Systemic venous diameters, collapsibility indices, and right atrial measurements in normal pediatric subjects

Compromise of right heart function is an important feature of many forms of congenital heart disease, and right atrial (RA) pressure is clinically relevant. Inferior vena cava (IVC) diameter and inspiratory collapse are indices of RA pressure, but pediatric data are lacking.

RA measurements, systemic venous diameters, and Doppler filling fractions were prospectively investigated in healthy volunteer children and adolescents. The IVC was measured in its long axis just above the junction with the hepatic veins in the subxiphoid view and the superior vena cava at its junction with the right atrium in the right parasternal view. The changes in IVC diameter (IVCD) during quiet respiration and with a sniff were recorded. Hepatic venous systolic filling fraction was calculated from Doppler velocities in the first hepatic vein. RA major-axis length, area, and volume were measured from the apical four-chamber view. Three measurements of each parameter were averaged over at least three respiratory cycles. The IVC collapsibility index (IVCCI) was calculated as [(IVCDmax - IVCDmin)/IVCDmax] × 100. Substituting IVCDsniff for IVCDmin in the formula, the IVCCIsniff was calculated.

Of 132 subjects enrolled, data in 120 (mean age, 8.3 ± 4.5 years) were analyzed. The maximal (expiratory) and minimal (inspiratory) diameters during free breathing were 12.1 ± 3.8 and 8.9 ± 3.8 mm for the IVC and 11.9 ± 3.4 and 7.9 ± 2.6 mm for the superior vena cava. IVCCImin and IVCCIsniff were 30 ± 13 and 47 ± 18, respectively. The RA major-axis length, area, and indexed maximal volume were 3.7 ± 0.7 cm, 10.3 ± 3.6 cm(2), and 22.3 ± 7.0 mL/m(2), respectively. Correlations of maximal superior vena cava and IVC dimensions with body surface area were slightly better than with age and much stronger than with RA volume. No significant correlation was found between IVCCIs and age, gender, or indexed RA volume.

Measurement of systemic venous diameters, collapsibility indices, and RA volumes is feasible in healthy children and adolescents. Venous diameters increase predictably with growth and so must be interpreted in light of body surface area. IVCCIs and hepatic venous filling fraction compare closely with those reported in adults. Pediatric nomograms for these parameters are provided, and they should next be evaluated for relation to directly measured RA pressure in this age group.