Evaluation Of Left Ventricular Systolic Function By Tissue Tracking And Its Relationship With Cardiomyocyte Apoptosis With Hyperthyroid Cardiomyopathy In Rabbits

Objective:1.To evaluate the left ventricular systolic function of different geometicpatterns with hyperthyroid cardiomyopathy in rabbits by tissue tracking (TT).2.To study the correlation of left ventricular systolic function with cardiomyocyteapoptosis and expression of bcl-2and bax of different geometric patterns withhyperthyroid cardiomyopathy in rabbits.Methods:Part one:Thirty New Zealand purebred rabbits were stochasticallydivided into two groups.There are20in experimental group and10in controlgroup.Hyperthyroidism models were established by peritoneal injection oflevothyroxine(L-Thy,45μg/kg) in every experimental rabbit everyday for4weeks.Thesame dose of saline was given to every rabbit in control group everyday for4weeks.Conventional echocardiographic parameters were obtained at the ending of4thweek in two groups.The parameters were as follows:left ventricular end diastolicdiameter(LVDd),interventricular septal thickness at end diastole(IVSTd), leftventricular inferolateral wall thickness at end diastole(IWTd),systolic mitralannulardisplacement by M-mode echocardiography(Dm). Then we calculated the leftventricular ejection fraction(LVEF),left ventricular fraction shortening(LVFS),relativewall thickness(RWT),left ventricular mass index(LVMI)and average Dm.According tothe changes of conventional parameters,the rabbits of experimental group weredivided into two subgroups:concentric hypertrophy(CH) subgroup and eccentrichypertrophy(EH) subgroup.TT parameters of systolic mitralannular displacement bytissue tracking(Ds) were also obtained at the ending of4thweek in two groups.Then wecalculated average Ds.Part two:The animal,group and heart function parameters were same as partone.Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick endlabeling(TUNEL) and immunohistochemistry were used to detect the apoptotic cardiomyocytes of different geometric patterns with hyperthyroid cardiomyopathy inrabbits.Results:Part one:Conventional ultrasound parameters:Compared with controlgroup,LVDd,IVSTd,IWTd and LVMI in EH subgroup increased significantly(allP<0.01) and LVEF,LVFS,average Dm in EH subgroup decreased significantly(allP<0.01).Compared with control group,IVSTd, IWTd,RWT and LVMI in CH subgroupincreased significantly(all P<0.01). There were no statistical differences inLVDd,LVEF,LVFS and average Dm between control group and CH subgroup(allP>0.05).Compared with CH subgroup,LVDd and LVMI in EH subgroup increased(allP<0.05) and RWT,LVEF,LVFS and average Dm decreased significantly(all P<0.01).TTparameters:Compared with control group and CH subgroup,average Ds in EH subgroupdecreased significantly(all P<0.01),while there were no statistical difference in averageDs between control group and CH subgroup(P>0.05).Part two:Index of apoptosis(AI):Compared with control group,AI in CH subgroupand EH subgroup increased significantly(all P<0.01). Compared with CH subgroup,AIin EH subgroup was significantly higher(P<0.01).Expression of bcl-2and baxprotein:Compared with control group,expression of bcl-2protein in CH subgroup andEH subgroup was significantly lower(all P<0.01).Compared with CHsubgroup,expression of bcl-2protein in EH subgroup was significantly lower(P<0.01).Compared with control group,expression of bax protein in CH subgroup and EHsubgroup was significantly higher(all P<0.01).Compared with CH subgroup, expressionof bax protein in EH subgroup was significantly higher(P<0.01). Average Ds in CHsubgroup and EH subgroup was negatively correlated with index of apoptoticcardiomyocytes(P<0.05).Average Ds in CH subgroup and EH subgroup wasconspicuously negatively correlated with expression of bax protein(P<0.01),whileaverage Ds in CH subgroup and EH subgroup was conspicuously positively correlatedwith expression of bcl-2protein (P<0.01).Conclusion:1.TT can assess accurately left ventricular systolic function ofdifferent geometric patterns with hyperthyroid cardiomyopathy in rabbits.2.The degrees of cardiomyocyte apoptosis are different in different patterns of leftventricular geometric models with hyperthyroid cardiomyopathy in rabbits.Theapoptosis of cardiomyocyte is closely related to left ventricular systolic function ofdifferent geometric patterns with hyperthyroid cardiomyopathy in rabbits.