The Utilization and Interpretation of Cardiac Biomarkers During Pregnancy

Cardiac biomarkers are widely used in the nonpregnant population when acute cardiovascular (CV) pathology is suspected; however, the behavior of these biomarkers in the context of pregnancy is less well understood. Pregnant individuals often have symptoms that mimic those of cardiac dysfunction, and complications of pregnancy may include CV disease. This paper will summarize our current knowledge on the use of cardiac biomarkers in pregnancy and provide suggestions on how to use these tools in clinical practice based on the available evidence. Natriuretic peptides and troponin should not be measured routinely in uncomplicated pregnancy, where values should remain low as in the nonpregnant population. In the context of pre-existing or suspected CV disease, these biomarkers retain their negative predictive value. Elevations of both natriuretic peptides and troponin may occur without clear clinical significance in the immediate postpartum period. Elevations of these markers should always prompt further investigation into possible CV pathology.

biomarkers can be integrated into clinical practice provides an important means of identifying pregnant individuals who require further cardiovascular evaluation.This paper will summarize our current knowledge on the use of cardiac biomarkers in pregnancy and provide suggestions on how to optimally use these tools in clinical practice based on the available evidence.

HEMODYNAMICS CHANGES OF PREGNANCY
The normal cardiovascular hemodynamic adaptations to pregnancy include a rise in plasma volume, heart rate and thus cardiac output (CO), and a decline in peripheral vascular resistance as shown in Figure 1. 1,2ring labor and delivery, CO is increased further due to increased venous return from the contracting uterus as well as an increase in the heart rate.Immediately postpartum, auto transfusion of blood from uterine involution, increased venous return due to decreased IVC compression, and rapid mobilization of dependent edema all result in increased CO.Afterload increases due to the loss of the low vascular resistance placental unit.These adaptations are amplified in individuals with multiple gestations 1 and are of particular importance in patients with pre-existing cardiac disease who may not tolerate volume overload.artery disease, high-risk aortopathy, lack of prior cardiac intervention, and late pregnancy assessment. 3As such, pregnancies among these individuals are particularly high risk and merit close multidisciplinary care and monitoring.

B-TYPE NATRIURETIC PEPTIDES AND N-TERMINAL PRO-B-TYPE NATRIURETIC PEPTIDE
The natriuretic peptides include the biologically active B-type natriuretic peptide (BNP) and the inert N-terminal pro-B-type natriuretic peptide (NT-proBNP); both arise from a common precursor peptide proBNP, liberated when the parent peptide is cleaved by corin and/or furin.Natriuretic peptides can be released in response to numerous stimuli but predominantly reflect cardiomyocyte stretch, which may occur due to structural heart disease.Because of their sensitivity for myocardial dysfunction, BNP and NT-proBNP have become gold standards in the biomarker diagnosis of heart failure. 4Since pregnancy represents a physiologic state characterized by a marked increase in circulating volume reflected by increases in cardiac chamber size, there have been several studies investigating the behavior of natriuretic peptides in pregnancy and early puerperium.
A summary of BNP/NT-proBNP characteristics in normal pregnancy, preeclampsia, cardiovascular disease, and obesity is outlined in Table 1.
HEALTHY PREGNANCY.6][7][8][9] In a series of 116 patients with serial BNP and NT-proBNP measured during pregnancy and the immediate postpartum period, natriuretic peptide levels increased within 48 hours postpartum, with a mean BNP of 85 AE 71 pg/mL and a mean NT-proBNP of 158 AE 167 pg/mL.Left ventricular and left atrial volumes HIGHLIGHTS Cardiac biomarker testing is widely utilized in the nonpregnant population; however, their use in the context of pregnancy is less well understood.
Cardiac biomarkers, particularly natriuretic peptides, retain their negative predictive value during pregnancy.
Biomarker elevations should prompt investigation into cardiac pathology but can occur immediately postpartum without apparent consequence.
Several novel biomarkers remain of interest in pregnancy and merit further investigations.Both BNP and NT-proBNP retain their negative predictive value to exclude heart failure in pregnancy and peripartum period such that low concentrations help to exclude the diagnosis.PREECLAMPSIA.Several small studies have reported higher natriuretic peptide concentrations among pregnancies complicated by preeclampsia than among normotensive pregnancies [11][12][13][14][15][16] as shown in Tables 2 and 3. Individuals with early-onset preeclampsia and those with severe features exhibit higher values than those with milder disease and normotensive pregnancies. 12,15      Sarma et al

Cardiac Biomarkers During Pregnancy
A U G U S T 2 0 2 2 : 1 0 0 0 6 4 Other natriuretic peptides may be abnormal in hypertensive disorders of pregnancy.Lin et al reported that concentrations of N-terminal pro-atrial natriuretic peptide (NT-proANP) were significantly increased in hypertensive disorders of pregnancy.
This inert N-terminal fragment of ANP is easier to measure (as ANP is rapidly degraded by neprilysin, which is in abundance in the circulation in the pregnant state).Notably, higher levels of corin (an enzyme involved in processing of both A-and B-type natriuretic peptides) were also elevated in those with hypertension and adverse pregnancy outcomes. 21ese results support a role of natriuretic peptide release in hypertensive disorders of pregnancy, pre-  m 2 . 34To address this issue, lower reference limits may be utilized in obesity; for example, guidelines from the European Society of Cardiology suggest a 50% reduction in cut points for BNP with obesity. 35e pathophysiologic mechanisms relating obesity and low concentrations of natriuretic peptides have not been fully elucidated.While some enhanced clearance of BNP through excess neprilysin production from adipose tissue might explain the finding, NT-proBNP remains unaffected and, therefore, may be of value in obese population.[38] The effect of obesity during pregnancy on natri-  that myocardial injury describes a disorder of elevated troponin above the 99th percentile upper reference limit and is considered acute if associated with a rise and fall in values. 40Not only this has facilitated rapid evaluation of acute myocardial infarction (AMI) but also high-sensitivity cardiac troponin (hs-cTn) assays are increasingly utilized at a population level to screen for CVD and heart failure, where both hs-cTnI and hs-cTnT have been strongly associated with prevalent CVD/heart failure and also prognosticate their onset. 41Table 4 summarizes the characteristics of cardiac troponin in pregnancy.
NORMAL PREGNANCY AND PREECLAMPSIA.Current evidence suggests that conventional (non-highsensitivity) cTn remains negative in normal pregnancies but may increase above the normal threshold in pregnancies complicated by preeclampsia although the data are inconsistent. 42A recent comprehensive review on cTn using non-highsensitivity methods reported in uncomplicated pregnancy that the median cTnI was 30 ng/L (range: 10-300 ng/L), and in preeclampsia, it was 460 ng/L (range: 155-1,020 ng/L). 42Fleming et al 43 reported a statistically significant increase in cTnI in individuals  with increased prolactin levels, and 51% with elevated C-reactive protein (CRP) levels.However, data regarding cardiac biomarkers in pregnancy are more limited. 50Mercedes et al studied 154 pregnant individuals with COVID infection at 32 AE 3.7 weeks of gestation and found that 15 (9.7%) had elevated NT-proBNP (median: 209 pg/mL, 184-246 pg/mL) and troponin I (median: 34.6 ng/mL, 14.4-55.5 ng/mL).All of these patients had abnormal findings on echocardiogram with mean left ventricular ejection fraction of 38%.In this cohort, all 15 individuals were critically ill and admitted to the intensive care unit, 13 were intubated and 2 died. 51This study, albeit small, suggests that similar to the nonpregnant population, biomarker elevation in the setting of COVID infection serves as a marker for adverse outcomes and mortality. 52    FETAL GROWTH RESTRICTION.Fetal growth restriction is associated with an increased risk for pregnancy loss and postnatal complications; accurate methods for its prediction are important yet remain limited.Adipokines have been measured for this purpose without significant evidence for utility. 62,63her biomarkers have been explored for predicting fetal growth restriction; however, challenges remain with respect to timing (eg, which trimester to measure) and optimal cut points to determine an abnormal result.Among the markers examined are included pregnancy-associated placental protein-A, free b-human chorionic gonadotropin, a fetoprotein, unconjugated estriol, and inhibin A. 63 Each of these is poorly sensitive but highly specific for fetal growth restriction; of the candidates, pregnancy-associated placental protein-A appears most promising but remains relatively insensitive.Emerging data suggest measurement use of omics approaches to quantify metabolites or members of the transcriptome such as micro-RNA might enhance ability to predict fetal growth restriction; however, these data remain preliminary. 64,65GIOGENESIS-RELATED FACTORS.Abnormalities of placental function are associated with risk for hypertensive disorders of pregnancy. 66Not only angiogenesis-related factors, including soluble fmslike tyrosine kinase 1 and placental growth factor, are participants in placental dysfunction but also evidence suggests their measurement is significantly associated with the ability to predict risk for Sarma et al

Cardiac Biomarkers During Pregnancy
A U G U S T 2 0 2 2 : 1 0 0 0 6 4 preeclampsia. 67For example, when measured during the first trimester, the soluble fms-like tyrosine kinase 1-to-placental growth factor ratio may provide important information regarding subsequent development of preeclampsia, and later in pregnancy, the panel of these 2 biomarkers may be useful to diagnose preeclampsia in symptomatic mothers (including recognition of preeclampsia in individuals with antecedent gestational hypertension). 67Abnormal balance in these biomarkers of the "angiogenic placental syndrome" may also provide information regarding fetal growth restriction 64 as well as risk for cardiomyopathy.
INFLAMMATORY BIOMARKERS.Measurement of biomarkers associated with inflammation may have a role in several circumstances in pregnancy.For example, clinically, elevated concentrations of CRP in early pregnancy may be associated with fetal growth patterns and risk for neonatal complications. 68ditional roles for CRP measurement might include its application for assessment of risk for adverse outcomes of placental or respiratory infection from novel coronavirus. 69Lastly, emerging data focused on measurement of small, noncoding fragments of ribonucleic acid known as micro-RNA has revealed further connection between inflammatory processes and adverse pregnancy outcomes. 69More data are needed regarding measurement of inflammatory markers or mediators in pregnancy.
PROTEOMICS.Though the topic exceeds the scope of the discussion, use of targeted or untargeted proteomics to simultaneously measure hundreds to thousands of proteins in the pregnant state may be useful for discovery of previously unsuspected biological pathways of disease and potentially identify newer biomarkers for clinical measurement. 70,71As a proof of concept, when studying the proteome of women early in pregnancy, Myers et al 72 CARDIOVASCULAR RISK STRATIFICATION.Several tools are available for risk stratification among individuals with pre-existing cardiovascular disease, including the CARPREG (Cardiac Disease in Pregnancy Study) II, ZAHARA (Zwangerschap bij Aangeboren HARtAfwijking Pregnancy in Women with Congenital Heart disease), and the modified World Health Organization classification.The CARPREG II study demonstrated that individuals with preexisting cardiovascular disease were at risk for pulmonary edema as early as 13 weeks of gestation extending up to 24 weeks postpartum.Predictors of adverse outcomes included a history of prior cardiac events, baseline New York Heart Association (NYHA) functional class III-IV or cyanosis, the presences of a mechanical valve, ventricular dysfunction, high-risk left-sided valve disease or left ventricular outflow tract obstruction, pulmonary hypertension, coronary N S A N D A C R O N Y M S AMI = acute myocardial infarction BMI = body mass index BNP = B-type natriuretic peptide CHD = congenital heart disease CO = cardiac output cTnI = troponin I cTnT = troponin T CVD = cardiovascular disease Hs-cTN = high-sensitivity cardiac troponin NT-proBNP = N-terminal pro-B-type natriuretic peptide P-SCAD = pregnancyassociated spontaneous coronary artery dissection PPCM = peripartum cardiomyopathy Sarma et al J A C C : A D V A N C E S , V O L . 1 , N O . 3 , 2 0 2 2 Cardiac Biomarkers During Pregnancy A U G U S T 2 0 2 2 : 1 0 0 0 6 4 similarly increased, but there were no differences in measures of diastolic function 48 hours postpartum as compared with the nonpregnant state and no reported adverse outcomes.Values returned to their presumed nonpregnant values (as assessed 6-12 months postpartum) by 6 to 12 weeks postpartum. 9In a study of 260 healthy pregnant individuals, Dockree et al reported a 95% upper reference limit for BNP of 50 pg/mL with no significant trimester-related differences.BNP degradation is influenced by neprilysin, which is released by the placenta into the maternal circulation.The authors proposed that because of excess placenta-derived circulating neprilysin, the sensitivity of BNP might be reduced and NT-proBNP (which is not a target of neprilysin) may be a more robust marker during pregnancy.More data regarding this interesting hypothesis are needed.The upper reference limit for NT-proBNP in the same study was 200 pg/mL in the first and second trimester and 150 pg/mL in the third, suggesting an effect of hemodilution with the increased volume of later pregnancy. 7

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A C C : A D V A N C E S , V O L . 1 , N O . 3 , 2 0 2 2 Sarma et al A U G U S T 2 0 2 2 : 1 0 0 0 6 4 postpartum).Data are more limited with respect to this recently appreciated entity; from a single institution (n ¼ 22), median BNP measured at incident presentation was 424 pg/mL (interquartile range [IQR]: 190-645).

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A C C : A D V A N C E S , V O L . 1 , N O . 3 , 2 0 2 2 Sarma et al A U G U S T 2 0 2 2 : 1 0 0 0 6 4 Cardiac Biomarkers During Pregnancy OBESITY AND PLASMA NATRIURETIC PEPTIDES PREGNANCY.It is well known that overweight and obese individuals have lower BNP and NT-proBNP values than do those with normal BMI. 33Lowering of BNP and NT-proBNP in obesity may result in lower sensitivity if using standard cutoffs in those with higher BMI; in one study, the diagnosis of heart failure was missed in one of 5 patients with a BMI $35 kg/ uretic peptide levels has not been well studied.A recent analysis of 260 healthy pregnant individuals sampled each trimester found significantly lower NT-proBNP values in overweight individuals in the third trimester when stratified by BMI <25 kg/m 2 or >25 m 2 , but BMI was not stratified further. 7The relationship of BMI for pregnant individuals who are obese or morbidly obese remains a knowledge gap for future analysis.NATRIURETIC PEPTIDES AND SUGGESTIONS FOR CLINICAL PRACTICE (CENTRAL ILLUSTRATION). 1.In healthy asymptomatic pregnant individuals, natriuretic peptides should not be routinely measured.2. To prevent delayed diagnosis of heart failure, we suggest measuring natriuretic peptides in pregnant or postpartum individuals with new clinical symptoms or suggestive signs of heart failure a) The suggested upper reference limit for BNP is 50 pg/mL, with no significant trimester-related differences.b)The suggested upper reference limit for NT-proBNP is 200 pg/mL in the first and second trimester and 150 pg/mL in the third trimester and postpartum period.

3 .
In individuals with established cardiovascular disease who are at risk for heart failure during pregnancy (eg, CHD, pre-existing cardiomyopathy, significant valvular disease), measuring natriuretic peptides prior to conception (when feasible) or early in pregnancy, followed by serial natriuretic peptide measurement throughout each trimester and the early postpartum period, should be considered.Values should be measured in the event of symptoms suggestive of heart failure.Such CENTRAL ILLUSTRATION The Utilization of Cardiac Biomarkers During Pregnancy: Suggestions for Clinical Practice Sarma AA, et al.JACC Adv.2022;1(3):100064.approach may help guide clinical management and distinguish the symptoms of normal pregnancy from those of hemodynamic decompensation.a) Low concentrations (BNP [<100 pg/mL] or NT-proBNP [<128 pg/mL]) have a high negative predictive value; thus, concentrations below these thresholds make cardiovascular dysfunction unlikely, based on limited data.b) An elevated BNP or NT-proBNP should prompt further clinical evaluation, although elevations can be observed without clear clinical consequence.For such patients, an echocardiogram is a reasonable next step.c) Lower thresholds for abnormal natriuretic peptide levels should be considered with obesity, though there are very limited data to guide use during pregnancy.A normal value does not preclude the diagnosis of heart failure in the obese population and should be clinically correlated.CARDIAC TROPONINS Biomarkers play an important role in detection of myocardial injury.Previously used biomarkers such as creatine kinase and its MB isoenzyme have poor specificity for myocardial injury in pregnancy and the postpartum period. 39On the other hand, troponin T (cTnT) and I (cTnI)-components of the cardiomyocyte contractile apparatus-have high specificity and have therefore supplanted creatine kinase in the diagnosis of acute myocardial injury.With a shift to assays providing high sensitivity at lower troponin concentrations, the fourth Universal Definition of Myocardial Infarction has articulated

3 .
with gestational hypertension compared to normotensive individuals (median: 89 vs 30 ng/L, P < 0.001) and a subsequent increase in individuals with preeclampsia compared to gestational hypertension (155 vs 89 ng/L, P ¼ 0.03).Studies evaluating normative values of highsensitivity assays in pregnancy and preeclampsia are limited.Prior studies to date have demonstrated that a significant portion of individuals with uncomplicated pregnancies have undetectable hs-cTnI concentrations.25,44Among 880 pregnant individuals at various trimesters (predominately third), hs-cTnI was very low (median: 1.0 ng/L, IQR: 0.0-1.0) in 842 uncomplicated pregnancies but higher in those who developed preeclampsia (median: 12.0 ng/L, IQR: 3.0-97.5)or pregnancy-induced hypertension (11.0 ng/L, IQR: 6.0-22.3).44 Utilizing hs-cTnI, Morton et al found elevations above the upper limit of normal in 25% of preeclamptic individuals around the time of delivery, with normalization of values within 72 hours postpartum implying increased myocardial stress associated with preeclampsia; lending credence to this, concentrations of hs-cTnI further correlated with peak mean arterial pressure, though clinically evident cardiovascular dysfunction or myocardial ischemia was not evident.More data are needed in this area.45Using a hs-cTnT assay in 150 healthy individuals, Smith et al46 reported a 4.3% incidence of concentrations in excess of the 99th percentile for a general, healthy population (14 ng/L) 8 to 24 hours postdelivery; considering sex-specific cutoffs for individuals are even lower (9 ng/L), the overall incidence of an abnormal hs-cTnT in this study was even higher.However, most of these elevated values were of no clinical significance and thus the etiology and interpretation of elevated hs-cTn remains uncertain in the context of uncomplicated labor.Further, the distribution of troponin elevations did not differ between individuals considered high vs low risk for cardiovascular complications.46PRE-EXISTING CARDIOVASCULAR DISEASE.There are insufficient data with respect to troponin utilization among pregnant individuals with pre-existing cardiovascular pathology, including those with prior ischemic disease.In the absence of pregnancyspecific data, clinical inferences must be made from cardiovascular disease trends in the nonpregnant population.Regardless of the etiology, elevated troponin in the nonpregnant state is associated with increased mortality and adverse outcomes.40Clinical correlation coupled with knowledge of the pathophysiology of cardiac biomarker release is essential to provide optimal perinatal care, while minimizing unnecessary, risky, or costly workup.AMI IN PREGNANCY.While AMI occurs uncommonly during pregnancy, pregnancy substantially increases the risk of experiencing an AMI (3-to 4-fold), as well as associated mortality w11%.47Similarly, pregnancyassociated spontaneous coronary artery dissection (P-SCAD) presents more aggressively than P-SCAD outside the context of pregnancy.48As with the nonpregnant population, troponin is elevated in the context of AMI during pregnancy, though whether the degree of elevation differs as compared with the nonpregnant population is unknown.Given the significant morbidity and risk for mortality that AMI during pregnancy carries, an elevated troponin during pregnancy and the postpartum period (when most pregnancy-associated P-SCAD occurs) should prompt investigation into potential ischemia.PPCM.Limited data currently exist on the use of cardiac troponin in PPCM.One study of non-highsensitivity cTnT in 106 patients with PPCM revealed that a troponin concentration >0.04 ng/mL at diagnosis was inversely predictive of left ventricular ejection fraction at 6 months (with a sensitivity of 54.9% and specificity of 90.9%).49Given that hs-cTn is not confounded by obesity like BNP or NT-proBNP are, and the normal values for hs-cTn in healthy younger individuals are typically very low (implying even high-normal values might indicate pathology), there may be advantages to its measurement in pregnancy, particularly to identify and prognosticate acute diagnosis such as preeclampsia or PPCM.Additional studies are clearly needed.CARDIAC TROPONINS AND SUGGESTIONS FOR CLINICAL PRACTICE (CENTRAL ILLUSTRATION). 1. Troponin concentration should only be measured during pregnancy and the postpartum period in the context of clinical concern for myocardial ischemia or infarction.2. Use of hs-cTN assays are the preferred test for evaluating pregnancy-related complications.Elevated troponin concentrations should prompt further cardiovascular evaluation.It should be recognized that small increases may occur in the normal peripartum period and preeclampsia without known clinical significance with utilization of high-sensitivity assays.Despite this, abnormal concentrations of troponin are extremely rare in younger, healthy individuals and Sarma et al J A C C : A D V A N C E S , V O L . 1 , N O . 3 full evaluation to rule out potential acute cardiovascular pathology.4. Measurement of troponin at index PPCM diagnosis has prognostic implications for left ventricular recovery, based on limited studies.SPECIAL CIRCUMSTANCES COVID-19 INFECTION AND PREGNANCY.Pregnant individuals are at an increased risk for severe complications from COVID-19 infection including intensive care unit admission, mechanical ventilation, and use of extracorporeal membrane oxygenation.Data from the living systematic review inclusive of 270,470 pregnant and postpartum mothers with confirmed or suspected COVID-19 found elevations in laboratory studies similar to the nonpregnant population, including 33% with lymphopenia, 28% with elevated white cell counts, 8% with thrombocytopenia, 32%

(n ¼ 227
) study of pregnant and immediately postpartum women with COVID-19 infection in which D-dimer levels did not correlate with disease severity and need for supplemental oxygen. 54PULMONARY EMBOLISM AND D-DIMER.Elevation of natriuretic peptides and troponin in nonpregnant patients with pulmonary embolism is associated with an increased risk of death and poor outcomes reflected by the presence of right ventricular strain and damage.Data among the pregnant population are lacking to determine whether this differs among the pregnant population.In the absence of data to suggest otherwise, elevated natriuretic peptides and troponin in the context of pulmonary embolism should raise concern for concomitant right ventricular strain.D-dimer is often used in the nonpregnant population during the evaluation of suspected venous thromboembolism.During pregnancy, however, Ddimer increases (particularly in the third trimester) and declines rapidly postpartum (within 4-6 weeks).
to prognosticate onset and course of dysglycemia would be of interest.Although early research indicated that adipokines might be useful for prognosticating incident gestational diabetes (particularly measurement of chemerin), the data remain conflicting, and it is unlikely measurement of adipokines will gain traction for this indication.61 Normal Cardiovascular Adaptations of Pregnancy 2A rise in plasma volume and heart rate result in a 30% to 50% increase in cardiac output.
Systemic vascular resistance (SVR) falls associated with a drop in systolic blood pressure (SBP) that rises toward normal nearer term.Red blood cell (RBC) mass increases, though to a lesser extent than plasma volume, resulting in a dilutional anemia with fall in hematocrit.These adaptations are amplified in individuals with multiple gestations.Reprinted by permission from Springer Nature: Current Treatment Options in Cardiovascular Medicine Pregnancy in Women with Congenital Heart Disease.19(9):73 [copyright] 2017.

TABLE 2
BNP in Normal vs Preeclamptic Pregnancies Values are median (IQR) a Interquartile range unavailable.
Dr Sarma has received the CRICO patient safety award and the MGH Department of Medicine Innovation grant.Dr Januzzi has received the Hutter Family Professorship; is a trustee of the American College of Cardiology; is a board member of Imbria Pharmaceuticals; has received grant support from Abbott Diagnostics, Applied Therapeutics, Innolife, and Novartis; has received consulting income from Abbott Diagnostics, Boehringer Ingelheim, Jana Care, Janssen, Novartis, Prevencio, and Roche Diagnostics; and participates in clinical end point committees/data safety monitoring boards for AbbVie, Siemens, Takeda, and Vifor.Dr Quesada has received support from the NIH (K23-HL151867).Dr Briller is an unpaid consultant for the Illinois Maternal Mortality Committee; and is on the Steering committee for the REBIRTH trial of bromocriptine in Peripartum Cardiomyopathy (NCT05180773).All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.Sharma G, Ying W, Silversides CK.The importance of cardiovascular risk assessment and pregnancy heart team in the management of cardiovascular disease in pregnancy.Cardiol Clin.2021;39:7-19.Yurteri-Kaplan L, Saber S, Zamudio S, et al.Brain natriuretic peptide in term pregnancy.