Estimation of coronary artery hyperemic blood flow based on arterial lumen volume using angiographic images

The purpose of this study is to develop a method to estimate the hyperemic blood flow in a coronary artery using the sum of the distal lumen volumes in a swine animal model. The limitations of visually assessing coronary artery disease are well known. These limitations are particularly important in intermediate coronary lesions where it is difficult to determine whether a particular lesion is the cause of ischemia. Therefore, a functional measure of stenosis severity is needed using angiographic image data. Coronary arteriography was performed in 10 swine (Yorkshire, 25–35 kg) after power injection of contrast material into the left main coronary artery. A densitometry technique was used to quantify regional flow and lumen volume in vivo after inducing hyperemia. Additionally, 3 swine hearts were casted and imaged post-mortem using cone-beam CT to obtain the lumen volume and the arterial length of corresponding coronary arteries. Using densitometry, the results showed that the stem hyperemic flow (Q) and the associated crown lumen volume (V) were related by Q = 159.08 V3/4 (r = 0.98, SEE = 10.59 ml/min). The stem hyperemic flow and the associated crown length (L) using cone-beam CT were related by Q = 2.89 L (r = 0.99, SEE = 8.72 ml/min). These results indicate that measured arterial branch lengths or lumen volumes can potentially be used to predict the expected hyperemic flow in an arterial tree. This, in conjunction with measured hyperemic flow in the presence of a stenosis, could be used to predict fractional flow reserve based entirely on angiographic data

Intravascular Ultrasound

Intravascular ultrasound (IVUS) is a cardiovascular imaging technology using a specially designed catheter with a miniaturized ultrasound probe for the assessment of vascular anatomy with detailed visualization of arterial layers. Over the past two decades, this technology has developed into an indispensable tool for research and clinical practice in cardiovascular medicine, offering the opportunity to gather diagnostic information about the process of atherosclerosis in vivo, and to directly observe the effects of various interventions on the plaque and arterial wall. This book aims to give a comprehensive overview of this rapidly evolving technique from basic principles and instrumentation to research and clinical applications with future perspectives

Integration of patient-specific myocardial perfusion in CT-based FFR computations

Computed Tomography based Fractional Flow Reserve (FFRCT) is a non-invasive simulation based measure for diagnosing ischaemia causing arterial stenoses. One drawback of simulation based measures are the assumptions made that are usually based on population studies that may not apply to all patients. This study describes the fundamental characteristics to FFRCT simulations and how the simulations can be simplified where it can and where assumptions break down. The investigation starts with assessing whether the simulations can be simplified to a steady flow, whilst uncharacteristic of typical coronary blood flow, it was demonstrated that with regards to the diagnostic measures of FFR, and its variants dFFR or iFR, that steady flow was applicable, which reduces the complexity of the simulation, saving computational time and resources as well as removing uncertainty in the input assumptions.[1] The next phase of the study explored the downstream conditions of the FFRCT simulation scheme. The microvasculature is too small to resolve in CT imaging and therefore assumptions are made regarding its form and function. Whilst form function relationships of the microvasculature are well established in the literature for the structure of microvessels at rest, assumptions regarding stress or hyperaemia are used for FFRCT to simulate maximal blood flow through the coronary arteries. The investigation utilised perfusion imaging to assess the validity of this assumption and showed how variable the microvascular response to hyperaemia is, and the effect that has on FFRCT.[2][3] The last part of the study produced a novel method of estimating the microvascular response using patient metrics such as age, sex, diabetes, smoker status etc, from a training dataset of 101 patients. By using the patient-specific microvascular response, FFRCT simulations better represent the coronary artery health of the patient. On a separate dataset of 10 patients, the FFRCT measurements using this novel method was also validated against the gold standard invasive FFR and has demonstrated a better diagnostic performance (94% accuracy) than the conventional method (82% accuracy). Secondly the novel method also created a probabilistic spread of FFRCT values that may provide better utility than a strict binary measure. Whilst this novel method will require further validation with larger studies, it nevertheless has potential to address some of the current drawbacks of FFRCT methods when applied to a varied patient demographic

Patient-Specific Modeling of Altered Coronary Artery Hemodynamics to Predict Morbidity in Patients with Anomalous Origin of a Coronary Artery

Anomalous aortic origin of a coronary artery (AAOCA) is a condition where a coronary artery arises from the opposite aortic sinus, often with acute angle of origin (AO). AAOCA is associated with ischemia.1 This is especially concerning when the anomalous coronary artery takes an intramural course within the aortic wall, creating the potential for distortion or compression. Unroofing surgery replaces a restrictive ostium and intramural segment with a large ostium from the appropriate sinus and aims to create a less acute AO. Although these anatomical features may alter coronary artery blood flow patterns, hemodynamic indices such as time averaged wall shear stress (TAWSS), oscillatory shear index (OSI) and fractional flow reserve (FFR) that impact a patient’s future risk for ischemia and morbidity 2–6 remain largely unexplored. We hypothesized that morphology of the anomalous coronary artery has a significant impact on local hemodynamics of AAOCA and aimed to 1) characterize hemodynamic alterations in AAOCA by patient-specific simulation of patients pre-operative and post-unroofing using advanced coronary artery boundary conditions, 2) assess the impact of AO on the severity of hemodynamic alterations, and 3) characterize the hemodynamic effect of proximal narrowing of the anomalous artery and hyperemic resistance of the downstream vasculature (HMR) on FFR. Findings from Aim 1 suggested that different flow patterns exist natively between right and left coronary arteries, a reduction in TAWSS is observed post-unroofing, and that unroofing may normalize TAWSS but with variance related to the AO. Data from Aim 2 indicated that AO alters TAWSS and OSI in simulations run from a patient-specific model with virtually rotated AOs. The arterial wall experienced lower TAWSS for more acute AO near the ostium. Distal to the ostium, arterial wall experienced higher TAWSS for more acute AO. Findings from Aim 3 showed that for a given narrowing, higher HMR resulted in higher FFR thereby mimicking the interaction of the upstream and downstream micro-vasculature resistance to regulate FFR for the first time using computational models of AAOCA. Virtual manipulation of the anomalous artery provided a direct comparison for the effect of the anatomic high-risk features. Collectively, these results serve as the foundation for larger studies of AAOCA that could correlate hemodynamics with outcomes for risk stratification and surgical evaluation