Quantification of ventricular stress in univentricular hearts during early childhood using age-independent zlog-NT-proBNP.

BACKGROUND: Children with univentricular hearts (UVH) undergo up to three palliative surgical procedures to achieve complete circulatory separation (Fontan circulation). As a marker of cardiac wall stress, NT-proBNP is a promising tool to assess systemic ventricular load in these patients. However, different reference intervals (RI) apply to each stage, as NT-proBNP is highly age-dependent. METHODS: Children undergoing systemic-to-pulmonary (SP) shunt placement (stage 1), bidirectional cavopulmonary shunt (BCPS, stage 2) or total cavopulmonary connection (TCPC, stage 3) between 2011 and 2021 with NT-proBNP measurement within 7 days before surgery were included. Furthermore, outpatients after TCPC with NT-proBNP measurement were enrolled. Biomarker levels were evaluated using its age-adjusted z-score ("zlog-NT-proBNP"; age-independent RI, -1.96 to +1.96), allowing comparison between different stages and revealing changes in systemic ventricular load independent of the marked physiological decline in RI with age. RESULTS: Overall, 289 children (227 before, 62 after TCPC) met the eligibility criteria. Median time between blood sampling and surgery (SP shunt/BCPS/TCPC) was 2 [1-3] days and 3.2 [2.0-4.5] years after TCPC. Age-adjusted zlog-NT-proBNP levels were 3.47 [2.79-3.93] in children with native UVH (before SP shunt), 3.10 [1.89-3.58] at stage 1 (before BCPS), 1.08 [0.51-1.88] at stage 2 (before TCPC), and 1.09 [0.72-1.75] at stage 3 (after TCPC/Fontan completion). Consequently, BCPS revealed the strongest decrease (median - 2.02 logarithmized standard deviations, p < 0.001). CONCLUSIONS: In children with UVH undergoing staged Fontan palliation, zlog-NT-proBNP is a highly promising tool for course assessment of systemic ventricular load, independent of the age-related decline in physiological NT-proBNP concentration.

NT-proBNP and Zlog-transformed NT-proBNP values predict extubation failure in critically ill neonates with pulmonary hypertension and ventricular dysfunction.

OBJECTIVES: Critically ill neonates with a history of pulmonary hypertension (PH) or ventricular dysfunction are at risk to experience an extubation failure (EF) after liberation from mechanical ventilation (MV). Due to insufficient data from neonatal cohorts, it remains unclear whether NT-proBNP is an appropriate biomarker to predict EF in this cohort. The Zlog-transformation of NT-proBNP (further named NT-proBNPZlog ) is an additional tool to optimize the interpretation of NT-proBNP since absolute NT-proBNP values are varying with the age of these infants. PATIENTS AND METHODS: This was a retrospective single-center analysis at the University Children's Hospital, Bonn, Germany, during the study period from January 2020 until December 2021. Forty-three neonates met the inclusion criteria and were screened for study participation. INCLUSION CRITERIA: prolonged (>24 h) MV with at least one extubation attempt, with a history of PH and/or ventricular dysfunction in the echocardiographic assessment at admission to the neonatal intensive care unit or during the period of MV, NT-proBNP measurements before (max. 24 h, baseline) and after (max. 24 h, follow-up) the first extubation attempt. The primary clinical endpoint was defined as EF with need for reintubation (0-72 h). Neonates with an EF were allocated to group A and neonates with successful liberation from MV to group B. MAIN RESULTS: The primary clinical endpoint (EF) was reached in 21% (nine infants). Absolute mean NT-proBNP values (NT-proBNPabs ) at baseline did not differ significantly in infants of group A and B (6931 vs. 7136 pg/ml, p = 0.227). NT-proBNPZlog values at baseline (2.35 vs. 1.57, p = 0.073) tended to higher values in group A. NT-proBNPabs values measured at follow-up were significantly higher in infants allocated to group A (11120 vs. 7570 pg/ml, p = 0.027). Likewise, NT-proBNPZlog values at follow-up were significantly higher in infants allocated to group A (3.05 vs. 1.93, p = 0.009). NT-proBNPabs values at follow-up and NT-proBNPZlog values at baseline correlated significantly with the severity of PH. Regarding the receiver operating characteristic-analysis, a NT-proBNPabs value at follow-up of ≥4622 pg/ml was calculated as optimal cut-off value for the prediction of EF (area under the curve [AUC] 0.742, p = 0.001). A NT-proBNPZlog value at baseline of ≥1.63 and at follow-up of ≥2.14 was calculated as optimal cut-off for the prediction of EF (AUC: 0.690/p = 0.027, and 0.781/p = 0.000, respectively). CONCLUSION: NT-proBNPabs and NT-proBNPZlog might be valuable biomarkers for the prediction of EF in critically ill neonates. The Zlog-transformation of NT-proBNP allows an age-independent interpretation of NT-proBNP and should be considered for clinical routine.

A zlog-based algorithm and tool for plausibility checks of reference intervals.

OBJECTIVES: Laboratory information systems typically contain hundreds or even thousands of reference limits stratified by sex and age. Since under these conditions a manual plausibility check is hardly feasible, we have developed a simple algorithm that facilitates this check. An open-source R tool is available as a Shiny application at github.com/SandraKla/Zlog_AdRI. METHODS: Based on the zlog standardization, we can possibly detect critical jumps at the transitions between age groups, regardless of the analytical method or the measuring unit. Its advantage compared to the standard z-value is that means and standard deviations are calculated from the reference limits rather than from the underlying data itself. The purpose of the tool is illustrated by the example of reference intervals of children and adolescents from the Canadian Laboratory Initiative on Pediatric Reference Intervals (CALIPER). RESULTS: The Shiny application identifies the zlog values, lists them in a colored table format and plots them additionally with the specified reference intervals. The algorithm detected several strong and rapid changes in reference intervals from the neonatal period to puberty. Remarkable jumps with absolute zlog values of more than five were seen for 29 out of 192 reference limits (15.1%). This might be attenuated by introducing shorter time periods or mathematical functions of reference limits over age. CONCLUSIONS: Age-partitioned reference intervals will remain the standard in laboratory routine for the foreseeable future, and as such, algorithmic approaches like our zlog approach in the presented Shiny application will remain valuable tools for testing their plausibility on a wide scale.

Predicting Major Adverse Cardiovascular Events in Children With Age-Adjusted NT-proBNP.

BACKGROUND: N-terminal pro-B-type natriuretic peptide (NT-proBNP) is frequently used as a valuable prognostic biomarker in cardiac diseases. In children, however, it has not been established because of its strong age dependency. To overcome this obstacle, we recently introduced the zlog value of N-terminal pro-B-type natriuretic peptide (zlog-proBNP) as an age-adjusted reference. OBJECTIVES: This study evaluates the prognostic power of zlog-proBNP for the occurrence of major adverse cardiovascular events (MACE) throughout childhood in patients with congenital heart diseases (CHD). METHODS: A total of 910 children with CHD (median age 5 months; range 0.0-18.0 years) were included. MACE was defined as death, resuscitation, mechanical circulatory support, or hospitalization caused by cardiac decompensation. Because the physiological NT-proBNP concentration decreases significantly during childhood, zlog values were applied for an age-independent evaluation. RESULTS: MACE occurred in 138 children during a median follow-up of 6 months (range 1 day to 7.6 years). High zlog-proBNP values (>+3.0) were most strongly associated with adverse events (n = 93; adjusted HR: 21.1; 95% CI: 2.9-154.2; P < 0.001). Among all evaluated indicators, zlog-proBNP was the best predictor for MACE (adjusted HR: 1.52; 95% CI: 1.31-1.76; P < 0.001) along with age and predictively superior to absolute NT-proBNP values. A cutoff value of +1.96 (age-independent upper limit of the physiological NT-proBNP concentration) achieved a negative predictive value of >96%. CONCLUSIONS: Zlog-proBNP overcomes the strong age dependency of NT-proBNP and is a powerful prognostic marker for age-independent exclusion and prediction of MACE in children with CHD. We therefore expect zlog-proBNP to play a pivotal role in the future management of children with heart diseases.

Continuous, complete and comparable NT-proBNP reference ranges in healthy children.

Background: NT-proBNP is one of the most important biomarkers for the diagnosis and risk assessment of heart failure in adults. Age- and gender-independent reference intervals (RIs) have been reported. In contrast, RIs in children are strongly age-dependent, do not exist for all ages and reveal a right-skewed distribution. Accordingly, no common Z-score can be formed and a cross-age interpretive method, so far, is missing. Methods: Within the paper on hand, new evaluation techniques are applied to already published NT-proBNP study results and additionally to newly gained data. Upper limits (ULs), lower limits (LLs) and 50th percentiles are tested for power-like behavior as a function of age using linear regression analysis. Functions for continuous RIs are derived and reference limits are calculated on a per day basis. A corresponding Zlog formula is deduced and its usefulness is stated in two clinical examples. Results: The power-like behavior of NT-proBNP concentration from birth to 18 years is demonstrated. With age in days t and measured NT-proBNP value x in pg/mL, an age-specific Zlog value may directly be calculated using the equation:ZlogNT-proBNP=log x+0.512⋅log t-3.4171.489+0.014⋅log t⋅3.92${\rm{Zlo}}{{\rm{g}}_{{\rm{NT - proBNP}}}} = {{\log \;x + 0.512 \cdot \log \;t - 3.417} \over {1.489 + 0.014 \cdot \log \;t}} \cdot 3.92$. Conclusions: Using formulas for UL and LL, continuous RIs from 0 to 18 years may be obtained. Continuity corresponds to physiological changes in the body much better than discrete RIs. With the advent of an NT-proBNP-specific Zlog value, a cross-age Z-score equivalent is providing an easy interpretation aid in everyday pediatric practice. This new approach allows to identify clinical worsening much better, sooner and more clearly than previous absolute values.