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Japan is uniquely positioned in contemporary percutaneous coronary intervention (PCI); few countries have integrated intravascular imaging (IVI) into routine practice as consistently – or as broadly across clinical presentations – as Japan. The “near-default” use of intravascular ultrasound (IVUS) and the growing penetration of optical coherence tomography (OCT) create an opportunity to study imaging guidance when it is woven into routine PCI decision-making.
In this issue of EuroIntervention, Takegawa and colleagues used the National Database of Health Insurance Claims and Specific Health Checkups of Japan – an administrative dataset with anonymised patient-level information on diagnoses, procedures, prescriptions, and medical devices across inpatient and outpatient care – to evaluate the association between IVI-guided PCI and outcomes in patients presenting with acute coronary syndrome (ACS), approximately two-thirds of whom had acute myocardial infarction (AMI)1. A patient-matching approach enabled the long-term follow-up of more than 90% of patients.
Between April 2014 and March 2021, 492,303 ACS patients underwent their first PCI. Over that period, OCT-guided PCI increased from 4.7% to 6.9%, IVUS-guided PCI increased from 77.0% to 87.9%, and angiography-guided PCI alone decreased from 17.0% to 4.8%. Median follow-up was 1,113 days. The primary outcome – ACS recurrence after discharge – was lower with IVI-guided PCI compared with angiography-guided PCI (hazard ratio [HR] 0.76, 95% confidence interval [CI]: 0.70-0.82; p<0.001). A key secondary outcome – the composite of all-cause death and ACS recurrence – was also lower with IVI guidance (HR 0.85, 95% CI: 0.82-0.89; p<0.001). These findings were consistent when IVUS and OCT guidance were analysed separately. Because Japan represents an environment in which the adoption of IVI is high, these data raise an immediate question of generalisability to regions where IVI is used selectively.
A useful contrast comes from the British Cardiovascular Intervention Society (BCIS) registry. Among 598,921 patients undergoing PCI for ACS (60% non-ST-segment elevation myocardial infarction [NSTEMI] and 40% ST-segment elevation myocardial infarction [STEMI]); from 2006 to 2019, 41,716 (7.0%) procedures used IVI, increasing from 1.4% in 2006 to 13.5% in 20192. Within the IVI group, 5.6% used IVUS and 1.4% used OCT. Compared with angiography-guided PCI, IVI use was associated with lower odds of in-hospital mortality (1.7% vs 2.4%; p<0.001) and lower odds of in-hospital major adverse cardiovascular and cerebrovascular events (3.3% vs 3.8%; p<0.001), particularly in patients undergoing left main and left main/left anterior descending PCI. (Of note, a presentation of the most recent BCIS data3 reported that IVI use in ACS patients increased to 28% in 2025.)
In Japan, angiography guidance alone was more common in elderly patients, females, patients with comorbidities, and AMI patients. In the United Kingdom, IVI guidance was used more commonly in younger patients; in patients with left ventricular dysfunction, prior AMI, prior PCI, comorbidities (diabetes mellitus, hypertension, kidney disease, peripheral vascular disease, and cerebrovascular disease); and in patients with in-stent restenosis and increased disease complexity. In other words, “who gets IVI” reflects a local mix of reimbursement, training culture, workflow, and perceived incremental value, thus making patient selection and confounding central interpretive issues important in registry comparisons. Importantly, an additional layer of confounding is physician-level variability; the differences in operator preference, experience, threshold to image, and image interpretation/optimisation standards are difficult to measure – and even harder to fully adjust for – in administrative and procedural registries.
One practical question in ACS is not whether IVUS or OCT guidance is “better”, but which modality best answers the clinical question in front of the operator and in which patients is IVI most likely to change management. In the OPINION ACS randomised trial and in the Korean Acute Myocardial Infarction Registry (KAMIR), there was no significant difference in clinical outcomes between IVUS and OCT guidance45. The one subgroup in which IVI guidance did not improve outcomes was cardiogenic shock6. OCT offers higher axial resolution, enabling detailed assessment of fibrous cap disruption and superficial plaque erosion – at the cost of additional contrast and potential limitations in heavy thrombus. IVUS provides deeper penetration, assessment of vessel size and remodelling, with fewer contrast constraints – at the cost of lower resolution for some superficial features. In ACS, the modality should match the clinical problem.
ACS registries rarely capture ACS mechanisms – precisely where IVI may deliver its most distinctive clinical value. A thin-cap fibroatheroma is present in 95% of cases of plaque rupture, and plaque rupture accounts for approximately half of ACS events. Fibrous lesions may cause acute thrombosis due to plaque erosion, accounting for 30-40% of ACS events, a proportion that appears to be increasing in the context of contemporary preventive therapy, mirroring an increasing prevalence of NSTEMI versus STEMI; and 50% of NSTEMI have either no angiographic culprit or multiple potential culprits7. Eruptive calcified nodules cause 5% of acute events, a prevalence that may also be increasing as the patient population ages. The mechanism matters because it plausibly both modifies the need for stenting and adds prognostic information. Eruptive calcified nodules have the highest rate of post-PCI events, while plaque erosion has the lowest rate of post-PCI events8.
This principle was illustrated by the OCT-based EROSION studies. In the proof-of-concept EROSION I study, a strategy of a purely antithrombotic treatment without PCI was associated with a major adverse cardiovascular events (MACE) rate of 7.5% at 1 year9. This was followed by the EROSION III multicentre randomised trial in which 246 STEMI patients were randomised to OCT or angiography guidance. In the OCT-guided arm, two-thirds of patients had underlying plaque rupture, whilst one-quarter had plaque erosion10. OCT guidance was associated with less stent implantation (43.8% vs 58.8%; p=0.024) and equal MACE at 1 year (1.8% vs 2.6%; p=0.67) compared with an angiography-guided PCI. ACS can also be caused by spontaneous coronary dissection or present as non-obstructive disease (myocardial infarction with non-obstructive coronary artery disease [MINOCA]). In MINOCA, outcomes are worse if the non-obstructive disease has an underlying atherosclerotic morphology11. Angiography alone often cannot reliably define the culprit mechanism or even the culprit lesion, which can result in inappropriate PCI in both MINOCA patients and NSTEMI patients.
Even when thoughtfully designed, registries cannot account for the impact of these morphological differences. Randomised trials, therefore, remain crucial. The ACS-IVUS trial in China randomised 3,505 ACS patients (roughly one-third STEMI, one-third NSTEMI, and one-third unstable angina) to IVUS-guided PCI (n=1,753) versus angiography-guided PCI (n=1,752) between 2019 and 202212. The primary endpoint – target vessel failure (TVF; cardiac death, target vessel myocardial infarction [MI], or clinically driven target vessel revascularisation) at 1 year – occurred in 4.0% in the IVUS group and 7.3% in the angiography group (HR 0.55, 95% CI: 0.41-0.74; p=0.0001), driven by reductions in target vessel MI or target vessel revascularisation across multiple subgroups (ACS types, diabetes status, and biomarker positivity). The ACS-IVUS investigators subsequently developed a TVF-ACS risk score. Approximately 25% of patients were considered high risk, and these patients exhibited a higher 1-year rate of TVF compared with low-risk patients (19.8% vs 5.7%; HR 3.81, 95% CI: 2.06-7.02; p=0.00002). Among 3,486 randomised patients, IVUS guidance compared with angiography guidance reduced 1-year TVF in high-risk patients (6.9% vs 17.6%; HR 0.38, 95% CI: 0.24-0.59) but had a lesser effect in low-risk patients (3.2% vs 4.3%; HR 0.75, 95% CI: 0.51-1.11)13.
No matter how you look at the problem, IVI guidance should be a central tool in treating patients who present with ACS. It begins by defining culprit morphology and lesion complexity, continues with triage to PCI versus medical therapy, and ends with stent optimisation when PCI is appropriate. The incremental value of imaging in ACS is likely greatest where angiography is most likely to miss the mechanism or underoptimise the result.
Conflict of interest statement
G.S. Mintz reports consulting fees and honoraria from Panovision, SpectraWAVE, Boston Scientific, Philips, and Abbott. C. Collet reports institutional grants from Abbott, Boston Scientific, HeartFlow Inc, Insight Lifetech, Shockwave Medical, GE HealthCare, CryoTherapeutics, and Pie Medical Imaging; direct payment for IP license from Coroventis Research; consulting fees from Abbott, AngioInsight, CryoTherapeutics, Shockwave Medical, GE HealthCare, and Medyria; honoraria from Abbott, Boston Scientific, HeartFlow Inc, Insight Lifetech, Shockwave Medical, GE HealthCare, CryoTherapeutics, CathWorks (Medtronic), and Medyria; support for attending meetings from Shockwave Medical, Abbott, Insight Lifetech, GE HealthCare, and Medyria; patents (US12190504B2, EP3956904A1, US20210173603A1, WO2024038156A1); and stock/stock options with Medyria, Xenter, CathFlow, and Powerful Medical.
