| The development of heart from newborn, infants, teenager until adult is a dynamic, continuous process, morphology of the heart will gradually mature, therefore the global and regional cardiac function will change with along the development of any age stages, and the regional myocardial function will be different between children and adult. Noninvasive evaluation of regional myocardial function in normal children is important, it can provide normal reference for congenital heart disease, cardiomyopathy, Kawasaki disease and other heart disease. At present, the noninvasive assessment of regional left ventricular function in children may be based on a qualitative or quantitative approach, qualitative methods are visual interpretation of radial endocardial excursion and regional ventricular wall thickening, but qualitative methods are lack of quantitative criteria and rely on the experience of the observer. Quantitative methods are M-mode technique, strain and strain rate based on Color Doppler and speckle tracking, the volume-time curve of three-dimensional echocardiography, velocity vector imaging and so on. M-mode method only can evaluate regional myocardial function which is perpendicular to the sample line. With the development of anatomical M-mode method, it is possible to quantitative the regional function of more left ventricular segments, but anatomical M-mode method can only detect the radial motion of myocardial. And also the TDI method can not evaluate the every segments' function because angel dependency. Therefore a novel method of measurement of regional myocardial strain and strain rate in 2 dimensions echocardiography by speckle tracking technique was recently introduced. One important advantage of this new method is not limited by dependency on the angle of insonation, and can evaluate longitudinal, radial, circumferential myocardial movement and torsion. So the new method can evaluate all segments of ventricular in three directions.Assessment of strain and strain rate in acquired and congenital heart disease children by TDI and speckle tracking imaging can detect the regional dysfunction of ventricular earlier.Nowadays, there were some studies which focused on the strain and strain rate in normal children. Weidemann evaluation regional color Doppler-based strain and strain rate in 4-16 years old healthy children, only a weak correlation was found between strain with age, strain rate with heart rate and age. Boettler established reference values for left ventricular(LV) longitudinal strain and strain rate in both systole and diastole in 129 healthy infants and children over a age range from 1 day to 16.9 years, for many segments, there were significant effects of heart rate(HR), weight, length, age, and body surface area on systolic, early and late diastolic strain and late diastolic strain rate, but the influence were more strongly by HR. However the above study were applied on the basis of color Doppler-based strain and strain rate, it is unidimensional and angle-dependent, so only a small part of left ventricular segments can be evaluated.Lorch measured longitudinal systolic strain, systolic and diastolic strain rate in left ventricular septal and lateral segments in 284 healthy 0-18 years children by speckle tracking echocardiography, this study established reference values for longitudinal strain and strain rate, and found systolic and early diastolic SR declined until age 5 to10 years. Some scholars also compared strain and strain rate of children with adults by speckle tracking technique, and they found that the globe longitudinal and circumferential strain rate in children were significant larger than adults. There is no comprehensive evaluation about regional speckle tracking-based strain and strain rate of all left ventricular segments in healthy children, and the relation with age and heart rate.In this study, we evaluated regional peak systolic strain and strain rate of all left ventricular segments in three directions (longitudinal, radial, circumferential) for 164 normal children ,the purpose of our study was①to establish their characteristics of longitudinal, radial and circumferential strain and strain rate.②to discern the relative influence of age and heart rate on these LV functional indices.③we divided the children into 5 groups according to age, and evaluated the characteristic of regional longitudinal, radial, circumferential strain and strain rate in normal children at different groups by speckle tracking imaging. The study was divided into three parts as follows:Part 1 Evaluation of the characteristic of left ventricular regional strain and strain rate in normal children by speckle tracking imagingObjective:To evaluate the characteristic of longitudinal, radial, circumferential strain and strain rate in normal children by speckle tracking imaging.Methods The study group consisted of 164 normal children(90 male,64 female), mean age (9.08±5.73)years. We performed parasternal left ventricular apical four-chamber, three-chamber, two-chamber views and short axis views in mitral valve, papillary muscle and apex levels. Regional longitudinal, radial and circumferential strain and strain rate of left ventricular wall during the systole was measured by speckle tracking imaging which was installed in the GE EchoPAC workstation。Results①The characteristic of regional longitudinal systolic peak strain (SL) and strain rate (SrL) in normal children:The shapes of the SL curves and the SrL curves of the left ventricular regional myocardium were similar. The apical SL and SrL of left ventricular wall were larger than the middle one and the basal one. Significant differences were found between apical and basal or middle segments in left ventricular walls except anterior wall.②The characteristic of regional radial systolic peak strain (SR) and strain rate (SrR) in normal children:The shapes of the SR curves and the SrR curves of the left ventricular regional myocardium were similar. At the base level there were no statistically significant of SR except the basal anterior septum and lateral segment. At the middle level there were no statistically significant of SR except the anterior septum and anterior segment. At the base level and the middle level, there were no statistically significant of SrR except the basal anterior septum and the middle anterior septum .There were no statistically significant of SrR, SR in apex level. Significant difference of SR, SrR were found in most segments which were in the same wall but at the different levels.③The characteristic of regional circumferential systolic peak strain (SC) and strain rate (SrC):The shapes of the SC curves and the SrC curves of the left ventricular regional myocardium were similar. There were statistically significant of SC in the basal and middle level, but we found no difference in the apex. Significant difference of SrC were found in most segments which were in the same level. Significant difference of SC, SrC were found in most segments which were in the same wall but at the different levels.Conclusion:The shapes of the regional longitudinal, radial and circumferential strain and strain rate curves of the left ventricular regional myocardium were similar, which was showed that the motion of regional left ventricular myocardium were in the same direction. Regional longitudinal, radial and circumferential strain and strain rate of normal children had characteristics, there were difference between different segments. The heterogeneity distribution of regional strain and strain rate in normal children was related to myocardial fiber arrangement, different periods of the heart anatomy and physiology of children, and the anisotropic characteristics of the myocardial structure.Part 2 Impact of age and heart rate on strain and strain rate by speckle tracking imaging:a study in normal childrenObjective:To evaluate the relationship between age and longitudinal, radial, circumferential strain and strain rate in normal children, also, assesses the effect of heart rate.Method:Transthoracic two-dimensional echocardiographic examinations were performed on a total of 164 normal children. Left ventricular apical four-chamber, three-chamber, two-chamber views and short axis views at the basal level, middle level and apex were performed, and the dynamic 2-dimensional gray images in 3 heart cycles were obtained. All images were analysed off-line in GE EchoPAC workstation and regional strain, strain rate were acquired, and then analysed the relationship between regional strain, strain rate and age, heart rate by regression analysis.Results:①Age and heart rate have significant correlation with SL of the basal and the middle posterior septum segments, but age, heart rate have no correlation with SL of the middle anterior septum segment. Other segments only associated with age(P<0.05,R2=0.165-0.042)。The strongest correlations of regional SrL were the middle posterior septum with age (R2=0.377) and the middle inferior segment with heart rate (R2=0.226), whereas other segments except the middle anterior wall have weaker correlations with age, heart rate.②The significant but weak correlation of regional SR were the basal anterior septum with heart rate (R2= 0.025, P=0.042),other segments'SR were independent of age and heart rate. SrR of all segments at the basal level correlated with heart rate (P<0.05, R2= 0.066-0.123). SrR of all segments at the middle level correlated with heart rate or age (P<0.05, R2=0.088-0.268). SrR of all segments at the apex correlated with heart rate (P<0.05,R2=0.048-0.127).③Regional SC correlated with age and (or) heart rate in most segments (P<0.05, R2=0.144-0.024),except the basal, middle segments of anterior septum, anterior basal segment and apical segment of posterior septum. Correlation was found with age and (or) heart rate in most segments for regional SrC (P<0.05, R2=0.182-0.024), except basal posterior segment, apical segments of anterior, lateral and posterior wall.Conclusions:When we evaluate the regional strain and strain rate in children by speckle tracking echocardiography, age and heart rate effects must be considered. However, due to regional SR were independent of age and heart rate, it tips us that regional SR can be used as an indicator which can quantify the long-term follow-up cardiac function in children after surgery, and regional SR also can be used to quantify the cardiac function in normal children at different age stages.Part 3 Quantification of regional strain and strain rate in normal children at different age stages by speckle tracking imagingObjective:To evaluate the characteristic of regional longitudinal,radial, circumferential strain and strain rate in normal children at different age stages by speckle tracking imaging. Methods:164 healthy children were divided into 5 groups:classing 0 to 2 years old children together as group A, and 3 to 5 years old as group B,6 to 9 years old as group C, 10 to 12 years old as group D,13 to 18 years old as group E. Left ventricular apical four-chamber, three-chamber, two-chamber views and short axis views at the basal level, middle level and apex were performed, and the dynamic 2-dimensional gray images in 3 heart cycles were obtained. All images were analysed off-line in GE EchoPAC workstation and regional longitudinal, radial and circumferential strain, strain rate were acquired.Results:①These parameters of the five groups for SL and SrL trend to decrease as well as the growth of age. Compared with group D and E, SL of left ventricular wall were significantly increased in group A except anterior wall, and SL were significantly increased in group B except apical segments of the posterior wall and apical segments of the anterior septum. SrL in group A were larger than group E except the middle segments of anterior and lateral wall. Significant difference for SrL was found between group D and group A in septum and inferior wall.②The parameters for SR in 5 groups were homogeneous (P>0.05). SrR trend to decrease as well as the growth of age. Significant difference for SrR was found between group A and group D, E except the apical segments of anterior and lateral wall.③At the mitral valve level, SC trend to increase as well as the increasing age in the lateral and inferior wall, SC in group A was significant less than group E. SC increased as well as the increasing age at the papillary level in the lateral, posterior and inferior wall, SC in group A was significant less than group E. At the apex, SC in anterior septum, anterior, lateral and posterior wall increased with age, significant difference was also found between group A and group E. However, SrC decreased with increasing age in septum and anterior wall at the mitral valve and the papillary level, group A was significant lager than group E.Conclusions:The parameters of SL, SrL, SrR, SC and SrC were heterogeneous in healthy children at different age stages, the differences were mainly between infant and adolescent, but it has a certain regularity, which represents the regional longitudinal strain and strain rate, radial strain rate and circumferential strain rate decrease with increasing age, and the regional circumferential strain increases with increasing age.
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