The right atrium (RA) is playing an increasing role in congenital heart surgeries, however, RA function has never been evaluated in children. We studied 4 children (age: 0.75-2.2 years) with pressure-overloaded RA(tetralogy of Fallot, TOF) and 4 age and weight matched controls (C). RA pressure-area loops were generated from RA pressure recorded by a micromanometer and RA area measured simultaneously by automatic border detection technique of echocardiography. RA loading conditions were altered by a rapid fluid bolus. RA systolic function was assessed from the slope of RA end-systolic pressure-area relationship, generated by volume loading and was termed RA end-systolic elastance (RA Ees). RA diastolic function was assessed from the chamber stiffness constant (k) using an exponential relationship P=bekA, where P is RA pressure, b is Y intercept, e is base of natural logarithm and A is RA area (fig. 1B). RA mean pressure was increased in TOF vs C group (10.6±2.6 vs 5.4±2.1 mm Hg, p>0.05). RA pressure-area loops have a typical“figure-of-eight” appearance defined by A and V loops (fig. 1A). RA Ees remained unaltered in TOF vs C group (1.31±1.1 vs 1.21±0.08 mm H g cm-2 p>0.05), however k was increased (0.28±0.09 vs 0.11±0.06. mm Hg·cm-2 p<0.05).

Fig 1
figure 1

RA pressure-area loop from a C patient(A) and a family of pressure-area loops from a TOF patient (B). Normalization of RA Ees and k by body weight produced the same directional changes as non-normalized data.

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Conclusions: RA pressure-area relationship provided a unique insight into RA systolic and diastolic function. In pressure-overloaded RA, systolic function remained unaltered but RA stiffness increased which may influence the type and timing of congenital heart surgeries such as Fontan operations.