Computer analysis of cardiac contractility variables obtained by M-mode echocardiography in normal newborns

Comprehensive echocardiographic assessment of biventricular function in the rabbit, animal model in cardiovascular research: feasibility and normal values

Quantification of cardiac structure and function is central in cardiovascular research. Rabbits are valuable research models of cardiovascular human disease; however, there is little normal data available. The aim of this study was to investigate feasibility and provide normal values for comprehensive echocardiographic assessment of biventricular function in rabbits. New Zealand white rabbits underwent trans-thoracic echocardiography using a general electric (GE) Vivid 7/E9 system with a 10 MHz transducer, under light sedation, to evaluate biventricular function and dimensions. Images for two-dimensional, M-mode, tissue Doppler imaging (TDI) and speckle-tracking strain echocardiography were acquired and analysed. 55 male rabbits (sized matched with a newborn human baby) were studied, mean weight was 2.9 ± 0.23 kg. Adequate images were obtained in 90% for the left ventricle (LV) and 80% for the right ventricle (RV). Two-dimensional speckle-tracking strain was feasible in 60%. Average heart rate was 248 ± 36 beats per minute; LV ejection faction 72 ± 8.0; RV fractional area change 45.9 ± 9.0%; RV myocardial performance index 0.39 ± 0.35; tricuspid annular planar systolic excursion 0.60 ± 0.24 cm. LV TDI parameters were S' 8.6 ± 3.1 cm/s; E' 12.0 ± 4.46 cm/s. RV TDI parameters were S' 10.49 ± 3.18; E' 14.95 ± 4.64 cm/s. LV and RV global peak systolic longitudinal strain were -17 ± 5 and -22 ± 8%, respectively. Comprehensive investigation of biventricular dimensions and function by echocardiography is feasible in the rabbit. Apical views and strain imaging have lower feasibility. Normal values of LV and RV functional parameters are with comparable values to human children. Animal cardiovascular research is key to develop new goals in clinical practice.

Changes of the cardiovascular system during the perinatal period

After describing the particular features of the fetal circulation, changes in the pattern of blood flow at the time of birth and during early neonatal life are explained. From animal studies it is wellknown that during the first hours and weeks after birth newborns are characterized by an extremely high cardiac output due to high metabolic demands. In order to meet this marked volume loading, already under resting conditions the neonatal heart appears to be operating nearly at its full capacity without reserves in contractility, preload and afterload. Consequently the newborn heart has less ability to cope with additional acute afterload and/or preload stress. Few investigations on cardiac output and myocardial performance in healthy human newborns provide presumptive evidence that the postnatal human heart performs probably as well as the heart of other species. These observations may influence the therapeutic approach in clinical situations with additional alterations in loading conditions.

Altered early left ventricular diastolic cardiac function in the premature infant

Developmental changes in diastolic ventricular function were assessed in 31 premature infants and in 10 normal-term infants. They were studied during the first 72 hours of life using instantaneous rates of change of left ventricular (LV) cavity dimension, derived from M-mode echocardiography. Maximal velocity of lengthening of the LV cavity was significantly lower in premature infants (38 +/- 7 mm/s) than in term infants (88 +/- 15 mm/s). This variable increased with increasing maturity over the 4 gestational age groups evaluated (r = 0.87). This index normalized for instantaneous LV dimension was lower in the most immature infants (4.5 +/- 1 s-1) than in term infants (6.8 +/- 2 s-1). Eight of the premature infants were studied serially at 1, 3 and 7 days of age. Maximal velocity of lengthening divided by stroke dimension improved from 12.9 +/- 2 s-1 at 1 day of age to 16.5 +/- 3 s-1 at 7 days. These results suggest depressed early diastolic function in premature infants.

Normal serial variability for M-mode and digitized echocardiography in a pediatric population

The normal serial variability of M-mode and digitized echocardiography was assessed in 18 healthy children aged 3-16 years. M-mode echocardiograms were done one month apart in each child and two sets of three beats were analyzed twice for each month's tracing. Ejection fraction and shortening fraction were obtained in the standard manner and the tracing digitized and analyzed for peak and normalized left ventricular velocities, and for posterior wall and septal wall velocities in systole and diastole. The component variabilities were determined by a univariate four-factor hierarchical variance components analysis and the sum of these variability limits established. Standard M-mode echocardiographic measurements of shortening fraction and ejection fraction (15% and 10% of mean) were the least variable. Peak and normalized velocities were more variable with left ventricular velocities (18%-29% of mean), posterior wall velocities (26%-45% of mean) and septal velocities (38%-68% of mean) showing increasing variabilities. Thus there is less variability in M-mode echocardiography than digitized echocardiography. The normal limits of variability are established and should be used for follow-up studies.