The midwall EF in the LVH group was significantly lower than that in the control group and midwall EF was correlated with the degree of LVH. Our study showed the utility of midwall EF for assessing systolic performance of the hypertrophic left ventricle. Also, this method may be clinically useful and is likely to have low observer variability. As far as we are aware, there has only been one previous study of midwall EF. Jung et al. found that the midwall EF also discriminates the systolic function between patients with LVH and normal subjects , but the method used required manual tracing of echocardiographic images and a complicated calculation of echocardiographic data, which limits the clinical utility.
LVH is an independent predictor of adverse cardiovascular events in hypertension [9, 15]. Accurate assessment of cardiac function in patients with LVH is important in clinical practice. LV systolic function has been wildly assessed as the ratio of observed LV endocardial FS or EF to value predicted by the level of end-systolic stress in normal subjects . The degree of shortening and the level of opposing forces in myocardium in patients with LVH is different from normal subjects . The previous study reported that LVEF and LVFS are preserved in patients with LVH, despite depression of LV myocardial systolic function [1, 3–6]. In this study, the midwall EF in the LVH group was significantly lower than that in the control group and the correlation of LVMI with midwall EF was higher than that with any other parameters, including midwall FS. Thus, midwall EF can be used to monitor LV systolic dysfunction, which is not possible with conventional LVEF and LVFS.
Midwall FS has been used to detect depressed LV systolic function in patients with LVH [1, 3–5]. A previous study found significant differences in midwall measurements of the fiber shortening and lengthening velocities in normal and hypertrophic patients . The midwall FS measurement is preferred because systolic wall thickening is non-uniform, with the inner wall thickening to a substantially greater extent than the outer wall. This may be because fibers in the subendocardial and subepicardial myocardium are orientated longitudinally, whereas those in the midwall region are orientated circumferentially [4, 7]. Ishizu et al. also showed differences in radial strain between the inner and outer halves of the myocardium and differences in circumferential strain among the three layers in the endocardial, midwall, and epicardial myocardium by strain analysis using 2D STE . For these reasons, the LV midwall FS is a more physiologically appropriate measurement of LV systolic performance in patients with LVH, compared to conventional FS [1, 2, 4–9]. However, midwall FS measurements are inherently flawed because of foreshortening errors and reliance upon geometric models that may be inaccurate in the diseased heart . Also, echocardiographic calculation of midwall FS is a geometry-based index derived from linear measurement of the posterior and septal walls, and consequently cannot distinguish between septal and posterior wall function . Therefore, calculation of midwall FS is made from a limited region of the LV. In contrast, midwall EF can estimate foreshortening without use of a geometric model because midwall EF is calculated in planes. Thus, measurement of midwall EF is a relatively new approach that can mitigate the errors inherent in midwall FS.
The correlation of LVMI with midwall EF was higher than with TDI parameters. It has been suggested that TDI can be used to quantify regional ventricular function objectively and the mitral annular velocity may be a more sensitive index of LV function . However, TDI is particularly affected by translational and tethering effects, and angle-dependency. Therefore, there is some limitation in interpretation of measurements by TDI. In contrast, analysis of midwall EF is relatively free of the influence of these adverse affects. Thus, in a clinical setting, measurement of midwall EF is effective for quantifying the impairment of LV function due to LVH. It is reported that the longitudinal strain is a useful method for assessing myocardium systolic dysfunction in patients with LVH . Nonetheless, the correlation of LVMI with midwall EF was higher than with longitudinal strain in our study. Midwall EF measurements may be superior to detect myocardial systolic dysfunction in patients with LVH than longitudinal strain.
Our study also showed the usefulness of 2D STE for measurement of midwall EF. The STE technique relies on tracking of natural acoustic markers in the myocardium from frame to frame throughout the cardiac cycle using a sum of absolute differences algorithm . Thus, the application of 2D STE method has been widely used in the study of subclinical or overt LV dysfunction . Evaluation of midwall EF by 2D STE does not require difficult or lengthy acquisition and offline reconstruction, which are impractical in routine clinical use. The 2D STE method also allows automatic measurements of LV volume to be performed without the need for manual tracings. We positioned the initial ROI manually on the midpoint of the wall thickness at the end of diastole only. Then, we automatically obtained the volume curve using a speckle tracking algorithm throughout the cardiac cycle. In systole, the initial ROI was not positioned at the midpoint of the wall thickness because the systolic thickening of the inner layer is larger than that of the outer layer. Ishizu et al. also proved this phenomenon using a speckle tracking method . Thus, our method is similar to the mathematical midwall mechanism reported in previous studies [1, 2, 4–9] and may be clinically useful and is likely to have low observer variability.
In this study, midwall EF correlated with the degree of LVH. Patients with LVH have intrinsic dysfunction in both systole and diastole. Our study showed that midwall EF can detect LV systolic dysfunction, which cannot be detected by conventional EF. This may be an important sign of LV dysfunction in patients with hypertension, which may not always be due to diastolic dysfunction, but can often be caused by systolic dysfunction, as assessed by midwall EF . Evaluation of midwall EF may allow assessment of LV systolic performance in patients with various LV geometries. Our method is relatively easy to apply in conventional echocardiography, with clinical settings similar to those for volume measurement by the routine biplane method.
Our methods demonstrated that the midwall EF is clinically useful for detecting the systolic function in addition to midwall FS, TDI, and strain. Midwall EF can detect LV systolic dysfunction, which cannot be detected by conventional EF. The intrinsic systolic dysfunction may affect predictive of subsequent morbidity and mortality in patients with LVH. Midwall EF will have possibilities to detect the beneficial change of intrinsic systolic dysfunction by medical treatment in clinical settings.