Comparison between instantaneous wave-free ratio versus morphometric assessments by intracoronary imaging

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.

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.

Diagnostic performance and limitation of quantitative flow ratio for functional assessment of intermediate coronary stenosis

BACKGROUND

This study aimed to simultaneously investigate diagnostic performance and limitation of quantitative flow reserve (QFR) for assessing functionally significant coronary stenosis, focusing on factors affecting diagnostic accuracy of QFR.

METHODS

This study evaluated 1) QFR diagnostic accuracy compared with fractional flow reserve (FFR) in patients with stable coronary artery disease (Cohort-A, n = 95) and 2) QFR reproducibility for non-culprit lesions (NCLs) assessment between acute and staged (14±5 days later) procedures in patients with ST-segment elevation myocardial infarction (STEMI) (Cohort-B, n = 65). All coronary angiography image acquisition was performed before the introduction of QFR system into our institution.

RESULTS

Cohort-A showed good correlation (r = 0.80, p<0.0001) between QFR and FFR; diagnostic accuracy of QFR for FFR ≤0.80 was 85.2% (sensitivity 80.4%, specificity 91.0%, positive predictive value 91.1%, negative predictive value 80.0%). There were 14 lesions showing discordance between QFR and FFR, which was primarily attributable to inadequate lesion visualization due to vessel overlap/tortuosity and/or insufficient intra-coronary contrast-media injection. In Cohort-B, there was also excellent correlation between acute and staged QFR; classification agreement of acute and staged QFR was 92.3%. Five lesions showed discordance between acute and staged QFR, 4 were due to limited image acquisition and/or high coronary flow velocity at acute phase of STEMI and 1 was borderline ischemia.

CONCLUSIONS

QFR-derived physiological assessment of intermediate coronary stenosis is feasible, even in the acute setting of STEMI. Adjusting some technical factors may further improve the diagnostic performance of QFR.

Effect of QTU prolongation on hyperemic instantaneous wave-free ratio value: a prospective single-center study

We hypothesized that in patients with QT prolongation, resistance might not decrease in the wave-free period, because QTU prolongation cannot be detected by instantaneous wave-free ratio (iFR) analysis software. We investigated whether corrected QTU (QTUc) prolongation affects the hyperemic iFR value. Forty-two consecutive patients with intermediate stenosis (≥ 50%) in the left anterior descending coronary artery (LAD) were analyzed. Fractional flow reserve (FFR) and hyperemic iFR were simultaneously and continuously recorded with intravenous adenosine triphosphate (ATP) and papaverine infusions. In 17 patients with stenosis in the proximal LAD, coronary flow was measured. Patients were divided into two groups according to the median absolute deviation of the QTUc by ATP administration/QTUc by papaverine administration. FFR, hyperemic iFR, and flow data were compared between each stimulus and group. Moreover, influences of pressure and electrocardiogram parameters on differences in iFR values under ATP and papaverine administration were compared between the following two groups (group 1: the absolute difference of hyperemic iFR values between ATP and papaverine administration is ≤ 0.05; group 2: that is > 0.05). The paired t test and t test were used in analysis. Hyperemic iFR values of patients under the use of papaverine were lower than those of patients under the use of ATP when QTUc was more prolonged by papaverine administration than by ATP administration (ATP 0.74 ± 0.14, papaverine 0.71 ± 0.15, P = 0.025). No significant differences were observed in the FFR value and flow data between the groups. Regarding QTU, QTUc, and QTUc by ATP/QTUc by papaverine, significant differences were observed between group 1 and group 2. Pressure parameters did not induce significant differences. QTUc prolongation induced by papaverine was associated with lower hyperemic iFR values. An iFR-based assessment might lead to inappropriate treatment of patients with QTUc prolongation.

Clinical feasibility of resting full-cycle ratio as a unique non-hyperemic index of invasive functional lesion assessment

The resting full-cycle ratio (RFR) is a new physiologic index to assess myocardial ischemia. RFR and fractional flow reserve (FFR), the conventionally used index, have not been directly compared in evaluating the entire cardiac cycle. Accordingly, we aimed to compare the diagnostic performance of RFR directly with FFR and clarify the clinical feasibility of RFR as a unique non-hyperemic index in evaluating the cardiac cycle. The diagnostic performance of RFR was compared with FFR using an automated online calculation software. A total of 156 consecutive patients with 220 intermediate lesions were enrolled. RFR showed significant correlation with FFR (r = 0.774, p < 0.001). RFR systole and RFR diastole did also with FFR (r = 0.918, p < 0.001, and r = 0.733, p < 0.001, respectively). With FFR < 0.80 as a reference standard, RFR showed good diagnostic accuracy (DA: 80.5%), similar DA between RFR systole and RFR diastole (79.6% and 87.5%, p = 0.58, respectively), and good DA in any lesion locations, especially in non-left anterior descending coronary artery (LAD) lesions (73.7% and 87.6% for LAD vs. non-LAD, p < 0.05, respectively). RFR is a feasible and reliable non-hyperemic index regardless of the difference in cardiac cycle in evaluating physiological lesion severity in daily practice.