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Background and ObjectivePrevious studies on left ventricular strain in patients with essential hypertension have indicated by our group that systolic longitudinal strain decreased in the early stage, and multidimensional strain was affected later. But the morphological basis of this progression is still unclear. This study was aimed to investigate left ventricular systolic strain and morphology changes with aging in spontaneously hypertensive rat (SHR) by using two-dimensional strain echocardiography(2DSE).Method6012-week-old male SHR confirmed with hypertension by tail-cuff were randomly divided into6groups(n=8-10). Left ventricular hemodynamic and, echocardiagraphic paremeters and myocardial histology and ultrastructure was observed at12w,16w,28w,45w and66w respectively.2DSE measurements included SL, SR and SC of six segments of LV at papillary muscle level, and myocardial histology included myocyte diameter, CVF and PVCA by HE and Masson stain. The relationship between CVF, PVCA and SL were studied by correlation analysis.ResultCompared with12w group, the ventricular wall thickness, LVDd, LAD, LVM in28w,45w and66w groups were higher (p<0.05) especially in45w and66w groups. While E and E/A were significantly decreased only in66w (p<0.05), and LVEF and FS showed no difference between each group. On the contrary to LVEDP, which decreased with age and reached its minimum at28w, LV+dp/dt, LV-dp/dt and myocardial strain increased with age and reached its maximum at28w, than decreased (p<0.05),Cardiomyocytes diameter and PVCA indicated growth trend since16w, but only significantly increased in66w, compared to45w (p<0.05). And compared with12w and16w group, CFV increased in28w (p<0.05),45w (compared with28w, p>0.05) and66w (compared with45w,p<0.01) groups. CVF, PVCA and myocardial longitudinal strain showed negatively correlated (r=-0.503,-0.592; p=0.04,0.029). Cardiomyocyte hypertrophy, myofilament local dissolving, mtiochondra swelling and sporadic collagen fibers proliferation appeared from28w, and getting more obviously in66w group.Conclusion1. In12-16week, left ventricular myocardial systolic strain of SHR still remain in development stage, which may last till28week, when myocardial proliferation starts. So, it should be condidered to choose the time point of SHR in the related research.2. The myocardial remodeling, such as cardiomyocyte hypertrophy, collagen fibers proliferation and the thickness of vascular wall, progressed along with the aging of SHR, and reached its maximum at66week, which showed the same variation time-line as diastolic function.3Although, LVEF showed no significant change in28-66w, considering the damage of myocardial systolic strain, which correlated to the proliferation of collagen fibers, systolic function may be effected by reducing cellular oxygen supply.
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