Troponin-T as a biomarker in neonates with perinatal asphyxia

Abstract

BACKGROUND:

Troponin-T is a commonly used cardiac biomarker, which could be useful in perinatal asphyxia. We aimed to analyze troponin-T concentrations in asphyxiated neonates and to correlate the concentrations with clinical outcomes.

METHODS:

Data were collected from electronic medical records of neonates diagnosed with perinatal asphyxia over a period of four years.

RESULTS:

There were 63 neonates with moderate to severe encephalopathy, in whom serial troponin-T concentrations had been done on days 1, 3, and 7. 53 (84%) asphyxiated infants had troponin-T concentration >100 pg/ml at 2–4 h of life.

The difference in troponin-T concentrations between moderate and severe encephalopathy was not statistically significant (173 vs. 263 pg/ml, p value 0.40). The difference in the concentrations at 72 hours between cooled and non-cooled neonates was not significant (48.5 vs. 62.5 pg/ml, p value 0.22). Troponin-T concentration was significantly higher in babies with hypotensive shock and hepatic injury, but not acute kidney injury. There was no significant correlation between troponin-T and the extent of resuscitation needed.

Troponin-T concentration on day 1 of life was significantly higher in babies who died than who survived (407 vs. 168 pg/ml, p value 0.03). ROC curve for troponin-T to predict mortality had an area under the curve (AUC) of 0.803; the best cut-off value (190 pg/ml) had 82% sensitivity and 80% specificity.

CONCLUSION:

There was no significant difference in troponin-T concentrations between cooled and non-cooled neonates. Troponin-T concentration had a good predictive accuracy for mortality before discharge.

Keywords

Troponin-T perinatal asphyxia hypoxic-ischemic encephalopathy therapeutic hypothermia organ dysfunction outcome

Abbreviations

AKI

Acute kidney injury

BNP

Brain natriuretic peptide

PPV

Positive pressure ventilation

Therapeutic hypothermia

1 Background

Perinatal asphyxia is a leading cause of neonatal mortality, accounting for 23% of the 3.6 million neonatal deaths worldwide [1]. Numerous biochemical markers in serum, urine and cerebrospinal fluid are being evaluated to predict the severity of encephalopathy, the various organ dysfunction and the short and long term outcome of perinatal asphyxia [2]. Troponin-T is a commonly used cardiac biomarker, which could be useful in perinatal asphyxia [3 –5]. We aimed to analyze troponin-T concentrations in asphyxiated neonates treated with or without therapeutic hypothermia (TH) and to correlate the troponin-T concentrations with the severity of asphyxia, clinical features and the outcome.

2 Methods

The study was done in a tertiary care neonatal unit in India. Serial troponin-T concentrations were being done at 2–4 hours, 72 hours and on day 7 of life, as part of routine clinical care in asphyxiated neonates. We performed a retrospective analysis of babies with perinatal asphyxia and serum troponin-T concentrations, treated in our unit from January 2012 to December 2015. The study was approved by the Institutional Review Board and Ethics Committee. All the relevant clinical data such as baseline demographics, severity of asphyxia, stage of encephalopathy, details of multi-organ dysfunction, outcome and laboratory results were collected from the online medical records.

Therapeutic hypothermia (TH) was provided to infants ≥35 weeks gestational age and ≥1800 grams with a minimum of one physiological (Inborn babies - pH <7 or base deficit >12 in cord blood gas/postnatal arterial gas in the first hour of life; 5-minute Apgar <5; need for resuscitation for >10 minutes. Outborn babies, where blood gas and Apgar scores are not available –the need for resuscitation at birth/not breathing normally at 5 minutes/flaccid since birth) along with one neurological criteria (moderate or severe encephalopathy as per modified Sarnat staging (5) or seizures).

TH was started within 6 hours after birth and continued for 72 hours, followed by slow rewarming over 10–12 hours. Phase changing material (MiraCradle^TM-Neonate Cooler) was used to provide TH and the target temperature was 33.5±0.5C.

Inotropic support was required for one or more of the following: hypotension, clinical evidence of poor perfusion, metabolic acidosis with high lactate and echocardiographic evidence of myocardial dysfunction. Elevated transaminases was defined as AST >100 IU/L and ALT >50 IU/L. Acute kidney injury (AKI) was defined as serum creatinine >1 mg/dL on day 3 of life. Urine output was not taken as a criterion for AKI, since the data was inadequate.

Troponin-T estimation was done in the clinical biochemistry laboratory by a fourth generation high-sensitivity chemiluminescent immunoassay (Cobas e411, Roche Diagnostics GmbH, Mannheim, Germany). The measuring range of the assay is 3 to 10,000 pg/ml with inter-assay variability of <3.5%.

3 Statistical analysis

Baseline characteristics were represented as mean and standard deviation (SD), median and interquartile range (IQR), or number and percentage. Median and IQR was used to report troponin-T, as the concentrations were non-normally distributed. Mann-Whitney U test or Kruskal-Wallis test was used to compare troponin-T concentrations between the groups. Receiver operating characteristic (ROC) curve was used to establish the optimal cut-off concentration of troponin-T for the outcome measures. All statistical analyses were done using SPSS 16.0. A p-value less than 0.05 was considered statistically significant.

4 Results

Figure 1 shows the study flow diagram. There were 63 neonates with perinatal asphyxia and troponin-T concentrations during the 4-year study period. Table 1 shows the baseline characteristics of the study infants. There were 53 (84.1%) infants with moderate and 10 (15.9%) infants with severe encephalopathy (6). 36 (57.1%) babies were cooled and 27 (42.9%) babies were not cooled due to various reasons such as randomization to non-cooling arm in a concurrent randomized trial, lack of parents’ consent, and others.

Fig.1

Study flow diagram.

Table 1

Baseline characteristics

Baseline characteristics	Total cohort (n = 63)
Gestational age, weeks; mean (SD)	39.1 (1.4)
Gender; n (%) of boys	36 (58.1)
Birth weight, grams; mean (SD)	2989 (509)
Small for gestational age; n (%)	16 (25.4)
Mode of delivery; n (%)
Normal	27 (42.9)
Instrumental	10 (15.9)
Caesarean section	26 (41.3)
Out born; n (%)	27 (42.9)
Apgar; median (IQR)
1 minute, n = 45	3 (2, 3)
5 minutes, n = 45	5 (4, 7)
10 minutes, n = 27	7 (6, 7)
15 minutes, n = 9	6 (6, 7)
20 minutes, n = 4	5 (5, 6)
Severity of encephalopathy; n (%)
Moderate	53 (84.1)
Severe	10 (15.9)
Cooling
Cooled	36 (57.1)
Non-cooled	27 (42.9)

Serial troponin-T concentrations at 2–4 hours, 72 hours, and day 7 were 192.5 (119.7, 315.1), 36.4 (52.5, 87.5), and 39.3 (67.9, 99.4) pg/ml respectively. Fifty-three (84%) infants had troponin-T concentration >100 pg/ml at 2–4 hours of life.

Table 2 shows the troponin-T concentrations in infants with various organ dysfunction and clinical outcome. The concentration was higher in babies with severe encephalopathy, compared to those with moderate encephalopathy; however the difference was not statistically significant. Troponin-T was significantly higher in babies with hypotensive shock, but not in babies who required inotropic support for poor perfusion or metabolic acidosis. The concentrations were significantly higher in babies with hepatic injury, but not acute kidney injury.

There was no significant correlation between troponin T concentrations and severity of asphyxia, as assessed by cord blood pH or duration of positive pressure ventilation. There was a non-significant trend towards higher troponin-T concentrations in babies who received chest compressions during resuscitation.

Table 2

Day-1 Troponin T concentration versus clinical outcomes

Troponin T concentration	Yes Median (IQR)	No Median (IQR)	P value
Neurological parameters
Severe encephalopathy	263.0 (139.4, 445.3)	173.1 (106.8, 312.4)	0.40
Cardiovascular parameters
Need for inotropes	212.4 (127.8, 326.5)	167.1 (109.8, 332.6)	0.76
Hypotensive shock	628.0 (118.0, 651.5)	191.0 (119.7, 841.3)	0.049
Renal parameters
Acute kidney injury	211.0 (142.5, 415.4)	192.5 (119.9, 326.5)	0.90
Hepatic parameters
Elevated transaminases	281.3 (135.8, 415.0)	158.8 (116.8, 236.9)	0.03
Resuscitation parameters
PPV >10 minutes	223.1 (168.6, 407.7)	172.3 (84.8, 307.0)	0.18
Cord pH <7	192.5 (134.1, 411.6)	352.7 (320.7, 563.4)	0.13
Chest compressions	424.3 (255.0, 545.0)	182.8 (103.2, 326.5)	0.09
Outcome parameters
Hospital stay >10 days	194.4 (150.2, 363.1)	155.6 (101.0, 288.6)	0.70
Death	407.7 (255.0, 475.2)	168.8 (106.8, 303.5)	0.03

Abbreviations: IQR, Inter-quartile range; PPV, Positive pressure ventilation.

Figure 2 shows the troponin-T concentrations in cooled and non-cooled neonates. The baseline concentrations at 2–4 hours before cooling were comparable between the groups (167 vs. 264 pg/ml, p value 0.21). By 72 hours, the concentrations decreased to <100 pg/ml in both the groups and the difference was not statistically significant (48.5 vs. 62.5 pg/ml, p value 0.22).

Fig.2

Box and whisker plot showing serial troponin T concentrations in cooled versus non-cooled infants.

There was a significant correlation between troponin-T concentration on day 1 of life and mortality before discharge. ROC curve for troponin-T to predict mortality had an area under the curve (AUC) of 0.803 (Fig. 3); for the best cut-off value of 190 pg/ml, sensitivity was 81.8% and specificity was 79.7%.

Fig.3

ROC curve (Troponin-T vs. Mortality).

We also correlated the troponin-T concentrations with mode of delivery and other clinical outcomes such as refractory seizures (need for ≥3 anti-epileptic drugs to control seizures), severe metabolic acidosis requiring bicarbonate correction, need for mechanical ventilation and coagulopathy, but the results were not significant (Data not shown).

5 Discussion

The study correlates troponin T concentrations with short-term outcomes in asphyxiated newborn infants. Troponins are contractile proteins, which are released into the circulation on structural damage to the myocardium. Previous studies have shown that troponin-T concentrations correlate with clinical, electrocardiographic and echocardiographic markers for myocardial injury in asphyxia [3, 7]. In our study, the concentration on day 1 of life was significantly higher in babies with hypotensive shock, but not in all babies who required inotropic support. We did not have adequate data on electrocardiographic or echocardiographic markers of myocardial dysfunction to correlate with the troponin-T concentrations.

Whether TH reduces asphyxia induced myocardial damage or not is unclear. Animal experiments have shown that TH reduces myocardial injury, as evidenced by fewer ischemic lesions on histopathology, better cardiac function in echocardiography and significantly lower troponin-I concentration [8, 9]. The evidence from 2 human studies using troponin-I is controversial [10, 11]. Liu et al. showed that cooled neonates had significantly lower troponin-I concentration on day 1 of life, compared to non-cooled neonates [10]. However, in the study by Vijlbrief et al., troponin-I concentrations at 24, 48 and 84 hours were similar in cooled and non-cooled infants; whereas brain natriuretic peptide (BNP) concentrations were lower in cooled neonates suggesting that cooling improves myocardial function but not the structural damage [11]. There is no previous study to evaluate troponin-T concentrations in neonates treated with TH. In our study, there was no significant difference in troponin-T concentrations at 72 hours between cooled and non-cooled neonates. The concentrations decreased to <100 pg/mL by 72 hours in both cooled and non-cooled groups.

Troponin-T concentration is higher in neonates than adults; the 99th percentile is 100 pg/ml in infants compared to 10 pg/ml in adults [4 , 12–14]. In adults with myocardial infarction, troponin-T starts rising after 1-2 hours, peaks at 24–48 hours and remains elevated for 5–10 days [15]. In perinatal asphyxia, the precise timing of myocardial injury is not known. In our study, 53/63 babies had troponin-T concentration >100 pg/ml (99th percentile) at 2–4 hours of life, translating to a sensitivity of 84% to predict moderate or severe encephalopathy.

Our study shows that troponin-T concentration on day 1 of life has a good predictive value for mortality before discharge, similar to the findings of the previous studies [6, 7]. We also estimated the optimal cut-off value using ROC curve. The best cut-off value of 190 pg/ml had 82% sensitivity and 80% specificity. In a previous study, troponin-I >135 pg/ml had 85% sensitivity and 69% specificity to predict mortality (AUC 0.82) [7]. While troponin-I was found to be predictive of neurodevelopmental outcome at 18–22 months, there is no study correlating troponin-T and neurodevelopmental outcome [10, 16].

Though troponin-T is a specific biomarker of myocardial dysfunction, the concentrations had also been shown to correlate with severity of encephalopathy, renal and hepatic injury [4, 5]. The difference in the troponin-T concentration in babies with moderate and severe encephalopathy was not statistically significant in our study, which could be due to the small sample size. In a previous study by Gunes et al., the troponin-T concentrations in severe encephalopathy was significantly higher compared to moderate encephalopathy (340 vs. 120 pg/ml) and the concentrations remained high till day 7 of life [4]. In our study, there was significant correlation between troponin-T concentration and hepatic injury (elevated transaminases). However, there was no significant correlation between troponin-T concentration and acute kidney injury.

There were some limitations in the study. This was a retrospective study and there were no controls. The sample size was small, which would have contributed to the non-significant nature of the differences in the troponin-T concentrations. We did not have adequate follow up data to assess the predictive value of troponin-T concentration for long-term neurodevelopmental outcome.

6 Conclusion

Troponin-T concentration on day 1 of life had good predictive accuracy for mortality before discharge. There was no significant difference in troponin-T concentrations between cooled and non-cooled neonates. The concentrations were significantly higher in neonates with hypotensive shock. There was no significant correlation between troponin-T and severity of encephalopathy, extent of resuscitation needed and acute kidney injury.

Competing interest/conflict of interest

None

Funding/financial support

This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.

Footnotes

Acknowledgment

Nil

References

Lawn

, Kerber

, Enweronu-Laryea

, et al. 3.6 million neonatal deaths–what is progressing and what is not? Semin Perinatol 2010;34:371–86.

Ramaswamy

, Horton

, Vandermeer

, et al. Systematic review of biomarkers of brain injury in term neonatal encephalopathy. Pediatr Neurol 2009;40:215–26.

Rajakumar

, Bhat

, Sridhar

, et al. Cardiac enzyme concentrations in myocardial dysfunction in newborns with perinatal asphyxia. Indian J Pediatr 2008;75:1223–5.

Güneś

, Öztürk

, Köklü

, et al. Troponin-T concentrations in perinatally asphyxiated infants during the first 15 days of life. Acta Paediatr 2005;94:1638–43.

Sadoh

, Eregie

, Nwaneri

, et al. The diagnostic value of both troponin t and creatinine kinase isoenzyme (ck-mb) in detecting combined renal and myocardial injuries in asphyxiated infants. D’Auria

, editor. PLoS One 2014;9:e91338.

Shankaran

, Laptook

, Ehrenkranz

, et al. Whole-body hypothermia for neonates with hypoxic-ischemic encephalopathy. N Engl J Med 2005;353:1574–84.

Simovic

, Prijic

, Knezevic

, et al. Predictive value of biochemical, echocardiographic and electrocardiographic markers in non-surviving and surviving asphyxiated full-term newborns. Turk J Pediatr 2014;56:243.

Hsu

C-Y

, Huang

C-H

, Chang

W-T

, et al. Cardioprotective effect of therapeutic hypothermia for postresuscitation myocardial dysfunction. Shock 2009;32(2):210–6.

Liu

, Tooley

, Løberg

, Suleiman

, Thoresen

, et al. Immediate hypothermia reduces cardiac troponin I after hypoxic-ischemic encephalopathy in newborn pigs. Pediatr Res 2011;70:352–6.

10.

Liu

, Chakkarapani

, Stone

, et al. Effect of cardiac compressions and hypothermia treatment on cardiac troponin I in newborns with perinatal asphyxia. Resuscitation 2013;84:1562–7.

11.

Vijlbrief

, Benders

MJNL

, Kemperman

, van Bel

, de Vries

. Cardiac biomarkers as indicators of hemodynamic adaptation during postasphyxial hypothermia treatment. Neonatology 2012;102:243–8.

12.

Sweetman

, Armstrong

, Murphy

, et al. Cardiac biomarkers in neonatal hypoxic ischaemia: Cardiac biomarkers in neonatal hypoxic ischaemia. Acta Paediatr 2012;101:338–43.

13.

Baum

, Hinze

, Bartels

, et al. Reference values for cardiac troponins T and I in healthy neonates. Clin Biochem 2004;37:1079–82.

14.

AHB

, Apple

, Gibler

, et al. National academy of clinical biochemistry standards of laboratory practice: Recommendations for the use of cardiac markers in coronary Artery diseases. Clin Chem 1999;45:1104–21.

15.

Mahajan

, Jarolim

. How to interpret elevated cardiac troponin concentrations. Circulation 2011;124:2350–4.

16.

Montaldo

, Rosso

, Chello

, Giliberti

. Cardiac troponin I concentrations as a marker of neurodevelopmental outcome at 18 months in newborns with perinatal asphyxia. J Perinatol 2014;34:292–5.