Subclinical systolic dysfunction and myocardial deformation: From GLS to VVI

Left ventricular (LV) systolic function can be evaluated using echocardiography by ejection fraction (by LV volume in 2D and 3D methods), Tissue Doppler Imaging or myocardial strain by 2D or 3D speckle tracking echocardiography—STE, global longitudinal strain—GLS, radial strain—GRS, and circumferential strain—GCS, and associated peak strain rates (GLSr, GRSr, GCSr). Besides longitudinal myocardial deformation, radial, and circumferential myocardial deformation is important in understanding myocardial motion in the short-axis direction. In addition, there are some new derived STE methods, which are not part of the daily clinical practice. Novel techniques derived from STE have gained advantages in overcoming the disadvantages of classical deformation methods. However, Tissue Doppler Imaging was the first method used for directly measuring myocardial deformation by echocardiography. Due to the angle dependency, it is now less used, being replaced by GLS and vector velocity imaging (VVI). There is no echocardiographic technique in 2D or 3D, which is perfect, each of them having advantages and disadvantages (Figure 1). Jianwei Shi et al1 assessed the LV systolic function in patients with Parkinson's disease by LV ejection fraction, GLS, GRS, and GCS, and their associated peak strain rates. They analyzed the correlation between LV dysfunction and the severity of Parkinson's disease symptoms using the modified Hoehn–Yahr scale. This score and the Parkinson's disease duration were correlated with reduced LV systolic function. The severity of LV impairment was influenced by blood pressure, heart rate variability, and blood glucose. The authors considered that it is feasible to assess subclinical LV global systolic dysfunction in patients with Parkinson's disease by VVI.1 This study is very important for clinical practice because monitoring the cardiac function in patients with Parkinson disease, the second most prevalent neurodegenerative disease, will allow the detection of the progression of this disease. The LV works as a complex structure of muscular fibers, organized in layers. In LV, longitudinal myocardial fibers are oriented clockwise in subepicardial layer and counter clockwise in subendocardial layer, circumferential fibers are mid myocardial situated. During contraction and relaxation, these fibers will determine a complex deformation of the LV myocardium. LV ejection fraction, the first imaging modality for assessing LV systolic function, does not account for the multiplanar and multidirectional components of myocardial deformation being assessed by LV volumes. Therefore, in the last years it was an intensively contested ultrasound parameter. Myocardial regional mechanics (strain or deformation) could be assessed by echocardiography. It was described four principal types of strain or deformation: longitudinal, radial, circumferential, and rotational deformation (or circumferential–longitudinal shear) the last occurs along the long axis of the LV. There have been demonstrated that myocardial strain is more sensitive in predicting earlier LV systolic dysfunction (subclinical LV systolic dysfunction).2 Therefore, this modality for assessing LV systolic function, strain echocardiography, is considered a more sensitive and accurate instrument of myocardial function than LV ejection fraction. It is very useful in earlier institution of specific therapeutic interventions or therapy monitoring, and as a prognostic marker by stratifying the risk in a variety of cardiomyopathies.2 The new echocardiographic techniques are also used in various non-cardiac pathologies in relationship with cardiovascular disease. The main advantages of deformation image are imaging based on LV mechanics; free from geometric assumption and foreshortening; free from angle dependency; less depending to loading condition (Figure 1). The value of GLS is obtained by averaging the segmental strain values of 18 segments (six segments in each of the three apical views). Another method derived from STE is VVI, which quantifies longitudinal and circumferential myocardial deformation; the latter is important in understanding myocardial motion in the short-axis direction. It is applied through a combination of mitral annulus motion, tissue-blood border detection, and STE, which requires a high-quality image.3 This advanced echocardiographic method based on STE, allows the assessment of the cardiac mechanics and the quantification of global and regional cardiac function. Using gray scale images, VVI can accurately track speckles frame by frame, allowing the reconstruction of the deformation and motion, the motion of flow and tissue.3 Based on the motion of the tracked points between the frames and the knowledge of the time interval between frames, 2D tissue velocity is computed.3 Strain and strain rate are computed by the change in the relative distance between localized tracked trace points, combined with the difference in the relative displacement of the tissue motion behind the tracked points.2 VVI seems a feasible modality for assessing LV GLS. In practice, during VVI technique is easier to achieve long-axis (representing 75% of cardiac function) than short-axis imaging views3; therefore, circumferential and radial strain was not so frequently used in clinical practice. Badran et al4 analyzed 3D GLS and global area strain as it reflects both longitudinal and circumferential strain vectors and compared it to VVI derived GLS. They founded an excellent agreement for regional and GLS between VVI and 3D-STE strain in patients with hypertrophic cardiomyopathy. Comparison of global peak circumferential strain measured by 2D STE and VVI showed that strain by STE was significantly higher than the VVI peak strain.5 3D-STE seems to overcome at least one limitation of 2D-STE for the assessment of LV global and regional systolic function by avoiding the loss of speckles because of out-of-plane motion.4 The reproducibility of VVI longitudinal strain marker appeared to be superior to that of 3D echocardiography imaging for longitudinal mechanics analyses.4 In terms of time-consuming, VVI seems faster than conventional 2D-STE.4 Another echocardiographic method, which use STE, is vector flow mapping (VFM). Vector flow mapping combine Color-Doppler and STE data for quantifying energy loss,6 which indirectly reflects cardiac effort. Clinical applications of VFM are impaired diastolic and systolic function, cardiomyopathies, valvular diseases (aortic and mitral valve), rhythm disorders, congenital heart diseases. It also may be an auxiliary diagnostic tool for assessing atherosclerotic arterial disease.7 Echocardiographic noninvasive assessment of intracardiac flow is attractive for physicians but it is not part of the clinical practice. Loading conditions can change strain values. Myocardial work is the newest echocardiographic parameter for assess LV function. It uses pressure–strain loops taking into account LV afterload for assess global work index, constructive work, wasted work, and work efficiency. Myocardial work index is defined as ventricular–arterial coupling estimation derived by pressure-left ventricular GLS loop during one cardiac cycle by STE. Speckle tracking measurement of GLS combined with brachial artery blood pressure allows for noninvasive estimated of myocardial work indices. These parameters seem to be a more sensitive tool for the detection of subclinical changes in cardiac function in cardiometabolic disease states.8 In addition, it might be a new echocardiographic tool in cardiotoxicity detection during cancer treatment.9, 10 Absolute GLS, change in GLS, and change in GWI are useful risk stratification parameters for the development of cancer therapeutic related cardiac dysfunction. This study of Jianwei Shi et al1 brings to attention again the importance of detecting LV systolic dysfunction and the way of evaluation it, in patients with comorbidities in relation to heart diseases. With a simple, noninvasive tool like VVI, it is possible to detect symptoms deterioration due to the progressive neurological damage in patients with Parkinson's disease. Myocardial deformation assessed by 2D or 3D echocardiography could have diagnostic, parameters mortality, sudden cardiac death11; it is also useful for monitoring treatment outcomes before and after medical, percutaneous, and surgical interventions. Thanks to these noninvasive techniques, patients with progressive heart disease or systemic disease affecting the heart or vice versa may be identified and treated timely. The authors declare no conflict of interest. Data sharing not applicable to this article as no datasets were generated or analyzed during thecurrent study.