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Clinical Utility of Global Longitudinal Strain
In the past two decades, two-dimensional speckle-tracking global longitudinal strain (GLS) has become one of the most important new echocardiographic parameters for the assessment of cardiac diseases. Indeed, it has been widely demonstrated that GLS provides reliable and early information regarding the diagnosis and prognosis in several clinical settings, and it is more practical than conventional parameters such as left ventricular ejection fraction (LVEF) because it detects early alterations that other parameters do not. Indeed, compared with LVEF, GLS was superior in predicting major adverse cardiac events in patients with heart failure, acute myocardial infarction, valvular heart disease, and miscellaneous cardiac diseases. Moreover, it can provide an estimation not only of global but also of regional function through its polar projection, the so-called bull’s eye map, that identifies typical patterns of myocardial damage that can help obtain the correct diagnosis , ( Fig. 6.1 ).
Bull’s eye maps of global longitudinal strain (GLS) depicting different patterns of left ventricular hypertrophy: a normal subject ( A ), hypertension ( B ), hypertrophic cardiomyopathy ( C ), amyloidosis with the classical “apical-sparing” pattern ( D ), anterior myocardial infarction ( E ), and aortic stenosis with hypertrophy of basal segments ( F ). ANT, anterior; ANT SEPT, anteroseptal; INF, inferior; LAT, lateral; POST, posterior; SEPT, septal.
Modified from Zito C, et al: Ten years of 2D longitudinal strain for early myocardial dysfunction detection: a clinical overview, Biomed Res Int 8979407, 2018.
GLS was developed as a parameter for the assessment of LV systolic function, and its effectiveness is well recognized in the current American Society of Echocardiography recommendations. However, more recently, the use of GLS has been extended to different cardiac structures, including the right ventricle and atria, providing interesting results that require further study. Technical issues concerning how to perform GLS, and the limitations of this measurement have been widely discussed in other chapters of this book. This chapter discusses the diagnostic and prognostic role of GLS for the assessment of LV systolic function in the main clinical settings; moreover, data about the effectiveness of this measurement in the evaluation of right ventricle (RV) and left atrium (LA) are provided.
Evaluation of Left Ventricular Systolic Function
Left Ventricular Hypertrophy
LV hypertrophy (LVH) is a very common finding, but often it is quite difficult to distinguish between physiologic and pathological hypertrophy, and, within the latter group, to identify the underlying disease. In this context, GLS and regional longitudinal strain (LS) have had a significant role in detecting myocardial dysfunction correlated to fibrosis or storage or infiltrative cardiac disease. Indeed, it has been widely demonstrated that GLS is normal in athletes (see Fig. 6.1A ), who show benign LVH caused by systematic training. On the contrary, GLS is reduced in patients with asymptomatic hypertension (see Fig. 6.1B ) even when LVH has not occurred yet. GLS is also markedly reduced in all cardiomyopathies that cause LVH, including hypertrophic cardiomyopathy (HCM) (see Fig. 6.1C ), cardiac amyloidosis (CA) (see Fig. 6.1D ), and Anderson-Fabry disease. HCM is the most noticeable example of severe pathological LVH. In this context, a pronounced impairment of GLS with a significant gradient of decreasing LS from the apex to the base, although EF is often normal or supernormal. The regional alterations of strain in the polar maps identify the most damaged myocardial segments with increased fibrosis, with a very high correspondence with cardiac magnetic resonance. Moreover, the impairment of GLS can be an independent predictor of cardiac death or defibrillator discharge in this population of patients. Similarly, GLS and regional LS plays an important role in the diagnosis of CA. Indeed, even if EF can be normal in the first stage of the disease, GLS is always reduced. In addition, the bull’s eye polar map shows a very typical pattern, characterized by a regional and progressive variations in LS from the base to the apex with a relative LV “apical-sparing” pattern. The evidence of this pattern, even not exclusive of CA, is quite accurate in the diagnosis of the disease, providing a significant support in the differential diagnosis. On the other hand, in Anderson-Fabry cardiomyopathy, a decrease of LS at the basal posterolateral wall has been reported. However, this finding needs to be further confirmed.
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