Relationship between optical coherence tomography-derived morphological criteria and functional relevance as determined by fractional flow reserve

Relationship of OCT-defined plaque characteristics with CCTA-derived coronary inflammation and CMR-derived global coronary flow reserve in patients with acute coronary syndrome

BACKGROUND

The relationship of layered plaque detected by optical coherence tomography (OCT) with coronary inflammation and coronary flow reserve (CFR) remains elusive. We aimed to investigate the association of OCT-defined layered plaque with pericoronary adipose tissue (PCAT) inflammation assessed by coronary computed tomography angiography (CCTA) and global (G)-CFR assessed by cardiac magnetic resonance imaging (CMR) in patients with acute coronary syndrome (ACS).

METHODS

We retrospectively investigated 88 patients with first ACS who underwent preprocedural CCTA, OCT imaging of the culprit lesion prior to primary/urgent percutaneous coronary intervention (PCI), and postprocedural CMR. All patients were divided into two groups according to the presence and absence of OCT-defined layered plaque at the culprit lesion. Coronary inflammation was assessed by the mean value of PCAT attenuation (-190 to -30 HU) of the three major coronary vessels. G-CFR was obtained by quantifying absolute coronary sinus flow at rest and during maximum hyperemia. CCTA and CMR findings were compared between the groups.

RESULTS

In a total of 88 patients, layered plaque was detected in 51 patients (58.0%). The patients with layered plaque had higher three-vessel-PCAT attenuation value (-68.58 ± 6.41 vs. -71.60 ± 5.21 HU, P = 0.021) and culprit vessel-PCAT attenuation value (-67.69 ± 7.76 vs. -72.07 ± 6.57 HU, P = 0.007) than those with non-layered plaque. The patients with layered plaque had lower G-CFR value (median, 2.26 [interquartile range, 1.78, 2.89] vs. 3.06 [2.41, 3.90], P = 0.003) than those with non-layered plaque.

CONCLUSIONS

The presence of OCT-defined layered plaque at the culprit lesion was associated with high PCAT attenuation and low G-CFR after primary/urgent PCI in patients with ACS. OCT assessment of culprit plaque morphology and detection of layered plaque may help identify increased pericoronary inflammation and impaired CFR, potentially providing the risk stratification in patients with ACS and residual microvascular dysfunction after PCI.

When coronary imaging and physiology are discordant, how best to manage coronary lesions? An appraisal of the clinical evidence

BACKGROUND

Discordant physiology and anatomy may occur when nonsevere angiographic stenosis has positive physiology as well as the opposite situation.

AIM

To underline the reasons behind the discrepancy in physiology and anatomy and to summarize the information that coronary imaging may add to physiology.

METHODS

A review of the published literature on physiology and intravascular imaging assessment of intermediate lesions was carried out.

RESULTS

The limitations of angiography, the possibility of an underlying diffuse disease, the presence of a "grey zone" in both techniques, the amount of myocardial mass that subtends the stenosis, and plaque vulnerability may play a role in such discrepancy. Intracoronary imaging has a poor diagnostic accuracy compared to physiology. However, it may add information about plaque vulnerability that might be useful in deciding whether to treat or not a certain lesion.

CONCLUSIONS

Coronary revascularization is recommended for patients with ischemia based on physiology. Intracoronary imaging adds information on plaque vulnerability and can help on the decision whether to revascularize or not a lesion.

OCT-Derived Plaque Morphology and FFR-Determined Hemodynamic Relevance in Intermediate Coronary Stenoses

Background: optical coherence tomography (OCT) might allow identifying lesion features reportedly associated with plaque vulnerability and increased risk of clinical events. Previous studies on correlation between OCT and functional lesion significance indices reported contradictory results, yet integration of complementary information from both modalities is gaining increased interest. The aim of the study was to compare plaque morphology using OCT in hemodynamically relevant vs. non-relevant lesions by fractional flow reserve (FFR). Methods: consecutive patients with intermediate grade coronary stenoses by angiography were evaluated by both FFR and OCT in this single-center study. Stenoses were labeled hemodynamically relevant in case of the FFR ≤ 0.80. Minimal lumen area (MLA), fibrous cap thickness (FCT), minimal cap thickness over the calcium, angle of the calcium, and necrotic core within the lesions were evaluated. Results: a total of 105 patients (124 vessels) were analyzed. Of them, 65 patients were identified with at least one lesion identified as hemodynamically relevant by FFR (72 vessels, 58.1%). Lesions with FFR ≤0.80 presented with lower mean and minimal lumen area (3.46 ± 1.29 vs. 4.65 ± 2.19, p =0.001 and 1.84 ± 0.97 vs. 2.66 ± 1.40, p = 0.001) compared to patients with FFR > 0.80. No differences were found between groups in the mean and minimal FCT, mean, and maximal necrotic core, calcium angle, as well as the overall rate of calcified and lipid plaques. Conclusion: hemodynamic relevance of intermediate grade lesions correlated moderately with the luminal assessment by OCT. No differences were identified in the plaque morphology between relevant and non-relevant coronary stenoses by FFR.

FFR=1.0 flow changes after percutaneous coronary intervention

BACKGROUND

The present study investigated the relationships between physiological indices and increased coronary flow during percutaneous coronary intervention (PCI) using a novel index of "anticipated maximum flow" [AMF; theoretical coronary flow of fractional flow reserve (FFR) = 1]. FFR-guided PCI aims to increase coronary flow, whereas recent studies have reported that PCI does not necessarily increase coronary flow despite improvement in FFR.

METHODS

This retrospective analysis was performed in 71 functionally significant lesions treated with elective PCI. AMF obtained by hyperemic average peak coronary flow velocity (h-APV) divided by FFR would not change after PCI given the constant microvascular resistance, which is the assumption of FFR as a surrogate of coronary flow. We evaluated the relationship between AMF and coronary flow during PCI.

RESULTS

Post-PCI AMF was significantly different from pre-PCI AMF (p = 0.022), which impacted discordance between FFR improvement and change in coronary flow. Coronary flow increase >50% was associated with smaller minimum lumen diameter (p = 0.010), greater diameter stenosis (p = 0.003), lower pre-PCI FFR (p < 0.001), lower pre-PCI coronary flow reserve (p = 0.001), higher pre-PCI hyperemic stenosis resistance (p < 0.001), lower pre-PCI h-APV (p = 0.001), and lower pre-PCI AMF (p = 0.031). Pre-PCI AMF provided significant incremental predictive capability for coronary flow increase >50% when added to the clinical model including pre-PCI FFR.

CONCLUSION

Pre-PCI AMF provided incremental ability to predict increased coronary flow after PCI and impacted the discordance between FFR improvement and increased coronary flow.

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.