Global And Regional Systolic Cardiac Function Evaluated By Speckle Tracking Echocardiography In The Murine Model Of Cardiovascular Disease And Related Study

Part Ⅰ The impact of heart rate on speckle tracking echocardiographic parameters in the mouse models of pressure overloadObjectives Genetic altered mice are widely applied in cardiovascular research for the extrapolation of human diseases. Echocardiography is an essential tool for evaluating cardiac and hemodynamic functions in murine. The goal of our research is to test the effects of heart rate on conventional as well as speckle tracking echocardiographic (STE) parameters under healthy and pathological conditions using a murine model of pressure overload and to provide the best range of heart rate in the process of STE measurements with minimum cardiac contraction depression.Methods①38adult C57/BL6mice were randomly divided into Sham group (n=10), Mild trans-aortic banding (TAB) group (n=14) and Severe TAB group (n=14). Mice in Mild TAB and Severe TAB group were subjected to the mild or severe aortic banding with a25Gauge (G) or28G needle. Mice in the Sham group shared the identical procedure except the ligation.②STE studies were performed in each group. Heart rate was altered in the following conditions:low heart rate (LH, heart rate ranged from400-450beat/min), high heart rate (HH, heart rate ranged from480-520beat/min), and Awake heart rate (AH; Just before the mice woke up, Heart rate≥550beat/min).Results①STE parameters in Mild TAB, Severe TAB and Sham groups stayed almost the same between AH and HH conditions(P<0.05) but were significantly depressed in the LH condition(P>0.05).②Pearson correlation analysis revealed that STE parameters in Mild TAB, Severe TAB and Sham group correlated positively with Heart rate.③The test and re-test of STE parameters in Sham group at the interval of12days showed that STE parameters owned a high reproducibility under AH and HH(P>0.05), but changed significantly under LH(P<0.05).Conclusion STE echocardiography can be performed under relative high heart rate(above480beat/min) in different physiological and pathological conditions without significantly depressing cardiac function. Part Ⅱ Age related global and regional left ventricular deformation parameters and their reproducibility in mice:analysis based on two dimension speckle tracking echocardiographyObjective Depression of myocardial contractility is accompanied with aging. However, it is rather difficult for noninvasively testing the effect of aging on cardiac function. Mice models of aging are widely applied in the field of cardiovascular. The goals of this study are to test whether two-dimension speckle tracking echocardiography can be used to detect global and regional contraction dysfunction in aging mice and the inter-and intra reproducibility of speckle tracking echocardiographic parameters.Methods①Conventional echocardiography was applied in mice of month1, month4, month8, month12and month16(n=10for each group).②Speckle tracking echocardiography (STE) was used in each group of mice to test the regional and global alteration of longitudinal strain (LS), radial strain in long axis(RS), circumferential Strain(CS) and radial strain in short axis (RSS).③Masson’s trichrome stain was used for the histology characteristics of percent fibrosis of left ventricle. The Pearson correlation between the percent fibrosis and STE parameter was further analyzed.④The Pearson correlation and Bland-Altman analysis were applied to test the intra-observer and inter-observar reproducibility of LS, RS, CS and RSS.Result①Conventional echocardiography revealed that in the1month group, the Fraction shortening(FS) was increased (.P<0.05). However, the LVEDD (left ventricular end diastolic diameter), LVESD (left ventricular end systolic diameter) and LV mass was smaller as compared to the rest of the groups(P<0.05). No differences of EF, FS, LVEDD, LVESD and LV mass were found among the mice of4month,8month and12month. In the16month mice, the FS was reduced (P<0.05), the LVEDD, LVESD and LV mass was elevated (P<0.05).②STE analysis revealed that all the STE parameters was increased in1month mice(P<0.05). STE parameters remained stable in4month and8month mice. Howere, at the age of12mo, LS was decreased (P<0.05) while CS and RS was preserved(P>0.05). In the16mo mice, LS, CS and RS were significantly depressed(P<0.05). RSS was unchanged among all groups of mice (P>0.05). Regional strain analysis revealed that in mice’s age between4-16month, LS was largest in apex region (P<0.05) and RS was smallest in apex region(P<0.05).③Masson’s trichrome stain suggested that the changes of STE parameters were accompanied with elevation in percentage of fibrosis. While LS was reduced in12mo group, percentage area of fibrosis was also increased (P<0.05). In the16mo mice, with the reduction of RS, CS and LS, the percentage area of fibrosis was continually increasing as compared to12mo mice. Pearson correlation analysis revealed that LS, CS and RS correlated with percentage area of fibrosis and LS showed strongest correlation. RSS showed no correlation with the percentage area of fibrosis. The parameters of STE showed good inter and intra observer reproducibility. To be specific, among LS, RS CS and RSS, LS showed lowest coefficient of variance (COV) and the narrowest line of agreement(LOA) and RSS showed highest COV and the widest LOA.Conclusion①STE can be used to estimate the age related global and regional contractility of heart in mice.②STE parameters correlated positively with the fibrosis of the heart. LS can be used as an effective index to evaluate the fibrosis of the heart.④Analysis of intra and inter observer variability revealed that LS showed promising intra-and inter-observer reproducibility,followed by CS, RS and lowest for RSS. For quantitative follow-up of cardiac function, RSS may be excluded. Part Ⅲ Assessment of Global and Regional Strain by Speckle Tracking Echocardiography in the Mice Model of Pressure Overload and related studyObjective Speckle Tracking Echocardiography (STE) has been applied to the evaluation of cardiac contraction dysfunction. However, studies focuses on alteration of STE parameters in the process of hypertrophy and heart failure are quite rare. The aim of the study was to detect global and regional cardiac dysfunction by STE in the mice model of pressure overload and to further compare the STE parameters with pressure-volume (P-V) loop analysis and myocardium fibrosis.Methods①Adult mice were subjected to Mild or Severe aortic banding with a25Gauge (G) or28G needles. After surgery, STE and conventional Echocardiography was assessed to the Sham (n=10), Mild TAB (trans-aortic banding, n=14) and Severe TAB group (n=10) for8weeks following surgery.②Masson’s trichrome stain was used in each group for the histology characteristics in percentage area of fibrosis. The Pearson correlation between the percentage area of fibrosis and STE parameter was analyzed.③LV Pressure Volume loop analysis was applied at week8after surgery in each group using pressure-conductance micro-catheter. The load-independent contractility parameters (preload recruitable stroke work, PRSW; end systolic elastance, Ees) were calculated. The correlations between the PRSW, Ees and STE parameters were further analyzed.Result①Mice subjected to Severe TAB showed a significant change of Fraction shortening (FS), Ejection fraction (EF), Left ventricular mass (LV mass), and Left ventricular diastolic diameter (LVEDD, P<0.05for each parameter) from week1after banding. Meanwhile, compared to the Sham group, no differences in FS, EF and LVEDD were observed (P>0.05for each parameter) in Mild TAB group throughout the experiment period. However, the left wall thickness (LVWT) and LV mass were increased in the Mild TAB group.②TE analysis revealed that as compare to the Sham group, longitudinal strain (LS) in the Mild TAB group was decreased (P<0.05) from week1after banding and circumferential strain (CS) was preserved (P>0.05) in the whole experiment period. Radial strain (RS) in the Mild TAB group was reduced at week6(P<0.05). LS, CS and RS in the Severe TAB group were significantly decreased as compared to the Sham and the Mild TAB group (P<0.05for each comparison) from week1after surgery. Regional contraction dysfunction was analyzed in both hypertrophic and failing myocardium in longitudinal and radial direction. It showed that LS was largest in the apex region and RS was smallest in the apex region in the healthy and hypertrophic myocardium. It also showed that compared to the Sham TAB group, only base LS in the Mild TAB group was decreased. Each of regional Strain in the Severe TAB group was uniformly depressed in radial and longitudinal direction.③Masson’s trichrome stain suggested that the percentage area of fibrosis was increased (P<0.05) in the Mild TAB group as compared to the Sham group. In the Severe TAB group, the percentage area of fibrosis was continuingly increasing (P<0.05). Pearson correlation analysis revealed that LS, CS and RS correlated significantly with percentage area of fibrosis and LS showed strongest correlation.④Pressure volume loop analysis revealed that contractility parameters was depressed in the Severe TAB group (P<0.05) but increased in the Mild TAB group (P>0.05). Pearson correlation analysis revealed that LS, CS and RS correlated significantly with PRSW and Ees.Among them, LS showed the poorest correlation for both PRSW and Ees.Conclusion STE is a feasible and reliable method to detect regional and global contraction dysfunction in the murine model. The change of LS tends to reflect the extent of myocardium fibrosis and the change of CS and RS reflect the impairment of intrinsic contract function in the mouse models.