Strong relationship between NT‐proXNP levels and cardiac output following cardiac surgery in neonates and infants

Background: NT‐proXNP, a new natriuretic peptide analyte, incorporates information about the concentrations of both N‐terminal pro‐atrial and pro‐brain natriuretic peptides (NT‐proANP, NT‐proBNP). We aimed to investigate whether NT‐proXNP is a reliable indicator of the cardiac index (CI) and the hemodynamic state in neonates and infants undergoing an open heart surgery. Methods: We enrolled 26 children under the age of 1 year into this prospective study. All patients underwent an elective cardiac operation with cardiopulmonary bypass (CPB) to achieve complete biventricular repair. Peri‐operative hemodynamic parameters were assessed by transpulmonary thermodilution and natriuretic peptide levels were recorded. Results: The NT‐proXNP level correlated significantly with the simultaneously measured NT‐proANP level (r=0.60, P<0.001), but more strongly with the NT‐proBNP level (r=0.89, P<0.001) and the arithmetic sum of both (r=0.88, P<0.001). NT‐proXNP had a strong correlation with CI (r=?0.85, P<0.001), the stroke volume index (r=?0.80, P<0.001) and the global ejection fraction (r=?0.67, P<0.009) throughout the post‐operative period. Conventionally measured parameters such as heart rate, mean arterial pressure and pulse‐pressure product exhibited weaker correlations with CI than NT‐proXNP. Among laboratory values, creatinine levels correlated significantly with CI (r=?0.77, P<0.001) and NT‐proXNP (r=0.76, P<0.001) during the post‐operative period. A post‐operative NT‐proXNP level of 3079 pmol/l was diagnostic for CI <3 l/min/m² with 89% sensitivity and 90% specificity (area under the curve: 0.91 ± 0.05). Conclusion: NT‐proXNP is a good marker of cardiac output following pediatric cardiac surgery and might be a useful tool in the recognition of a low output state.