Electrocardiographic findings during parturition and blood gas tensions immediately after birth in thoroughbred foals.

In 101 newborn Thoroughbred foals and foaling mares, 45 fetal (FECGs) and 101 neonatal electrocardiograms (NECGs) were obtained to investigate neonatal arrhythmias and other parameters including changes in fetal (FHR) and neonatal heart rate (NHR). Moreover, umbilical arterial, venous and jugular venous blood gas tensions and pH immediately after birth were analyzed to compare with the type and the degree of neonatal arrhythmias. Before delivery, in 37 fetuses FHR gradually decreased while in 8 cases it increased after rupture of the chorio-allantois. Abnormal deliveries were related in 5 of the 8 cases. In foals born with sinus rhythm, NHR at birth was 22 beats per minute higher than the FHR immediately before birth, gradually decreased for 1-2 min and then increased. Various types of neonatal arrhythmias and their combinations were recorded in 92 of the 101 NECGs. No arrhythmias demonstrated in NECGs were detected in the FECGs. The mean values for umbilical arterial pH, PCO2 and PO2 indicated that newborn foals at birth were exposed to hypoxemic, hypercapnic and acidemic conditions. The relationship between the umbilical arterial PO2 value as an indicator of the degree of hypoxemia of the foal and the type of arrhythmias was not apparent. However, the PO2 value in the group with severe arrhythmias was comparatively lower than that in the group with mild arrhythmias. It was suggested that hypoxemia played an important role in neonatal arrhythmias.