The angle of insonation for Doppler measurements of left and rightventricular output in newborns and infants

Background: The angle of insonation can be an important determinant of Doppler-derived cardiac output measurements. It is known anatomically that there is a larger insonation angle for the left vs. right ventricular outflow area, but variability and calculated angles have not been described. The aim of this study was to describe the anatomical position of the left and right outflow areas and determine the geometric angle of insonation in newborn and infants. Methods: Magnetic resonance images of infants ≤ 2 years of age were explored. For each outflow, the position was determined relative to an anatomical reference point. To obtain the angle of insonation, the angle between the outflow and the hypothetical position of the ultrasound probe beam was calculated. Results: Forty-five patients were included with a median age of 71 days old. Anatomically, the left outflow is directed almost vertically upwards in sagittal images with a 40o angle to the right in coronal images. The right outflow is directed 53o upwards in sagittal images with a slight angle to the left on axial images. The median (range) angle of insonation for the left ventricular outflow area using the apical or subcostal view was 40° (22-51) and 28° (7-47) respectively, and 23° (2-40) for the right ventricular outflow area using the parasternal view. Conclusions: The median geometric angle of insonation of the left outflow was larger than the right. The variation within the group was large, but in each individual case the angle for left was larger than for right.