Investigation On The Characteristics Of Left Ventricular Layer-specific Strain In Different Stages Of Cardiac Dysfunction In Spontaneously Hypertensive Rats

Backgrounds and ObjectivesOur previous studies about spontaneously hypertensive rats(SHR)have found that the Longitudinal strain(LS)impaired in the early stage when LVEF was still preserved,while Circumferential strain(CS)and radial strain(RS)were impaired in the late stage when LVEF was reduced,suggesting that CS and RS play a key role in the retention of left ventricular pump function.In this study,2D layer-specific strain was used to further observe the characteristics of multi-directional left ventricular layer-specific strain in different stages of cardiac dysfunction in SHR and its relationship with global cardiac function.Methods83 SHRs and 47 WKY rats were purchased and fed from 12 weeks.The left ventricular echocardiographic and cardiac catheter index were investigated at the interval of 8-12 weeks in rats of 12-102 weeks.Indexes including left ventricular end-diastolic pressure(LVEDP),left atrium diameter(LAD),interventricular septum thickness,(IVST),left ventricular post wall thickness(LVPWT),left ventricular internal diameter at end-diastole(LVIDd),left ventricular internal diameter at end-systole(LVIDs).Two-dimensional layer-specific strain analysis were performed on EchoPAC system to obtain two-dimensional strain values of the whole,subendcardial,and epicardial of LS,CS,and whole RS.All measurements above was acquired based on the images data of our previous studies.Results74 SHRs were classified into group A(normal cardiac function group,n=13),group B1(diastolic dysfunction group,LVEF?70% with increased LVEDP and LAD,n=20),and group B2(systolic dysfunction group,LVEF<70%,n=17),and WKY rats at the similar weeks of age were chosen as controls.In group B1,LS was significantly weakened in the whole layer and subendocardial than the group A(whole LS:-13.78±1.85% VS-17.62±1.94%,subendocardial LS:-16.26±1.88% VS-22.66±2.23%,both P<0.0001),and the subendocardial CS was slightly weaker than the group A(-21.83±3.27% VS-24.78±1.58%,P<0.05),the epicardial LS,whole CS,epicardial CS and whole RS were preserved.In the group B2,all layers of LS,CS and whole RS were significantly weaker than the group A and group B1,and the CS and RS were more weaker than LS.In addition,the decline of CS in the group B2 was more significantly than the group B1.The LS and CS in WKY rats decreased gradually from the subendocardial layer to the epicardial layer.All layers and directions of strain in WKY rats did not change with age.In SHR,all layers and directions of strain were significantly correlated with LVMI and LVEF(P all<0.05),with the best correlation between CS,RS and LVEF(r absolute value=0.603~0.676,P all<0.01).When the correlation of strain and LVEF were analyzed in the group B1 and B2 respectively,all layers of CS and RS were highly correlated with LVEF only in group B2(r absolute value=0.771~0.881,P all<0.01).ConclusionIn the development of cardiac dysfunction in SHRs,subendocardial LS was significantly impaired with slightly damage to the subendocardial CS in the diastolic dysfunction group.When the transmural collagen deposition happened in the stage of systolic dysfunction,all layers and directions of LV strain were significantly decreased,especially the CS and RS.