Evaluation of the Effect of Sigmoid-Shaped Interventricular Septum on Left Ventricular Systolic Function in Patients with Essential Hypertension by Two-Dimensional Speckle Tracking Echocardiography

Objective: To evaluate left ventricular regional and global systolic function by measuring left ventricular longitudinal strain (LS) in hypertensive patients with sigmoid-shaped interventricular septum (SIS) by two-dimensional speckle tracking (2D-STE); in order to explore whether the sigmoid-shaped interventricular septum affects the left ventricular systolic function in patients with hypertension. Methods: Routine echocardiographic parameters were measured in 30 hypertensive patients with SIS (SIS group) and 30 hypertensive patients without SIS (non-SIS group). The left ventricular segments and global LS were measured by 2D-STE, and the two sets of parameters were compared. Results: The value of the thickness of the basal segment of the interventricular septum (IVSBT), the thickness of the middle segment of the interventricular septum (IVSMT) and the ratio of the basal segment of the ventricular septum to the middle segment of the interventricular septum (IVSBT/IVSMT) in SIS group was higher than that in non-SIS group. However, the value of left ventricular outflow tract diameter (LVOTD) in SIS group was lower than that in non-SIS group. There was a significant difference between the two groups (all P < 0 05). The LS values of the basal segment of the left ventricular anterior wall and the posterior wall of the left ventricle in the SIS group were lower than those in the non-SIS group. The difference was statistically significant (all P < 0.05). Conclusion: SIS affects left ventricular regional systolic function of patients with hypertension. 2D-STE can early evaluate left ventricular longitudinal systolic function in hypertensive patients with SIS. How to cite this paper: Zhang, Z.F., Xu, W., Peng, Y.D., Zhang, H. and Zhang, Q. (2020) Evaluation of the Effect of Sigmoid-Shaped Interventricular Septum on Left Ventricular Systolic Function in Patients with Essential Hypertension by Two-Dimensional Speckle Tracking Echocardiography. Yangtze Medicine, 4, 62-69. https://doi.org/10.4236/ym.2020.41006 Received: November 2, 2019 Accepted: March 27, 2020 Published: March 30, 2020 Copyright © 2020 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access


Introduction
Sigmoid-shaped interventricular septum (SIS) was first proposed by Goor et al. [1] in 1969. It refers to the local thickening and protruding to the left ventricular outflow tract at the base of the interventricular septum, resulting in the shape of S-shaped blood flow through the left ventricular outflow tract. The Framingham Heart Research Center showed that the total prevalence rate of SIS was 1.5%, compared with 17.8% of subjects aged 85 and older [2]. There is a close relationship between SIS and hypertension. In the observational study of SIS, the prevalence rate of hypertension is often between 55% and 85% [2] [3] [4]. So far, there is no consensus on the clinical significance of SIS [5]. It is not clear whether SIS affects left ventricular systolic function in patients with hypertension. As a non-invasive technique for quantitative evaluation of myocardial motion, two-dimensional speckle tracking echocardiography (2D-STE) has no angle dependence and can accurately evaluate left ventricular myocardial motion function [6]. The purpose of this study was to evaluate the left ventricular regional and global systolic function in hypertensive patients with SIS by 2D-STE, and to explore whether SIS affects the left ventricular systolic function in hypertensive patients.

Subjects
Thirty patients with essential hypertension with SIS (SIS group) examined in the University. All the subjects signed informed consent forms.

Instruments and Methods
As shown in Figure 1 fraction (LVEF) by biplane Simpson. Adjust the frame rate of the instrument > 60 frames/s, collect the two-dimensional dynamic images of the standard left ventricular apical four-chamber, three-chamber and two-chamber sections for three consecutive cardiac cycles, store them and export them to the Q-LAB workstation for 2D-STE offline analysis. The longitudinal strain (LS) of the whole and each segment on the three-chamber, four-chamber and two-chamber section strain curves of the left ventricular apex were measured. After the analysis of the three sections, the software will automatically generate a bovine eye diagram showing each segment.

Statistical Analysis
The data were analyzed and processed by SPSS 19.0 statistical software package, and the measurement data were expressed as mean ± standard deviation ( x ± s). Independent sample t-test was used to compare with the two groups. The difference was statistically significant (P < 0.05).

Comparison of Clinical Data and Echocardiographic Parameters between Non-SIS Group and SIS Group
There was no significant difference in LVEF, LVPWT, LVOTV, Age, HR, SBP and DBP between the two groups (P > 0.05). The value of IVSBT, IVSMT and IVSBT/IVSMT in SIS group was higher than that in non-SIS group, while the value of LVOTD in SIS group was lower than that in non-SIS group. There was significant difference between the two groups (P < 0.05). See Table 1.

Comparison of Ultrasonic Two-Dimensional Spot Tracking Parameters between Non-SIS Group and SIS Group
As shown in Table 2, compared with the non-SIS group, the LS of the basal

Discussion
In this study, the value of LS measured by 2D-STE was used to evaluate left ven-  [4]. With the aging of the population in China, more and more SIS have been found, especially in patients with hypertension. Due to the special anatomical structure of SIS, the hearts of these hypertensive patients with SIS may need to overcome more peripheral vascular resistance, further increase the cardiac afterload, cause high load work, and may lead to left ventricular overcontraction. In this case, the protruding base of the interventricular septum comes into contact with the active mitral valve lobe, which narrows the outflow tract, where the blood flowed converges to produce high-speed blood flow, which together promotes the increase in the pressure difference in the left ventricular outflow tract. It may cause left ventricular outflow tract obstruction and corresponding clinical manifestations, resulting in cardiovascular adverse consequences. Therefore, it is particularly important to evaluate the left ventricular systolic function and take effective measures to prevent the occurrence of cardiovascular adverse events in hypertensive patients with SIS as soon as possible.
As a non-invasive technique for quantitative evaluation of myocardial motion, 2D-STE has no angle dependence and is less affected by cardiac load, so it can accurately evaluate left ventricular myocardial motion function [6]. Among them, left ventricular myocardial LS has high sensitivity in evaluating local and global systolic function in cardiac subclinical stage [12]. Therefore, in this study, 2D-STE was used to measure left ventricular LS in hypertensive patients with SIS to evaluate left ventricular regional and global systolic function.
In this study, the results of conventional ultrasound measurement showed that the LVEF values of the were (59.0 ± 1.41)% and (59.14 ± 2.59)% in non-SIS groups and SIS groups respectively. There was no significant difference between the two groups (P > 0.05). However, the LVEF values of the two groups were in the normal range (50% -70%), indicating that the left ventricular systolic function was normal in both groups when evaluating left ventricular systolic function by conventional LVEF. Compared with non-SIS group, the values of IVSBT, IVSMT and IVSBT/IVSMT increased in SIS group, especially in IVSBT. However, the measured value of LVOTD decreased. The difference was statistically significant (all P < 0.05). The results showed that in the SIS group, except for the obvious thickening of the base of the interventricular septum, the thickness of the other ventricular wall was approximately normal, and the decrease of the inner diameter of the left ventricular outflow tract suggested that it might be re-lated to the occurrence of left ventricular outflow tract obstruction. The results of two-dimensional spot tracking showed that the LS of the basal segment of the anterior and posterior wall of the left ventricle in the SIS group was significantly lower than that in the non-SIS group. The difference was statistically significant (all P < 0.05). However, there was no significant difference in other left ventricular segments and global LS between SIS group and non-SIS group (P > 0.05). That is, compared with the non-SIS group, the longitudinal deformation ability of the basal segment of the left ventricular anterior wall and the posterior wall of the left ventricle in the SIS group decreased, indicating that the left ventricular regional systolic function of the SIS group was decreased, which mainly occurred at the base of the interventricular septum. The reason may be related to the unique morphological characteristics of SIS.

Summary
In summary, compared with hypertensive patients without SIS, SIS affects the left ventricular regional systolic function in hypertensive patients, which mainly results in the decrease of myocardial longitudinal systolic function of the basal segment of interventricular septum. Therefore, SIS cannot be classified as a benign manifestation of cardiac aging. Under the condition of normal LVEF, the LS measured by 2D-STE can early evaluate the involvement of left ventricular regional systolic function. This is helpful for clinicians to evaluate hypertension patients with SIS as early as possible and take effective measures to control hypertension and its related risk factors, which has important clinical significance to prevent the occurrence of cardiovascular adverse events.