Validation of Minimal Luminal Area Measured by Intravascular Ultrasound for Assessment of Functionally Significant Coronary Stenosis

Evolving Diagnostic and Management Advances in Coronary Heart Disease

Despite considerable improvement in diagnostic modalities and therapeutic options over the last few decades, the global burden of ischemic heart disease is steadily rising, remaining a major cause of death worldwide. Thus, new strategies are needed to lessen cardiovascular events. Researchers in different areas such as biotechnology and tissue engineering have developed novel therapeutic strategies such as stem cells, nanotechnology, and robotic surgery, among others (3D printing and drugs). In addition, advances in bioengineering have led to the emergence of new diagnostic and prognostic techniques, such as quantitative flow ratio (QFR), and biomarkers for atherosclerosis. In this review, we explore novel diagnostic invasive and noninvasive modalities that allow a more detailed characterization of coronary disease. We delve into new technological revascularization procedures and pharmacological agents that target several residual cardiovascular risks, including inflammatory, thrombotic, and metabolic pathways.

The assessment of intermediate coronary lesions using intracoronary imaging

Intermediate coronary artery stenosis, defined as visual angiographic stenosis severity of between 30-70%, is present in up to one quarter of patients undergoing coronary angiography. Patients with this particular lesion subset represent a distinct clinical challenge, with operators often uncertain on the need for revascularization. Although international guidelines appropriately recommend physiological pressure-based assessment of these lesions utilizing either fractional flow reserve (FFR) or quantitative flow ratio (QFR), there are specific clinical scenarios and lesion subsets where the use of such indices may not be reliable. Intravascular imaging, mainly utilizing intravascular ultrasound (IVUS) and optical coherence tomography (OCT) represents an alternate and at times complementary diagnostic modality for the evaluation of intermediate coronary stenoses. Studies have attempted to validate these specific imaging measures with physiological markers of lesion-specific ischaemia with varied results. Intravascular imaging however also provides additional benefits that include portrayal of plaque morphology, guidance on stent implantation and sizing and may portend improved clinical outcomes. Looking forward, research in computational fluid dynamics now seeks to integrate both lesion-based physiology and anatomical assessment using intravascular imaging. This review will discuss the rationale and indications for the use of intravascular imaging assessment of intermediate lesions, while highlighting the current limitations and benefits to this approach.

Ischemia-based Coronary Revascularization: Beyond Anatomy and Fractional Flow Reserve

Treatment strategies for patients with coronary artery disease (CAD) should be based on objective evidence of inducible ischemia in the subtended myocardium to improve clinical outcomes, symptoms, and cost-effectiveness. Fractional flow reserve (FFR) is the most verified index to-date for invasively evaluating lesion-specific myocardial ischemia. Favorable results from large clinical trials that applied FFR-guided percutaneous coronary intervention (PCI) prompted changes in coronary revascularization guidelines to emphasize the importance of this ischemia-based strategy using invasive coronary physiology. However, the frequency of functional evaluations is lacking in daily practice, and visual assessment still dominates treatment decisions in CAD patients. Despite recent efforts to integrate functional and anatomical assessments for coronary stenosis, there is considerable discordance between the 2 modalities, and the diagnostic accuracy of simple parameters obtained from current imaging tools is not satisfactory to determine functional significance. Although evidence that supports or justifies anatomy-guided PCI is more limited, and FFR-guided PCI is currently recommended, it is important to be aware of conditions and factors that influence FFR for accurate interpretation and application. In this article, we review the limitations of the current anatomy-derived evaluation of the functional significance of coronary stenosis, detail considerations for the clinical utility of FFR, and discuss the importance of an integrated physiologic approach to determine treatment strategies for CAD patients.

Comparison of Accuracy of One-Use Methods for Calculating Fractional Flow Reserve by Intravascular Optical Coherence Tomography to That Determined by the Pressure-Wire Method

Although the identification of the hemodynamic significance of coronary lesions becomes important for revascularization strategy, the potential role of 3-dimensional high-resolution intracoronary optical coherence tomography (OCT) for predicting functional significance of coronary lesions remains unclear. We assessed the diagnostic performance of 2 computational approaches for deriving fractional flow reserve (FFR) from intravascular OCT images. We developed 2 methods to derive FFR-OCT by AFD (FFR-OCT_AFD) and FFR-OCT by CFD (FFR-OCT_CFD). Among 217 eligible patients between 2011 and 2014, 104 were included for data analysis (9 for derivation, 95 for validation). Luminal geometries from 3-dimensional OCT were used for both FFR-OCT_AFD and FFR-OCT_CFD calculations. The analytical fluid dynamics method calculated FFR from the blood flow resistance estimated using Poiseuille's law. For computational fluid dynamics, we numerically solved the Navier-Stokes equation in a steady-state flow with the distal porous media model for the capillary vessels. We examined the diagnostic performance of FFR-OCT_AFD and FFR-OCT_CFD compared with the pressure-wire measured FFR. The accuracy, sensitivity, specificity, PPV, and NPV were 86%, 65%, 94%, 81%, and 88% for FFR-OCT_AFD and 86%, 73%, 91%, 76%, and 90% for FFR-OCT_CFD. The area under the curve of the receiver-operating characteristic curve was 0.88 for FFR-OCT_AFD and 0.86 for FFR-OCT_CFD. FFR-OCT_AFD and FFR-OCT_CFD showed a strong linear correlation with the measured FFR (r = 0.631; p <0.001, r = 0.655; p <0.001, respectively). FFR derived from high-resolution volumetric OCT images showed high diagnostic performance for the detection of coronary ischemia. In conclusion, OCT-derived FFR may be useful for guiding the management of coronary artery disease.

Impact of plaque characteristics on the degree of functional stenosis

Coronary CT angiography (CCTA) is mainly regarded as a gatekeeper for invasive coronary angiography, in face of its widely recognized value to noninvasively rule out significant coronary stenosis. Nevertheless, it is also increasingly recognized that this noninvasive modality can depict several atherosclerotic plaque features and quantify total coronary plaque burden. This opens a new field for cardiac CT, since these atherosclerotic features beyond stenosis severity have been correlated with the degree of functional significance, and are the focus of the present manuscript. Although recently acknowledged and documented in CCTA studies, the relation between plaque burden and functional significance has been previously described using several intracoronary imaging modalities, which are also reviewed in the manuscript, to help put in perspective the relation between anatomy and function in coronary artery disease.

[Clinical outcomes of intravascular ultrasound in guiding the treatment of non-left main intermediate coronary lesions for patients with acute coronary syndrome]

OBJECTIVE

To evaluate the long-term clinical outcomes of intravascular ultrasound(IVUS) in guiding the treatment of non-left main intermediate coronary lesions for patients of acute coronary syndrome (ACS).

METHODS

A total of 25 patients with intermediate coronary lesions(stenosis of 40%-70%) confirmed by coronary angiography were performed with IVUS. When MLA≥4 mm², we deferred the PCI treatment and performed optimal medical treatment (OMT). The patient were followed up for 12 month. The primary outcome was target vessel revascularization (TVR) and secondary outcome was major adverse cardiac events (MACEs).

RESULTS

A total of 25 lesions of 25 patients were examined by IVUS. 19(76%) lesions were attenuated plaque, 4(16%)were echo-lucent plaque, 2(8%) were calcified plaque. Most of the plaque (18/25, 72%) were eccentric. Positive remodeling was found in 20(80%) lesions and negative remodeling in 5(20%) lesions with meanremodeling index of 1.17=0.15. Thrombus was found in 1 case, accounting for 4%. The diameter stenosis, area stenosis, minimal lumen area and the reference diameter mea-sured by IVUS were larger than those measured by quantitative coronary angiography (all P<0.05). One patient with non-ST segment elevated myocardiac infarction was performed revascularization because MI attacked again, and 2 patients with Unstable angina were treated with OMT but they were still rehospitalization because of angina occurred repeatedly. The incidence of TVR was 4.00%, so as 16.00% of MACE.

CONCLUSION

IVUS can be used to guide the treatment of non-left main intermediate coronary lesions for patients of acute coronary syndrome.

Intracoronary optical coherence tomography: a review of clinical applications

Optical coherence tomography (OCT) is a light-based technology that provides very high spatial resolution images. OCT has been initially employed as a research tool to investigate plaque morphology and stent strut coverage. The introduction of frequency domain OCT allowing fast image acquisition during a prolonged contrast injection via the guiding catheter has made OCT applicable for guidance of coronary interventions. In this manuscript, the various applications of OCT are reviewed, from assessment of plaque vulnerability and severity to characteristics of unstable lesions and thrombus burden to stent optimization and evaluation of late results.

Clinical Outcomes in Patients with Intermediate Coronary Stenoses: MINIATURE Investigators (Korea MultIceNter TrIal on Long-Term Clinical Outcome According to the Plaque Burden and Treatment Strategy in Lesions with MinimUm Lumen ARea lEss Than 4 mm(2) Using Intravascular Ultrasound)

Background and Objectives

We evaluated the two-year clinical outcomes in patients with angiographically intermediate lesions according to the plaque burden and treatment strategy.

Subjects and Methods

We prospectively enrolled patients with angiographically intermediate lesions (diameter stenosis 30-70%) with an intravascular ultrasound (IVUS) minimum lumen area (MLA) <4 mm² with 50-70% plaque burden of 16 Korean percutaneous coronary intervention centers. Patients were divided into medical therapy group (n=85) and zotarolimus-eluting stent group (ZES; Resolute) group (n=74). We evaluated the incidences of two-year major adverse cardiovascular events (MACE).

Results

A two-year clinical follow-up was completed in 143 patients and MACE occurred in 12 patients. There were no significant differences in the incidences of death (1.3% vs. 3.0%, p=0.471), target vessel-related non-fatal myocardial infarction (0.0% vs. 0.0%, p=1.000) and target vessel revascularizations (7.8% vs. 4.5%, p=0.425) between medical and ZES groups. Independent predictors of two-year MACE included acute myocardial infarction {odds ratio (OR)=2.87; 95% confidence interval (CI) 1.43-6.12, p=0.014}, diabetes mellitus (OR=2.46; 95% CI 1.24-5.56, p=0.028) and non-statin therapy (OR=2.32; 95% CI 1.18-5.24, p=0.034).

Conclusion

Medical therapy shows comparable results with ZES, and myocardial infarction, diabetes mellitus and non-statin therapy were associated with the occurrence of two-year MACE in patients with intermediate lesion with IVUS MLA <4 mm² with 50-70% of plaque burden.

Clinical utility of intravascular imaging and physiology in coronary artery disease

Intravascular imaging and physiology techniques and technologies are moving beyond the framework of research to inform clinical decision making. Currently available technologies and techniques include fractional flow reserve; grayscale intravascular ultrasound (IVUS); IVUS radiofrequency tissue characterization; optical coherence tomography, the light analogue of IVUS; and near-infrared spectroscopy that detects lipid within the vessel wall and that has recently been combined with grayscale IVUS in a single catheter as the first combined imaging device. These tools can be used to answer questions that occur during daily practice, including: Is this stenosis significant? Where is the culprit lesion? Is this a vulnerable plaque? What is the likelihood of distal embolization or periprocedural myocardial infarction during stent implantation? How do I optimize acute stent results? Why did thrombosis or restenosis occur in this stent? One of the legacies of coronary angiography is to presume that one technique will answer all of these questions; however, that often has been proved inaccurate in contemporary practice.

Impact of Intravascular Ultrasound in Clinical Practice

Intravascular ultrasound (IVUS) has expanded our understanding of atherosclerotic plaque morphology, and provides an opportunity to guide cardiovascular interventions and evaluate results. Use of this technique requires understanding of ultrasound physics, catheter differences, skills in vessel, plaque and stent quantification and knowledge of artifacts and various physiologic and pathologic findings. Optimal cardiovascular interventions should result in absence of inflow or outflow obstruction, precise geographic landing, while attaining the largest feasible luminal gain without plaque protrusion, vessel dissection or perforation and, if deployed, with complete stent expansion and apposition to the vessel wall. IVUS is safe, cost efficient and effectively optimises cardiovascular interventions. In addition, IVUS improves outcomes when used to guide coronary interventions using bare metal stents (BMS) and drug eluting stents (DES). The role of IVUS in endovascular therapy is rapidly expanding. This review will focus on the impact of IVUS in clinical practice.

Clinical outcomes after intravascular ultrasound and fractional flow reserve assessment of intermediate coronary lesions. Propensity score matching of large cohorts from two institutions with a differential approach

AIMS

Assessment of intermediate coronary lesions can be done with fractional flow reserve (FFR) and intravascular ultrasound (IVUS). There are no randomised trials and only a small registry from one centre is available but this is subject to important bias. We sought to evaluate the clinical outcomes of an FFR strategy compared with an IVUS strategy for intermediate lesion assessment.

METHODS AND RESULTS

We compared the outcome of patients assessed with FFR and IVUS in two centres with a differential approach. After propensity score matching 400 pairs of patients were included. Revascularisation was done when FFR was <0.75 or minimum lumen area was <4 mm2 in vessels >3 mm, and <3.5 mm2 in vessels 2.5-3 mm, along with plaque burden >50%. After FFR and IVUS, 72% and 51.2% of lesions, respectively, were left untreated (p<0.001). At one and two years no significant differences in MACE-free survival were observed in overall groups (97.7% at one year and 93.1% at two years in the FFR group and 97.7% at one year and 95.6% at two years in the IVUS group; p=0.35) and among those with deferred intervention (97.9% at one year and 94.2% at two years in the FFR group and 96.5% at one year and 93.6% at two years in the IVUS group; p=0.7).

CONCLUSIONS

IVUS and FFR may be safely used to defer revascularisation of intermediate lesions. IVUS induces a higher degree of revascularisation but much lower than previously reported and does not affect the clinical outcome.

Effect of myocardial contractility on hemodynamic end points under concomitant microvascular disease in a porcine model

In this study, coronary diagnostic parameters, pressure drop coefficient (CDP: ratio of trans-stenotic pressure drop to distal dynamic pressure), and lesion flow coefficient (LFC: ratio of % area stenosis (%AS) to the CDP at throat region), were evaluated to distinguish levels of %AS under varying contractility conditions, in the presence of microvascular disease (MVD). In 10 pigs, %AS and MVD were created using angioplasty balloons and 90-μm microspheres, respectively. Simultaneous measurements of pressure drop, left ventricular pressure (p), and velocity were obtained. Contractility was calculated as (dp/dt)max, categorized into low contractility <900 mmHg/s and high contractility >900 mmHg/s, and in each group, compared between %AS <50 and >50 using analysis of variance. In the presence of MVD, between the %AS <50 and >50 groups, values of CDP (71 ± 1.4 and 121 ± 1.3) and LFC (0.10 ± 0.04 and 0.19 ± 0.04) were significantly different (P < 0.05), under low-contractility conditions. A similar %AS trend was observed under high-contractility conditions (CDP: 18 ± 1.4 and 91 ± 1.4; LFC: 0.08 ± 0.04 and 0.25 ± 0.04). Under MVD conditions, similar to fractional flow reserve, CDP and LFC were not influenced by contractility.

Optical coherence tomography: from research to practice

Optical coherence tomography (OCT) is a high-resolution imaging technique with great versatility of applications. In cardiology, OCT has remained hitherto as a research tool for characterization of vulnerable plaques and evaluation of neointimal healing after stenting. However, OCT is now successfully applied in different clinical scenarios, and the introduction of frequency domain analysis simplified its application to the point it can be considered a potential alternative to intravascular ultrasound for clinical decision-making in some cases. This article reviews the use of OCT for assessment of lesion severity, characterization of acute coronary syndromes, guidance of intracoronary stenting, and evaluation of long-term results.