A modified method of noninvasive computed tomography derived fractional flow reserve based on the microvascular growth space
Introduction
Epicardial coronary artery stenosis may lead to myocardial ischemia, and obstructive coronary artery disease (CAD) caused by this is one of the primary causes of death globally [1], [2], [3], [4]. Currently, fractional flow reserve (FFR) is an effective technique to functionally evaluate the significance of coronary artery stenosis, but its clinical application was limited by its invasive operation, high cost, and requirement for the drug-induced hyperemic state [5], [6], [7], [8]. To overcome these limitations, computational fluid dynamics (CFD) has been employed for analyzing hemodynamics [9,10].
Notably, non-invasive computed tomography-derived FFR (CT-FFR) has shown great diagnostic accuracy in quantitatively assessing the severity of coronary artery stenosis [11], [12], [13], [14], [15]. There are three main steps to derive hemodynamics of coronary arteries in CFD simulation [16,17]: (1) Reconstruction of patient-individualized 3D model of coronary artery tree[10]; (2) Determination of personalized inlet and outlet boundary conditions (BC) [18,19]; (3) Numerical solver for Navier-Stokes equation and continuity equation [20]. Thus, the determination of BCs is critical for hemodynamics simulation, and the accurate BCs following physiological laws seriously affect the accuracy of calculated FFR [21].
In previous studies, Taylor et al. determined the unique resistance value of each outlet according to the left ventricular myocardium mass, the allometric scaling laws, and the morphometry laws [20]. They simulated the adenosine-induced hyperemia state by reducing the downstream microcirculation resistance. Moreover, Lo et al. connected a two-element Windkessel model at each outlet to represent the downstream vascular system, providing pressure BCs [17]. In Tesche et al.’s study, the outlet BCs were provided by the coronary microvascular model and estimated based on static state conditions including systolic and diastolic blood pressure, heart rate and ventricular size [22]. However, the resistance of microcirculation assumed according to physiological laws and hypotheses in aforementioned researches may not reflect the real microvascular resistance, and more accurate methods warrant exploration. In addition, previous studies used brachial artery pressure (BAP) as the inlet BC. However, BAP has diurnal fluctuations that may have an impact on the simulation results, but was ignored in the above studies [23].
Previous studies demonstrated that the growth of downstream microcirculation is related to the left ventricular myocardium. In our study, our purpose was to optimize the CT-FFR simulation from the perspective of outlet BCs. Moreover, we verified the stability of BCs by taking the circadian fluctuation of inlet boundary conditions into account. The feasibility of this calculation method has also been verified in this study.
Section snippets
Study population
All study procedures were approved by the Ethics Committee of Zhongshan Hospital, Fudan University. Symptomatic consecutive adult patients with clinically suspected stable CAD in the Department of Cardiovascular Medicine, Zhongshan Hospital, Fudan University underwent preoperative CCTA with standard protocol and following invasive coronary angiography (ICA) and invasive FFR measurement within fifteen days if CCTA suggested the presence of stenosis in the main branch coronary arteries (greater
Patient and lesion characteristics
Patients’ demographics and clinical characteristics are summarized in Table 1. Nineteen patients (male/female: 11/8; age: 60.8 ± 8.1) with coronary artery stenosis (10 lesions) were retrospectively studied. Among these patients, 10.5% have diabetes, 5.3% have a family history, 5.3% have hyperlipidemia, 47.4% have hypertension, and 26.3% have current smoking. Of 19 coronary arteries with an average stenosis degree of 71.3%, 17 are left anterior descending arteries (LAD), 1 is right coronary
Discussion
In this retrospective study, we established a modified method to optimize the outlet BC, considering the whole myocardial as the growth space for microcirculation. The effect of circadian fluctuation of BAP on CT-FFR simulation was also investigated. It was demonstrated that the modified CT-FFR method was feasible and stable with high diagnostic accuracy, suggesting the potential of CT-FFR as a benefit assessment for discrimination of myocardial ischemia.
Accurate BC reflecting patient-specific
Conclusions
This study established a modified method for more accurate CT-FFR, considering the whole myocardial as the growth space for microcirculation. Circadian fluctuations in BAP were found to be negligible when it was used as the inlet BC. The results suggest high diagnostic accuracy and short time consumption for diagnosing myocardium ischemia compared with invasive FFR.
Declaration of Competing Interest
It should be understood that none of the authors have any financial or scientific conflicts of interest about the research described in this manuscript.
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These authors contributed equally to this work.