Model validation for a noninvasive arterial stenosis detection problem

Copyright @ 2013 American Institute of Mathematical SciencesA current thrust in medical research is the development of a non-invasive method for detection, localization, and characterization of an arterial stenosis (a blockage or partial blockage in an artery). A method has been proposed to detect shear waves in the chest cavity which have been generated by disturbances in the blood flow resulting from a stenosis. In order to develop this methodology further, we use both one-dimensional pressure and shear wave experimental data from novel acoustic phantoms to validate corresponding viscoelastic mathematical models, which were developed in a concept paper [8] and refined herein. We estimate model parameters which give a good fit (in a sense to be precisely defined) to the experimental data, and use asymptotic error theory to provide confidence intervals for parameter estimates. Finally, since a robust error model is necessary for accurate parameter estimates and confidence analysis, we include a comparison of absolute and relative models for measurement error.The National Institute of Allergy and Infectious Diseases, the Air Force Office of Scientific Research, the Deopartment of Education and the Engineering and Physical Sciences Research Council (EPSRC)

Material parameter estimation and hypothesis testing on a 1D viscoelastic stenosis model: Methodology

This is the post-print version of the final published paper that is available from the link below. Copyright @ 2013 Walter de Gruyter GmbH.Non-invasive detection, localization and characterization of an arterial stenosis (a blockage or partial blockage in the artery) continues to be an important problem in medicine. Partial blockage stenoses are known to generate disturbances in blood flow which generate shear waves in the chest cavity. We examine a one-dimensional viscoelastic model that incorporates Kelvin–Voigt damping and internal variables, and develop a proof-of-concept methodology using simulated data. We first develop an estimation procedure for the material parameters. We use this procedure to determine confidence intervals for the estimated parameters, which indicates the efficacy of finding parameter estimates in practice. Confidence intervals are computed using asymptotic error theory as well as bootstrapping. We then develop a model comparison test to be used in determining if a particular data set came from a low input amplitude or a high input amplitude; this we anticipate will aid in determining when stenosis is present. These two thrusts together will serve as the methodological basis for our continuing analysis using experimental data currently being collected.National Institute of Allergy and Infectious Diseases, Air Force Office of Scientific Research, Department of Education, and Engineering and Physical Sciences Research Council

Evaluation of pulse wave analysis to assess coronary artery disease

Conventional risk factors for cardiovascular disease, such as age, gender, hyperlipidaemia and hypertension are useful clinical markers of coronary artery disease (CAD) in asymptomatic patients or those without a prior history of atherosclerosis. In patients referred for a cardiology opinion, modification of risk factors by lifestyle changes and cardiac medications as well as confounding co-morbidities limit the value of these markers. Patients are often referred for diagnostic coronary angiography to determine the presence and severity of CAD, stratify the risk of future events and determine appropriate management. Despite the use of a variety of tests to best identify those requiring angiography, up to half of all patients referred do not have significant disease. Pulse wave analysis (PWA) is a novel method to derive indices of central (aortic) blood pressure and arterial stiffness. Pressure waveforms are obtained non-invasively from the radial artery using a simple tonometry method and have been shown to correlate with clinical outcomes and cardiovascular events in selected populations. This thesis will explore, for the first time, the clinical potential for PWA as a non-invasive marker of CAD in an unselected contemporary cohort of patients referred for elective coronary angiography. The main hypotheses tested are first that PWA is a suitable tool for clinical use, including those with cardiac and non-cardiac co-morbidities and second that abnormalities of PWA are independent predictors of the presence and severity of CAD. Data have been derived from a prospective, protocol-driven, multi-centre cohort of 550 patients recruited from 2006-8. Results suggest that PWA has a useful clinical role in stratifying the risk of coronary disease. PWA variables were independent of conventional blood pressure measurement and superior to baseline risk factors, biomarkers and other non-invasive tests

Standardized image interpretation and post-processing in cardiovascular magnetic resonance - 2020 update : Society for Cardiovascular Magnetic Resonance (SCMR): Board of Trustees Task Force on Standardized Post-Processing

With mounting data on its accuracy and prognostic value, cardiovascular magnetic resonance (CMR) is becoming an increasingly important diagnostic tool with growing utility in clinical routine. Given its versatility and wide range of quantitative parameters, however, agreement on specific standards for the interpretation and post-processing of CMR studies is required to ensure consistent quality and reproducibility of CMR reports. This document addresses this need by providing consensus recommendations developed by the Task Force for Post-Processing of the Society for Cardiovascular Magnetic Resonance (SCMR). The aim of the Task Force is to recommend requirements and standards for image interpretation and post-processing enabling qualitative and quantitative evaluation of CMR images. Furthermore, pitfalls of CMR image analysis are discussed where appropriate. It is an update of the original recommendations published 2013

Cardiac exercise studies with bioelectromagnetic mapping

Bioelectric currents in the heart give rise to differences in electric potential in the body and on its surface. The currents also induce a magnetic field within and outside the thorax. Recording of the electric potential on the surface of the body, electrocardiography (ECG), is a well established clinical tool for detecting insufficient perfusion of blood, i.e., ischemia during exercise testing. In a more recent technique, magnetocardiography (MCG), the cardiac magnetic field is recorded in the vicinity of the chest. Despite the clinical significance of the exercise ECG recordings in patients with suspected coronary artery disease (CAD), little is known about the effect of stress in the MCG of healthy subjects and patients with CAD. Methods for analysing multichannel MCG signals, recorded during physical exercise testing, were developed in this thesis. They were applied to data recorded in healthy subjects to clarify the normal response to exercise in the MCG, and to data of patients with CAD to detect exercise-induced myocardial ischemia. Together with the MCG, spatially extensive ECG, i.e., body surface potential mapping (BSPM) was studied and the exercise-induced alterations in the two mappings were compared. In healthy volunteers, exercise was found to induce more extensive alterations in the MCG than in the BSPM during the ventricular repolarisation. In patients with CAD, when optimal recording locations were found and evaluated, alterations of the ST segment in the MCG could be used as indicators of ischemia. Also, ischemia was found to induce a rotation of magnetic field maps (MFMs) which illustrate the spatial MCG signal distribution. The MFM orientation could successfully be used as a parameter for ischemia detection. In the BSPM, regions sensitive to ischemia-induced ST segment depression, ST segment elevation, and ST segment slope decrease were identified. An analysis method was also developed for monitoring the development of the MCG and the BSPM distributions. It enables examination of different features of the MCG and the BSPM signals as a function of time or the heart rate. In this thesis, the method was used for quantifying exercise-induced change in the orientation of MFMs. Adjustment of the orientation change with the corresponding alteration of the heart rate was found to improve ischemia detection by the exercise MCG. When data recorded during the recovery period of exercise testing were evaluated with similar type of analysis methods, the MCG showed better performance in ischemia detection than the simultanously recorded 12-lead ECG.reviewe

Subendocardial contractile impairment in chronic ischemic myocardium: assessment by strain analysis of 3T tagged CMR

<p>Abstract</p> <p>Background</p> <p>The purpose of this study was to quantify myocardial strain on the subendocardial and epicardial layers of the left ventricle (LV) using tagged cardiovascular magnetic resonance (CMR) and to investigate the transmural degree of contractile impairment in the chronic ischemic myocardium.</p> <p>Methods</p> <p>3T tagged CMR was performed at rest in 12 patients with severe coronary artery disease who had been scheduled for coronary artery bypass grafting. Circumferential strain (C-strain) at end-systole on subendocardial and epicardial layers was measured using the short-axis tagged images of the LV and available software (Intag; Osirix). The myocardial segment was divided into stenotic and non-stenotic segments by invasive coronary angiography, and ischemic and non-ischemic segments by stress myocardial perfusion scintigraphy. The difference in C-strain between the two groups was analyzed using the Mann-Whitney U-test. The diagnostic capability of C-strain was analyzed using receiver operating characteristics analysis.</p> <p>Results</p> <p>The absolute subendocardial C-strain was significantly lower for stenotic (-7.5 ± 12.6%) than non-stenotic segment (-18.8 ± 10.2%, p < 0.0001). There was no difference in epicardial C-strain between the two groups. Use of cutoff thresholds for subendocardial C-strain differentiated stenotic segments from non-stenotic segments with a sensitivity of 77%, a specificity of 70%, and areas under the curve (AUC) of 0.76. The absolute subendocardial C-strain was significantly lower for ischemic (-6.7 ± 13.1%) than non-ischemic segments (-21.6 ± 7.0%, p < 0.0001). The absolute epicardial C-strain was also significantly lower for ischemic (-5.1 ± 7.8%) than non-ischemic segments (-9.6 ± 9.1%, p < 0.05). Use of cutoff thresholds for subendocardial C-strain differentiated ischemic segments from non-ischemic segments with sensitivities of 86%, specificities of 84%, and AUC of 0.86.</p> <p>Conclusions</p> <p>Analysis of tagged CMR can non-invasively demonstrate predominant impairment of subendocardial strain in the chronic ischemic myocardium at rest.</p

Antithrombotic Therapy in Patients Undergoing Coronary Artery Bypass Grafting: A Systematic Review and Network Meta-Analysis

Comprehensive evidence on the comparative effects of various oral antithrombotic agents on the prevention of saphenous vein graft failure (SVGF) for patients undergoing coronary artery bypass is lacking. A systematic review and frequentist random-effects network meta-analysis of 18 RCTs (n=3,413 patients) comparing the effect of antithrombotic agents on SVGF and clinical outcomes was performed. Based on moderate quality evidence, among the six eligible interventions, dual-antiplatelet therapy with aspirin and clopidogrel was superior to aspirin monotherapy in reducing SVGF (OR: 0.63; 95% CI: 0.41-0.97). No statistical differences were found for major bleeding, mortality, and myocardial infarction between antithrombotic agents, owing to low number of events for most comparisons. Though significant heterogeneity or incoherence was not found, the quality of network evidence for these outcomes ranged from very low to moderate. Adequately-powered multi-arm RCTs are needed to ascertain the effects of antithrombotic therapies to help clinicians and patients achieve optimal treatment decisions

Biomarker zur Mortalitätsprädiktion im infarktbezogenen kardiogenen Schock

Hintergrund: Trotz der intensiven Behandlungsmöglichkeiten im infarktbezogenen kardiogenen Schock sind hohe Mortalitätsraten (ca 40-50%) weiterhin zu beobachten. Eine Reihe klinischer, angiografischer und laborchemischer Parameter sind hinsichtlich ihrer prognostischen Aussagekraft im Einzelnen oder in kleineren Gruppen untersucht worden. Bisherige Mortalitätsprädiktionsmodelle benötigen das Einholen klinischer/anamnestischer, angiografischer und biochemischer Variablen, was zu einer erschwerten Anwendbarkeit im klinischen Alltag führt. Eine frühe und valide Risikostratifizierung ist notwendig um weitere Therapieentscheidungen zu treffen und unterschiedliche Risikopopulationen für zukünftige klinische Studien zu identifizieren.   Ziele: In der vorliegenden Arbeit sollte unter Einbezug einer großen Bandbreite von klinischen Parametern, sowie neuen und etablierten Biomarkern, ein Risikoscore entwickelt werden, der nur die relevantesten Prädiktoren der 30-Tage-Mortalität einschließt, um so ein einfach anzuwendendes Tool zur Risikostratifizierung zu erstellen. Methoden: Der Risikoscore wurde anhand von 458 Patient:innen aus der multizentrischen randomisierten CULPRIT-SHOCK Studie mittels Least Absolute Shrinkage Selection Operator (LASSO), einem penalisierten multivariaten logistischen Regressionsmodell entwickelt. Als externe Validierungskohorte dienten 163 Patient:innen der IABP-SHOCK II Studie. Die prädiktive Aussagekraft wurde in interner, intern-extern (zeitlicher) und externer Validierung durch Diskrimination (AUC, c-Statistik), Kalibration, Klinischer Nutzen (decision curve analysis) und Kaplan-Meier-Kurven analysiert. Anschließend wurde der Risikoscore mit bisherigen Prognosemodellen hinsichtlich der diskriminativen Kraft (AUC, c-Statistik) verglichen. Ergebnisse: Aus 58 Kandidatenvariablen (30 klinische Parameter, 28 Biomarker) wurden nur vier als relevante Prädiktoren identifiziert. Aus Cystatin C, Laktat, Interleukin-6 und NTproBNP wurde somit der CLIP Score gebildet. In der internen Validierung wurde eine AUC von 0.82 (95% CI: 0.77-0.85) erreicht, in der intern-externen (zeitlichen) Validierung eine AUC von 0.83 (95% CI 0.76 – 0.90). Die externe Validierung ergab eine AUC von 0.73 (95% CI: 0.65 – 0.80). Es zeigte sich eine gute Kalibrierung und ein großer positiver Nettobenefit im klinischen Nutzen. Der CLIP Score überragte den SAPS II risk score (0.830 95% CI 0.765-0.896 vs 0.626 95% CI 0.528-0.725; P<0.001) und den IABP-SHOCK II risk score (0.830 95% CI 0.765-0.896 vs 0.761 95% CI 0.685-0.837; P=0.03) in der intern-externen (zeitlichen) Validierungskohorte. Zusammenfassung/Schlussfolgerung: Wir entwickelten und validierten einen reinen Biomarker Risikoscore zur Vorhersage der 30-Tage-Mortalität im infarktbezogenen kardiogenen Schock. Er stellt ein wertvolles Tool zur Unterstützung bei Entscheidungen für Therapieeskalation oder –deeskalation dar. Er kann automatisch aus vier rund um die Uhr verfügbaren Routinebiomarkern berechnet werden und übertrifft bisherige Risikoscores.:Einführung 3 1. Akuter Myokardinfarkt 3 2. Infarktbezogener kardiogener Schock 5 2.1. Definiton, Ätiologie, Epidemiologie und Klassifikation 5 2.2. Therapieansätze 8 2.3. Die CULPRIT-SHOCK Studie 10 2.4. Bisherige Biomarkeruntersuchungen 10 2.5. Bisherige Prognosemodelle 11 3. Rationale der vorliegenden Studie 14 Formatierte Publikation 15 Zusammenfassung 25 Literaturverzeichnis 28 Anlagen (Abkürzungsverzeichnis, Supplemental Materials der Publikation) 33 Darstellung des eigenen Beitrags 55 Selbstständigkeitserklärung 59 Lebenslauf 60 Publikationen 62 Danksagungen 6