Doing More With Less in Coronary Intervention

Corresponding Author

Functional and intravascular imaging assessments offer distinct yet complementary perspectives in coronary intervention, integrating physiological and anatomical information to guide clinical decision-making. Functional metrics, such as fractional flow reserve (FFR), are pivotal in determining “whether intervention is necessary,” whereas morphologic assessments via intravascular ultrasound (IVUS) or optical coherence tomography (OCT) guide “how to optimize the intervention” and identify vulnerable plaques. Although functional assessments evaluate ischemia to reduce stent implantation rates, they remain unable to characterize plaque morphology—a critical gap addressed by intravascular imaging. Intravascular imaging provides high-resolution images, enabling precise quantification of lumen area and plaque morphology (including fibrous cap thickness, lipid core, and calcification). This allows for the identification of high-risk features, such as high plaque burden and thin-cap fibroatheroma, which are pivotal for predicting long-term adverse events.^1,2 Such morphologic insights into vulnerable plaques remain beyond the scope of current functional assessments.

However, the conventional sequential use of separate pressure wires and imaging catheters significantly prolongs procedural duration and increases healthcare costs. This operational burden often discourages the routine combined application of both modalities, even in complex cases where comprehensive data are most needed. Interventional cardiologists thus face a dilemma: They aim to minimize intravascular instrumentation to enhance efficiency while simultaneously striving to acquire both functional and anatomical insights to ensure optimal patient outcomes. Therefore, the development and selection of efficient, integrated diagnostic strategies that can seamlessly provide both functional and anatomical information remain a critical challenge and a key opportunity for improving the management of complex coronary lesions. In this issue of JACC: Asia, Liu et al³ report the results of the FEATURE study (NCT05694065), a single-center prospective evaluation of the diagnostic accuracy of artificial intelligence (AI)–enhanced ultrasonic flow ratio (UFR) for assessing the functional significance of coronary stenosis in the catheterization laboratory. Consecutive patients with suspected ischemia and at least 1 de novo lesion showing 50% to 80% diameter stenosis and a reference vessel diameter of ≥2.5 mm were prospectively enrolled. UFR achieved a diagnostic accuracy of 94% (95% CI: 88%-97%), which was significantly higher than the prespecified target of 78% (P < 0.001). It demonstrated excellent diagnostic performance, with 88% sensitivity (95% CI: 75%-96%), 97% specificity (95% CI: 90%-99%), 93% positive predictive value (95% CI: 81%-97%), and 94% negative predictive value (95% CI: 88%-97%). Upgrades to the AI algorithm reduced the need for manual correction from 76.3% to 15.3%, with an average processing time of <3 minutes. Despite this residual operator dependence, the fully automated computation achieved a robust area under the curve of 0.89 (95% CI: 0.83-0.94). The emergence of UFR enables IVUS-guided strategies to retain their morphologic assessment while compensating for the lack of physiological evaluation. Moreover, it reduces procedural complexity and costs by eliminating the need for pressure wires and pharmacologically induced hyperemia. Therefore, the combination of IVUS-derived anatomical information and UFR-based functional assessment enables operators to tailor optimal interventional strategies for coronary lesions, thereby enhancing clinical outcomes. In this single-center prospective study, UFR demonstrated robust diagnostic performance, including favorable discriminative ability in the gray zone (FFR: 0.75-0.80), where it correctly classified 16 of 20 lesions. However, the limited number of FFR-positive (n = 43, 32.8%) and gray-zone (n = 20, 15.3%) cases limits the applicability of the study findings. Furthermore, the single-center design restricts external validity, particularly because UFR’s diagnostic accuracy is fundamentally dependent on high-quality IVUS images. Variations in operator proficiency and equipment across different institutions can significantly affect image quality, a heterogeneity not captured in this study. Therefore, multicenter validation in larger cohorts is essential to confirm UFR’s reliability.

Given its robust diagnostic performance, the application of UFR in complex coronary anatomies could be further explored. The most common application of IVUS in the catheterization laboratory is to guide percutaneous coronary intervention (PCI) and optimize the intervention for complex lesions, including left main, diffuse long, chronic total occlusion, and severely calcified lesions, by providing precise anatomical information. Landmark studies such as IVUS-XPL, ULTIMATE, and RENOVATE-COMPLEX-PCI have demonstrated that IVUS guidance offers significant advantages over angiography-guided PCI in the management of various complex coronary lesions by optimizing interventional strategies and improving patient outcomes.4, 5, 6 The clinical benefits of intravascular imaging in complex lesions extend beyond the identification of high-risk characteristics to providing critical decision support, such as correcting stent underexpansion. The RENOVATE-COMPLEX-PCI study demonstrated that the use of intravascular imaging led to more frequent adjunctive postdilation with noncompliant balloons. Consequently, the mean minimum lumen diameter after PCI was significantly larger in the intravascular imaging group (2.8 ± 0.5 mm) than in the angiography-guided group (2.7 ± 0.5 mm).⁶ Liu et al³ excluded left main stenosis ≥50%, chronic total occlusion, and segments with severe tortuosity or angulation based on angiographic criteria. This exclusion is understandable given the study’s focus on validating the pre-PCI diagnostic performance of UFR. However, given that the primary clinical value of IVUS lies in managing such complex lesions and recognizing the importance of postprocedural assessment for evaluating efficacy and prognosis, extending future research to these challenging anatomical scenarios would be highly valuable. We look forward to future studies exploring the combined application of UFR and IVUS in postprocedural assessment. It would be particularly insightful to determine whether this dual anatomical and functional guidance strategy provides additive value and yields clinical outcomes superior to those achieved by either modality alone in the management of complex lesions.

Advances in computational fluid dynamics and the widespread adoption of AI are accelerating the integration of intravascular imaging with computational coronary physiology. Growing evidence underscores the clinical value of integrating intravascular imaging with computational coronary physiology. For instance, a retrospective study demonstrated that combining post-PCI optical coherence tomography with quantitative flow ratio significantly enhances risk stratification in patients with acute coronary syndrome.⁷ Complementing this, a post hoc analysis of the FLAVOUR study recommended integrating angiography-derived fractional flow reserve with plaque morphologic assessment to improve outcomes in patients undergoing IVUS-guided deferred treatment.⁸ Collectively, these findings advocate for integrating computational coronary physiology with anatomical imaging to optimize PCI decision-making. Currently, several prospective randomized controlled trials, including the FLAVOUR III study (NCT06218485), are underway to further validate these integrated strategies. Moreover, the emergence of novel technologies such as UFR promises to expand the tool kit for precision coronary intervention, offering new avenues for comprehensive multimodal assessments.

Funding Support and Author Disclosures

The authors have reported that they have no relationships relevant to the contents of this paper to disclose.