A deep understanding of RV function is helpful for improving the prognosis of patients with cardiovascular disease[16–19]. Unfortunately, non-invasive techniques evaluating RV function remain hampered because of RV’s complex structure. Unlike LV, RV consists of two layers of fibres that contribute to contraction. The superficial myocardial fibres which arranged in a circumferential direction and paralleled to the atrioventricular groove were thinner and mainly participate in the transverse contraction of RV. While the deep myocardial fibres which was longitudinally aligned from the apex to base was relatively thick and mainly engaged in the longitudinal contraction of RV[20]. In general, RV longitudinal contraction accounts for 80% of RV systolic function[21, 22].
Assessment of RV systolic function is of great importance in clinical. The current methods for the assessment of RV contraction include CMR, 2-dimensional and 3-dimensional echocardiography. Typically, CMR is regarded as a gold standard to evaluate RV geometry and function, whereas the use of CMR is limited due to its high cost as well as time consumption and for patients who had implantable devices cannot be used, too[5, 6]. New technique such as 3-dimension echocardiography allows comprehensive and quantitative assessment of RV geometry and function, but this method requires special echocardiography training and is also time-consuming[23].
TAPSE, which is a simple and reusable indicator to assess RV systolic function by longitudinal displacement of the anterior tricuspid annulus, was first validated by Kaul in 1984[24] and has been considered to represent RV contraction for years[25]. It was recommended to be used routinely to estimate RV systolic function in adults with a lower limit (16mm) of reference values for impaired RV systolic function by ASE 2010 Guideline[7]. In 2015, ASE changed the cutoff value from 16mm to 17mm, which means the TAPSE values less than 17mm represents impaired RV systolic function[26]. Both these two guidelines are recommendations for adults, whereas there is no guideline or expert consensus that recommends TAPSE reference values for children. So far, there are only several studies from abroad determinated reference values of TAPSE for children. Koestenberger from Austria first reported the reference values and Z-scores of TAPSE in children in 2009[11], then several studies from other countries such as Spain, Turkey, Japan and sub-Saharan Africa determinated reference values of TAPSE in children except China[8, 11–13, 27]. As has been reported by Fahrettin Uysal[8], the mean TAPSE value of Turkish children in 6-12 months age group is only 13.46 mm while it is 15.17 mm in Spanish children at the same age group[13]; in Japan, the mean TAPSE value of the 6-12 months children is 16.9 mm[12], which is much higher than both of the former two countries. As stated above, TAPSE values in children was different among various countries. Up to now, reference values of TAPSE in Chinese children has not been reported yet. Therefore, our study was undertaken to attain growth-related reference values of TAPSE in Chinese Children. We found that TAPSE increased with age and BSA in Chinese children under 15 years old, which is consistent with previous studies from different countries. However, when we compared our specific growth-related reference values of TAPSE with other studies, we found significant differences among these different countries. In our study, we found that the mean TAPSE values in Chinese children reached the adult level (17.0mm) in 1 year old, which grew faster than that of Turkish as well as Spanish children; while in Japan, TAPSE showed the most proximal reference values with Chinese children, as has been mentioned before. All of these differences might be explained by genetic diversity, economic status and diet habits[8, 12].
This finding is meaningful for Chinese children, especially for those with cardiopulmonary diseases, as RV function could be affected by different disease states such as acute respiratory distress syndrome (ARDS) as well as post-operation period in congenital heart diseases and different treatment. For instance, RV systolic function influences strategies to adjust positive end-expiratory pressure (PEEP) in patients with ARDS[28]; procedures involving tricuspid valvuloplasty[29] and cardiopulmonary bypass (CPB) with pericardial incision[20] were shown to have adverse effects on RV systolic function. Therefore, applying improper reference values of TAPSE can lead to the misjudgment of RV systolic function, which may interfere the decision-making in treatment. Accordingly, TAPSE values between different countries must be well-realized and each country must have its own reference values of TAPSE to evaluate RV systolic function.
In conclusion, we established the growth-related normal ranges of TAPSE for children aged between 0-15 years in China. We found that TAPSE showed different reference values among different countries and increased with age and BSA without gender difference. Besides, the mean value of TAPSE remains a lower level than adult (17mm) until 1 year old in China. We hope these reference values could be used for assessing RV systolic function for Chinese children. However, there are two limitations in our present study. First, children aged between 16-18 are scarce in children’s hospital, therefore, in this study, we included children aged 0-15 year old instead of 0-18 year old. Second, this was a single-center study and we think multi-center study from different area of China is supposed to be performed in the future to reflect the whole spectrum of TAPSE in Chinese children.