Referencing echocardiographic measurements for premature and low-birth weight infants

Abstract

Introduction: Reference ranges for cardiac measurement are available for adults, children and term infants but the same cannot be said for preterm or small for gestational age (SGA) infants surviving as a result of modern intensive care units. No published data of reference ranges for preterm infants exists for the South African population. Infants with congenital heart disease are twice as likely to be small for their gestational age and these reference ranges may affect clinical management decisions, therapeutic response and prognosis of these neonates. The aim was thus to establish reference ranges for cardiac dimensions and functional values for preterm and low birth weight infants for central South Africa and compare them with international standards. Methods: A total of 290 infants of less than 34 weeks of age and weighing less than 2500g at birth were examined during a twelve month period by echocardiography during the first 0-28 days of life. The study assessed normative cardiac measurements divided in M-Mode, 2-D and functional measurement for these infants in 3 weight groups. Exclusion criteria were applied to any condition affecting the size and functionality of the cardiac system. The following dimensions were measured: Standard M-Mode values for the left ventricle, 2D measurements of valve mitral and tricuspid orifices, as well as functional assessments including Shortening fraction (SF %), Ejection fraction (EF %), and Muscle performance Index (MPI)-index of the Left and Right ventricle. Measurements were done by the leading edge methodology following the ASE recommendations. A longitudinal study was also done to examine changes in these indices over the first month- on day 14 and day 28 of life. Interobserver differences were calculated for the variability between measurements of a single scan- 25 babies were re-measured and produced good repeatability. Results: 290 infants were included to produce Referance ranges of measurements (means and standard deviations) for 3 weight groups namely: <0.999g, 1000-1499g, and 1500g – 2500g. The gestational age’s ranges between 26-38 weeks with a median of 31 weeks, gender distribution was almost equal with a slight female preponderance. Body surface area ranged from a minimum from 0.076 m² and a maximum of 0.184 m², the body weight ranged between a minimum of 690g and a maximum of 2500g with a median of 1360g. Discussion: The left ventricular diastolic and systolic, interventricular septum, posterior wall, aortic and left atrium dimensions showed a proportionate increase in diameter with an increase in body weight There were no differences in cardiac dimensions between Small for Gestational age” (SGA) versus “Average for Gestational age” (AGA). Gender and race played no role in any functional measurements or with the cardiac sizes. Weight correlated well with BSA and the data suggest that weight only can be used to develop tables for clinical use. Cardiac chambers increased with BSA and weight and functional measurements stayed the same throughout the weight groups. Systolic and global functions were remarkably similar and constant throughout weight categories. . The longitudinal study also confirmed that the values are applicable to all low birth weight infants up to 28 days of age. Differences existed between some of the average South African infant’s cardiac chambers and international values. The Inter Ventricular Septum (IVS) and Posterior Wall (PW) measured thicker and the Left Atrium larger. This could be due to numerous factors that should be investigated further. Conclusion: The study emphasized the profound effect of growth and weight gain on the cardiac structure and that population specific reference values should therefore be developed and used.