segunda-feira, junho 01, 2009
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Assessment of myocardial ischemia and viability using tissue Doppler and deformation imaging: the lessons from the experimental studies.
Arch Cardiovasc Dis. 2008 Jan;101(1):61-8.
^Tissue Doppler imaging and strain rate imaging are quantitative methods for assessing myocardial function and have been shown to overcome the limitations of current ultrasound methods in assessing the complex changes in regional myocardial function that occur in differing ischemic substrates. Tissue Doppler imaging (TDI) measures in real time the myocardial velocity gradient which is an index of myocardial deformation. Strain and strain rate (SR) imaging has been shown to be a sensitive technique for quantifying regional myocardial deformation. Strain rate is less load-dependent that strain and provides therefore a better measure of contractility. In the setting of ischemia, experimental studies have shown that strain imaging was an accurate method for quantitative evaluation of regional myocardial function and may yield important physiological data. In myocardial infarction, transmural extension of scar distribution in the infarct zone is proportionally related to the reduction in systolic function measured by the radial transmural velocity gradient or by strain rate imaging. Measurement of both systolic and post-systolic deformation both at rest and during a graded dobutamine infusion may help to distinguish between transmural and non transmural infarcts. In conclusion, strain imaging has the ability to evaluate of regional myocardial function. Strain rate has not replaced conventional grey-scale imaging in the assessment of regional left ventricular function and the implement of these new indices in the routine clinical practice will need additional clinical and large-scale studies.