Comparison of Instantaneous Wave-Free Ratio (iFR) and Fractional Flow Reserve (FFR) with respect to Their Sensitivities to Cardiovascular Factors: A Computational Model-Based Study

Coronary protection using a pressure wire during transcatheter aortic valve implantation

Coronary obstruction is a rare but life-threatening complication of transcatheter aortic valve implantation (TAVI). This article describes the case of a patient with severe aortic valve stenosis treated with TAVI, during which preventive coronary wiring using a pressure wire was performed for coronary protection. After the deployment of the transcatheter heart valve (THV), the values of the fractional flow reserve (FFR) and resting full-cycle ratio (RFR) remarkably decreased, although the findings of transesophageal echocardiography and coronary angiography did not suggest coronary obstruction. Intravascular ultrasound revealed severe stenosis in the left main trunk due to the displacement of the calcified native leaflets. The decrease in the FFR and RFR values after THV deployment led to a diagnosis of partial coronary obstruction, and percutaneous coronary intervention was successfully performed. In patients at a high risk for coronary obstruction, coronary protection with a pressure wire is useful for the diagnosis and prevention of coronary flow deterioration during TAVI. Functional assessment using a pressure wire before and after TAVI may contribute to the accurate diagnosis of coronary obstruction.

Learning objective

Accurate diagnosis of coronary obstruction during transcatheter aortic valve implantation (TAVI) is important for successful management. In patients at a high risk for coronary obstruction, coronary protection with a pressure wire is useful for the diagnosis and prevention of coronary flow deterioration during TAVI. The remarkable decrease in the fractional flow reserve and resting full-cycle ratio values after the deployment of the transcatheter heart valve may suggest coronary obstruction.

Simulation of coronary capillary transit time based on full vascular model of the heart

Capillary transit time (CTT) is a fundamental determinant of gas exchange between blood and tissues in the heart and other organs. Despite advances in experimental techniques, it remains difficult to measure coronary CTT in vivo. Here, we developed a novel computational framework that couples coronary microcirculation with cardiac mechanics in a closed-loop system that enables prediction of hemodynamics in the entire coronary network, including arteries, veins, and capillaries. We also developed a novel "particle-tracking" approach for computing CTT where "virtual tracers" are individually tracked as they traverse the capillary network. Model predictions compare well with blood pressure and flow rate distributions in the arterial network reported in previous studies. Model predictions of transit times in the capillaries (1.21 ± 1.5 s) and entire coronary network (11.8 ± 1.8 s) also agree with measurements. We show that, with increasing coronary artery stenosis (as quantified by fractional flow reserve, FFR), intravascular pressure and flow rate downstream are reduced but remain non-stationary even at 100 % stenosis because some flow (∼3 %) is redistributed from the non-occluded to the occluded territories. Importantly, the model predicts that occlusion of a large artery results in higher CTT. For moderate stenosis (FFR > 0.6), the increase in CTT (from 1.21 s without stenosis to 2.23 s at FFR=0.6) is caused by a decrease in capillary flow rate. In severe stenosis (FFR = 0.1), the increase in CTT to 14.2 s is due to both a decrease in flow rate and an increase in path length taken by "virtual tracers" in the capillary network.

Research on individualized distribution approach of coronary resting blood flow for noninvasive calculation of fractional flow reserve

BACKGROUND AND OBJECTIVES

The distribution of coronary resting blood flow is critical for accurately calculating the computed tomography (CT) angiography-derived fractional flow reserve (FFRCT). However, the diagnostic accuracy of FFRCT calculated by the fixed exponents between two risk factors and coronary resting blood flow, including myocardial mass and diameter of the coronary artery branch, was insufficient compared with invasive fractional flow reserve (FFR). In this study, we proposed the individualized distribution of coronary resting blood flow based on coronary ultrasound blood flow measurement, to improve the diagnostic accuracy of FFRCT calculation.

METHODS

Five risk factors and an unknown coefficient K were integrated to calculate the individualized distribution of coronary resting blood flow. The K value was fit using the least square method based on coronary ultrasound blood flow measurement results of 30 volunteers. We developed a novel approach for calculating the individualized distribution of coronary resting blood flow and applied it to calculate FFRCT (FFRCTI). Then, we tested the performance of the individualized distribution approach by comparing it with the approach proposed by Taylor based on coronary ultrasound blood flow measurement results of 13 volunteers. Finally, we tested the diagnostic accuracy of FFRCT calculated by two approaches in invasive FFR of 121 vessels with coronary stenosis.

RESULTS

We identified five risk factors and 6.83×10-5 for K value, including cardiac output, mean arterial pressure, myocardial mass, coronary artery volume, and diameter of the coronary artery branch, to calculate the individualized distribution of coronary resting blood flow. The mean square error of the individualized distribution approach (0.0088) was significantly less than that of the approach proposed by Taylor (0.0799). The diagnostic accuracy of FFRCTI calculated by the individualized distribution approach (91.74%) was higher than that of the approach proposed by Taylor (FFRCTT) (82.64%).

CONCLUSIONS

The individualized distribution approach of coronary resting blood flow can significantly improve the diagnostic accuracy of FFRCT calculation compared with invasive FFR, and support its wide clinical application for diagnosing myocardial ischemia caused by coronary stenosis.

Comparative study of fractional flow reserve and diastolic pressure ratio using a guidewire with a sensor for measuring intravascular pressure

PURPOSE

This study aimed to evaluate the correlation and diagnostic agreement between diastolic pressure ratio (dPR) and fractional flow reserve (FFR) in a Japanese real-world setting.

DESIGN

Prospective multicenter observational study.

METHODS

This study included 100 patients with intermediate coronary artery stenosis at 4 Japanese hospitals. For these lesions, FFR and dPR were measured using a guidewire with a sensor and a monitor to measure intravascular pressure. The correlation and diagnostic agreement between FFR and dPR were assessed. When both FFR and dPR were negative or positive, the results were considered to be concordant. When one was positive and the other was negative, the result was regarded as discordant (positive discordance, FFR > 0.80 and dPR ≤ 0.89; negative discordance, FFR ≤ 0.80 and dPR > 0.89).

RESULTS

Overall, the FFR and dPR were well-correlated (R = 0.841). FFR and dPR were concordant in 89% of cases (concordant normal, 43%; concordant abnormal, 46%) and discordant in 11% (positive discordance, 7%; negative discordance, 4%). No significant difference was observed in the rate of concordant results between patients with and without diabetes mellitus. The diagnostic concordance rate was significantly different among the 3 coronary arteries (right coronary artery, 93.3%; left anterior descending artery, 93.2%; and left circumflex artery, 58.3%; P = .001). Additionally, the rate of concordant results tended to be higher when using intravenous administration of adenosine than when using intracoronary bolus injection of nicorandil (adenosine, 95.1%; nicorandil, 84.7%; P = .103).

CONCLUSION

We found that dPR was highly correlated with FFR, and diagnostic discordance was observed in 11% of the lesions. Several factors, including lesion location and medication for hyperemia, may cause the diagnostic discordance between dPR and FFR.

Effect of Elevated Left Ventricular End Diastolic Pressure on Instantaneous Wave-Free Ratio and Fractional Flow Reserve Discordance

Background

Instantaneous wave-free ratio (iFR)-guided physiological assessment has been shown to be non-inferior to fractional flow reserve (FFR)-guided assessment for deciding best treatment strategy for angiographically intermediate stenosis. The diagnostic accuracy of iFR compared to FFR reported in various studies is around 80%. Many factors can lead to iFR/FFR discordance, though underlying physiological mechanism of discordance and its associated factors have not been fully evaluated. The effect of left ventricle end diastolic pressure (LVEDP) on iFR/FFR discordance is unknown and needs further evaluation.

Methods

We performed a single center, non-randomized, both retrospective and prospective study. A total of 65 patients with intermediate coronary stenosis undergoing physiological assessment were included in the study. Patients were assigned to two groups (normal LVEDP and high LVEDP group) based on LVEDP cutoff of 15 mm Hg. iFR and FFR were measured for each patient and iFR/FFR results were compared between the two groups.

Results

A significantly large number of patients in elevated LVEDP group had iFR/FFR discordance compared to normal LVEDP group (42.8% vs. 6.7%, P = 0.001). More patients with acute coronary syndrome (ACS) had discordance compared to stale coronary artery disease (CAD) patients (53% vs. 15%, P = 0.003).

Conclusions

Elevated LVEDP can affect iFR and FFR measurements and can lead to discordance. Further studies are required to determine effect of elevated LVEDP on iFR/FFR discordance and whether such discordance is clinically relevant. “Normal range” iFR results should be cautiously interpreted in patients with elevated LVEDP, especially those with ACS.

In vitro Biomodels in Stenotic Arteries to Perform Blood Analogues Flow Visualizations and Measurements: A Review

Cardiovascular diseases are one of the leading causes of death globally and the most common pathological process is atherosclerosis. Over the years, these cardiovascular complications have been extensively studied by applying in vivo, in vitro and numerical methods (in silico). In vivo studies represent more accurately the physiological conditions and provide the most realistic data. Nevertheless, these approaches are expensive, and it is complex to control several physiological variables. Hence, the continuous effort to find reliable alternative methods has been growing. In the last decades, numerical simulations have been widely used to assess the blood flow behavior in stenotic arteries and, consequently, providing insights into the cardiovascular disease condition, its progression and therapeutic optimization. However, it is necessary to ensure its accuracy and reliability by comparing the numerical simulations with clinical and experimental data. For this reason, with the progress of the in vitro flow measurement techniques and rapid prototyping, experimental investigation of hemodynamics has gained widespread attention. The present work reviews state-of-the-art in vitro macro-scale arterial stenotic biomodels for flow measurements, summarizing the different fabrication methods, blood analogues and highlighting advantages and limitations of the most used techniques.