***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: BACKGROUND Disagreement of strain measurements among different vendors has provided an obstacle to the clinical use of strain . A joint st and ardization task force between professional societies and industry was initiated to reduce intervendor variability of strain . Although feedback from this process has been used in software up grade s , little is known about the effects of efforts to improve conformity . The aim of this study was to assess whether intervendor agreement for global longitudinal strain ( GLS ) has improved after st and ardization initiatives . METHODS Eighty-two subjects ( mean age , 52 ± 21 years ; 55 % men ) prospect ively underwent two sequential examinations using two most common ultrasound systems ( Vivid E9 and iE33 ) . GLS was calculated using proprietary software ( EchoPAC-PC BT12 [ E12 ] and BT13 [ E13 ] vs QLAB version 8.0 [ Q8 ] , QLAB version 9.0 [ Q9 ] , and QLAB version 10.0 [ Q10 ] ) . Agreements in GLS were evaluated with Bl and -Altman plots . Coefficients of variation ( CVs ) were compared using the Friedman test and compared with CVs of left ventricular volumes and ejection fraction ( LVEF ) . RESULTS Median GLS using E12 was -19.2 % ( interquartile range [ IQR ] , -15.2 % to -23.2 % ) , compared with -19.3 % ( IQR , -14.9 % to -23.7 % ) for E13 , -15.7 % ( IQR , -11.4 % to -20 % ) for Q8 , -19 % ( IQR , -15.7 % to -22.3 % ) for Q9 , and -18.7 % ( IQR , -15.7 % to -21.7 % ) for Q10 . The CVs of prest and ardization GLS ( 12 ± 8 % [ E12/Q8 ] and 14 ± 8 [ E13/Q8 ] ) were significantly larger than that of LVEF ( 5 ± 5 ) ( P < .001 ) . Since st and ardization , the CVs of GLS have shown improvement ( 6 ± 4 [ E12/Q9 ] , 7 ± 4 [ E12/Q10 ] , 6 ± 4 [ E13/Q9 ] , and 7 ± 4 [ E13/Q10 ] ) and are similar to those of LVEF . CONCLUSIONS Subsequent to the joint st and ardization task force , there has been improvement in between-vendor concordance in GLS between two leading ultrasound manufactures , the variability of which is now analogous to that of LVEF . The removal of concerns about measurement variability should allow wider use of GLS BACKGROUND The aim of this study was to investige serial changes of myocardial deformation using two-dimensional speckle-tracking echocardiographic ( 2DSTE ) imaging in children undergoing balloon valvuloplasty for congenital valvular aortic stenosis ( VAS ) . METHODS Thirty-seven children with isolated congenital VAS were enrolled in this study prospect ively . Patients underwent echocardiographic evaluation at three instances : before balloon valvuloplasty , 6 months after intervention , and 3 years after intervention . Longitudinal , circumferential , and radial peak systolic strain values were determined , as well as systolic strain rate and the time to peak global systolic strain . Linear mixed statistical models were used to assess changes in 2DSTE parameters after balloon intervention . Using one-way analysis of variance , 2DSTE results at 3-year follow-up were compared with 2DSTE measurements in 74 healthy age-matched children and 76 children with uncorrected VAS whose severity of stenosis corresponded to residual stenosis of study subjects at 3-year follow-up . RESULTS Global peak strain and strain rate measurements in all three directions were decreased before intervention compared with healthy children . Global peak strain and strain rate measurements increased significantly ( P < .001 ) several months after balloon valvuloplasty and continued to increase at 3-year follow-up . However , at 3-year follow-up , global peak strain and strain rate in the longitudinal and circumferential directions were significantly lower ( P < .001 ) compared with both control groups . Measurements of time to peak global systolic strain were significantly shorter at early follow-up compared with measurements before intervention ( P < .05 ) . CONCLUSIONS Shortly after balloon valvuloplasty for severe congenital VAS , there is an improvement in systolic myocardial deformation . However , 2DSTE parameters do not return to normal at 3-year follow-up . These abnormalities in systolic deformation can not be fully attributed to residual stenosis or aortic regurgitation Background Speckle tracking echocardiography is increasingly being used to assess cardiac function in neonates . The objective was to compare speckle tracking strain indices between asphyxiated infants and healthy controls and to ascertain correlations between strain and 2D Doppler derived indices and cardiac troponin ( biochemical marker of myocardial injury ) . Methods Clinical and echocardiographic data from severely asphyxiated infants undergoing therapeutic hypothermia  was evaluated retrospectively . This was compared with prospect i ve data from healthy infants . Correlations between variables were assessed using Pearson ’s coefficient of correlation . Results Twenty four infants with severe perinatal asphyxia were admitted during the study period of which 3 were not cooled and were excluded . The gestational age and birth weights of cases and controls were comparable . The mean left ventricular global longitudinal strain ( GLS ) from apical 4 chamber view was noted to be significantly impaired in the asphyxiated infants ( – 11.01 % ± 2.48 vs – 21.45 % ± 2.74 , p < 0.001 ) . Cardiac output was significantly lower in the asphyxiated infants ( 97 ± 26 vs 230 ± 60 ml/kg/min ) . In asphyxiated infants , GLS correlated positively with cardiac output ( r2 = 0.86 , p < 0.001 ) and negatively with serum troponin levels ( r2 = 0.64 , p < 0.001 ) . GLS was less impaired in infants on inotropes compared to those not on inotropic support , -12.55 % ( 1.9 ) vs -10.2 % ( 1.3 ) , p= 0.018 . Infants who died had a lower global strain value compared to survivors , – 9.7 % ( 1.6 ) vs – 12.8 % ( 2.6 ) , p = 0.02 . Conclusions 2D Speckle derived strain was impaired in asphyxiated infants . Significant correlations between GLS and cardiac output and troponin were noted Background Recent advances in technology have provided the opportunity for off-line analysis of digital video-clips of two-dimensional ( 2-D ) echocardiographic images . Commercially available software that follows the motion of cardiac structures during cardiac cycle computes both regional and global velocity , strain , and strain rate (SR).The present study aims to evaluate the clinical applicability of the software based on the tracking algorithm feature ( studied for cardiology purpose s ) and to derive the reference values for longitudinal and circumferential strain and SR of the left ventricle in a normal population of children and young adults . Methods 45 healthy volunteers ( 30 adults : 19 male , 11 female , mean age 37 ± 6 years ; 15 children : 8 male , 7 female , mean age 8 ± 2 years ) underwent transthoracic echocardiographic examination ; 2D cine-loops recordings of apical 4-four 4-chamber ( 4C ) and 2-chamber ( 2C ) views and short axis views were stored for off-line analysis .Computer analyses were performed using specific software relying on the algorithm of optical flow analysis , specifically design ed to track the endocardial border , installed on a Windows ™ based computer workstation . Inter and intra-observer variability was assessed . Results The feasibility of measurements obtained with tissue tracking system was higher in apical view ( 100 % for systolic events ; 64 % for diastolic events ) than in short axis view ( 70 % for systolic events ; 52 % for diastolic events ) . Longitudinal systolic velocity decreased from base to apex in all subjects ( 5.22 ± 1.01 vs. 1.20 ± 0.88 ; p < 0.0001 ) . Longitudinal strain and SR significantly increased from base to apex in all subjects ( -12.95 ± 6.79 vs. -14.87 ± 6.78 ; p = 0.002 ; -0.72 ± 0.39 vs. -0.94 ± 0.48 , p = 0.0001 , respectively ) . Similarly , circumferential strain and SR increased from base to apex ( -21.32 ± 5.15 vs. -27.02 ± 5.88 , p = 0.002 ; -1.51 ± 0.37 vs. -1.95 ± 0.57 , p = 0.003 , respectively).Values of global systolic SR , both longitudinal and circumferential , were significantly higher in children than in adults ( -1.3 ± 0.2 , vs. -1.11 ± 0.2 , p = 0.006 ; -1.9 ± 0.6 vs. -1.6 ± 0.5 , p = 0.0265 , respectively ) . No significant differences in longitudinal and circumferential systolic velocities were identified for any segment when comparing adults with children . Conclusion This 2D based tissue tracking system used for computation is reliable and applicable in adults and children particularly for systolic events . Measured with this technology , we have established reference values for myocardial velocity , Strain and SR for both young adults and children Chemotherapy and particularly anthracycline exposure are associated with acute and chronic cardiotoxicity . Few data exist on the effect of cardiac function after in utero exposure to maternal chemotherapy . Our recently published multicenter prospect i ve study showed no significant changes in systolic function using conventional echocardiographic parameters . The purpose of this study was to further investigate whether early functional changes can be detected using tissue Doppler imaging ( TDI ) and two-dimensional ( 2D ) speckle tracking echocardiography ( STE ) .  Sixty-two children ( median/range age 1.7 ( 1–9.8 ) years ) exposed to chemotherapy during fetal life were enrolled and compared to 62 age- and gender-matched controls .  TDI velocities were measured at the basal interventricular septum ( IVS ) and right and left ventricular ( LV ) free walls . LV global longitudinal and circumferential systolic strains were derived using 2D STE . We found small but significant differences between the groups ( patients versus controls ) in LV fractional shortening [ 35 (29–46)% versus 39 (28–53)% , p < 0.001 ] , LV ejection fraction [ 66 (57–79)% versus 70 (57–83)% , p < 0.001 ] , LV posterior wall thickness z score [ −0.15 ( −2.32–1.81 ) versus −0.10 ( −1.9–2.0 ) , p < 0.001 ] , and IVS thickness z score [ −1.06 ( −2.6–1.3 ) versus −0.5 ( −2.1–1.7 ) , p < 0.001 ] . No significant differences in TDI velocities or LV global strains were observed . Within the patient group , the cardiac functional parameters did not correlate to the number of cycles of anthracycline or the cumulative anthracycline dose . Children exposed to fetal chemotherapy have a lower normal fractional shortening and mildly lower left ventricular wall thickness . Tissue Doppler and strain measurements are within normal range and not statistically different from normal controls . The long-term implication s of these findings will be further studied in this prospect i ve cohort study BACKGROUND Left ventricular ( LV ) dysfunction is common in adults late after repair of tetralogy of Fallot ( TOF ) .  The early detection of myocardial dysfunction may be important , but LV myocardial strain and dyssynchrony are not well studied in children with TOF . The objective of this study was to investigate LV strain and dyssynchrony in asymptomatic children and adolescents after contemporary repair of TOF .  The hypothesis was that impaired LV myocardial mechanics are related to pulmonary regurgitation , right ventricular ( RV ) enlargement , and exercise capacity . METHODS Children and adolescents were prospect ively studied after TOF repair .  LV regional strain and dyssynchrony were assessed using two-dimensional speckle-tracking echocardiography .  Ventricular volumes , ejection fraction , and pulmonary regurgitation were assessed using magnetic resonance imaging . Exercise capacity was determined using metabolic exercise testing . RESULTS One hundred twenty-four subjects ( 53 patients with TOF and 71 controls ) were studied .  Regional circumferential ( e.g. , basal lateral wall , -15.0 ± 7.0 % vs -19.0 ± 7.0 % , P = .02 ) and radial ( e.g. , basal posterior wall , 
    Output:
    
LV segmental longitudinal strain has a stable apex-to-base gradient that is preserved throughout maturation .