Classification performance of instantaneous wave-free ratio (iFR) and fractional flow reserve in a clinical population of intermediate coronary stenoses: results of the ADVISE registry

Contemporary Use of Coronary Physiology in Cardiology

Coronary angiography has a limited ability to predict the functional significance of intermediate coronary lesions. Hence, physiological assessment of coronary lesions, via fractional flow reserve (FFR) or instantaneous wave-free ratio (iFR), has been introduced to determine their functional significance. An accumulating body of evidence has consolidated the role of physiology-guided revascularization, particularly among patients with stable ischemic heart disease. The use of FFR or iFR to guide decision-making in patients with stable ischemic heart disease and intermediate coronary lesions received a class I recommendation from major societal guidelines. Nevertheless, the role of coronary physiology testing is less clear among certain patients' groups, including patients with serial coronary lesions, acute coronary syndromes, aortic stenosis, heart failure, as well as post-percutaneous coronary interventions. In this review, we aimed to discuss the utility and clinical evidence of coronary physiology (mainly FFR and iFR), with emphasis on those specific patient groups.

Diagnostic accuracy of diastolic pressure ratio using a pressure microcatheter for intracoronary physiological assessment

Recently, instantaneous wave-free ratio (iFR) has emerged as an alternative to the fractional flow reserve (FFR) for intracoronary physiological assessment. Although all diastolic resting indices are reportedly identical to the iFR, limited data exist on diastolic pressure ratio (dPR) measured using a microcatheter (dPRmicro). This study aimed to evaluate the diagnostic accuracy of dPRmicro compared to FFR measured using a microcatheter (FFRmicro) in real-world practice for intracoronary physiological assessment. This was a single-center, retrospective, observational study. We identified 103 consecutive suspected angina pectoris patients (107 lesions) who underwent dPRmicro and FFRmicro measurement using the Navvus® catheter at Takasaki Heart Hospital from March 2019 to June 2019. A total of 103 lesions in 103 patients were finally included in the study. The mean FFRmicro and dPRmicro values were 0.80 and 0.88, respectively. With an FFRmicro ≤ 0.80, the dPRmicro showed a diagnostic accuracy of 79.6%, sensitivity of 74.6%, specificity of 87.5%, positive predictive value of 90.4%, and negative predictive value of 68.6%. The area under the receiver operating characteristic (ROC) curve was 0.894 (95% confidence interval, 0.833-0.956), and the optimal cut-off value for dPRmicro derived from the ROC analysis was 0.90. dPRmicro and FFRmicro values were discordant in 21/103 cases (20.4%). As a multivariable logistic regression analysis was performed, the male sex (vs. female) had a statistically significant association with a dPRmicro-FFRmicro discordance (OR 4.91; 95% CI, 1.04-23.0; P = 0.044). No other factors were found to be significantly associated with the discordance. In conclusion, dPRmicro measured using a microcatheter had good diagnostic accuracy and correlation with FFRmicro, hence, it can be useful for making revascularization decisions. However, re-studies in larger populations will be needed to better understand the properties of diastolic resting index measured using a microcatheter in clinical settings.

Instantaneous wave free ratio value impact on left internal mammary artery graft patency

OBJECTIVES

To assess whether instantaneous wave - free ratio (iFR) value is associated with left internal mammary artery (LIMA) graft failure at 12 months follow-up post coronary artery bypass graft (CABG).

BACKGROUND

Data suggests bypass to a non-significant left anterior descending artery (LAD) lesion due to visual over-estimation may lead to LIMA graft failure. Implementing iFR may result in better arterial graft patency.

METHODS

In iCABG (iFR guided CABG) study patients planned to undergo an isolated CABG procedure was prospectively enrolled and iFR was performed for LAD. Coronary computed tomography angiography was performed at 2 and 12 months follow-up. The primary endpoint of this study was to determine the rate of LIMA graft occlusion or hypoperfusion at 2 and 12-months follow-up. We considered a composite secondary endpoint of Major adverse cardiovascular and cerebrovascular event (MACCE) as a secondary outcome.

RESULTS

In total 69 patients were included with no differences regarding age, sex and risk factors. At 2 months, 50 of LIMAs with pre-CABG iFR median 0.855 (0.785 - 0.892) were patent. Hypoperfusion was found in 8 LIMAs (median iFR 0.88 (0.842 - 0.90)). While, 7 LIMAs (median iFR 0.91 (0.88 - 0.96)) were occluded (p = 0.04). At 12 months, when iFR of LAD was >0.85: just 12 (31.6% out of all patent LIMAS) grafts were patent and 24 (100.0% out of all hypoperfused/occluded) grafts were hypoperfused or occluded (p < 0.001). In terms of MACCE, no difference (p = 1.0) was found between all 3 groups divided according to iFR value.

CONCLUSIONS

Instantaneous wave - free ratio value above 0.85 in LAD is a powerful tool predicting LIMA graft failure at 1-year follow up period.

Predictors of discordance between fractional flow reserve (FFR) and diastolic pressure ratio (dPR) in intermediate coronary lesions

Background

Recently, non-hyperemic pressure ratios (NHPRs) have been validated as a reliable alternative to fractional flow reserve (FFR). However, a discordance between FFR and NHPRs is observed in 20-25% of cases. The aim of this study is to evaluate predictors of discordance between FFR and diastolic Pressure ratio (dPR).

Methods

PREDICT is a retrospective, single center, investigator-initiated study including 813 patients (1092vessels) who underwent FFR assessment of intermediate coronary lesions (angiographic 30%-80% stenosis). dPR was calculated using individual pressure waveforms and dedicated software. Clinical, angiographic and hemodynamic variables were compared between patients with concordant and discordant FFR and dPR values.

Results

Median age was 65 (IQR:59-73) years and 70% were male. Hemodynamically significant lesions, as defined by FFR ≤ 0.80, and dPR ≤ 0.89, were identified in 29.6% and 30.3% of cases, respectively. Overall, FFR and dPR values were discordant in 22.1% patients (17.4% of the vessels). Discordance was related to FFR+/dPR- and FFR-/dPR + in 11.8% and 10.3% of patients, respectively.In case of FFR-dPR discordance, a higher prevalence of left anterior descending arteries lesions was observed (70.5% vs. 53.1%, p < 0.001) and mean values of both FFR and dPR were significantly lower (FFR 0.81 ± 0.05 vs 0.85 ± 0.08, p < 0.001, and dPR 0.89 ± 0.04 vs 0.92 ± 0.08,p < 0.001) as compared to vessels with FFR and dPR concordance. Following multivariable adjustment, dPR delta (defined as the absolute difference between measured dPR to the cut-off value of 0.89) turned out to be the only independent predictor of discordance (OR = 0.74, 95% CI 0.68-0.79, p < 0.001).

Conclusion

Our study suggests that FFR-to-dPR discordance occurs in approximately one-fifth of patients. Absolute dPR delta appears to be the only independent predictor of discordance.

A high-fidelity geometric multiscale hemodynamic model for predicting myocardial ischemia

BACKGROUND AND OBJECTIVES

Coronary computed tomography angiography (CCTA) derived fractional flow reserve (CT-FFR) requires a maximal hyperemic state to be modeled by assuming the total coronary resistance decreased to a constant 0.24 of that under the resting state. However, this assumption neglects the vasodilator capacity of individual patients. Herein, we proposed a high-fidelity geometric multiscale model (HFMM) to characterize coronary pressure and flow under the resting state, seeking to better predict myocardial ischemia by using CCTA-derived instantaneous wave-free ratio (CT-iFR).

METHODS

Fifty-seven patients (62 lesions) who had undergone CCTA and were then referred to invasive FFR were prospectively enrolled. The coronary microcirculation resistance hemodynamic model (RHM) under the resting condition was established on a patient-specific basis. Coupled with a closed-loop geometric multiscale model (CGM) of their individual coronary circulations, the HFMM model was established to non-invasively derive the CT-iFR from CCTA images.

RESULTS

With the invasive FFR being the reference standard, accuracy of the obtained CT-iFR in identifying myocardial ischemia was greater than those of the CCTA and non-invasively derived CT-FFR (90.32% vs. 79.03% vs. 84.3%). The overall computational time of CT-iFR was 61 ± 6 min, faster than that of the CT-FFR (8 h). The sensitivity, specificity, positive predictive value, and negative predictive value of the CT-iFR in discriminating an invasive FFR > 0.8 were 78% (95% CI: 40-97%), 92% (95% CI: 82-98%), 64% (95% CI: 39-83%), and 96% (95% CI:88-99%), respectively.

CONCLUSIONS

A high-fidelity geometric multiscale hemodynamic model was developed for rapid and accurate estimation of CT-iFR. Compared with CT-FFR, CT-iFR is of less computational cost and enables assessment of tandem lesions.

Coronary Physiology: Modern Concepts for the Guidance of Percutaneous Coronary Interventions and Medical Therapy

Recent evidence on ischemia, rather than coronary artery disease (CAD), representing a major determinant of outcomes, has led to a progressive shift in the management of patients with ischemic heart disease. According to most recent guidelines, myocardial revascularization strategies based on anatomical findings should be progressively abandoned in favor of functional criteria for the guidance of PCI. Thus, emerging importance has been assigned to the assessment of coronary physiology in order to determine the ischemic significance of coronary stenoses. However, despite several indexes and tools that have been developed so far, the existence of technical and clinical conditions potentially biasing the functional evaluation of the coronary tree still cause debates regarding the strategy of choice. The present review provides an overview of the available methods and the most recent acquirements for the invasive assessment of ischemia, focusing on the most widely available indexes, fractional flow reserve (FFR) and instant-wave free ratio (iFR), in addition to emerging examples, as new approaches to coronary flow reserve (CFR) and microvascular resistance, aiming at promoting the knowledge and application of those "full physiology" principles, which are generally advocated to allow a tailored treatment and the achievement of the largest prognostic benefits.

Clinical Outcome of Revascularization Deferral With Instantaneous Wave-Free Ratio and Fractional Flow Reserve: A 5-Year Follow-Up Substudy From the iFR-SWEDEHEART Trial

Background Although physiology-based assessment of coronary artery stenosis using instantaneous wave-free ratio (iFR) and fractional flow reserve (FFR) are established methods of guiding coronary revascularization, its clinical outcome in long-term deferral needs further evaluation, especially with acute coronary syndrome as a clinical presentation. The aim was to evaluate the long-term clinical outcome of deferral of revascularization based on iFR or FFR. Methods and Results This is a substudy of the iFR-SWEDEHEART (Instantaneous Wave-Free Ratio Versus Fractional Flow Reserve in Patients With Stable Angina Pectoris or Acute Coronary Syndrome) randomized clinical trial, where patients deferred from revascularization from each study arm were selected. Nine hundred eight patients deferred from coronary revascularization with iFR (n=473) and FFR (n=435) were followed for 5 years. The national quality registry, SWEDEHEART (Swedish Web-System for Enhancement and Development of Evidence-Based Care in Heart Disease Evaluated According to Recommended Therapies), was used for patient data collection and clinical follow-up. The end point was major adverse cardiac events and their individual components all-cause death, cardiovascular death, noncardiovascular death, nonfatal myocardial infarction, and unplanned revascularization. No significant difference was found in major adverse cardiac events (iFR 18.6% versus FFR 16.8%; adjusted hazard ratio, 1.08 [95% CI, 0.79-1.48]; P=0.63) or their individual components. Conclusions No differences in clinical outcomes after 5-year follow-up were noted when comparing iFR versus FFR as methods for deferral of coronary revascularization in patients presenting with stable angina pectoris and acute coronary syndrome. Registration URL: https://www.clinicaltrials.gov; Unique identifier: NCT02166736.

Discordance between fractional flow reserve and instantaneous wave-free ratio in patients with severe aortic stenosis: A retrospective cohort study

BACKGROUND

Discordance between fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR) occurs in approximately 20 % of cases. However, no studies have reported the discordance in patients with severe aortic stenosis (AS). We aimed to evaluate the diagnostic discordance between FFR and iFR in patients with severe AS.

METHODS

We examined 140 consecutive patients with severe AS (164 intermediate coronary artery stenosis vessels). FFR and iFR were calculated in four quadrants based on threshold FFR and iFR values of ≤0.8 and ≤0.89, respectively (Group 1: iFR >0.89, FFR >0.80; Group 2: iFR ≤0.89, FFR >0.80; Group 3: iFR >0.89, FFR ≤0.80; and Group 4: iFR ≤0.89, FFR ≤0.80). Concordant groups were Groups 1 and 4, and discordant groups were Groups 2 and 3. Positive and negative discordant groups were Groups 3 and 2, respectively.

RESULTS

The median (Q1, Q3) FFR and iFR were 0.84 (0.76, 0.88) and 0.85 (0.76, 0.91), respectively. Discordance was observed in 48 vessels (29.3 %). In the discordant group, negative discordance (Group 2: iFR ≤0.89 and FFR >0.80) was predominant (45 cases, 93.6 %). Multivariate analysis showed that the left anterior descending artery [odds ratio (OR), 3.88; 95 % confidence interval (CI): 1.54-9.79, p = 0.004] and peak velocity ≥5.0 m/s (OR, 3.21; 95%CI: 1.36-7.57, p = 0.008) were independently associated with negative discordance (FFR >0.8 and iFR ≤0.89).

CONCLUSIONS

In patients with severe AS, discordance between FFR and iFR was predominantly negative and observed in 29.3 % of vessels. The left anterior descending artery and peak velocity ≥5.0 m/s were independently associated with negative discordance.

Intracoronary nicorandil induced hyperemia for physiological assessments in the coronary artery lesions

Objective

Maximal hyperemia is a key element of invasive physiological examination. The aim of this study was to investigate the efficacy and safety of intracoronary (IC) nicorandil in comparison with adenosine 5′-triphosphate (ATP) intravenous (i.v.) injection for fractional flow reserve (FFR) measurement in coronary artery lesions.

Materials and methods

In this study, 46 patients who had their FFR measured were enrolled, including 51 lesions. Hyperemia was induced by bolus 2 mg nicorandil and ATP (40 mg ATP + 36 ml saline, weight × 10 ml/h) for FFR measurement. The safety and efficacy of IC nicorandil were evaluated.

Results

The mean FFR values measured by nicorandil and ATP were 0.810 ± 0.013 and 0.799 ± 0.099, p &lt; 0.001, respectively. There was a strong correlation between FFR measured by nicorandil and ATP (r = 0.983, R2 = 0.966, FFRnicorandil = 0.937 × FFRATP + 0.061). The rate of FFR ≤ 0.75 in the nicorandil and ATP groups was 31.37 vs. 35.29%, respectively (p = 0.841), the consistency rate was 96.08%; the FFR ≤ 0.8 rate was 41.18 and 43.14%, respectively (p = 0.674), and the consistency rate was 90.20%. In five lesions, the FFR value measured by nicorandil ranged between 0.79 and 0.82, indicating inconsistency according to FFR ≤ 0.8. The blood pressure changes caused by nicorandil and ATP were 12.96 ± 6.83 and 22.22 ± 11.44 mmHg (p &lt; 0.001); the heart rate changes were 2.43 ± 1.31 and 6.52 ± 2.87 beats/min, respectively (p &lt; 0.001); and the PR interval changes were 6.0 (1.0–11.0) and 9.0 (2.0–19.0) ms, respectively (p &lt; 0.001). Visual analog scale (VAS) scores in the nicorandil group were all in the range 0–2, while in the ATP group were mostly in the range of 3–5.

Conclusion

Intracoronary bolus of nicorandil (2 mg) infusion induces stable hyperemia, and it could be considered as an alternative drug to ATP for FFR measurement with a lower side effect profile in most patients.

Non-hyperaemic assessment of coronary ischaemia: application of machine learning techniques

Aims

Hyperaemic and non-hyperaemic pressure ratios (NHPR) are routinely used to identify significant coronary lesions. Machine learning (ML) techniques may help better understand these indices and guide future practice. This study assessed the ability of a purpose-built ML algorithm to classify coronary ischaemia during non-hyperaemia compared with the existing gold-standard technique (fractional flow reserve, FFR). Further, it investigated whether ML could identify components of coronary and aortic pressure cycles indicative of ischaemia.

Methods and results

Seventy-seven coronary vessel lesions (39 FFR defined ischaemia, 53 patients) with proximal and distal non-hyperaemic pressure waveforms and FFR values were assessed using supervised and unsupervised learning techniques in combination with principal component analysis (PCA). Fractional flow reserve measurements were obtained from the right coronary artery (13), left anterior descending (46), left circumflex (11), left main (1), obtuse marginal (2), and diagonal (4). The most accurate supervised learning classification utilized whole-cycle aortic with diastolic distal blood pressure waveforms, yielding a classification accuracy of 86.9% (sensitivity 86.8%, specificity 87.2%, positive predictive value 86.8%, negative predictive value 87.2%). Principal component analysis showed subtle variations in coronary pressures at the start of diastole have significant relation to ischaemia, and whole-cycle aortic pressure data are important for determining ischaemia.

Conclusions

Our ML algorithm classifies significant coronary lesions with accuracy similar to previous studies comparing time-domain NHPRs with FFR. Further, it has identified characteristics of pressure waveforms that relate to function. These results provide an application of ML to ischaemia requiring only standard data from non-hyperaemic pressure measurements.

PERSONALIZED FLOW DIVISION METHOD BASED ON THE LEFT-RIGHT CORONARY CROSS-SECTIONAL AREA

This paper proposes a personalized method to estimate blood flow distribution based on the cross-sectional area of the left-right coronary artery openings. According to the cross-sectional area of the left-right coronary artery in 30 cases, a personalized flow distribution model was derived. A 0D/3D geometric multiscale model was used for the numerical simulation of FFR. To evaluate the accuracy of the cross-sectional area method, invasive FFR was used as the standard. The diagnostic efficiency of the proposed method was verified through the simulation results of the volume and the fixed ratio methods. The flow of the left-right coronary artery was proportional to the 3/4 power of the cross-sectional area. The 95% LOA between the cross-sectional area method, volume method, fixed ratio method and FFR were [Formula: see text]0.06 ([[Formula: see text]0.22, 0.10]), [Formula: see text]0.03 ([[Formula: see text]0.35, 0.28]), and [Formula: see text]0.05 ([[Formula: see text]0.30, 0.20]), the accuracy values were 94.44%, 77.78%, and 77.78%, respectively. Flow distribution based on the cross-sectional area represents the supply and demand relationship of the myocardium. The flow of the left-right coronary arteries is proportional to the 3/4 exponent of the cross-sectional area, which affects the accuracy of FFRCT by affecting the exit boundary conditions of the 0D/3D model.

Predictors of fractional flow reserve/instantaneous wave-free ratio discordance: impact of tailored diagnostic cut-offs on clinical outcomes of deferred lesions

BACKGROUND

Patient-related and lesion-related factors may influence instantaneous wave-free ratio (iFR)/fractional flow reserve (FFR) concordance, potentially affecting the safety of revascularization deferral.

METHODS

Consecutive patients with at least an intermediate coronary stenosis evaluated by both iFR and FFR were retrospectively enrolled. The agreement between iFR and FFR at their diagnostic cut-offs (FFR 0.80, iFR 0.89) was assessed. Predictors of discordance were assessed using multivariate analyses. Tailored iFR cut-offs according to predictors of discordance best matching an FFR of 0.80 were identified. The impact of reclassification according to tailored iFR cut-offs on major cardiovascular events (MACE: cardiovascular death, myocardial infarction or target-lesion revascularization) among deferred lesions was investigated.

RESULTS

Two hundred and ninety-nine intermediate coronary stenosis [FFR 0.84 (0.78-0.89), iFR 0.91 (0.87-0.95), 202 left main/left anterior descending (LM/LAD) vessels, 67.6%] of 260 patients were studied. Discordance rate was 23.4% (n = 70, 10.7% iFR-negative discordant, 12.7% iFR-positive discordant). Predictors of discordance were LM/LAD disease, multivessel disease, non-ST-elevation myocardial infarction, smoking, reduced eGFR and hypertension. Lesion reclassification with tailored iFR cut-offs based on patient-level predictors carried no prognostic value among deferred lesions. Reclassification according to lesion location, which was entirely driven by LM/LAD lesions (iFR cut-offs: 0.93 for LM/LAD, 0.89 for non-LM/LAD), identified increased MACE among lesions deferred based on a negative FFR, between patients with a positive as compared with a negative iFR (19.4 vs. 6.1%, P = 0.044), whereas the same association was not observed with the conventional 0.89 iFR cut-off (15 vs. 8.6%, P = 0.303).

CONCLUSION

Tailored vessel-based iFR cut-offs carry prognostic value among FFR-negative lesions, suggesting that a one-size-fit-all iFR cut-off might be clinically unsatisfactory.

Diagnostic accuracy of on-site coronary computed tomography-derived fractional flow reserve in the diagnosis of stable coronary artery disease

PURPOSE

Invasive fractional flow reserve (FFR), the reference standard for identifying significant coronary artery disease (CAD), can be estimated non-invasively by computed tomography-derived fractional flow reserve (CT-FFR). Commercially available off-site CT-FFR showed improved diagnostic accuracy compared to coronary computed tomography angiography (CCTA) alone. However, the diagnostic performance of this lumped-parameter on-site method is unknown. The aim of this cross-sectional study was to determine the diagnostic accuracy of on-site CT-FFR in patients with suspected CAD.

METHODS

A total of 61 patients underwent CCTA and invasive coronary angiography with FFR measured in 88 vessels. Significant CAD was defined as FFR and CT-FFR below 0.80. CCTA with stenosis above 50% was regarded as significant CAD. The diagnostic performance of both CT-FFR and CCTA was assessed using invasive FFR as the reference standard.

RESULTS

Of the 88 vessels included in the analysis, 34 had an FFR of ≤ 0.80. On a per-vessel basis, the sensitivity, specificity, positive predictive value, negative predictive value and accuracy were 91.2%, 81.4%, 93.6%, 75.6% and 85.2% for CT-FFR and were 94.1%, 68.5%, 94.9%, 65.3% and 78.4% for CCTA. The area under the receiver operating characteristic curve was 0.91 and 0.85 for CT-FFR and CCTA, respectively, on a per-vessel basis.

CONCLUSION

On-site non-invasive FFR derived from CCTA improves diagnostic accuracy compared to CCTA without additional testing and has the potential to be integrated in the current clinical work-up for diagnosing stable CAD.

Instantaneous wave-free ratio compared with fractional flow reserve in PCI: A cost-minimization analysis

BACKGROUND

Coronary physiology is a routine diagnostic tool when assessing whether coronary revascularization is indicated. The iFR-SWEDEHEART trial demonstrated similar clinical outcomes when using instantaneous wave-free ratio (iFR) or fractional flow reserve (FFR) to guide revascularization. The objective of this analysis was to assess a cost-minimization analysis of iFR-guided compared with FFR-guided revascularization.

METHODS

In this cost-minimization analysis we used a decision-tree model from a healthcare perspective with a time-horizon of one year to estimate the cost difference between iFR and FFR in a Nordic setting and a United States (US) setting. Treatment pathways and health care utilizations were constructed from the iFR-SWEDEHEART trial. Unit cost for revascularization and myocardial infarction in the Nordic setting and US setting were derived from the Nordic diagnosis-related group versus Medicare cost data. Unit cost of intravenous adenosine administration and cost per stent placed were based on the average costs from the enrolled centers in the iFR-SWEDEHEART trial. Deterministic and probabilistic sensitivity analyses were carried out to test the robustness of the result.

RESULTS

The cost-minimization analysis demonstrated a cost saving per patient of $681 (95% CI: $641 - $723) in the Nordic setting and $1024 (95% CI: $934 - $1114) in the US setting, when using iFR-guided compared with FFR-guided revascularization. The results were not sensitive to changes in uncertain parameters or assumptions.

CONCLUSIONS

IFR-guided revascularization is associated with significant savings in cost compared with FFR-guided revascularization.

The stability of flow velocity and intracoronary resistance in the intracoronary electrocardiogram-triggered pressure ratio

Assessment of coronary artery lesions using the fractional flow reserve and instantaneous flow reserve (iFR) measurements has been found to reduce the incidence of further cardiovascular events. Here, we investigated differences in terms of coronary flow velocity and resistance within the analysis interval between the iFR and the intracoronary electrocardiogram (IC-ECG)-triggered distal/aortic pressure (Pd/Pa) ratio (ICE-T). We enrolled 23 consecutive patients (n = 33 stenoses) who required coronary flow measurements. ICE-T was defined as the average Pd/Pa ratio in the period corresponding to the isoelectric line of the IC-ECG. We compared the index value, flow velocity, and intracoronary resistance during the analysis intervals of the iFR and the ICE-T, both at rest and under hyperemia. ICE-T values and ICE-T intracoronary resistance were both found to be significantly lower, whereas flow velocity was significantly higher than those of the iFR at both rest and under hyperemia (P < 0.001), and all fluctuations in ICE-T values were also significantly smaller than those in the iFR. In conclusion, the ICE-T appears theoretically superior to pressure-dependent indices for analyzing phases with low and stable resistance, without an increase in invasiveness.

Borderline coronary lesion assessment with quantitative flow ratio and its relation to the instantaneous wave-free ratio

PURPOSE

Quantitative flow ratio (QFR) is a recently developed image-based index for the assessment of borderline coronary artery disease. We sought to investigate a correlation between QFR and instantaneous wave-free ratio (iFR) for the assessment of intermediate coronary stenoses.

MATERIALS AND METHODS

Patients with borderline coronary lesions (40-90% by visual assessment) undergoing iFR assessment were enrolled. QFR was derived from a modeled hyperemic flow velocity derived from angiography without adenosine-induced hyperemia. Pressure wire-derived iFR served as the reference.

RESULTS

Values of QFR and iFR from 110 vessels with a mean percent diameter stenosis of 44.6 ​± ​12.0% were compared. Mean iFR was 0.90 ​± ​0.07 and 38 (34.5%) had iFR ≤0.89. Mean QFR was 0.81 ​± ​0.10 and 44 (40%) had QFR ≤0.80. A good agreement between QFR and iFR measurements was confirmed with a mean difference of 0.09 (95%CI -0.027 to 0.207) and intraclass correlation coefficient of 0.87 (95%CI 0.81-0.91). The overall diagnostic accuracy (AUC in ROC analysis) of QFR in detecting iFR ≤0.89 was 0.87 (95%CI 0.79-0.93; p ​< ​0.001). Regarding iFR ≤0.89, the optimal cutoff value of QFR was 0.79 with sensitivity, specificity, and accuracy of 76.3%, 83.3%, and 80.0%, respectively. A 100% sensitivity was observed for a QFR cutoff value of 0.88 and a 100% specificity for a QFR cutoff value of 0.69.

CONCLUSIONS

Our study confirmed good QFR diagnostic performance and correlation with iFR for detecting the functional ischemia caused by intermediate lesions in coronary arteries. However, the pressure wire assessment with iFR might be warranted in 2/3 of patients after QFR assessment.

Plaque characteristics on coronary CT angiography associated with the positive findings of fractional flow reserve and instantaneous wave-free ratio

BACKGROUND

Fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR) are useful in determining indications for revascularization of coronary artery disease (CAD). Although the discordance of FFR and iFR was noted in approximately 20%, this cause has not been well established. We investigated patient background and features on coronary CT angiography (CCTA) showing not only FFR- and iFR-positive findings but also discordance between FFR ≤ 0.8 and iFR ≤ 0.89.

METHODS

Subjects were consecutively treated in 83 cases with 105 vessels in which stenosis of 30-90% was detected at one vessel of at least 2 mm or more in the major epicardial vessels and FFR and iFR was performed within subsequent 90 days, among suspected CAD which underwent CCTA. The factors affecting not only FFR- and iFR-positive findings, respectively, but also discordance between FFR and iFR was evaluated using logistic regression analysis on per-patient and per-vessel basis.

RESULTS

FFR- and iFR-positive findings were observed in 42 vessels (40.0%) and 34 vessels (32.3%), respectively. Discordance between FFR ≤ 0.8 and iFR ≤ 0.89 was observed in 22 vessels (21.0%) of 21 patients. In multivariate logistic analysis, LAD (OR 3.55; 95%CI 1.20-11.71; p = 0.0217) and lumen volume/myocardial weight (L/M) ratio (OR 0.93; 0.86-0.99, p = 0.0290) were significant predictors for FFR-positive findings. For iFR-positive findings, LAD (OR 3.86; 95%CI 1.12-13.31; p = 0.0236) was only significant predictor. In FFR ≤ 0.8 and iFR > 0.89 group (15 vessels, 14.3%), positive remodeling (PR) (OR 5.03, 95%CI 1.23-20.48, p = 0.0205) was significant predictor. In FFR > 0.8 and iFR ≤ 0.89 group (7 vessels, 6.7%), there were no significant predictors.

CONCLUSION

On CCTA characteristics, a relevant predictor for FFR-positive findings included low L/M ratio. PR was significant predictor in FFR-positive, iFR-negative patients among those with discordance between the FFR and iFR.

Prognostic impact of FFR/contrast FFR discordance

BACKGROUND

Contrast fractional flow reserve (cFFR) is a relatively new tool for the assessment of intermediate coronary artery stenosis and represents a reliable surrogate of FFR with the advantage of potentially simplifying functional evaluation. We aimed to compare the incidence of major adverse cardiac events (MACE) in patients undergoing functional evaluation with both FFR and cFFR based on the results of the two indexes.

METHOD AND RESULT

We retrospectively analyzed outcomes in 488 patients who underwent functional evaluation with FFR and cFFR. Patients were divided into four groups using the cutoff values of 0.80 for FFR and 0.85 for cFFR: -/- (n = 298), +/+ (n = 134), -/+(n = 31) and +/- (n = 25). All patients were treated according to FFR value. MACE rate was assessed in each group, including death, myocardial infarction and urgent target vessel revascularization (TVR). Mean follow-up time was 22 ± 15 months. Incidence of MACE at follow-up was 8.3% in FFR-/cFFR-, 14.0% in FFR+/cFFR+, 16.0% in FFR-/cFFR+ and 8.0% in FFR+/cFFR- without a significant difference amongst the 4 groups (p = 0.2). Nevertheless, a significant difference in the rate of TVR comparing FFR-/cFFR- (n = 17) and FFR-/cFFR+ (n = 5) was found at 24 months (5.7% vs 16.0%; p = 0.027).

CONCLUSION

cFFR is accurate in predicting FFR and consequently reliable in guiding coronary revascularization. In the rare case of discordance, while FFR+/cFFR- patients show a prognosis similar to FFR-/cFFR- patients, FFR-/cFFR+ patients show a prognosis similar to FFR+/cFFR+ patients.

Diagnostic Performance and Pressure Stability of a Novel Myocardial Ischemic Diagnostic Index - The Intracoronary-Electrocardiogram-Triggered Distal Pressure/Aortic Pressure Ratio

Background: We hypothesized that the intracoronary-electrocardiogram (IC-ECG)-based pressure index would be more stable and precise than the instantaneous flow reserve (iFR). We investigated the usefulness of the IC-ECG-based pressure index for diagnosing myocardial ischemia. Methods and Results: Thirty-seven consecutive patients with coronary stenosis requiring physiological assessment were enrolled in the study. iFR was measured at rest and under hyperemia in 51 and 40 lesions, respectively. The IC-ECG-triggered distal pressure (Pd)/aortic pressure (Pa) ratio (ICE-T) was defined as the mean Pd/Pa ratio in the period corresponding to the isoelectric line. The ICE-T was significantly lower than the iFR both at rest and during hyperemia (P<0.00001 for both). Fluctuations in the ICE-T pressure parameters (Pd/Pa, Pa, and Pd) were significantly smaller than those of iFR both at rest and during hyperemia. The diagnostic accuracy of predicting a fractional flow reserve (FFR) ≤0.80 of the ICE-T at rest was significantly higher than that of iFR (P=0.008). Receiver operating characteristic curve analyses showed that the ICE-T predicts FFR ≤0.80 more accurately than the iFR (area under curve 0.897 vs. 0.810 for ICE-T and iFR, respectively). Conclusions: We identified the period in the IC-ECG in which resting Pd/Pa was low and constant. The IC-ECG-based algorithm may improve the accuracy of diagnosing myocardial ischemia, without increasing invasiveness, compared with pressure-dependent indices.

Agreement between nonculprit stenosis follow-up iFR and FFR after STEMI (iSTEMI substudy)

Objective

To evaluate agreement between instantaneous wave free ratio (iFR) and fractional flow reserve (FFR) for the functional assessment of nonculprit coronary stenoses at staged follow-up after ST-segment elevation myocardial infarction (STEMI).

Results

We measured iFR and FFR at staged follow-up in 112 STEMI patients with 146 nonculprit stenoses. Median interval between STEMI and follow-up was 16 (interquartile range 5–32) days. Agreement between iFR and FFR was 77% < 5 days after STEMI and 86% after ≥ 5 days (p = 0.19). Among cases with disagreement, the proportion of cases with hemodynamically significant iFR and non-significant FFR were different when assessed < 5 days (5 in 8, 63%) versus ≥ 5 days (3 in 15, 20%) after STEMI (p = 0.04). Overall classification agreement between iFR and FFR was comparable to that observed in stable patients. Time interval between STEMI and follow-up evaluation may impact agreement between iFR and FFR.

Effect of Sex Difference on Discordance Between Instantaneous Wave-Free Ratio and Fractional Flow Reserve

BACKGROUND

Physiology-guided percutaneous coronary intervention (PCI) has demonstrated to improve clinical outcomes. Previous trials showed the agreement between iFR and FFR is approximately 80%, however the details of discordance pattern remain to be elucidated.

METHODS

We retrospectively reviewed 1024 consecutive intermediate stenotic lesions for which functional evaluation using both iFR and FFR were performed between January 2015 and June 2016. The lesions were classified into 4 groups according to iFR and FFR concordance [(iFR+/FFR+) and (iFR-/FFR-)] or discordance [(iFR+/FFR-) and (iFR-/FFR+)].

RESULTS

Our study evaluated 451 lesions, 264 lesions (58.5%) from men and 187 lesions (41.5%) from women. iFR was similar between women and men, however FFR was significantly higher in women than men. The rate of discordance between iFR and FFR was 21.3% (iFR+/FFR- 12.4% and iFR-/FFR+ 8.9%) in overall cohort. The prevalence of overall concordance and discordance were similar between men and women, however iFR+/FFR- discordance was significantly higher in women (17.1% vs. 9.1%) whereas iFR-/FFR+ discordance was significantly higher in men (11.3% vs. 4.8%). In multivariable analysis, female sex and older age were significantly associated with iFR+/FFR- discordance (odds ratio 1.88 and 1.48, respectively). Conversely, younger age, higher stenosis, and concomitant chronic total occlusion were independent predictors for iFR-/FFR+ discordance (odds ratio 0.67, 1.82, and 4.32, respectively).

CONCLUSIONS

Despite similar prevalence of overall concordance and discordance between men and women, iFR+/FFR- discordance was higher in women and iFR-/FFR+ discordance was higher in men. Multivariable analysis showed female sex to be independent predictor of iFR+/FFR- discordance.

Algorithmic Versus Expert Human Interpretation of Instantaneous Wave-Free Ratio Coronary Pressure-Wire Pull Back Data

Objectives

The aim of this study was to investigate whether algorithmic interpretation (AI) of instantaneous wave-free ratio (iFR) pressure-wire pull back data would be noninferior to expert human interpretation.

Background

Interpretation of iFR pressure-wire pull back data can be complex and is subjective.

Methods

Fifteen human experts interpreted 1,008 iFR pull back traces (691 unique, 317 duplicate). For each trace, experts determined the hemodynamic appropriateness for percutaneous coronary intervention (PCI) and, in such cases, the optimal physiological strategy for PCI. The heart team (HT) interpretation was determined by consensus of the individual expert opinions. The same 1,008 pull back traces were also interpreted algorithmically. The coprimary hypotheses of this study were that AI would be noninferior to the interpretation of the median expert human in determining: 1) the hemodynamic appropriateness for PCI; and 2) the physiological strategy for PCI.

Results

Regarding the hemodynamic appropriateness for PCI, the median expert human demonstrated 89.3% agreement with the HT in comparison with 89.4% for AI (p < 0.01 for noninferiority). Across the 372 cases judged as hemodynamically appropriate for PCI according to the HT, the median expert human demonstrated 88.8% agreement with the HT in comparison with 89.7% for AI (p < 0.0001 for noninferiority). On reproducibility testing, the HT opinion itself changed 1 in 10 times for both the appropriateness for PCI and the physiological PCI strategy. In contrast, AI showed no change.

Conclusions

AI of iFR pressure-wire pull back data was noninferior to expert human interpretation in determining both the hemodynamic appropriateness for PCI and the optimal physiological strategy for PCI.

Comparison of diagnostic performance between quantitative flow ratio, non-hyperemic pressure indices and fractional flow reserve

Background

Quantitative flow ratio (QFR) is an estimate of fractional flow reserve (FFR) and is derived from 3-dimensional quantitative coronary angiography. The DILEMMA score is an angiographic technique developed to predict FFR. Unlike other diastolic indices such as instantaneous wave-free ratio (iFR), diastolic pressure ratio (dPR) and dPR_25-75, neither QFR nor DILEMMA score require pressure wires. This study sought to compare the diagnostic performance of QFR, diastolic indices and DILEMMA score to predict FFR.

Methods

Between January 2010 and December 2013, patients who underwent invasive coronary angiography and FFR assessments were retrospectively studied. iFR and dPR were derived from FFR pressure tracings. QFR was computed using commercial software.

Results

Eighty-five lesions (25% FFR significant) were included in this study. Median FFR was 0.88 (0.81-0.92). QFR (r_s=0.801), iFR (r_s=0.710), dPR (r_s=0.716), dPR_25-75 (r_s=0.715) and DILEMMA score (r_s=-0.623) significantly correlated with FFR (P<0.001). QFR ≤0.8 had a specificity, sensitivity, positive predictive value (PPV) and negative predictive value (NPV) of 95%, 86%, 86% and 95% respectively of predicting significant FFR (P<0.001). Receiver-operating characteristic (ROC) analysis revealed the AUC to predict significant FFR for QFR (0.947), iFR (0.880), dPR (0.883), dPR_25-75 (0.880) and DILEMMA score (0.916) were not significantly different. However, QFR was a better predictor of FFR than iFR (0.947 vs. 0.770, P<0.01).

Conclusions

QFR had excellent correlation and accuracy as measured against FFR. When compared to other diastolic indices and DILEMMA score, QFR performed at least as well as the other indices. QFR predicts FFR better than it predicts iFR. QFR is a convenient tool to assess significance of coronary stenosis and a reliable alternative to pressure-wire based indices. Prospective studies are required to investigate the performance and cost-effectiveness of QFR when independently used to guide clinical decision making.

DFENet: Deep Feature Enhancement Network for Accurate Calculation of Instantaneous Wave-Free Ratio

Accurate iFR calculation can provide important clinical information for intracoronary functional assessment without administration of adenosine, which needs to locate object points in the pressure waveforms: peak, the dichrotic notch and the pressure nadir at the end of diastole. We propose a DFENet that is capable of locating object points to calculate iFR accurately. We first design a SFRA into DFENet with the idea of DenseNet. To avoid overfitting when dealing with sparse signals, we set appropriate number of network layers, growth rate of dense blocks and compression rate of transition blocks in 1D DenseNet. Then, we introduce a feature enhancement mechanism named 1D SE block for enhancing inconspicuous but vital features from SFRA, which guides DFENet to focus on these important features via feature recalibration. Finally, we prove an effective interaction mode between SFRA and 1D SE block to locate object points accurately. Adequate experiments demonstrate that DFENet reaches a high accuracy of 94.22%, error of 5.6 on object point localization of 1D pressure waveforms that include 1457 samples from 100 subjects via a cross-validation of Leave-One-Out. Comparison experiment demonstrates that the accuracy of DFENet exceeds other state-of-the-art methods by 3.35%, and ablation experiment demonstrates that the accuracy of SFRA and cSE exceed the other variations by 6.63% and 2.56% respectively. Importantly, we reveal how the DFENet enhance inconspicuous but vital feature by applying gradient-weighted class activation maps. DFENet can locate object points accurately, which is applicable to other signal processing tasks, especially in health sensing.

Evaluation of Myocardial Ischemia with iFR (Instantaneous Wave-Free Ratio in the Catheterization Laboratory: A Pilot Study

BACKGROUND

The Instantaneous Wave-Free Ratio (iFR) is an invasive functional evaluation method that does not require vasoactive drugs to induce maximum hyperemia.

OBJECTIVE

To evaluate the contribution of the iFR to the therapeutic decision-making of coronary lesions in the absence of non-invasive diagnostic methods for ischemia, or in case of discordance between these methods and coronary angiography.

METHOD

We studied patients older than 18 years, of both sexes, consecutively referred for percutaneous treatment between May 2014 and March 2018. Coronary stenotic lesions were classified by visual estimation of the stenosis diameter into moderate (41-70% stenosis) or severe (71%-90%). An iFR ≤ 0.89 was considered positive for ischemia. Logistic regression was performed using the elastic net, with placement of stents as outcome variable, and age, sex, arterial hypertension, diabetes, dyslipidemia, smoking, family history, obesity and acute myocardial infarction (AMI) as independent variables. Classification trees, ROC curves, and Box Plot graphs were constructed using the R software. A p-value < 0.05 was considered statistically significant.

RESULTS

Fifty-two patients with 96 stenotic lesions (56 moderate, 40 severe) were evaluated. The iFR cut-off point of 0.87 showed a sensitivity of 0.57 and 1-specificity of 0.88, demonstrating high accuracy in reclassifying the lesions. Diabetes mellitus, dyslipidemia, and presence of moderate lesions with an iFR < 0.87 were predictors of stent implantation. Stents were used in 32% of lesions in patients with stable coronary artery disease and AMI with or without ST elevation (non-culprit lesions).

CONCLUSION

The iFR has an additional value to the therapeutic decision making in moderate and severe coronary stenotic lesions, by contributing to the reclassification of lesions and decreasing the need for stenting.

Instantaneous wave-free ratio cutoff values for nonculprit stenosis classification in patients with ST-segment elevation myocardial infarction (an iSTEMI substudy)

OBJECTIVES

The instantaneous wave-free ratio cutoff value of <0.90 for hemodynamic significance of coronary stenoses has been validated in stable patients. We examined different cutoff values in the evaluation of nonculprit stenoses in patients with ST-segment elevation myocardial infarction.

METHODS

We measured instantaneous wave-free ratio across nonculprit stenoses in the acute setting and at follow-up in 120 patients with ST-segment elevation myocardial infarction and 157 nonculprit stenoses, of which, 113 patients with 147 nonculprit stenoses completed follow-up.

METHODS

The prevalence of nonculprit stenosis hemodynamic significance was 52% in the acute setting and 41% at follow-up. With follow-up, instantaneous wave-free ratio as reference, acute instantaneous wave-free ratio >0.90 had a negative predictive value of 89%. Acute instantaneous wave-free ratio <0.90 had a positive predictive value of 68%. Acute instantaneous wave-free ratio >0.93 had a negative predictive value of 100%. Acute instantaneous wave-free ratio <0.86 and <0.83 had positive predictive values of 71 and 77%. Using acute instantaneous wave-free ratio <0.90 as cutoff for hemodynamic significance yielded the highest degree of classification agreement between acute and follow-up instantaneous wave-free ratio.

CONCLUSIONS

In patients with ST-segment elevation myocardial infarction, acute instantaneous wave-free ratio with the cutoff values <0.90 for hemodynamic significance appears optimal in the evaluation of nonculprit stenoses and has a high negative predictive value and a moderate positive predictive value.

Diagnostic performance of a vessel-length-based method to compute the instantaneous wave-free ratio in coronary arteries

The instantaneous wave-free ratio (iFR) is a recently introduced vasodilator-free index to assess the functional severity of coronary stenosis in the resting state, while fractional flow reserve (FFR) is the gold standard index in hyperemia. The computed instantaneous wave-free ratio (CT-iFR) is a noninvasive method to estimate iFR using computer simulations. Here, we developed a vessel-length-based CT-iFR method in patient-specific models of coronary arteries. This method was implemented by coupling a three-dimensional computational fluid dynamics model with a lumped parameter model (LPM) of coronary circulation in a non-hyperemic resting state. A time-varying resistance in the LPM was used for the iFR simulation. In total, 50 coronary vessels of 32 patients were computed, and their CT-iFR values were compared with clinically measured iFRs to evaluate the diagnostic performance of the present CT-iFR method. The area under the receiver operating characteristics curve of CT-iFR validation was 0.93. In diagnostic performances of CT-iFR, accuracy, sensitivity, and specificity were 86%, 83.3%, and 86.8%, respectively. These results indicate that this CT-iFR method can be used as a pre-operative aid to establish a percutaneous coronary intervention strategy as a noninvasive alternative to iFR.

Reclassification of Treatment Strategy With Instantaneous Wave-Free Ratio and Fractional Flow Reserve: A Substudy From the iFR-SWEDEHEART Trial

OBJECTIVES

The authors sought to compare reclassification of treatment strategy following instantaneous wave-free ratio (iFR) and fractional flow reserve (FFR).

BACKGROUND

iFR was noninferior to FFR in 2 large randomized controlled trials in guiding coronary revascularization. Reclassification of treatment strategy by FFR is well-studied, but similar reports on iFR are lacking.

METHODS

The iFR-SWEDEHEART (Instantaneous Wave-Free Ratio Versus Fractional Flow Reserve in Patients With Stable Angina Pectoris or Acute Coronary Syndrome Trial) study randomized 2,037 participants with stable angina or acute coronary syndrome to treatment guided by iFR or FFR. Interventionalists entered the preferred treatment (optimal medical therapy [OMT], percutaneous coronary intervention [PCI], or coronary artery bypass grafting [CABG]) on the basis of coronary angiograms, and the final treatment decision was mandated by the iFR/FFR measurements.

RESULTS

In the iFR/FFR (n = 1,009/n = 1,004) populations, angiogram-based treatment approaches were similar (p = 0.50) with respect to OMT (38%/35%), PCI of 1 (37%/39%), 2 (15%/16%), and 3 vessels (2%/2%) and CABG (8%/8%). iFR and FFR reclassified 40% and 41% of patients, respectively (p = 0.78). The majority of reclassifications were conversion of PCI to OMT in both the iFR/FFR groups (31.4%/29.0%). Reclassification increased with increasing number of lesions evaluated (odds ratio per evaluated lesion for FFR: 1.46 [95% confidence interval: 1.22 to 1.76] vs. iFR 1.37 [95% confidence interval: 1.18 to 1.59]). Reclassification rates for patients with 1, 2, and 3 assessed vessels were 36%, 52%, and 53% (p < 0.01).

CONCLUSIONS

Reclassification of treatment strategy of intermediate lesions was common and occurred in 40% of patients with iFR or FFR. The most frequent reclassification was conversion from PCI to OMT regardless of physiology modality. Irrespective of the physiological index reclassification of angiogram-based treatment strategy increased with the number of lesions evaluated.

Revisiting the Optimal Fractional Flow Reserve and Instantaneous Wave-Free Ratio Thresholds for Predicting the Physiological Significance of Coronary Artery Disease

BACKGROUND

There has been a gradual upward creep of revascularization thresholds for both fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR), before the clinical outcome trials for both indices. The increase in revascularization that has potentially resulted is at odds with increasing evidence questioning the benefits of revascularizing stable coronary disease. Using an independent invasive reference standard, this study primarily aimed to define optimal thresholds for FFR and iFR and also aimed to compare the performance of iFR, FFR, and resting distal coronary pressure (Pd)/central aortic pressure (Pa).

METHODS AND RESULTS

Pd and Pa were measured in 75 patients undergoing coronary angiography±percutaneous coronary intervention with resting Pd/Pa, iFR, and FFR calculated. Doppler average peak flow velocity was simultaneously measured and hyperemic stenosis resistance calculated as hyperemic stenosis resistance=Pa-Pd/average peak flow velocity (using hyperemic stenosis resistance >0.80 mm Hg/cm per second as invasive reference standard). An FFR threshold of 0.75 had an optimum diagnostic accuracy (84%), whereas for iFR this was 0.86 (76%). At these thresholds, the discordance in classification between indices was 11%. The accuracy of contemporary thresholds (FFR, 0.80; iFR, 0.89) was significantly lower (78.7% and 65.3%, respectively) with a 25% rate of discordance. The optimal threshold for Pd/Pa was 0.88 (77.3% accuracy). When comparing indices at optimal thresholds, FFR showed the best diagnostic performance (area under the curve, 0.91 FFR versus 0.79 iFR and 0.77 Pd/Pa, P=0.002).

CONCLUSIONS

Contemporary thresholds provide suboptimal diagnostic accuracy compared with an FFR threshold of 0.75 and iFR threshold of 0.86 (cutoffs in derivation studies). Whether more rigorous thresholds would result in selecting populations gaining greater symptom and prognostic benefit needs assessing in future trials of physiology-guided revascularization.

Impact of Hydrostatic Pressure Variations Caused by Height Differences in Supine and Prone Positions on Fractional Flow Reserve Values in the Coronary Circulation

Objectives

To examine the influence of hydrostatic pressure on fractional flow reserve (FFR) in vivo.

Background

Systematic differences in FFR values have been observed previously in the left anterior descending artery (LAD), left circumflex artery (LCX), and right coronary artery (RCA). It has been suggested that as the hydrostatic pressure variations caused by the height differences between the catheter tip (mean aortic pressure (Pa)) and pressure-wire sensor (mean distal intracoronary pressure (Pd)) are small, intracoronary pressure need not be corrected.

Methods

Resting Pd/Pa and FFR values in 23 patients (27 lesions) were measured and compared in supine and prone positions. These values were corrected by hydrostatic pressure influenced by height levels and compared. Height differences between Pa and Pd were calculated using coronary computed tomography angiographies.

Results

In LAD, resting Pd/Pa and FFR values were significantly higher in the prone position than in the supine position (0.97 ± 0.05 vs 0.89 ± 0.04, P < 0.001 (resting Pd/Pa); 0.81 ± 0.09 vs 0.72 ± 0.07, P < 0.001 (FFR)). Conversely, in LCX and RCA, these values were significantly lower in the prone position (LCX: 0.93 ± 0.03 vs 0.98 ± 0.03, P < 0.001 (resting Pd/Pa); 0.84 ± 0.05 vs 0.89 ± 0.04, P < 0.001 (FFR); RCA: 0.91 ± 0.04 vs 0.98 ± 0.03, P=0.005 (resting Pd/Pa); 0.78 ± 0.07 vs 0.84 ± 0.07, P=0.019 (FFR)). FFR values corrected by hydrostatic pressure showed good correlations in the supine and prone positions (R² = 0.948 in LAD; R² = 0.942 in LCX; R² = 0.928 in RCA).

Conclusions

Hydrostatic pressure variations due to height levels influence intracoronary pressure measurements and largely affect resting Pd/Pa and FFR, which might have caused systematic differences in FFR values between the anterior and posterior coronary territories.

Pathophysiological coronary and microcirculatory flow alterations in aortic stenosis

Regulation of coronary blood flow is maintained through a delicate balance of ventriculoarterial and neurohumoral mechanisms. The aortic valve is integral to the functions of these systems, and disease states that compromise aortic valve integrity have the potential to seriously disrupt coronary blood flow. Aortic stenosis (AS) is the most common cause of valvular heart disease requiring medical intervention, and the prevalence and associated socio-economic burden of AS are set to increase with population ageing. Valvular stenosis precipitates a cascade of structural, microcirculatory, and neurohumoral changes, which all lead to impairment of coronary flow reserve and myocardial ischaemia even in the absence of notable coronary stenosis. Coronary physiology can potentially be normalized through interventions that relieve severe AS, but normality is often not immediately achievable and probably requires continued adaptation. Finally, the physiological assessment of coronary artery disease in patients with AS represents an ongoing challenge, as the invasive physiological measures used in current cardiology practice are yet to be validated in this population. This Review discusses the key concepts of coronary pathophysiology in patients with AS through presentation of contemporary basic science and data from animal and human studies.

Relationship between coronary diastolic pressure indexes during the wave-free period and a novel pressure-derived index: Diastolic pressure ratio at the optimal point

OBJECTIVES

We aimed to determine the diastolic pressure ratio at the optimal point (DROP) using a simple measurement algorithm and to compare DROP with distal coronary-to-aortic pressure ratios during the wave-free period (PR_WFP ) and at the mid-diastolic point (PR_MD ).

METHODS

Distal coronary and aortic pressures were measured from color pressure images of 440 beats in 48 patients with coronary stenoses. The DROP measurement point was 67% for one beat between the two rising points on the aortic pressure curve according to the distribution of the wave-free period and the mid-diastolic point.

RESULTS

DROP correlated closely with PR_WFP (r = 0.993, P < 0.0001) and PR_MD (r = 0.997, P < 0.0001). The diagnostic efficiency was excellent (area under the receiver-operating characteristic curve, 0.997) for both PR_WFP  ≤ 0.89 (specificity, 0.99; sensitivity, 0.96) and PR_MD  ≤ 0.89 (specificity, 0.95; sensitivity, 1.00).

CONCLUSIONS

A simple pressure-derived physiological marker of coronary stenosis, DROP, might represent other diastolic pressure indexes with a numerical equivalency to the instantaneous wave-free ratio. DROP can be measured automatically assuming that the rising points on the aortic pressure curve are detectable. However, further large-scale clinical investigations are needed to determine whether DROP could contribute to the further generalization of physiology-guided percutaneous coronary intervention.

Diagnostic Performance of the Instantaneous Wave-Free Ratio: Comparison With Fractional Flow Reserve

BACKGROUND

Aim of the present study was to perform a meta-analysis of all available studies comparing the instantaneous wave-free ratio (iFR) with fractional flow reserve (FFR).

METHODS AND RESULTS

Published trials comparing the iFR with FFR were searched for in PubMed, Google Scholar, and Scopus electronic databases. A total of 23 studies were available for the analysis, including 6381 stenoses. First, a meta-analysis of all studies was performed exploring the correlation between FFR and iFR. Interestingly, we found good correlation (0.798 [0.78-0.82]) between the 2 indices (P<0.001). In addition, to evaluate the diagnostic performance of iFR to identify FFR-positive coronary stenoses, we performed an additional meta-analysis, summarizing the results of receiver operating characteristics analyses from individual studies reporting the area under the curve. Summing the results of these studies, we found that iFR has a good diagnostic performance for the identification of FFR-positive stenoses (area under the curve=0.88 [0.86-0.90]; P<0.001). Furthermore, our search results included 5 studies that compared iFR and FFR to a third independent reference standard. Interestingly, no significant differences between iFR and FFR were reported in those studies.

CONCLUSIONS

The present meta-analysis shows that iFR significantly correlates with standard FFR and shows a good diagnostic performance in identifying FFR-positive coronary stenoses. Finally, iFR and FFR have similar diagnostic efficiency for detection of ischemia-inducing stenoses when tested against a third comparator.

Quantitative Flow Ratio Identifies Nonculprit Coronary Lesions Requiring Revascularization in Patients With ST-Segment-Elevation Myocardial Infarction and Multivessel Disease

BACKGROUND

The nonculprit lesion (NCL) management in ST-segment-elevation myocardial infarction patients with multivessel disease is debated. We sought to assess whether quantitative flow ratio (QFR), a noninvasive tool to identify potentially flow-limiting lesions, may be reliable in this scenario.

METHODS AND RESULTS

The present proof-of-concept study is based on a 3-step process: (1) identification of the QFR reproducibility in NCLs assessment (cohort A, n=31); (2) prospective validation of QFR diagnostic accuracy in respect to fractional flow reserve (cohort B, n=45); and (3) investigation of long-term clinical outcomes of NCLs stratified according to QFR (cohort C, n=110). A blinded core laboratory computed QFR values for all NCLs. Cohort A showed a good correlation and agreement between QFR values at index (acute) and at staged (subacute, 3-4 days later) procedures (r=0.98; 95% confidence interval, 0.96-0.99; mean difference, 0.004 [-0.027 to 0.34]). The inter-rater agreement was κ=0.9. In cohort B, fractional flow reserve and QFR identified 16 (33%) and 17 (35%) NCLs potentially flow limiting. Sensitivity, specificity, negative, and positive predictive values were 88%, 97%, 94%, and 94%. The area under the receiver operating characteristics curve was 0.96 (95% confidence interval, 0.89-0.99). Finally, in cohort C, we identified 110 ST-segment-elevation myocardial infarction patients where at least 1 NCL was left untreated. Patients with NCLs showing a QFR value ≤0.80 were at higher risk of adverse events (hazard ratio, 2.3; 95% confidence interval, 1.2-4.5; P=0.01).

CONCLUSIONS

In a limited and selected study population, our study showed that QFR computation may be a safe and reliable tool to guide coronary revascularization of NCLs in ST-segment-elevation myocardial infarction patients.

Coronary artery height differences and their effect on fractional flow reserve

BACKGROUND

Fractional flow reserve (FFR) uses pressure-based measurements to assess the severity of a coronary stenosis. Distal pressure (Pd) is often at a different vertical height to that of the proximal aortic pressure (Pa). The difference in pressure between Pd and Pa due to hydrostatic pressure, may impact FFR calculation.

METHODS

One hundred computed tomography coronary angiographies were used to measure height differences between the coronary ostia and points in the coronary tree. Mean heights were used to calculate the hydrostatic pressure effect in each artery, using a correction factor of 0.8 mmHg/cm. This was tested in a simulation of intermediate coronary stenosis to give the "corrected FFR" (cFFR) and percentage of values, which crossed a threshold of 0.8.

RESULTS

The mean height from coronary ostium to distal left anterior descending (LAD) was +5.26 cm, distal circumflex (Cx) -3.35 cm, distal right coronary artery-posterior left ventricular artery (RCA-PLV) -5.74 cm and distal RCA-posterior descending artery (PDA) +1.83 cm. For LAD, correction resulted in a mean change in FFR of +0.042, -0.027 in the Cx, -0.046 in the PLV and +0.015 in the PDA. Using 200 random FFR values between 0.75 and 0.85, the resulting cFFR crossed the clinical treatment threshold of 0.8 in 43% of LAD, 27% of Cx, 47% of PLV and 15% of PDA cases.

CONCLUSIONS

There are significant vertical height differences between the distal artery (Pd) and its point of normalization (Pa). This is likely to have a modest effect on FFR, and correcting for this results in a proportion of values crossing treatment thresholds. Operators should be mindful of this phenomenon when interpreting FFR values.

Coronary Angiography With Pressure Wire and Fractional Flow Reserve

BACKGROUND

Approximately 800 000 coronary angiography procedures are per- formed in Germany each year, mainly in order to identify coronary artery stenoses. As a rule, revascularization is indicated only when coronary artery stenoses cause relevant ischemia, but this cannot be determined unequivocally by angiography alone. Pressure wire measurement and the measurement of fractional flow reserve (FFR) enable direct evaluation of the hemodynamic relevance of coronary artery stenoses during diagnostic coronary angiography.

METHODS

This review is based on publications retrieved by a selective search in PubMed focusing especially on large randomized trials, registry studies, and meta- analyses on either pressure wire measurement or FFR.

RESULTS

According to a registry study from France, the hemodynamic evaluation of a stenosis during coronary angiography affected decisions about revascularization in 43% of cases. Randomized multicenter trials have shown that a combined end- point consisting of death, myocardial infarction, or revascularization arose signifi- cantly less commonly in the FFR group than in the group receiving angiography without FFR (13.2% versus 18.3%; p = 0.02), and that patients with one or more hemodynamically significant coronary artery stenoses (FFR ≤ 0.80) benefited more from revascularization than from medical management alone (event rate, 8.1% versus 19.5%; p <0.001). It was also shown that revascularization yields no benefit if relevant ischemia has been ruled out, even if the angiogram shows high-grade coronary artery stenoses.

CONCLUSION

All cardiac catheter laboratories should be capable of performing pres- sure wire measurements and measurements of FFR and should do so regularly if ischemia due to coronary artery stenosis cannot be demonstrated non-invasively. A pathological FFR measurement is an indication for revascularization.

Instantaneous wave-free ratio (iFR®) to determine hemodynamically significant coronary stenosis: A comprehensive review

Coronary angiography is considered to be the gold standard in the morphological evaluation of coronary artery stenosis. The morphological assessment of the severity of a coronary lesion is very subjective. Thus, the invasive fractional flow reserve (FFR) measurement represents the current standard for estimation of the hemodynamic significance of coronary artery stenosis. The FFR-guided revascularization strategy was initially classified as a Class-IA-recommendation in the 2014 European Society of Cardiology/European Association for Cardio-Thoracic Surgery guidelines on myocardial revascularization. Both the Deferral vs Performance of Percutaneous Coronary Intervention of Functionally Non-Significant Coronary Stenosis and Flow Reserve vs Angiography for Multivessel Evaluation studies showed no treatment advantage for hemodynamically insignificant stenoses. With the help of FFR (and targeted interventions), clinical results could be improved; however, the use in clinical practice is still limited due to the need of adenosine administration and a significant prolongation of the length of the procedure. Instantaneous wave-free ratio (iFR®) is a new innovative approach for the determination of the hemodynamic significance of coronary stenosis, which can be obtained at rest without the use of vasodilators. Regarding the periprocedural complications as well as prognosis, iFR® showed non-inferiority to FFR in the SWEDEHEART and DEFINE-FLAIR trials. Furthermore, iFR®, enhanced by iFR®-pullback, provides the possibility to display the iFR®-change over the course of the vessel to create a hemodynamic map.

Evaluation of the cut-off value for the instantaneous wave-free ratio of patients with aortic valve stenosis

The aim of this study was to examine the clinical value of iFR for AS patients. Functional evaluation of coronary stenosis in patients with aortic valve stenosis (AS) is challenging because the stress-induced test is often thought to be a contraindication. AS patients have a unique coronary flow pattern dependent on the diastolic phase. The instantaneous wave-free ratio (iFR) is a vasodilator-free, invasive pressure wire index of the functional severity of coronary stenosis and is calculated under resting conditions. And iFR calculated during a specific period of diastole may have the potential benefit to assess the functional severity of coronary stenosis in AS patients. We examined 158 consecutive patients (217 stenoses) whose iFR and fractional flow reserve (FFR) were measured simultaneously. Among the 158 patients, AS was observed in 13 (8.2%). The iFR showed good correlation with FFR in AS patients. The best cut-off value of iFR for the receiver-operator curve analysis to predict FFR of 0.8 was 0.9 for non-AS patients. However, it was 0.73 for AS patients. The present study demonstrated good correlation between iFR and FFR for AS patients. Vasodilator-free assessment using iFR may provide potential benefits when evaluating coronary stenosis in patients with AS. In AS patients, the best cut-off of iFR value predicting FFR value of 0.8 was lower than 0.9 that is the standard predictive value of iFR.

Non-invasive instantaneous wave-free ratio using coronary CT angiography: diagnostic performance for evaluation of ischaemia-causing coronary stenosis confirmed by invasive fractional flow reserve

AIM

To determine the diagnostic performance of instantaneous wave-free ratio (iFR) derived from non-invasive coronary computed tomography angiography (CTA; iFR_CT) for ischaemia-causing coronary stenosis, and to compare the diagnostic efficacy of iFR_CT, CTA, and CTA plus iFR_CT.

METHODS AND MATERIALS

Thirty-nine patients (55 vessels) with known or suspected coronary artery disease were included. All patients underwent invasive coronary angiography and fractional flow reserve (FFR) according to CTA findings and clinical indicators. The same raw data used for CTA were used to build patient-specific computed flow dynamic models and to calculate iFR_CT.

RESULTS

On a vessel-based level, the correlation between iFR_CT and FFR was moderate (r=0.65, p<0.05); the optimal iFR_CT cut-off value was 0.85 based on an FFR cut-off value of 0.80, resulting in 85% sensitivity, 69% specificity, 61% positive predictive value (PPV), 89% negative predictive value (NPV), and 75% accuracy. The AUC showed significant differences between iFR_CT and CTA (vessel-based: 0.84 versus 0.68; patient-based: 0.84 versus 0.62; both p<0.01). The accuracy of CTA combined with iFR_CT was significantly increased compared to CTA alone for vessels with intermediate stenosis (83% versus 40%, p<0.01).

CONCLUSION

iFR_CT showed better diagnostic performance than CTA. iFR_CT may be a promising method for detection of ischaemia-causing coronary stenosis, even in vessels with intermediate stenosis.