optical frequency domain imaging.
Comparison of OCT-based and IVUS-based calcium scores for each case. (Upper row) OCT-based calcium scores and (Lower row) IVUS-based calcium scores for the same case. Each item is color-coded. The mean calcium score in the OCT-based and IVUS-based calcium scoring systems was 3.96 and 2.15, respectively (P<0.001). Ca, calcium; CN, calcified nodule; IVUS, intravascular ultrasound; OCT, optical coherence tomography.
Diagnostic rate of severe calcified lesions (score of 3 or 4 points) as assessed by the OCT- and IVUS-based calcium scoring systems. Ca, calcium; CN, calcified nodule; IVUS, intravascular ultrasound; OCT, optical coherence tomography.
The results of this comparative study suggest that the IVUS-based calcium score underestimates the severity of coronary artery calcium compared with OCT-based calcium scores, especially in cases without CNs. Because there are no criteria common to both scoring systems, a difference in calcium scores between the scoring systems would be expected. However, when a score of 3 or 4 points is considered as a “severe calcified lesion”, this diagnosis was very different between scoring system. Focusing on the criterion for calcium angle, there was a difference in weighting: >180° of calcium is scored 1 point by the OCT-based scoring system, whereas >270° of calcium is scored 1 point by the IVUS-based calcium scoring system. Thus, for a lesion with 180–270° of calcium, the IVUS-base calcium scoring system definitely underestimates the severity of coronary calcium compared with the OCT-based scoring system. In addition, the IVUS-based calcium scoring was not weighting lesions with >3.5 mm vessel diameter. According to a large-scale registry study that included patients undergoing PCI, 23% of the registered lesions were large (3.5–5.0 mm vessel diameter).13 If this prevalence was common in calcified coronary lesions, approximately one-fifth of lesions do not meet the criterion of “vessel diameter <3.5 mm at the calcified lesion”. Based on these observations, underdiagnosis by the IVUS-based calcium score is predictable and unavoidable as of now.
Another reason for this diagnostic discrepancy is probably the difference in the severity of coronary calcium between the subjects in the 2 original studies. The study assessing the OCT-based coronary calcium scoring system included general subjects including non- to severely calcified lesions.1 Among the highest (4 points) scored group in this OCT study, the mean calcium angle was 279° and the incidence of stent underexpansion was only 30%. However, the study assessing the IVUS-based calcium scoring system included only heavily calcified lesion with >270° of calcium, and the incidence of stent underexpansion was 30% of all the subjects.2 Considering the similarity in the incidence of stent underexpansion between the 2 groups, it is likely that most of the lesions included in the study assessing the IVUS-based calcium scoring system would have been scored 4 points by the OCT-based system. This selection bias may be associated with the underdiagnosis by the IVUS-based calcium scoring system compared with the OCT-based calcium scoring system.
On the other hand, the findings of our study suggest that the OCT-based calcium score might somewhat overestimate the severity of coronary calcification compared with the IVUS-based score. In the original validation studies of each scoring system, the IVUS-based study recommended plaque modification for lesions with a calcium score ≥2,1 whereas only lesions with a calcium score of 4 were recommended for such intervention in the OCT-based study.2 Furthermore, a recent single-center registry study assessing OCT-guided IVL for calcified lesion with an OCT-based calcium score of 4 indicated that additional factors not included in the original calcium scoring system (i.e., the presence of superficial calcium, smaller minimum calcium thickness, and the absence of nodular calcification) play important role in facilitating calcium fracture and optimal stent expansion.6 To more accurately assess the severity of coronary calcification and to guide the appropriate use of atherectomy devices and IVL, further studies are needed to develop a unified calcium scoring system, regardless of imaging modality.
In Japan, the indication of IVL for heavily calcified lesions is based on the Expert Consensus documents from CVIT.7 If we strictly follow this, IVL is less likely to be indicated when IVUS is used for intravascular imaging than when OCT is used. This underestimation may lead to a difficult procedure for heavily calcified lesions. For example, if the non-CN coronary lesion in a large (>3.5 mm) vessel has circumferential (360°) thick (>1.0 mm) and long diffuse (>5.0 mm) calcium (Supplementary Figure 2) that is potentially unexpandable by conventional PCI using conventional balloon angioplasty and stent, the OCT-based calcium score could be 4 points, indicating a high risk of stent underexpansion and appropriate candidate for a 3.5–4.0 mm IVL catheter. However, when assessing the same lesion by IVUS, the calcium score may be just 2 points, indicating conventional PCI. Therefore, for large coronary vessels without CNs, the IVUS-based calcium scoring system is more likely to be underdiagnose, which potentially leads to stent underexpansion. Additionally, because clinical outcomes after stenting in CN lesions is very poor,14 it is still unclear whether stenting following IVL is an appropriate treatment for a CN lesion with 3 or 4 points on the IVUS-based calcium score.
Study LimitationsFirst, the sample size was relatively small due to being a single-center retrospective study. As mentioned previously, further study including large-scale and multicenter registries is needed to determine the appropriate assessment for severity of coronary calcium. Second, because we performed dual modality imaging only for patients undergoing plaque modification, there could be selection bias. Thus, it remains unclear whether our results can be standardized for all patients with angiographically moderate or severe calcification. Third, because this was an observational comparative study, it remains unclear which calcium score more accurately predicts stent underexpansion. To confirm this issue, a randomized control trial to compare OCT-based and IVUS-based calcium scoring systems for guidance of PCI should be conducted in patients with heavily calcified lesions.
For angiographically severe calcified lesions requiring plaque modification, a significant discrepancy in the assessed severity of coronary artery calcium was observed between the IVUS- and OCT-based calcium scores, especially in cases without CNs. To avoid this diagnostic discrepancy, both calcium scoring system should be coordinated for a fairer evaluation of severe coronary calcification.
The authors thank Kanako Omiya, Yumiko Okuyama, and Kayoko Fujiwara for their editorial assistance.
M.I. has received lecture honoraria from Terumo Corporation. Y. Morino has received unrestrictive research funding from Abbott Medical Japan and Boston Scientific Japan, and lecture honoraria from Abbott Medical Japan, Boston Scientific Japan and Terumo Corporation. None of the remaining authors declare any conflicts of interest. Y.M. is a member of Circulation Journal’s Editorial Team.
This study group did not receive any funding support; however, product support (IVUS catheters) was provided by Terumo Corporation.
Approved by the Ethics Review Board of Iwate Medical University (IRB Committee reference no. MH2023-101).
The deidentified participant data will not be shared.
Please find supplementary file(s);
https://doi.org/10.1253/circj.CJ-25-0068
