**3. Diagnostic application of the natriuretic peptides**

### **3.1 Adult population**

In adults, diastolic dysfunction or asymptomatic aortic stenosis confirmed by echocardiography or angiography show marked correlations with brain natriuretic peptide (Gerber et al, 2003). Right-sided heart failure or complications after pulmonary embolism can accurately be detected by measuring natriuretic peptides, though the cut-off levels were only half of those for left ventricular dysfunction (Kucher et al, 2003). There are two widely accepted area for BNP testing; exclusion of non-cardiac origin of dyspnoe in emergency settings and prognostic information of various states of heart failure. NT-proBNP above 1065 pmol/l had a very high specificity and sensitivity for cardiac failure in our population, similar levels were found in decompensated heart failure, septic shock and acute pulmonary embolism with New York Heart Association III and IV symptoms (Seino et al, 2004). Additionally, lower postoperative cut-off value (513 pmol/l) bore high negative predictive power, indicating a level below which the occurrence of heart failure is unlikely. In these cases, NT-proBNP or BNP measurements are used. Levels above the cut-off level were independently associated with increased risk for mortality and cardiovascular morbidity including cardiac fibrillation. In adults, it has been shown that hyperthyroidism increases the NT-pro BNP level and could reect cardiac dysfunction secondary to thyreotoxicosis [Kato 2008, Welisch 2011].

ANP or NT-proANP reflect acute changes in atrial wall stress (Ruskoaho, 2003). Therefore, it is not suitable for long-term follow-up of congestive heart failure. Recently, a new immunoassay has been developed for a hybrid peptide (referred to as NT-proXNP) containing peptide sequences from both NT-proANP and NT-proBNP (Ala-Kopsala et al, 2005). This novel assay mimics the physiological signaling pathway since the actions of the different active natriuretic fragments on the target cells are mediated by a single natriuretic peptide receptor. The NT-proXNP assay measures the concentration of the new virtual natriuretic peptide, and thus provides combined information about the plasma levels of NTproANP and NT-proBNP. In cardiac diseases, the neurohormonal system of the heart is activated. The diagnostic performances of NT-proXNP in adults for coronary artery disease and valvular heart disease are greater than or equal to those of NT-proANP or NT-proBNP, individually. NT-proXNP seems to combine the characteristics of the two natriuretic peptides. Therefore, NT-proXNP will increase earlier during myocardial wall stress than the NT-proBNP alone.

GMP, the cytoplasmatic calcium availability will be decreased in the smooth muscles and it

Atrial stretching triggers release of the preformed prohormone of atrial natriuretic peptide (NT-proANP) in the atrial wall. During secretion, the prohormone of atrial natriuretic peptide (ANP) is cleaved to atrial natriuretic peptide and N-terminal pro-atrial natriuretic peptide (Kangawa et al, 1984). Although brain natriuretic peptide chemically resembles atrial natriuretic peptide to some extent, it is synthetized both in the atrial and ventricular myocardium due to volume and pressure overload. The production of BNP requires time (6- 12 hours), since RNA transcription of the prohormone precedes the secretion. Then, the prohormone of brain natriuretic peptide is cleaved to brain natriuretic peptide (BNP) and Nterminal pro-brain natriuretic peptide (NT-proBNP). N-terminal peptides have several times higher concentrations and longer half life time in blood circulation than atrial natriuretic peptide and brain natriuretic peptide, making them reliable markers (Ham et al, 1995).

In adults, diastolic dysfunction or asymptomatic aortic stenosis confirmed by echocardiography or angiography show marked correlations with brain natriuretic peptide (Gerber et al, 2003). Right-sided heart failure or complications after pulmonary embolism can accurately be detected by measuring natriuretic peptides, though the cut-off levels were only half of those for left ventricular dysfunction (Kucher et al, 2003). There are two widely accepted area for BNP testing; exclusion of non-cardiac origin of dyspnoe in emergency settings and prognostic information of various states of heart failure. NT-proBNP above 1065 pmol/l had a very high specificity and sensitivity for cardiac failure in our population, similar levels were found in decompensated heart failure, septic shock and acute pulmonary embolism with New York Heart Association III and IV symptoms (Seino et al, 2004). Additionally, lower postoperative cut-off value (513 pmol/l) bore high negative predictive power, indicating a level below which the occurrence of heart failure is unlikely. In these cases, NT-proBNP or BNP measurements are used. Levels above the cut-off level were independently associated with increased risk for mortality and cardiovascular morbidity including cardiac fibrillation. In adults, it has been shown that hyperthyroidism increases the NT-pro BNP level and could reect cardiac dysfunction secondary to thyreotoxicosis

ANP or NT-proANP reflect acute changes in atrial wall stress (Ruskoaho, 2003). Therefore, it is not suitable for long-term follow-up of congestive heart failure. Recently, a new immunoassay has been developed for a hybrid peptide (referred to as NT-proXNP) containing peptide sequences from both NT-proANP and NT-proBNP (Ala-Kopsala et al, 2005). This novel assay mimics the physiological signaling pathway since the actions of the different active natriuretic fragments on the target cells are mediated by a single natriuretic peptide receptor. The NT-proXNP assay measures the concentration of the new virtual natriuretic peptide, and thus provides combined information about the plasma levels of NTproANP and NT-proBNP. In cardiac diseases, the neurohormonal system of the heart is activated. The diagnostic performances of NT-proXNP in adults for coronary artery disease and valvular heart disease are greater than or equal to those of NT-proANP or NT-proBNP, individually. NT-proXNP seems to combine the characteristics of the two natriuretic peptides. Therefore, NT-proXNP will increase earlier during myocardial wall stress than the

will result in vasodilatation.(Silberbach & Roberts, 2001).

**3. Diagnostic application of the natriuretic peptides** 

**3.1 Adult population** 

[Kato 2008, Welisch 2011].

NT-proBNP alone.

Fig. 1. Refence mean and median values of healthy subjects

#### **3.2 Pediatric population**

Based on physiological considerations, BNP and NT-proBNP levels are age dependent in the first two weeks after birth (Albers et al, 2006-Schwachtgen et al, 2005). The perinatal transition from fetal to neonatal circulation is accompanied by an increase in the pulmonary blood flow and an increase in the systemic vascular resistance. These hemodynamic changes lead to pressure and volume load of the heart and it may stimulate the secretion and release of natriuretic peptides. From 31 days to 12 years of age, there is no significant change in healthy subjects (Cantinotti et al, 2010). From 14 years of age, gender related differences should be accounted and it is probably due to steroid sex hormones (Soldin et al, 2006). Agecorrected brain natriuretic peptide and NT-proBNP values should be used in the neonatal population (Cantinotti et al, 2010b), while gender should be considered in the adolescent population. Additionally, it is important to note that reference ranges, decision values are method dependent and it shows variations between the assays and consequently between the studies (Soldin et al, 2006, Cantinotti et al, 2010). These variations are seen in Figure 1. As in the adult population NT-proBNP is significantly higher in children with sepsis. In children with sepsis NT-proBNP levels are higher in some patients with leftventricular dysfunction (Fried 2006). In comparison to the adult population there are no paediatric studies in hyperthyroidism available at present (Welisch 2011).

#### **3.3 Pediatric population – Congenital heart disease**

Different requirements have been formulated for the natriuretic peptide assays in the pediatric population. One major area is the exclusion of cardiovascular disease particularly below one year of age. The clinical signs are poor or share the ones with other noncardiac diseases. The major symptoms are dyspnea, tachypnea, cold extremities, murmurs, tachycardia, hypotension, etc. The assay is easy to carry out and requires only 0.5 ml blood. The recent studies showed convincing results that the BNP test could be performed without difficulties from capillary stick and it had a high negative power both in neonates and infants (Law et al, 2009,Maher et al, 2008).

The anatomy of the congenital heart diseases is heterogenous. Additionally, the situation after different types of surgery complicates the hemodynamic state. An arbitrary classification is the following: ventricle volume overload, including left-right shunts, ventricular septal defects, patent ductus arteriosus, atrial septal defect, atrioventricular malformations, truncus arteriosus, etc; pressure overload, as a consequence of outflow tract obstruction or valvular stenosis, such as tetralogy of Fallot, pulmonary or aorta stenosis; univentricular physiology and non-clusterable complex malformations. Despite the age related BNP elevation in the neonatal period, the severity of heart failure can be determined and diagnosed (Cantinotti et al, 2010b, Law et al, 2009). Other studies have been described the linear relationship between BNP or NT-proBNP levels and the magnitude of left-right shunting (Kunii et al, 2003) and BNP levels were able to predict the need for ductus arteriosus closure (Paul et al, 2009). Echocardiographic studies have been confirmed the association between pressure gradient and natriuretic peptide levels (Cowley et al, 2004). In right sided pressure overload, the BNP levels were lower compared to left sided pressure overload (Cantinotti et al, 2009, Holmgren et al, 2005). In Table 1 and 2 pediatric studies measuring BNP and NT-proBNP levels are shown.

#### **3.4 Pediatric cardiac population postoperative period**

Monitoring of cardiac output is still a problematic issue, although early recognition of hemodynamic complications is essential in pediatric critical care. During the postoperative period, hemodynamically unstable patients are characterized by high volume intake, the need for considerable inotropic support, edema formation, hepatic congestion, lung

transition from fetal to neonatal circulation is accompanied by an increase in the pulmonary blood flow and an increase in the systemic vascular resistance. These hemodynamic changes lead to pressure and volume load of the heart and it may stimulate the secretion and release of natriuretic peptides. From 31 days to 12 years of age, there is no significant change in healthy subjects (Cantinotti et al, 2010). From 14 years of age, gender related differences should be accounted and it is probably due to steroid sex hormones (Soldin et al, 2006). Agecorrected brain natriuretic peptide and NT-proBNP values should be used in the neonatal population (Cantinotti et al, 2010b), while gender should be considered in the adolescent population. Additionally, it is important to note that reference ranges, decision values are method dependent and it shows variations between the assays and consequently between the studies (Soldin et al, 2006, Cantinotti et al, 2010). These variations are seen in Figure 1. As in the adult population NT-proBNP is significantly higher in children with sepsis. In children with sepsis NT-proBNP levels are higher in some patients with leftventricular dysfunction (Fried 2006). In comparison to the adult population there are no paediatric

Different requirements have been formulated for the natriuretic peptide assays in the pediatric population. One major area is the exclusion of cardiovascular disease particularly below one year of age. The clinical signs are poor or share the ones with other noncardiac diseases. The major symptoms are dyspnea, tachypnea, cold extremities, murmurs, tachycardia, hypotension, etc. The assay is easy to carry out and requires only 0.5 ml blood. The recent studies showed convincing results that the BNP test could be performed without difficulties from capillary stick and it had a high negative power both in neonates and

The anatomy of the congenital heart diseases is heterogenous. Additionally, the situation after different types of surgery complicates the hemodynamic state. An arbitrary classification is the following: ventricle volume overload, including left-right shunts, ventricular septal defects, patent ductus arteriosus, atrial septal defect, atrioventricular malformations, truncus arteriosus, etc; pressure overload, as a consequence of outflow tract obstruction or valvular stenosis, such as tetralogy of Fallot, pulmonary or aorta stenosis; univentricular physiology and non-clusterable complex malformations. Despite the age related BNP elevation in the neonatal period, the severity of heart failure can be determined and diagnosed (Cantinotti et al, 2010b, Law et al, 2009). Other studies have been described the linear relationship between BNP or NT-proBNP levels and the magnitude of left-right shunting (Kunii et al, 2003) and BNP levels were able to predict the need for ductus arteriosus closure (Paul et al, 2009). Echocardiographic studies have been confirmed the association between pressure gradient and natriuretic peptide levels (Cowley et al, 2004). In right sided pressure overload, the BNP levels were lower compared to left sided pressure overload (Cantinotti et al, 2009, Holmgren et al, 2005). In Table 1 and 2 pediatric studies

Monitoring of cardiac output is still a problematic issue, although early recognition of hemodynamic complications is essential in pediatric critical care. During the postoperative period, hemodynamically unstable patients are characterized by high volume intake, the need for considerable inotropic support, edema formation, hepatic congestion, lung

studies in hyperthyroidism available at present (Welisch 2011).

**3.3 Pediatric population – Congenital heart disease** 

infants (Law et al, 2009,Maher et al, 2008).

measuring BNP and NT-proBNP levels are shown.

**3.4 Pediatric cardiac population postoperative period** 


Table 1. Usefulness of Brain Natriuretic Peptide measurements. Prospective observational study PO, Brain natriuretic peptide BNP, Atrial natriuretic peptide ANP, cardiac Troponin cTNT, orthotope heart transplantation OHT, persistent Ductus arteriosus PDA, Atria septum defect ASD, pulmonary hypertension pulmHT, aquired heart disease AqHD, congenital heart disease congHD, cardiovascular disease CardVascDis.


19 serial NP correlate with level of unloading of heart & potential recovery

40 high NT-proBNP preop predictive of postop prolonged need for inotropic therapy

20 high NT-proBNP may help identify patients at risk for arythmias, rigth ventr failure after Fallot correction

26 NT-proXNP correlates with CI

43 risk to develop coronary artery lesions 10x higher with NTproBNP>1000pg/ml

34 NT-proBNP signif higher with BPD, NT-signif higher with Resp Distress

36 NT-proBNPincreases with malignant ventricular arrhythmia

36 serial NT-proBNP >1000pg/ml correlates with HF, echodardiographic measures correlate with NT-proBNP changes within patients

690 reference values for pediatr population

48 BNP differentiates between heart failure and lung disease, BNP for monitoring treatment for heart

failure

Syndr

**HD** 

15 DCM, 2 myocarditis, 1 CongHD, 1 Cardiac arrest in rejection after HTX

obstructive lesions/ l-r-shunt/ cyanotic defects

postop correction of Fallot tetralogy

biventriculair repair, <1year

Cong HD/ sepis/ current PDA exclusion criteria

none,idiopathic ventricular arrhythmia

no, no cardiac disease, no respiratory disease

yes (heterogeneous

group)

none NT-

**Cut-off// lowest level** 

18fmol/l NT-

NT-proXNP 3079pmol/l or NT-proBNP 2051pmol/l ~CI<3l/min/m2

proBNP>1000pg

66pg/ml median in group malign arryhthmia

proBNP>1000pg /ml; NT-proBNP <450pg/ml asymptomatic patients;

see table 1 combined

2940pg/ml none

NT-

/ml

250pg/ml on MCS

**Special remarks** 

none

risk stratificati on for surgery in CongHD

proBNP higher after TOFl correction

none

none

none

none

retrospect ive ;NTproBNP <450pg/ ml

study data

**Author Key words n Result Congenital** 

Heise G (Heise 2008)

Gessler P (Gessler 2006)

Pietrzak R (Pietrzak 2009)

Breuer T (Breuer 2010)

Kaneko K (Kaneko 2011)

Joseph L (Joseph 2010)

Mazurek B (2009)

Rusconi P (Rusconi 2010)

Nir A (Nir 2009)

Cohen S (Cohen 2005)

serial, natriuretic hormone system, pulsatile MCS (Berlin Heart EXCOR)

defect

NT-proXNP,

repair

lesions

failure

changes in echocardiographic evalutaion of HF

girls

problem

reference values neonates/infants, lognormal distribution, high NT-proBNP in pubertal

differenciate between cardiac or respiratory

risk stratification for lowrisk surgery in CongHD, RACHS-1 score, lactate, duration of CBP, cyanotic

Fallot correction, rigth ventricular failure, transannular patch, duration of QRS

neonates/infants <1 year, complete biventriculair

kawasaki syndrome,NTproBNP, coronary arterial

Bronchopulmonarydyspla sia,natriureticpeptides,pre maturity <34weeks gest

idiopathic ventricular arrhythmia,

asymptomatic circulatory

dilated cardiomyopathy (idiopathic, anthracyclinerelated, uremic, muscular dystrophy), heart failure,


Table 2. Usefulness of NT-proBrain Natriuretic Peptide measurements. Retrospective study r, n-terminal pro-brainnatriureticpeptide NT pro-BNP, brain natriuretic peptide BNP, dilated cardiomyopathy DCM, congestive heart failure congestiveHF, mechanical circulatory support MCS; cardiopulmonary bypass CPB, total corretion of Fallot TOF, persistent Ductus arteriosus PDA, Risk Adjustement for Congenital Heart Surgery RACHS-1 (Jenkins 2004)

dysfunction or the combination of them (Laussen & Roth, 2003). High lactate levels and low base excess on the first postoperative day have been reported to predict mortality and outcome in pediatric cardiac patients (Tibby et al, 1999, Carmona et al, 2008). Mir et al.found limited value of NT-proBNP levels in the perioperative period. In their study, dosage and duration of catecholamines and length of mechanical ventilation correlated with postoperative troponin T and arterial lactate levels, but not with NT-proBNP (Mir et al, 2006). Since catecholamine therapy is a consequence of hemodynamic instability and prolonged mechanical ventilation can be influenced by certain non-cardiac factors, the direct relationship might be concerned. Indeed, clinical signs and scores of congestive heart failure is difficult to apply as diaphoresis, respiratory rate, heart rate in the early postoperative period are strongly modified by inotropic, analgesic and sedative medication (Tibby et al, 1999). Preoperative NT-proBNP was associated with adverse postoperative outcome in children undergoing heart surgery, like duration of mechanical ventilation, dose of inotropic support, length of intensive care unit stay (33-Hsu et al, 2007). BNP and NT-proBNP levels usually exceed the peak maximum at 12 hours, and a second peak may occur about five days after surgery (Koch et al, 2007). Postoperative BNP and NT-proBNP levels have also been shown to have prognostic value after pediatric cardiac surgery. After cavopulmonary anastomosis a decrease in natriuretic peptides level compared to preoperative level were correlated with better outcomes (Hsu et al, 2008). Prognostic role of BNP was also reported after switch surgery in neonates (Lehot et al, 1992).

Our study investigated the prognostic role of NT-proXNP, a hybride analyte. NT-proXNP level correlated significantly with the simultaneously measured NT-proANP level (r = 0.60, p < 0.001), but more strongly with NT-proBNP level (r = 0.89, p < 0.001) and the arithmetic sum of both peptides throughout the perioperative period (r = 0.88, p < 0.001). Baseline NTproXNP level correlated with the age (r = -0.72, p < 0.001) and the weight of the patients (r = -0.47, p = 0.026). Preoperative creatinine level (53.3 ± 13.1 μmol/l) correlated with baseline NT-proXNP (r = 0.53, p = 0.013). The duration of operation and the duration of CPB were associated with the preoperative NT-proXNP level (r = 0.58, p = 0.005 and r = 0.62 p = 0.002,

Fig. 2. Correlation between logarithmic transformed NT-proXNP levels and cardiopulmonary bypass time

respectively) and the peak postoperative NT-proXNP level (r = 0.64, p < 0.001 and r = 0.67, p < 0.001, respectively). NT-proBNP showed similar correlations with the duration of operation and CPB (Breuer et al, 2010). In the postoperative period, natriuretic peptide levels correlated significantly with the simultaneously assessed hemodynamic parameters. NT-proXNP correlated stronger with the hemodynamic parameters except for extravascular lung water index than the arithmetic sum of NT-proANP and NT-proBNP. The correlation between NT-proXNP and CI remained significant after adjusting for age (r = 0.60, p = 0.018) or weight (r = 0.81, p < 0.001).

The hemodynamic parameters improved during the postoperative period as the myocardium recovered. The application of transpulmonary thermodilution was safe and reliable and it added useful information to the conventionally measured pressure values in neonates and infant following open heart surgery. We found lower global enddiastolic volume indices and higher extravascular lung water indices compared to adult ranges, whereas the cardiac indices were the same. Age related and disease specific reference values of the transpulmonary thermodilution parameters are yet to be determined in children.

In ROC analysis, a postoperative NT-proBNP level of 2051 pmol/l was diagnostic for cardiac index (CI) lower than 3 l/min/m2 with 79% sensitivity and 95% specificity (AUC: 0.87 ± 0.06), whereas a postoperative NT-proXNP level of 079 pmol/l was diagnostic for that with 89% sensitivity and 90% specificity (AUC: 0.91 ± 0.05). The length of mechanical ventilation and ICU stay did not correlate with the baseline or the peak natriuretic peptide

50 100 150 200

**ln NT-proXNP peak POP-48 = 6,35 + 0,02 \* cpbtime**

5,00

cardiopulmonary bypass time

or weight (r = 0.81, p < 0.001).

6,00

**ln N**

**T-pro**

**X**

**N**

**P P**

**O**

**P Peak (**

**p**

**m**

**ol/l)**

7,00

**R-Square = 0,45**

 

 

8,00

9,00

10,00

**CPB time (min)**

respectively) and the peak postoperative NT-proXNP level (r = 0.64, p < 0.001 and r = 0.67, p < 0.001, respectively). NT-proBNP showed similar correlations with the duration of operation and CPB (Breuer et al, 2010). In the postoperative period, natriuretic peptide levels correlated significantly with the simultaneously assessed hemodynamic parameters. NT-proXNP correlated stronger with the hemodynamic parameters except for extravascular lung water index than the arithmetic sum of NT-proANP and NT-proBNP. The correlation between NT-proXNP and CI remained significant after adjusting for age (r = 0.60, p = 0.018)

The hemodynamic parameters improved during the postoperative period as the myocardium recovered. The application of transpulmonary thermodilution was safe and reliable and it added useful information to the conventionally measured pressure values in neonates and infant following open heart surgery. We found lower global enddiastolic volume indices and higher extravascular lung water indices compared to adult ranges, whereas the cardiac indices were the same. Age related and disease specific reference values of the transpulmonary thermodilution parameters are yet to be determined in children. In ROC analysis, a postoperative NT-proBNP level of 2051 pmol/l was diagnostic for cardiac index (CI) lower than 3 l/min/m2 with 79% sensitivity and 95% specificity (AUC: 0.87 ± 0.06), whereas a postoperative NT-proXNP level of 079 pmol/l was diagnostic for that with 89% sensitivity and 90% specificity (AUC: 0.91 ± 0.05). The length of mechanical ventilation and ICU stay did not correlate with the baseline or the peak natriuretic peptide

Fig. 2. Correlation between logarithmic transformed NT-proXNP levels and

levels. NT-proBNP and NT-proXNP, but not NT-proANP level at 24 hours after surgery were correlated to the length of mechanical ventilation (r = 0.51, p = 0.015 and r = 0.47, p = 0.027, respectively). The area under the curve (AUC) of NT-proBNP and NT-proXNP at 24 hours after surgery for prolonged mechanical ventilation (> 72h) in ROC analysis was 0.81 ± 0.10 and 0.72 ± 0.11, respectively.
