Population and study protocol
Sixty patients were enrolled in the study. Patients were divided into two groups with LVH (n = 30) and without LVH (control group, n = 30). LVH was defined as an LV mass index (LVMI) >96 g/m2 for women and >114 g/m2 for men. The causative of patients with LVH was essential hypertension with the exception of chronic renal failure, idiopathic hypertrophic cardiomyopathy, amyloidosis. Patients with myocardial infarction, atrial fibrillation, valvular disorders, and any other structural heart disease were excluded. Patients with poor echocardiographic image quality in the apical 2-chamber and 4-chamber views were also excluded. LV function was measured using conventional echocardiography, tissue Doppler imaging (TDI), and 2D-STE. LV systolic function was assessed by EF, midwall FS, midwall EF, and longitudinal strain. Systolic function was compared between the two groups and the relationships of LVMI with LV systolic parameters, including midwall EF, were investigated. Ethical review board approval from our hospital was obtained.
Conventional echocardiography
Echocardiographic studies were performed using commercial equipment (X3 transducer, Philips iE33 system) with the patient in the left lateral decubitus position. Images were obtained using a 3.5-4.0 MHz transducer in the parasternal short-axis and apical 4-chamber views [12]. Interventricular septal thickness (IVST), posterior wall thickness (PWT), left ventricular end-diastolic diameter (LVDd), left ventricular end-systolic diameter (LVDs), left atrial dimension (LAD), stroke volume (SV), and left ventricular fractional shortening (LVFS) were determined using standard echocardiographic 2D or M-mode measurements. The IVST and PWT were measured in end diastole. LV mass was calculated from 2D echocardiographic measurements using the M-mode formula [13] and was normalized to body surface area. Mitral inflow velocity was traced and the peak early (E) and late (A) mitral flow velocities, the ratio of the early to late peak velocities (E/A), and the deceleration time (DCT) of the E velocity were derived from the velocity data. Midwall FS methods used the fact that the volume of myocardium between the midwall and the endocardium must be preserved although thickness of it was changed during cardiac cycle. Then, midwall FS was calculated using the model of Shimizu et al. [1, 5–7], as follows:
-
1.
Midwall FS = (LVID
d
+ H
d
/2) − (LVID
s
+ H
s
/2)/(LVID
d
+ H
d
/2).
-
2.
Volume of myocardium between the midwall and the endocardium = (LVID
d
+ H
d
/2)3 − LVID
d
3 = (LVID
s
+ H
s
/2)3 − LVID
s
3.
-
3.
H
d
= PWT + IVST.
where LVID is the LV internal dimension, d is end diastole, s is end systole, and H is the shell thickness. In diastole, the inner and outer shells have, by definition, equal thickness given by (PWT + IVST).
Tissue Doppler imaging
TDI was performed in all patients with images taken based on the guidelines of the American Society of Echocardiography [14]. Using the 4-chamber view, a 5-mm sample volume was placed at the septal and lateral border of the mitral annulus. Annular velocities were displayed in septal and lateral pulsed-wave TDI and the early systolic mitral annular velocity (S’), the early diastolic mitral annular velocity (E’), and the late diastolic annular velocity (A’) were determined from the average of septal and lateral data from the TDI recordings. The mitral E/E’ ratio was also calculated.
Real-time 2D imaging
2D image analysis was performed on digitally stored images (X3 transducer, Philips iE33 system). Real-time 2D data sets were obtained from the apical 2-chamber and 4-chamber images. Images were recorded to allow for reliable operation of the software (Q-Lab, Version 7.0, Philips Healthcare).
LV systolic strain measurement
Myocardial longitudinal strain measurement was assessed on 4-chamber image with speckle tracking analysis. The traced endcardium is automatically divided into six segments; septal, anteroseptal, anterior, lateral, posterior, and inferior. The average peak strain measured in the longitudinal directions defined as the longitudinal strain.
Midwall EF measurement
The midwall EF measurements were obtained using semiautomated speckle tracking (Q-Lab, Version 7.0, Philips Healthcare). Image acquisition was performed with end-expiratory breath holding to reduce the scattering of values. One cardiac cycle was analyzed in each patient. The position of the midwall was determined using the landmark of the midpoint between the epicardial and endocardial borders depending on the LV wall thickness. Anatomic landmarks, including these midpoints and a point on the apical endocardium, were manually initialized at the end of diastole only. Following this initialization, the software automatically positioned sixteen regions of interests (ROI) on the midwall LV cavity surface. In systole, the initial ROI was not positioned at the midpoint of the wall thickness because systolic thickening of the inner layer is larger than that of the outer layer. Further manual adjustments of the position of the ROI in the end-diastolic frame were performed as necessary [10]. A representative case is shown in Figure 1A and 1B. Then, we automatically obtained the volume curve using a speckle tracking algorithm throughout the cardiac cycle and measured the end diastolic and end systolic volumes. A volume curve obtained with the speckle tracking algorithm in a representative case is shown in Figure 1C. Midwall EF was then calculated by the biplane method using the average value in the apical 4-chamber and 2-chamber views.
EF measurement
These data were obtained using the same method as that for midwall EF measurement, except for the positions of ROIs, which were based on anatomic landmarks, including septal and lateral points on the mitral annulus and a point on the apical endocardium. The EF was then calculated from apical 4-chamber and 2-chamber views, as for the midwall EF in 2D STE.
Statistical analysis
Data are expressed as means ± SD. A Student t-test was used to compare continuous variables and a χ2 test was used for categorical variables. Simple linear regression analysis was used to evaluate relationships between variables of interest, with p < 0.05 considered to indicate significance.