845 research outputs found

    Whole-heart modelling with valves in a fluid–structure interaction framework

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    Computational modelling of whole-heart function is a useful tool to study heart mechanics and haemodynamics. Many existing heart models focus on electromechanical aspect without considering physiological valves and use simplified fluid models instead. In this study we develop a four-chamber heart model featuring realistic chamber geometry, detailed valve modelling, hyperelasticity with fibre architecture and fluid–structure interaction analysis. Our model is used to investigate heart behaviours with different modelling assumptions including restricted/free valve annular dynamics, and with/without heart-pericardium interactions. Our simulation results capture the interactions between valve leaflet and surrounding flow, typical left ventricular flow vortices, typical venous and transvalvular flow waveform, and physiological heart deformations such as atrioventricular plane movement. The improvement of ventricular filling and atrial emptying at early diastole is evident with free annulus. In addition, we find that the added pericardial forces on the heart have a predominant effect on atrial wall deformation especially during atrial contraction, and further help with the atrial filling process. Most importantly, the current study provides a framework for comprehensive multi-physics whole-heart modelling considering all heart valves and fluid–structure interactions

    Feasibility of non-gated dynamic fetal cardiac MRI for identification of fetal cardiovascular anatomy

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    INTRODUCTION To evaluate the feasibility of identifying the fetal cardiac and thoracic vascular structures with non-gated dynamic balanced steady-state free precession (SSFP) MRI sequences. METHODS We retrospectively assessed the visibility of cardiovascular anatomy in 60 fetuses without suspicion of congenital heart defect. Non-gated dynamic balanced SSFP sequences were acquired in three anatomic planes of the fetal thorax. The images were analyzed following a segmental approach in consensus reading by an experienced pediatric cardiologist and radiologist. An imaging score was defined by giving one point to each visualized structure, yielding a maximum score of 21 points. Image quality was rated from 0 (poor) to 2 (excellent). The influence of gestational age (GA), field strength, placenta position, and maternal panniculus on image quality and imaging score were tested. RESULTS 30 scans were performed at 1.5T, 30 at 3T. Heart position, atria and ventricles could be seen in all 60 fetuses. Basic diagnosis (>12 points) was achieved in 54 cases. The mean imaging score was 16.8+/-3.8. Maternal panniculus (r=-0.3; p=0.015) and gestational age (r=0.6; p<0.001) correlated with imaging score. Field strength influenced image quality, with 1.5T being better than 3T images (p=0.012). Imaging score or quality were independent of placenta position. DISCUSSION/CONCLUSION Fetal cardiac MRI with non-gated SSFP sequences enables recognition of basic cardiovascular anatomy

    The effects of running, cycling, and duathlon exercise performance on cardiac function, haemodynamics and regulation

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    This thesis examined the effects of prolonged exercise, specifically Olympic Distance (OD)duathlon upon ultrasound derived indices of cardiac function, cardiac autonomic regulation measured via heart rate variability (HRV), and high-sensitivity cardiac troponin T (hs-cTnT)release. The primary aims were to (1) ascertain the influence of Olympic distance (OD) duathlon performance on cardiac function; (2) to investigate potential relationships between autonomic regulation, hs-cTnT release, and cardiac function, and (3) to investigate the effect of the individual legs of an OD duathlon on post-exercise cardiac function and to quantify the potential performance reserve of highly-trained endurance athletes when completing standalone legs of the duathlon. Findings from a systematic review and meta-analysis(Chapter 1) on research that performed serial echocardiographic and troponin measurements before and after exercise, intensity predicted changes in post-exercise cardiac troponin release and diastolic function. The findings agreed with previous meta-analyses using a more recent sample of studies; however, the recommendation for future studies to implement advanced cardiac imaging techniques, such as myocardial speckle tracking into their data collection would provide a more sensitive measure of post-exercise cardiac function. Whilst a large degree of heterogeneity in the results exists, this was in part explained by study exercise heart rate, participant age, and the prevalence of cardiac troponin release above the clinical detection threshold. The study performed in Chapter 3 was the first to investigate the effects of OD duathlon exercise on immediate and 24 hours post-exercise cardiac function. Additionally, a second OD duathlon was performed by participants with intra-leg measurements of cardiac function. In a highly trained cohort, there was evidence of transient post-exercise reductions in cardiac function and elevated serum high-sensitivity cardiac troponin T (hs-cTnT) above the clinical reference value, which was largely resolved within 24h of recovery. This study also demonstrated the reliability of lab-based duathlon exercise in a highly trained cohort and identified the pacing features of experienced multi-sport athletes that partially explained the different findings between the running and cycling legs of the duathlon. By investigating each leg of the duathlon individually (10k run, 5k run, 40k cycle), both at duathlon race-pace (DM) and maximal (Max) intensity on separate occasions, the performance reserve of the highly-trained cohort was quantified and further explored. The studies presented in Chapters 4 and 5 revealed that experienced duathletes were able to improve their speed across each leg by between 5-15% in a laboratory setting, compared to the duathlon effort. Additionally, the maximal effort 10k run leg provoked the most persistent changes to cardiac function that were present at 6h of recovery. Changes in cardiac function post DM 10k confirmed the findings of Chapter 3 that the greatest magnitude of cardiac perturbations occur following the initial 10k run leg. Aside from the Max 10k run and 40k cycle trials, all perturbations had resolved within 6h of recovery after each bout of exercise, highlighting the importance of recovery following maximal intensity efforts. The lack of 6h and 24h recovery data in Chapter 4, and Chapters 5 and 6, respectively is a shortcoming of these findings and therefore limits interpretation in the context of providing athletic guidance. Future research in this area should endeavour to include 6h and 24h recovery measures as standard, as multi-sport athletes typically perform multiple daily training sessions. The implications of substantial cardiac fatigue accumulation over many years of endurance training history are still unclear, and athletes may benefit from preventingits occurrence

    Interaction of elastomechanics and fluid dynamics in the human heart : Opportunities and challenges of light coupling strategies

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    Das menschliche Herz ist das hochkomplexe Herzstück des kardiovaskulären Systems, das permanent, zuverlässig und autonom den Blutfluss im Körper aufrechterhält. In Computermodellen wird die Funktionalität des Herzens nachgebildet, um Simulationsstudien durchzuführen, die tiefere Einblicke in die zugrundeliegenden Phänomene ermöglichen oder die Möglichkeit bieten, relevante Parameter unter vollständig kontrollierten Bedingungen zu variieren. Angesichts der Tatsache, dass Herz-Kreislauf-Erkrankungen die häufigste Todesursache in den Ländern der westlichen Hemisphäre sind, ist ein Beitrag zur frühzeit- igen Diagnose derselben von großer klinischer Bedeutung. In diesem Zusammenhang können computergestützte Strömungssimulationen wertvolle Einblicke in die Blutflussdynamik liefern und bieten somit die Möglichkeit, einen zentralen Bereich der Physik dieses multiphysikalischen Organs zu untersuchen. Da die Verformung der Endokardoberfläche den Blutfluss antreibt, müssen die Effekte der Elastomechanik als Randbedingungen für solche Strömungssimulationen berücksichtigt werden. Um im klinischen Kontext relevant zu sein, muss jedoch ein Mittelweg zwischen dem Rechenaufwand und der erforderlichen Genauigkeit gefunden werden, und die Modelle müssen sowohl robust als auch zuverlässig sein. Daher werden in dieser Arbeit die Möglichkeiten und Herausforderungen leichter und daher weniger komplexer Kopplungsstrategien mit Schwerpunkt auf drei Schlüsselaspekten bewertet: Erstens wird ein auf dem Immersed Boundary-Ansatz basierender Fluiddynamik-Löser implementiert, da diese Methode mit einer sehr robusten Darstellung von bewegten Netzen besticht. Die grundlegende Funktionalität wurde für verschiedene vereinfachte Geometrien verifiziert und zeigte eine hohe Übereinstimmung mit der jeweiligen analytischen Lösung. Vergleicht man die 3D-Simulation einer realistischen Geometrie des linken Teils des Herzens mit einem körperangepassten Netzbeschreibung, so wurden grundlegende globale Größen korrekt reproduziert. Allerdings zeigten Variationen der Randbedingungen einen großen Einfluss auf die Simulationsergebnisse. Die Anwendung des Lösers zur Simulation des Einflusses von Pathologien auf die Blutströmungsmuster ergab Ergebnisse in guter Übereinstimmung mit Literaturwerten. Bei Simulationen der Mitralklappeninsuffizienz wurde der rückströmende Anteil mit Hilfe einer Partikelverfolgungsmethode visualisiert. Bei hypertropher Kardiomyopathie wurden die Strömungsmuster im linken Ventrikel mit Hilfe eines passiven Skalartransports bewertet, um die lokale Konzentration des ursprünglichen Blutvolumens zu visualisieren. Da in den vorgenannten Studien nur ein unidirektionaler Informationsfluss vom elas- tomechanischen Modell zum Strömungslöser berücksichtigt wurde, wird die Rückwirkung des räumlich aufgelösten Druckfeldes aus den Strömungssimulationen auf die Elastomechanik quantifiziert. Es wird ein sequenzieller Kopplungsansatz eingeführt, um fluiddynamische Einflüsse in einer Schlag-für-Schlag-Kopplungsstruktur zu berücksichtigen. Die geringen Abweichungen im mechanischen Solver von 2 mm verschwanden bereits nach einer Iteration, was darauf schließen lässt, dass die Rückwirkungen der Fluiddynamik im gesunden Herzen begrenzt ist. Zusammenfassend lässt sich sagen, dass insbesondere bei Strömungsdynamiksimula- tionen die Randbedingungen mit Vorsicht gewählt werden müssen, da sie aufgrund ihres großen Einflusses die Anfälligkeit der Modelle erhöhen. Nichtsdestotrotz zeigten verein- fachte Kopplungsstrategien vielversprechende Ergebnisse bei der Reproduktion globaler fluiddynamischer Größen, während die Abhängigkeit zwischen den Lösern reduziert und Rechenaufwand eingespart wird

    4D FLOW CMR in congenital heart disease

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    This thesis showed that the use of a cloud-based reconstruction applicationwith advanced eddy currents correction, integrated with interactiveimaging evaluation tools allowed for remote visualization and interpretationof 4D flow data and that was sufficient for gross visualizationof aortic valve regurgitation. Further, this thesis demonstrated that bulkflow and pulmonary regurgitation can be accurately quantified using 4Dflow imaging analyzed. Peak systolic velocity over the pulmonary valvemay be underestimated. However, the measurement of peak systolicvelocity can be optimized if measured at the level of highest velocity inthe pulmonary artery. Also correlated against invasive measurements (inan animal model), this thesis shows that aorta flow and pulmonary flowcan be accurately and simultaneously measured by 4D flow MRI.When applied in clinical practice, 4D flow has extra advantages, of beingable to visualize flow pattern, vorticity and to predict aortic growth. InASD patients it can measure shunt volume directly following the septumframe by frame. In Fontan patients in can visualize better than standardMRI the Fontan circuit and it can measure flow at multiple points alongthe Fontan circuit. We observed in our Fontan population that shunt lesionswere very common, most of the time via veno-venous collaterals.Further using advanced computations, we showed that WSS angle wasthe only independent predictor of aortic growth in BAV patients. We alsoshowed the feasibility of GLS analysis on 4D flow MRI and presented anintegrative approach in which flow and functional data are acquired inone sequence.From the technical point of view, 4D flow MRI has proved to complementthe traditional components of the standard cardiac MR exams, enablingin-depth insights into hemodynamics. At this moment it proved its addedvalue, but in most of the cases it is not able yet to replace the standardexam. This is still due to long scanning times and relatively longpost-processing times.<br/

    Myocardial, Valvular, and Vascular Structural and Functional Properties in Acromegaly

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    Acromegaly is an uncommon systematic endocrine disease caused by the hypersecretion of human growth hormone and, consequently, of insulin-like growth factor-1 during adulthood. Acromegaly could cause a typical cardiomyopathy characterized by left ventricular hypertrophy associated with diastolic dysfunction, which later could progress to systolic dysfunction. Moreover, some valvular and vascular abnormalities are also associated with acromegaly. This present review aims to summarize available information regarding acromegaly-associated abnormalities in myocardial, valvular, and vascular structural and functional properties and their relationship to disease activity and treatment options

    Quantitative Cardiac Magnetic Resonance Imaging Biomarkers for the Characterisation of Ischaemic Cardiomyopathy

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    Our understanding of the processes that determine outcomes in patients with ischaemic cardiomyopathy is based on conventional physiological concepts such as ischaemia and viability. Qualitative methods for characterising these processes tend to be binary and often fail to capture the complexity of the underlying biology. Importantly, these are perhaps inadequate to evaluate treatment effects, including the impact of coronary revascularisation. The aim of this thesis was to deploy novel quantitative cardiac magnetic resonance (CMR) techniques to evaluate and distinguish between the pathophysiological processes that determine outcomes in patients with ischaemic cardiomyopathy, through integration of anatomical, functional, perfusion and tissue characterisation information. The work is centred around the use of coronary artery bypass graft (CABG) surgery as the method for revascularisation, and focuses on the impact of myocardial blood flow alterations on cardiac physiology and clinical outcomes. In this work, I first evaluate the impact of surgical revascularisation on myocardial structure and function in patients with impaired left ventricular (LV) systolic function, using paired assessments before and after CABG. I found that at 6 months following revascularisation, despite improvement in functional capacity, more than a third of total myocardial segments examined are no longer considered revascularised. As a result, the overall augmentation in global myocardial blood flow (MBF) following CABG surgery is significantly blunted. There are however technical concerns regarding the quantitative estimation of myocardial blood flow in patients with coronary artery grafts, particularly in relation to the impact of long coronary grafts on contrast kinetics. I therefore evaluated the impact of arterial contrast delay on myocardial blood flow estimation in patients with left internal mammary artery (LIMA) grafts. I showed that absolute MBF estimation is minimally affected by delayed contrast arrival in patients with LIMA grafts, and that irrespective of graft patency, residual native disease severity is a key determinant of myocardial blood flow. Following these findings, I then assessed the prognostic impact of myocardial blood flow in a large cohort of patients with prior CABG. The only imaging study to date examining the prognostic role of quantitative perfusion indices in this population, it demonstrated that both stress MBF and myocardial perfusion reserve (MPR) independently predict adverse cardiovascular outcomes and all cause-mortality. Finally, using the existing quantitative perfusion technique and its associated framework, I co-developed and implemented a non-invasive, in-line method of measuring pulmonary transit time (PTT) and pulmonary blood volume (PBV) during routine CMR scanning. I then found that both imaging parameters can be used as independent quantitative prognostic biomarkers in patients with known or suspected coronary artery disease

    Multimodality imaging for transcatheter tricuspid valve repair and replacement

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    Transcatheter tricuspid intervention is a rapidly evolving field with multiple classes of therapeutic devices currently in development. Procedural success in tricuspid intervention is predicated on appropriate device selection for patient specific anatomy and satisfactory imaging for intra-procedural guidance. This review will outline protocols and methodology for multi-modality imaging assessment of the tricuspid valve and associated structures, with emphasis on anatomic and functional characteristics that determine suitability for each class of tricuspid intervention. Intra-procedural imaging requirements for each class of device, with design and procedural imaging guidance of specific devices, will also be addressed

    The Importance of mitral valve prolapse doming volume in the assessment of left ventricular stroke volume with cardiac MRI

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    There remains a debate whether the ventricular volume within prolapsing mitral valve (MV) leaflets should be included in the left ventricular (LV) end-systolic volume, and therefore factored in LV stroke volume (SV), in cardiac magnetic resonance (CMR) assessments. This study aims to compare LV volumes during end-systolic phases, with and without the inclusion of the volume of blood on the left atrial aspect of the atrioventricular groove but still within the MV prolapsing leaflets, against the reference LV SV by four-dimensional flow (4DF). A total of 15 patients with MV prolapse (MVP) were retrospectively enrolled in this study. We compared LV SV with (LV SVMVP) and without (LV SVstandard) MVP left ventricular doming volume, using 4D flow (LV SV4DF) as the reference value. Significant differences were observed when comparing LV SVstandard and LV SVMVP (p < 0.001), and between LV SVstandard and LV SV4DF (p = 0.02). The Intraclass Correlation Coefficient (ICC) test demonstrated good repeatability between LV SVMVP and LV SV4DF (ICC = 0.86, p < 0.001) but only moderate repeatability between LV SVstandard and LV SV4DF (ICC = 0.75, p < 0.01). Calculating LV SV by including the MVP left ventricular doming volume has a higher consistency with LV SV derived from the 4DF assessment. In conclusion, LV SV short-axis cine assessment incorporating MVP dooming volume can significantly improve the precision of LV SV assessment compared to the reference 4DF method. Hence, in cases with bi-leaflet MVP, we recommend factoring in MVP dooming into the left ventricular end-systolic volume to improve the accuracy and precision of quantifying mitral regurgitation
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