Melbourne Medical School Collected Works - Research Publications
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ItemNon-Newtonian Endothelial Shear Stress Simulation: Does It Matter?(FRONTIERS MEDIA SA, 2022-04-14)Patient-specific coronary endothelial shear stress (ESS) calculations using Newtonian and non-Newtonian rheological models were performed to assess whether the common assumption of Newtonian blood behavior offers similar results to a more realistic but computationally expensive non-Newtonian model. 16 coronary arteries (from 16 patients) were reconstructed from optical coherence tomographic (OCT) imaging. Pulsatile CFD simulations using Newtonian and the Quemada non-Newtonian model were performed. Endothelial shear stress (ESS) and other indices were compared. Exploratory indices including local blood viscosity (LBV) were calculated from non-Newtonian simulation data. Compared to the Newtonian results, the non-Newtonian model estimates significantly higher time-averaged ESS (1.69 (IQR 1.36)Pa versus 1.28 (1.16)Pa, p < 0.001) and ESS gradient (0.90 (1.20)Pa/mm versus 0.74 (1.03)Pa/mm, p < 0.001) throughout the cardiac cycle, under-estimating the low ESS (<1Pa) area (37.20 ± 13.57% versus 50.43 ± 14.16%, 95% CI 11.28-15.18, p < 0.001). Similar results were also found in the idealized artery simulations with non-Newtonian median ESS being higher than the Newtonian median ESS (healthy segments: 0.8238Pa versus 0.6618Pa, p < 0.001 proximal; 0.8179Pa versus 0.6610Pa, p < 0.001 distal; stenotic segments: 0.8196Pa versus 0.6611Pa, p < 0.001 proximal; 0.2546Pa versus 0.2245Pa, p < 0.001 distal) On average, the non-Newtonian model has a LBV of 1.45 times above the Newtonian model with an average peak LBV of 40-fold. Non-Newtonian blood model estimates higher quantitative ESS values than the Newtonian model. Incorporation of non-Newtonian blood behavior may improve the accuracy of ESS measurements. The non-Newtonian model also allows calculation of exploratory viscosity-based hemodynamic indices, such as local blood viscosity, which may offer additional information to detect underlying atherosclerosis.
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ItemType 2 MI and Myocardial Injury in the Era of High-sensitivity Troponin(RADCLIFFE CARDIOLOGY, 2022)Troponin has been the cornerstone of the definition of MI since its introduction to clinical practice. High-sensitivity troponin has allowed clinicians to detect degrees of myocardial damage at orders of magnitude smaller than previously and is challenging the definitions of MI, with implications for patient management and prognosis. Detection and diagnosis are no doubt enhanced by the greater sensitivity afforded by these markers, but perhaps at the expense of specificity and clarity. This review focuses on the definitions, pathophysiology, prognosis, prevention and management of type 2 MI and myocardial injury. The five types of MI were first defined in 2007 and were recently updated in 2018 in the fourth universal definition of MI. The authors explore how this pathophysiological classification is used in clinical practice, and discuss some of the unanswered questions in this era of availability of high-sensitivity troponin.
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ItemSensitivity analysis of FDA's benchmark nozzle regarding in vitro imperfections-Do we need asymmetric CFD benchmarks?(Walter de Gruyter GmbH, 2020-09-01)Abstract Modern technologies and methods such as computer simulation, so-called in silico methods, foster the development of medical devices. For accelerating the uptake of computer simulations and to increase credibility and reliability the U.S. Food and Drug Administration organized an inter-laboratory round robin study of a generic nozzle geometry. In preparation of own bench testing experiment using Particle Image Velocimetry, a custom made silicone nozzle was manufactured. By using in silico computational fluid dynamics method the influence of in vitro imperfections, such as inflow variations and geometrical deviations, on the flow field were evaluated. Based on literature the throat Reynolds number was varied Rethroat = 500 ± 50. It could be shown that the flow field errors resulted from variations of inlet conditions can be largely eliminated by normalizing if the Reynolds number is known. Furthermore, a symmetric imperfection of the silicone model within manufacturing tolerance does not affect the flow as much as an asymmetric failure such as an unintended curvature of the nozzle. In brief, we can conclude that geometrical imperfection of the reference experiment should be considered accordingly to in silico modelling. The question arises, if an asymmetric benchmark for biofluid analysis needs to be established. An eccentric nozzle benchmark could be a suitable case and will be further investigated.
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ItemThe invasive assessment of coronary atherosclerosis and stents using optical coherence tomography: a clinical update.(BMJ, 2013)Ischaemic heart disease (IHD) remains one of the leading causes of death. Atherosclerosis has been intensely researched given the IHD prevalence and the financial impacts on healthcare systems. More recently, in vivo characterisation of coronary atherosclerotic plaque and tissue responses following stent implantation in a coronary artery has been made possible by a novel technology called optical coherence tomography (OCT). OCT is a light-based, invasive, intracoronary imaging modality long applied to the field of ophthalmology and now in clinical use worldwide. It gives a unique view of within the coronary artery using near-infrared light with a resolution of 15 microns, 10 times higher than other invasive coronary imaging techniques like intravascular ultrasound. The technology is being adopted to comprehensively detect features that make plaques 'vulnerable' (eg, large lipid pool, thin, fibrous-cap atheroma), whether stents are implanted optimally within the artery, and visualise the small layers of tissue that form over stent metal surfaces over time, which in turn may provide surrogate markers for long-term stent safety and help guide the optimal duration of dual antiplatelet therapy, a topic of big discussion at the current point of time.
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ItemMicrovascular retinopathy and angiographically-demonstrated coronary artery disease: A cross-sectional, observational study(PUBLIC LIBRARY SCIENCE, 2018-05-08)Epidemiological studies suggest retinal microvascular abnormalities predict cardiac events. This study examined microvascular features associated with coronary artery abnormalities. This was a single-centre, cross-sectional, observational study of 144 consecutive subjects undergoing coronary angiography for clinical indications. Their angiograms were deidentified and graded for disease (Leaman score, LAD stenosis ≥ 70%, number of vessels stenosed ≥ 70%), and Thrombolysis in Myocardial Infarction (TIMI) blush score. Subjects also underwent retinal photography (KOWA non-mydriatic camera, Japan), and their deidentified retinal images were graded for hypertensive microvascular retinopathy (Wong and Mitchell classification), vessel calibre using a computer-assisted method (IVAN, U Wisconsin), and diabetic retinopathy (modified Airlie House scheme) independently by a trained grader and an ophthalmologist. Retinal abnormalities were compared between subjects with high and low angiography scores using one way ANOVA, Chi squared and logistic regression analysis (StataCorp, Texas). Subjects had a mean age of 61 years (range 32-88), and included 101 males (70%). Seventeen (12%) had Leaman scores > 10.5, 46 (32%) had LAD stenosis, 13 (9%) had ≥ 3 arteries stenosed, and 20 (14%) had TIMI blush scores < 1. Twenty-six subjects (18%) had a retinal hemorrhage, and 115 (74%) a mild or moderate hypertensive retinopathy. Fifty-five (38%) had diabetes, and 24 (17%) a background (n = 20) or proliferative (n = 4) diabetic retinopathy. A retinal hemorrhage (p = 0.046), moderate microvascular retinopathy (p = 0.08) and proliferative diabetic retinopathy (p = 0.04) were all associated with a higher Leaman score. Venular calibre was increased with triple vessel disease (205.7 ± 21.6 μm, and 193.7 ± 22.3 μm in normals, p = 0.03). Diabetic retinopathy correlated with an increased TIMI blush score (p = 0.01). Retinal microvascular imaging warrants further evaluation in identifying the presence, extent and nature of coronary artery disease.
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ItemNo Preview AvailableConsensus Guidelines for International Cardiology Services Delivery During COVID-19 Pandemic in Australia and New Zealand(ELSEVIER SCIENCE INC, 2020-06)The global coronavirus disease (COVID-19) pandemic poses an unprecedented stress on healthcare systems internationally. These Health system-wide demands call for efficient utilisation of resources at this time in a fair, consistent, ethical and efficient manner would improve our ability to treat patients. Excellent co-operation between hospital units (especially intensive care unit [ICU], emergency department [ED] and cardiology) is critical in ensuring optimal patient outcomes. The purpose of this document is to provide practical guidelines for the effective use of interventional cardiology services in Australia and New Zealand. The document will be updated regularly as new evidence and knowledge is gained with time. Goals Considerations.
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ItemSmall vessel disease and intracoronary plaque composition: a single centre cross-sectional observational study(NATURE PORTFOLIO, 2019-03-12)Cardiac events are commonly triggered by rupture of intracoronary plaque. Many studies have suggested that retinal small vessel abnormalities predict cardiac events. The present study examined retinal microvascular abnormalities associated with intracoronary plaque. This was a single centre cross-sectional observational study of consecutive subjects who underwent coronary angiography and intracoronary optical coherence tomography (OCT) of occlusive coronary artery disease. Subjects' retinal images were deidentified and graded for microvascular retinopathy (Wong and Mitchell classification), and vessel calibre using a semiautomated method based on Knudtson's modification of the Parr Hubbard formula. Control subjects had no significant plaque on angiography. Analysis used the Fisher's exact test or student t-test. Thirty-two subjects with intracoronary plaque including 22 males (79%) had a mean age of 62.6 ± 9.4 years. Twenty-four (86%) had hypertension, 10 (36%) had diabetes, and 21 (75%) were current or former smokers. Their average mean arterial pressure was 90.5 ± 5.8 mm Hg, and mean eGFR was 74 ± 15/min/1.73 m2. On angiography, 23 (82%) had a left anterior descending artery (LAD) stenosis, their mean diseased vessel score was 1.86 ± 1.21, and mean total stent number was 1.04 ± 1.00. Plaque type was mainly (>50%) fibrous (n = 7), lipid (n = 7), calcific (n = 10), or mixed (n = 4). Control subjects had a lower mean diastolic BP (p = 0.01), were less likely to have an LAD stenosis (p < 0.001), a lower mean diseased vessel score (p < 0.001) and fewer stents (p = 0.02). Subjects with plaque were more likely to have a moderate microvascular retinopathy than those with none (p = 0.004). Moderate retinopathy was more common with lipid (p = 0.05) or calcific (p = 0.003) plaque. Individuals with calcific plaque had a larger arteriole calibre (158.4 ± 15.2 µm) than those with no plaque (143.8 ± 10.6 µm, p = 0.02), but calibre was not related to diabetes or smoking. Calibre did not correlate with plaque length, thickness or arc angle. Thus, subjects with intracoronary artery plaque are more likely to have a moderate microvascular retinopathy. Those with calcific plaque have larger retinal arterioles which is consistent with our previous finding of larger vessel calibre in triple coronary artery disease. Retinal microvascular imaging warrants further evaluation in identifying severe coronary artery disease.
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ItemExpert recommendations on the assessment of wall shear stress in human coronary arteries: existing methodologies, technical considerations, and clinical applications(Oxford University Press (OUP), 2019-11-01)Abstract