Noninvasive Evaluation of Myocardial Ischemia and Left Ventricular Function
Abstract: The general aim of this thesis was, following the path of the ischemic cascade, to evaluate the feasibility of some new non-invasive techniques for the detection of myocardial ischemia, the extent of infarcted myocardium, and for the quantification of systolic left ventricular function.Reduced longitudinal myocardial velocity and displacement may be early signs of ischemia. We evaluated the diagnostic sensitivity and specificity of pulsed tissue Doppler for the detection of ischemia and scar during dobutamine stress testing and compared it with myocardial perfusion scintigraphy (SPECT) in patients with a history of unstable angina. Pulsed tissue Doppler was useful for objective quantification of left ventricular longitudinal shortening and for differentiation between patients with a normal, ischemic or necrotic myocardium.The coronary flow velocity reserve (CFVR) of the left anterior descending artery (LAD) was studied with transthoracic Doppler echocardiography (TTDE) during adenosine stress. Patients with a clinical suspicion of stress induced myocardial ischemia were investigated, and the results were compared with the findings from SPECT. A CFVR >2 in the LAD could exclude significant coronary artery disease in a clinical setting, however, in cases with low CFVR, multiple cardiovascular and metabolic risk factors as well as epicardial coronary artery disease or microvascular dysfunction might be responsible. TTDE is a promising tool, e.g. for follow-up after coronary interventions or for evaluating endothelial function over time.A third study focused on the importance of accurate and reproducible measurements of left ventricular volumes and ejection fraction (LVEF). Patients with known or suspected coronary artery disease with different levels of LVEF were enrolled. We compared the LVEF determined with an automatic echocardiographic method with manual planimetry, visual assessment of LVEF and with quantitative myocardial gated SPECT. The software using learned pattern recognition and artificial intelligence (AutoEF) applied on biplane apical echocardiographic views reduced the variation in measurements without increasing the time required. The method seems to be able to reduce variation in the assessment of LVEF in clinical patients, especially for less experienced readers.We evaluated a new feature tracking software for its ability to detect infarcted myocardium on cine-MR images. Patients were selected based on the presence or absence of myocardial scar in the perfusion area of the LAD. The software tracked myocardial wall motion and allowed the calculation of velocity, displacement and strain in radial and longitudinal directions. Feature tracking of cine-MR images detected scar segments with transmurality >50% within the distribution of the LAD with 80% sensitivity and 86% specificity (radial strain), without the need for the administration of gadolinium-based contrast.In summary, we have evaluated some of the noninvasive techniques in the wide array of diagnostic tools available for the diagnosis of ischemic heart disease. Their availability, low costs, freedom from radiation and repeatability are essential as well as their diagnostic ability.
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