**3. Myocardial deformation imaging**

Conventional methods for assessment of regional and global ventricular function, such as fractional shortening and ejection fraction, are largely dependent on loading conditions and geometric assumptions [28, 29]. Myocardial deformation imaging has introduced a new global parameter of left ventricular longitudinal deformation GLS (global longitudinal strain), which has turned out to be more sensitive for early detection of myocardial impairment compared to conventional echocardiographic systolic function parameters. Myocardial deformation parameters have diagnostic as well as prognostic values in several cardiac diseases [3].

Recent developments in the assessment of ventricular function are the measurement of myocardial tissue Doppler velocities (tissue Doppler imaging, TDI) and deformation imaging (strain and strain-rate quantification). TDI has some advantages over traditional echocardiographic techniques in providing measurements of cardiac tissue movements [7, 30]. Myocardial deformation analysis is a quantitative technique that helps define a global and regional function of both ventricles. Tissue deformation is measured by cardiac strain, and there is an additional parameter called strain rate that defines the rate of myocardial deformation in time [7].

Compared to traditional methods that measure cardiac function mainly in the radial direction, strain imaging does not rely on geometric assumptions and can quantify function in the longitudinal, radial, and circumferential direction of motion. Therefore, regional as well as global ventricular function may be better estimated. Strain rate measures the extent of shortening of the myocardium in the longitudinal and circumferential directions and thickening in the radial direction. These newer methods of myocardial function assessment have already shown great promise in several areas of pediatric echocardiography, but their use in clinical practice is still limited by the lack of data from large patient cohorts [1].

Recently, two-dimensional (2D) and three-dimensional (3D) speckle-tracking echocardiography (STE) has been introduced as a new method to quantify myocardial strain [29]. STE tracks the motion of speckles within the scan volume, allowing a more complete and accurate assessment of myocardial deformation in all three spatial dimensions [29, 31]. Strain imaging is a promising method for assessing left ventricular function for diagnosis, prognosis, and risk stratification of various congenital and acquired heart diseases; it is also useful for monitoring treatment outcomes before and after medical, percutaneous, and surgical interventions [29].

Strain and strain rate can be measured either from tissue Doppler velocities or with speckle-tracking techniques together with final analysis at the workstation. It


*Data are mean (95% CI—confidence interval); GLS, global longitudinal strain; GCS, global circumferential strain; GRS, global radial strain.*

#### **Table 2.**

*Normal left ventricular global longitudinal strain (GLS), global circumferential strain (GRS), and global radial strain (GRS) values for specific vendors' equipment based on data from the literature (adapted from Truong et al., Lang et al.).*

is necessary to be aware of the wide variability of the strain and strain rate measurements that depend on vendors, software packages, and echocardiographic laboratories, as shown in **Table 2** [32, 33]. Broad clinical use of the strain is still limited due to the intervendor differences and related difficult comparison of the results, thus, standardization is urgently needed [1, 34]. Higher heart rates, especially in younger children, require higher frame rates, particularly for strain rate imaging; therefore, this aspect of use requires further development. Another challenge for the implementation of strain imaging in everyday clinical practice is the availability of reference values for different age groups of children [1, 35].

3D speckle-tracking provides a more comprehensive evaluation of ventricular mechanics from pyramidal 3D datasets. Furthermore, it enables also more precise mechanical activation mapping compared to 2D strain, by being maximum opposing wall delay and SD (standard deviation) still significantly correlated with similar 2D strain measurements. 3D loops of regional strain are color-coded and divided into 16 or 18 segments for time-strain curves. The results are presented in a 16- or 18-segment polar map with segmental systolic strain values displayed in the bull's eye. GLS value is defined as the average peak longitudinal strain of the left ventricle [36, 37]. Future development and expansion of applications for 3D speckle tracking are anticipated.

Strain imaging has also been used to gain a greater understanding of the pathophysiology of cardiac ischemia and infarction, primary diseases of the myocardium, the effects of valvular disease on myocardial function, and understanding of diastolic function, as seen in **Table 3**. Strain imaging has also been used for heart failure patients undergoing cardiac resynchronization pacing therapy providing important quantitative information on the timing of mechanical activation. Strain imaging has become increasingly used for research purposes, in addition, it shows great potential for routine clinical practice in the light of the improved treatment of cardiovascular patients [37]. Therefore, deformation imaging also plays a role in the risk stratification of young individuals with a potentially increased risk for heart failure and sudden cardiac death [1, 38]. Strain imaging has also been used to help to differentiate between athlete's heart and individuals with potential cardiomyopathy [1, 39]. While multiple studies have shown the usefulness of strain quantification for risk stratification in various diseases, such as arterial hypertension, diabetes mellitus, metabolic


#### **Table 3.**

*Main clinical applications of myocardial deformation imaging.*

syndrome, chronic kidney disease, neuromuscular diseases, and others, the main limitation remains that strain values vary among methods, modalities, and software versions [40–42].

Ventricular morphology can be highly variable in CHD, and therefore traditional methods of assessment of ventricular function that rely on geometry are unreliable. Assessment of right ventricular function and evaluation of functional changes in patients with a single ventricle are particularly challenging. Assessment of regional function is also important in pediatric patients with coronary artery abnormalities [1]. Subtle impairment in myocardial function, detectable with strain imaging, can be used to identify asymptomatic patients who progress to require valve surgery, which improves timely planning of the appropriate treatment [43].

Due to geometric factors, strain imaging better reflects systolic function in patients with preserved ejection fraction (EF), which is also common in cardiomyopathies. Particularly, longitudinal shortening may vary in patients with cardiomyopathies significantly, as it has less effect on EF than circumferential shortening. Therefore, longitudinal shortening might potentially be a more sensitive marker of systolic dysfunction, which typically affects the subendocardial region first, and could be assessed with longitudinal strain [44]. Deformation parameters, especially global longitudinal strain, have better accuracy in detecting cardiac amyloidosis in patients with thickened hearts [45].

Strain imaging is a beneficial additional echocardiographic method in assessing the extent of the ischemic myocardium and ventricular function. Postsystolic shortening is an important feature of the ischemic myocardium as a marker of tissue viability, and when associated with systolic hypokinesis or akinesis, it indicates actively contracting myocardium. When combined with dyskinesis, however, postsystolic shortening seems to be a nonspecific marker of severe ischemia [46]. Semiautomated calculation of GLS is significantly related to all-cause mortality or heart failure in patients with myocardial infarction and left ventricular ejection fraction (LVEF) > 40% [47].

Strain imaging is effective in monitoring cardiac function in patients with the multisystem inflammatory syndrome in children (MIS-C), which occurs after COVID-19 infection. Patients with preserved LVEF in myocarditis within MIS-C had significantly lower GLS; furthermore, regional myocardial dysfunction may also be presented, as seen in **Figure 1**. Hence, even preserved EF patients show subtle changes in myocardial deformation, suggesting subclinical myocardial injury. During a follow-up of the patients with MIS-C, there was a good recovery of systolic function but the persistence of diastolic dysfunction [48, 49]. Speckle-tracking imaging can help in the diagnosis of acute myocarditis when cardiovascular magnetic resonance (CMR) is not readily available or cannot be performed. There is a good correlation between speckle-tracking imaging-based LVEF, global strain and magnetic resonance imaging (MRI) calculated LVEF [50].

Segmental strain curves in a four-chamber view (top left), two-chamber view (top right), three-chamber view/APLAX—apical long-axis view (bottom left), and

#### **Figure 1.**

*Lower global longitudinal strain and regional myocardial dysfunction in the patient with myocarditis within multisystem inflammatory syndrome in children (MIS-C).*

*Clinical Benefits of New Echocardiographic Methods DOI: http://dx.doi.org/10.5772/intechopen.104808*

18-segment model or bull's eye (bottom right). The numbers in segments in the bull's eye are the peak longitudinal strain values in systole. The calculated value of global longitudinal strain (GLS) is −13.3%. Systolic values of the longitudinal strain are reduced in basal and mid-cavity segments of the anterior and lateral wall (blue color).

The recognition of early left ventricular dysfunction in cancer patients after cardiotoxic therapy may allow the identification of individuals at risk of future heart failure, allowing targeted monitoring and possibly institution of potential therapies such as angiotensin-converting enzyme inhibitors. The potential of strain imaging to prevent future cardiac toxicity by modulating cancer therapy and the institution of cardiac protective therapy is promising [51, 52].

GLS is the preferred indicator of left ventricular global systolic function. Strain measurements have proven to be more reproducible than LVEF due to minor dependency on segmental variability than LVEF calculations. Additionally, strain measurements should be obtained with the same analysis system and software version [42, 53–55].

Strain imaging is designed for the echocardiographic assessment of regional and global myocardial function, and has been well studied in the adult population, however, its use in pediatrics appears to be limited [56–58]. The duration of the investigation and the need to perform post-processing are major barriers to the more widespread implementation of the strain. Fully automated analysis with algorithms validated in the pediatric population may remove this problem [58].
