Effect of Plaque Burden and Morphology on Myocardial Blood Flow and Fractional Flow Reserve

Coronary Microvascular Dysfunction by Myocardial Contrast Echocardiography in Nonelderly Patients Referred for Computed Tomographic Coronary Angiography

BACKGROUND

Microvascular dysfunction (MVD) is a potential cause of chest pain in younger individuals. The authors hypothesized that nonelderly patients referred for computed tomographic angiography (CTA) but without significant stenosis would have a high prevalence of MVD by myocardial contrast echocardiography (MCE). Secondary aims were to test whether the presence of nonobstructive coronary artery disease (CAD) or reduced brachial flow-mediated dilation (FMD) predicted MVD.

METHODS

Subjects ≤60 years of age undergoing CTA were recruited if they had either no evidence of coronary plaque or evidence of mild CAD (<50% stenosis) and at least one high-risk plaque feature. Subjects underwent quantitative perfusion imaging using MCE at rest and during regadenoson vasodilator stress. MVD was defined as global or segmental delay of microvascular refill (≥2 sec) during regadenoson. FMD of the brachial artery was also performed.

RESULTS

Of the 29 patients in whom MCE could be performed, 12 (41%) had MVD. These subjects, compared with those with normal microvascular function, had lower hyperemic perfusion (mean, 236 ± 68 vs 354 ± 161 intensity units/sec; P = .02) and microvascular flux rate (mean, 1.6 ± 0.4 vs 2.5 ± 0.9 sec-1; P = .002) on quantitative MCE. The degree of FMD was not significantly different in those with or without MVD (mean, 11 ± 4% vs 9 ± 4%; P = .32), and there was a poor correlation between results on stress MCE and FMD. Only eight of the 29 subjects were classified as having nonobstructive CAD. There were no groupwise differences in the prevalence of MVD function in those with versus without CAD (43% vs 38% for negative and positive findings on CTA, respectively, P = .79).

CONCLUSIONS

MVD is a common finding in the nonelderly population referred for CTA for evaluation of possible CAD but without obstructive stenosis. Neither the presence of noncritical atherosclerotic disease nor abnormal FMD increases the likelihood for detecting MVD in this population.

Coronary Computed Tomography Angiography as a Gatekeeper to Coronary Revascularization: Emphasizing Atherosclerosis Findings Beyond Stenosis

Purpose of Review

Coronary computed tomography angiography (CCTA) is the optimal non-invasive test to rule out coronary artery disease (CAD). Decisions to perform coronary revascularization have traditionally been based upon ischemia testing. This review summarizes the latest observations and trials evaluating the suitability of CCTA to select patients for invasive coronary angiography (ICA) and subsequent revascularization.

Recent Findings

Recent data shows that beyond stenosis, whole-heart quantification and characterization of coronary atherosclerotic plaque improves the estimation of myocardial ischemia. This comprehensive evaluation of the coronary artery tree has greater diagnostic accuracy for invasive fractional flow reserve (FFR) than conventional stress tests. Further, clinical trials have demonstrated that the performance of CCTA in patients with a clinical indication for ICA results in more effective patient care and significantly lower costs.

Summary

Besides the excellent ability to rule out CAD, recent data shows that quantification and characterization of the coronary artery tree results in high accuracy for ischemia and that CCTA-guided care to select patients for ICA and revascularization is effective. Trials evaluating revascularization based on CCTA findings may be needed.

Non-invasive fractional flow reserve derived from coronary computed tomography angiography in patients with acute chest pain: Subgroup analysis of the ROMICAT II trial

BACKGROUND

Non-invasive fractional flow reserve (FFR_CT) derived from coronary computed tomography angiography (CTA) permits hemodynamic evaluation of coronary stenosis and may improve efficiency of assessment in stable chest pain patients. We determined feasibility of FFR_CT in the population of acute chest pain patients and assessed the relationship of FFR_CT with outcomes of acute coronary syndrome (ACS) and revascularization and with plaque characteristics.

METHODS

We included 68 patients (mean age 55.8 ± 8.4 years, 71% men) from the ROMICAT II trial who had ≥50% stenosis on coronary CTA or underwent additional non-invasive stress test. We evaluated coronary stenosis and high-risk plaque on coronary CTA. FFR_CT was measured in a core laboratory.

RESULTS

We found correlation between anatomic severity of stenosis and FFR_CT ≤0.80 vs. FFR_CT >0.80 (severe stenosis 84.8% vs. 15.2%; moderate stenosis 33.3% vs. 66.7%; mild stenosis 33.3% vs. 66.7% patients). Patients with severe stenosis had lower FFR_CT values (median 0.64, 25th-75th percentile 0.50-0.75) as compared to patients with moderate (median 0.84, 25th-75th percentile, p < 0.001) or mild stenosis (median 0.86, 25th-75th percentile 0.78-0.88, p < 0.001). The relative risk of ACS and revascularization in patients with positive FFR_CT ≤0.80 was 4.03 (95% CI 1.56-10.36) and 3.50 (95% CI 1.12-10.96), respectively. FFR_CT ≤0.80 was associated with the presence of high-risk plaque (odds ratio 3.91, 95% CI 1.55-9.85, p = 0.004) after adjustment for stenosis severity.

CONCLUSION

Abnormal FFR_CT was associated with the presence of ACS, coronary revascularization, and high-risk plaque. FFR_CT measurements correlated with anatomic severity of stenosis on coronary CTA and were feasible in population of patients with acute chest pain.

Improved in vivo detection of atherosclerotic plaques with a tissue factor-targeting magnetic nanoprobe

Rupture of atherosclerotic plaques causes acute cardiovascular and cerebrovascular pathology. Tissue factor (TF) is a key factor that affects the development of atherosclerotic plaques and the formation of thrombus and thus constitutes a potential target for the detection of atherosclerotic plaques. In this study, the conjugation of the fusion protein 'enhanced green fluorescent protein with the first epidermal growth factor domain' (EGFP-EGF1) and superparamagnetic iron oxide nanoparticles (EGFP-EGF1-SPIONs) was explored for molecular imaging of TF-positive atherosclerotic plaques. EGFP-EGF1-SPIONs showed improved accuracy, superior contrast effects, and better cytocompatibility compared with common contrast agents in the detection of atherosclerotic plaques of apolipoprotein E knockout (ApoE^-/-) mice using magnetic resonance imaging. In conclusion, EGFP-EGF1-SPION is a promising TF-targeting nanoprobe to precisely and specifically detect atherosclerotic plaques, which may improve molecular imaging diagnosis of cardiovascular and cerebrovascular events for the comprehensive evaluation of atherosclerosis. STATEMENT OF SIGNIFICANCE: Traditional methods can only display the status of atherosclerosis, but not forecast the progress of lesions efficiently. It remains challenging to evaluate the plaques specifically and sensitively. In this study, we constructed a tissue factor-targeted magnetic nanoprobe to specifically detect plaques by magnetic resonance imaging in vivo, which will improve the diagnostic technology for atherosclerotic plaques and offer molecular level guidance to treat atherosclerosis. Furthermore, this strategy has critical clinical significance on prevention, diagnosis and therapeutic evaluation of cardio-cerebral vascular events.

Image reconstruction in cardiovascular CT: Part 2 - Iterative reconstruction; potential and pitfalls

The use of IR in CT previously has been prohibitively complicated and time consuming, however improvements in computer processing power now make it possible on almost all CT scanners. Due to its potential to allow scanning at lower doses, IR has received a lot of attention in the medical literature and has become a successful commercial product. Its use in cardiovascular CT has been driven in part due to concerns about radiation dose and image quality. This manuscript discusses the various vendor permutations of iterative reconstruction (IR) in detail and critically appraises the current clinical research available on the various IR techniques used in cardiovascular CT.

The best predictor of ischemic coronary stenosis: subtended myocardial volume, machine learning-based FFRCT, or high-risk plaque features?

OBJECTIVES

The present study aimed to compare the diagnostic performance of a machine learning (ML)-based FFR_CT algorithm, quantified subtended myocardial volume, and high-risk plaque features for predicting if a coronary stenosis is hemodynamically significant, with reference to FFR_ICA.

METHODS

Patients who underwent both CCTA and FFR_ICA measurement within 2 weeks were retrospectively included. ML-based FFR_CT, volume of subtended myocardium (V_sub), percentage of subtended myocardium volume versus total myocardium volume (V_ratio), high-risk plaque features, minimal lumen diameter (MLD), and minimal lumen area (MLA) along with other parameters were recorded. Lesions with FFR_ICA ≤ 0.8 were considered to be functionally significant.

RESULTS

One hundred eighty patients with 208 lesions were included. The lesion length (LL), diameter stenosis, area stenosis, plaque burden, V_sub, V_ratio, V_ratio/MLD, V_ratio/MLA, and LL/MLD⁴ were all significantly longer or larger in the group of FFR_ICA ≤ 0.8 while smaller minimal lumen area, MLD, and FFR_CT value were noted. The AUC of FFR_CT + V_ratio/MLD was significantly better than that of FFR_CT alone (0.935 versus 0.873, p < 0.001). High-risk plaque features failed to show difference between functionally significant and insignificant groups. V_ratio/MLD-complemented ML-based FFR_CT for "gray zone" lesions with FFR_CT value ranged from 0.7 to 0.8 and the combined use of these two parameters yielded the best diagnostic performance (86.5%, 180/208).

CONCLUSIONS

ML-based FFR_CT simulation and V_ratio/MLD both provide incremental value over CCTA-derived diameter stenosis and high-risk plaque features for predicting hemodynamically significant lesions. V_ratio/MLD is more accurate than ML-based FFR_CT for lesions with simulated FFR_CT value from 0.7 to 0.8.

KEY POINTS

• Machine learning-based FFR _CT and subtended myocardium volume both performed well for predicting hemodynamically significant coronary stenosis. • Subtended myocardium volume was more accurate than machine learning-based FFR _CT for "gray zone" lesions with simulated FFR value from 0.7 to 0.8. • CT-derived high-risk plaque features failed to correctly identify hemodynamically significant stenosis.

CT Myocardial Perfusion Imaging: A New Frontier in Cardiac Imaging

The past two decades have witnessed rapid and remarkable technical improvement of multidetector computed tomography (CT) in both image quality and diagnostic accuracy. These improvements include higher temporal resolution, high-definition and wider detectors, the introduction of dual-source and dual-energy scanners, and advanced postprocessing. Current new generation multidetector row (≥64 slices) CT systems allow an accurate and reliable assessment of both coronary epicardial stenosis and myocardial CT perfusion (CTP) imaging at rest and during pharmacologic stress in the same examination. This novel application makes CT the unique noninvasive "one-stop-shop" method for a comprehensive assessment of both anatomical coronary atherosclerosis and its physiological consequences. Myocardial CTP imaging can be performed with different approaches such as static arterial first-pass imaging, and dynamic CTP imaging, with their own advantages and disadvantages. Static CTP can be performed using single-energy or dual-energy CT, employing qualitative or semiquantitative analysis. In addition, dynamic CTP can obtain quantitative data of myocardial blood flow and coronary flow reserve. The purpose of this review was to summarize all available evidence about the emerging role of myocardial CTP to identify ischemia-associated lesions, focusing on technical considerations, clinical applications, strengths, limitations, and the more promising future fields of interest in the broad spectra of ischemic heart disease.

Coronary computed tomography angiography: a method coming of age

In patients with stable symptoms suggestive of coronary artery disease (CAD), coronary CT angiography (CTA) allows for assessing several aspects of coronary atherosclerosis. Coronary artery stenoses are reliably detected, plaque formation can be quantified and characterized as calcified or non-calcified, and markers of potential instability such as expansive vascular remodeling, spotty calcification, and atheroma size can be described. As opposed to invasive coronary angiography, CTA visualizes the vessel lumen and wall. Being a purely anatomic test, even small plaques are detected with excellent sensitivity. At the other end of the spectrum, the hemodynamic significance of large plaque burden is sometimes overestimated. This may in part be corrected using mathematical modeling. Computational fluid dynamics of vascular anatomy and subtended myocardial mass provide for measures of CT-based fractional flow reserve (FFR_CT). Large prospective trials have demonstrated the diagnostic utility of CTA in particular for ruling out obstructive CAD. The ability to detect non-obstructive plaque allows for improved risk prediction in comparison with functional testing, because even patients with sub-clinical atherosclerosis can be identified and selected for preventive medical treatment. This has led to incorporating CTA as one of several possible diagnostic tests for the evaluation of stable CAD in the actual European guidelines. Recently, it has even been forwarded as the first-line diagnostic test in the United Kingdom. The clinical implications of novel quantitative CTA-derived parameters such as FFR_CT and non-calcified plaque volume are being examined in ongoing studies.

Rationale and design of advantage (additional diagnostic value of CT perfusion over coronary CT angiography in stented patients with suspected in-stent restenosis or coronary artery disease progression) prospective study

BACKGROUND

Recent studies demonstrated a significant improvement in the diagnostic performance of coronary CT angiography (CCTA) for the evaluation of in-stent restenosis (ISR). However, coronary stent assessment is still challenging, especially because of beam-hardening artifacts due to metallic stent struts and high atherosclerotic burden of non-stented segments. Adenosine-stress myocardial perfusion assessed by CT (CTP) recently demonstrated to be a feasible and accurate tool for evaluating the functional significance of coronary stenoses in patients with suspected coronary artery disease (CAD). Yet, scarce data are available on the performance of CTP in patients with previous stent implantation.

AIM OF THE STUDY

We aim to assess the diagnostic performance of CCTA alone, CTP alone and CCTA plus CTP performed with a new scanner generation using quantitative invasive coronary angiography (ICA) and invasive fractional flow reserve (FFR) as standard of reference.

METHODS

We will enroll 300 consecutive patients with previous stent implantation, referred for non-emergent and clinically indicated invasive coronary angiography (ICA) due to suspected ISR or progression of CAD in native coronary segments. All patients will be subjected to stress myocardial CTP and a rest CCTA. The first 150 subjects will undergo static CTP scan, while the following 150 patients will undergo dynamic CTP scan. Measurement of invasive FFR will be performed during ICA when clinically indicated.

RESULTS

The primary study end points will be: 1) assessment of the diagnostic performance (diagnostic rate, sensitivity, specificity, positive predictive value, negative predictive value and diagnostic accuracy) of CCTA, CTP, combined CCTA-CTP and concordant CCTA-CTP vs. ICA as standard of reference in a territory-based and patient-based analysis; 2) assessment of sensitivity, specificity, positive predictive value, negative predictive value and diagnostic accuracy of CCTA, CTP, combined CCTA-CTP and concordant CCTA-CTP vs. invasive FFR as standard of reference in a territory-based analysis.

CONCLUSIONS

The ADVANTAGE study aims to provide an answer to the intriguing question whether the combined anatomical and functional assessment with CCTA plus CTP may have higher diagnostic performance as compared to CCTA alone in identifying stented patients with significant ISR or CAD progression.