Clinical Implications Of Reversible Left Ventricular Dysfunction Evaluated With New Echocardiographic Modalities In Patients With Acute Myocardial Infarction

The identification of viable but dysfunctional myocardium in the settings of acute myocardial infarction (AMI) or chronic myocardial ischemic patients with reduced left ventricular function has important clinical implications. For the viable myocardium, the re-establishment of coronary blood reperfusion in time will relieve myocardial ischemia, increase the electrocardiographic stability and improve the cardiac function, resulting in eventually the improvement of prognosis with reduced mortality from severe arrhythmia and heart failure. Especially at present, as the most effective strategies, coronary revascularization techniques such as catheter-based percutaneous coronary intervention and coronary by-pass operation have been becoming more and more popular at routine clinical settings. Hence, it is even more essential to differentiate the viable from the infarct myocardium for the selection of optimal strategies, the evaluation of therapeutical effects and the prediction of prognosis in patients with coronary artery disease (CAD). Several noninvasive imaging methods have evolved during the past decade to identify physiological markers of viable myocardium in regions with contractile dysfunction. These include F-18 deoxyglucose positron emission tomography (18F-FDG PET), single photon emission computed tomography (SPECT) imaging, magnetic resonance imaging (MRI) and echocardigraphy. Although PET has been taken as the gold standard for evaluation of viable myocardium and myocardial scintigraphy has also been proved to be a sensitive method for evaluation of viable myocardium, theirhigh-cost of machines and the radiation to human body limit their routine application at clinical settings. The conventional echocardiography can provide visual observation of the ventricular wall motion, but it is usually semi-quantitative, more subjective and manipulator dependent. Furthermore, it is impossible to differentiate the infarct from the viable but dysfunctional myocardium since both of them showed abnormal wall motion. For this reason, exercise or pharmacological stress echocardiography has been used to distinguish the infarct from the stunned or hibernating myocardium, but this approach can be dangerous in some extent when the residual stenosis exists in the infarct-related arteries. Contrastively to the conventional echocardiography, the new ultrasound modalities such as integrated backscatter (IBS), myocardial contrast echocardiography (MCE) and tissue Doppler imaging (TDI) have made it possible to evaluate the wall motion quantitatively, to describe the tissue characteristics and to observe micro-circulation of myocardium non-invasively. With the purpose of exploring new and clinically practical methods for clinical evaluation of viable myocardium, some new methods were used in patients with AMI to observe the changes of tissue characteristics and to assess quantitatively the myocardial velocities of contraction and relaxation in the present studies. The correlation of the changes of tissue characteristics and myocardial velocities with the remodeling and the functional recovery of left ventricle were also analyzed in order to evaluate the practical implications of these new modalities in the estimation of myocardial viability and the prediction of functional recovery of left ventricle.Integrated backscatter (IBS) is a new technique of ultrasonic tissue characterization (UTC) which permits quantitative detection of pathologic alterations in myocardium. It offers a promising method for assessment of myocardial contractile performance independent of wall motion. The main parameters are IBS and cyclic variation of integrated backscatter (CVIB).IBS is related with the content of collagen and CVIB is closely associated with myocardial contractile function. The quantitative analysis of IBS may be useful for the evaluation of histology characterization after myocardial infarction. In the first part of the studies, a series of observations of IBS in patients with AMI were made and their correlations...