DK2985_C000 1..28 - AlSharqia Echo Club

162 Transesophageal Echocardiographyclinical symptoms of angina, if they appear, are latemanifestations of ischemia.III.12332 3Figure 8.6 Septal branches of the left anterior descendingartery (1, myocardium; 2, left anterior descending; 3, septalbranches; 4, epicardial fat). (Courtesy of Nicolas Dürrleman.)GLOBAL SYSTOLIC FUNCTION CHANGESWhen transthoracic images are suboptimal (e.g. patientswho are obese, have chronic obstructive lung disease, orare in a postoperative state), in critically ill patient settingsor when assessing patients undergoing cardiac or noncardiacsurgery, it is often useful to evaluate global andregional ventricular function from the transesophagealapproach. This technique provides immediate dataregarding segmental wall motion abnormalities, globalventricular function, volume status, and the presence oftamponade. In particular, TEE provides very importantdata on ventricular function in the hypotensive patientand allows the detection of ventricular or atrial compressionfrom severe tamponade. The severely hypovolemicpatient will most often have a normal orhyperkinetic ventricular function and obliteration of theleft ventricular cavity in systole (7). Although acute ischemiais usually manifested echocardiographically as aregional wall motion abnormality, global ventricular dysfunctionmay result from high-grade obstruction of oneor more arteries perfusing a large area, the acute obstructionof one artery in the setting of previous infarction inother areas or the presence of an ischemic mechanicalcomplications such as papillary muscle rupture.4Global left ventricular systolic function can be evaluatedeither qualitatively or quantitatively. Global systolicfunction can be qualitatively classified as normal, mildly,moderately or severely reduced, but this information isconsidered incomplete by most clinicians. In contrast,determination of the left ventricular ejection fraction hasmajor prognostic significance in patients with coronaryartery disease (CAD). In the clinical setting, visual estimationof the left ventricular ejection fraction hasbecome common practice. The correlation between thevisual echocardiographic estimation (eye balling) and theradionuclide determination is surprisingly good, especiallyin patients with impaired ejection fraction. This method,however, requires experience and clinicians should validatetheir own performance with quantitative methods.All echocardiographic approaches for the assessment ofregional and global ventricular function need to take intoaccount the quality of endocardial border definition, theasynchronous contraction patterns observed with ventricularpacing or in the presence of conduction defects, the heterogeneityof normal ventricular function and the observedabnormality in septal wall motion frequent in the postoperativeperiod.The motion of the mitral annulus towards the apex canalso be used as an indirect measure of left ventricularsystolic function. It is usually measured in the apicalfour-chamber view, where the movement of the mitralannulus is parallel to the ultrasound beam and is normally12 + 2 mm. A motion of ,8 mm has been reported tohave a sensitivity of 98% and a specificity of 82% in theidentification of an ejection fraction less than 50% (8).Pai et al. (9) examined the mitral annular systolic excursionin 57 patients with a wide range of LV ejection fraction(13–84%) and found a good correlation (r ¼ 0.95,p , 0.001) between the mitral annulus motion and theejection fraction as measured by the radionuclide approach(Fig. 8.10).The quantitative assessment of global systolic functionrequires the determination of the left ventricular cavitydimensions on high-quality images. Volume estimationsare based on geometric assumptions about ventricularshape which range from a simple ellipsoid to a complexhemicylindrical hemiellipsoid shape. A description ofeach geometric shape, the corresponding formula andrequirements is beyond the scope of this chapter(Chapter 5). Nevertheless, the biplane modified Simpson’sformula, which divides the ventricular cavity into multiplecylindrical slices of known volume with the sum representingleft ventricular volume, is the most commonlyused approach in clinical practice to assess left ventricularvolume and global function. This involves tracing of theendocardial borders at end-systole and end-diastole inthe mid-esophageal four- and two-chamber views (transducerat 08 and 908, respectively). The left ventricular