RESUMO
To evaluate the changes of myocardial viability and systolic function in rabbits with different ischemic periods by layer‐specific strain of ultrasound speckled tracking imaging ( ST I) and low dose dobutamine stress echocardiography ( LDDSE ) . Methods T hirty‐six rabbits were randomly divided into 3 groups( n ＝12) : ①myocardial infarction group Ⅰ :coronary artery occlusion for 45 min ; ②myocardial infarction group Ⅱ :coronary artery occlusion for 60 min ; ③ myocardial infarction group Ⅲ :coronary artery occlusion for 90 min . Echocardiography examinations were performed at baseline ,after ligation and low dose dobutamine stress . After the experiment ,rabbits were killed and the hearts were taken to assess viable or nonviable mycardium , triphenyl tetrazolium chloride and Evans blue staining were applied . Results ①After coronary artery ligation ,left ventricular ejection fraction( LVEF) decreased in 3 groups ( all P ＜ 0 .05 ) , the ventricular global endocardial longitudinal strain ( GSLsys‐endo ) , global myocardial longitudinal strain( GSLsys‐mid) ,and global epicardial longitudinal strain( GSLsys‐epi) decreased in 3 groups ( all P ＜ 0 .05 ) ,the longitudinal strain of endocardium ( SLsys‐endo ) ,longitudinal strain of myocardium ( SLsys‐mid) ,longitudinal strain of epicardium ( SLsys‐epi) decreased in viable myocardial ( all P＜0 .05) ; ②While low dose dobutamine stressing ,the GSLsys and SLsys increased in each groups ,and the GSLsys‐endo ,GSLsys‐mid ,GSLsys‐epi and SLsys‐endo of viable segments in each group were increased ( P＜0 .05) ; ③After ligation and low dose dobutamine stress ,the GSLsys in endocardium in three groups were different( P ＜0 .05) ,and the SLsys in endocardium of viable segments in three groups were different ( P＜0 .05) . Conclusions Layer‐specific strain of STI combined with LDDSE can accurately evaluate the changes of myocardial viability and systolic function in different ischemic periods ,and the longitudinal strain of endocardium is more sensitive ;moreover ,with the increase of coronary artery occlusion time ,the infarcted myocardium increases ,myocardial viability and systolic function decrease .