Mono-dimensional, two-dimensional and Doppler echocardiographic measurements in healthy Standardbred neonatal foals in the first 5 days of life

Background: Bodyweight, age and breed influence the echocardiographic assessment of foals. There are no echocardiographic studies in Standardbred neonatal foals. Objectives: To describe echocardiographic values for selected variables, evaluate intra- and inter-observer variability and assess cardiac changes in the first 5 days of life in healthy Standardbred neonatal foals. Study Design: Prospective observational study. Methods: Fifty-six healthy Standardbred neonatal foals were examined by transthoracic echocardiography using standard right parasternal and subcostal views at three time points: in the first 48 h (T1), between 49 and 96 h (T2), and 97 and 144 h (T3) after birth. Descriptive statistics, variability analysis and linear mixed models assessed age-related changes in cardiac parameters. Intra/inter-observer variability was assessed using intraclass correlation coefficients (ICC). Results: A total of 114 echocardiographic examinations were performed. Intra-observer agreement was excellent for most variables, while inter-observer agreement was excellent in approximately half. An increase in end-diastolic left ventricular internal diameter (T1: 5.3 +/- 0.6 cm; T3: 5.6 +/- 0.8 cm; p < 0.01), left atrial diameter in the four-chamber view (T1: 5.8 +/- 0.6 cm; T3: 6.0 +/- 0.6 cm; p = 0.01), end-diastolic aortic sinus diameter in the left ventricular outflow tract view (T1: 3.0 +/- 0.3 cm; T3: 3.2 +/- 0.3 cm; p < 0.01) and peak velocity of the transmitral E wave (T1: 0.8 +/- 0.1 m/s; T3: 0.9 +/- 0.1 m/s; p < 0.01) were observed over time. Additionally, a gradual decrease in the end-diastolic pulmonary diameter at the sinus (T1: 2.8 +/- 0.3 cm; T3: 2.5 +/- 0.3 cm; p < 0.01) and at the valve (T1: 2.6 +/- 0.3 cm; T3: 2.5 +/- 0.4 cm; p = 0.03) levels was noted. Main Limitations: Some variables have fewer individuals; coefficients of variation are moderate to high for some variables. Conclusions: Changes in echocardiographic variables in a healthy Standardbred neonatal foal population reflect a physiological adaptation of the cardiorespiratory system from foetal to extrauterine life. These observations can be used as a reference in the assessment of neonatal foals of similar age and weight.