An update on cardiac troponins as circulating biomarkers in heart failure

Past, Present, and Future of Blood Biomarkers for the Diagnosis of Acute Myocardial Infarction-Promises and Challenges

Despite important advancements in acute myocardial infarction (AMI) management, it continues to represent a leading cause of mortality worldwide. Fast and reliable AMI diagnosis can significantly reduce mortality in this high-risk population. Diagnosis of AMI has relied on biomarker evaluation for more than 50 years. The upturn of high-sensitivity cardiac troponin testing provided extremely sensitive means to detect cardiac myocyte necrosis, but this increased sensitivity came at the cost of a decrease in diagnostic specificity. In addition, although cardiac troponins increase relatively early after the onset of AMI, they still leave a time gap between the onset of myocardial ischemia and our ability to detect it, thus precluding very early management of AMI. Newer biomarkers detected in processes such as inflammation, neurohormonal activation, or myocardial stress occur much earlier than myocyte necrosis and the diagnostic rise of cardiac troponins, allowing us to expand biomarker research in these areas. Increased understanding of the complex AMI pathophysiology has spurred the search of new biomarkers that could overcome these shortcomings, whereas multi-omic and multi-biomarker approaches promise to be game changers in AMI biomarker assessment. In this review, we discuss the evolution, current application, and emerging blood biomarkers for the diagnosis of AMI; we address their advantages and promises to improve patient care, as well as their challenges, limitations, and technical and diagnostic pitfalls. Questions that remain to be answered and hotspots for future research are also emphasized.

Circulating Biomarkers in Heart Failure

Biological markers have served for diagnosis, risk stratification and guided therapy of heart failure (HF). Our knowledge regarding abilities of biomarkers to relate to several pathways of HF pathogenesis and reflect clinical worsening or improvement in the disease is steadily expanding. Although there are numerous clinical guidelines, which clearly diagnosis, prevention and evidence-based treatment of HF, a strategy regarding exclusion of HF, as well as risk stratification of HF, nature evolution of disease is not well established and requires more development. The aim of the chapter is to discuss a role of biomarker-based approaches for more accurate diagnosis, in-depth risk stratification and individual targeting in treatment of patients with HF.

Pre-discharge and early post-discharge troponin elevation among patients hospitalized for heart failure with reduced ejection fraction: findings from the ASTRONAUT trial

AIMS

Troponin levels are commonly elevated among patients hospitalized for heart failure (HF), but the prevalence and prognostic significance of early post-discharge troponin elevation are unclear. This study sought to describe the frequency and prognostic value of pre-discharge and post-discharge troponin elevation, including persistent troponin elevation from the inpatient to outpatient settings.

METHODS AND RESULTS

The ASTRONAUT trial (NCT00894387; http://www.clinicaltrials.gov) enrolled hospitalized HF patients with ejection fraction ≤40% and measured troponin I prior to discharge (i.e. study baseline) and at 1-month follow-up in a core laboratory (elevation defined as >0.04 ng/mL). This analysis included 1469 (91.0%) patients with pre-discharge troponin data. Overall, 41.5% and 29.9% of patients had elevated pre-discharge [median: 0.09 ng/mL; interquartile range (IQR): 0.06-0.19 ng/mL] and 1-month (median: 0.09 ng/mL; IQR: 0.06-0.15 ng/mL) troponin levels, respectively. Among patients with pre-discharge troponin elevation, 60.4% had persistent elevation at 1 month. After adjustment, pre-discharge troponin elevation was not associated with 12-month clinical outcomes. In contrast, 1-month troponin elevation was independently predictive of increased all-cause mortality [hazard ratio (HR) 1.59, 95% confidence interval (CI) 1.18-2.13] and cardiovascular mortality or HF hospitalization (HR 1.28, 95% CI 1.03-1.58) at 12 months. Associations between 1-month troponin elevation and outcomes were similar among patients with newly elevated (i.e. normal pre-discharge) and persistently elevated levels (interaction P ≥ 0.16). The prognostic value of 1-month troponin elevation for 12-month mortality was driven by a pronounced association among patients with coronary artery disease (interaction P = 0.009).

CONCLUSIONS

In this hospitalized HF population, troponin I elevation was common during index hospitalization and at 1-month follow-up. Elevated troponin I level at 1 month, but not pre-discharge, was independently predictive of increased clinical events at 12 months. Early post-discharge troponin I measurement may offer a practical means of risk stratification and should be investigated as a therapeutic target.

Cardiac troponin I, cardiac troponin-specific autoantibodies and natriuretic peptides in children with hypoplastic left heart syndrome

OBJECTIVES

To evaluate serum levels of cardiac troponin I (cTnI), autoantibodies against cardiac troponin (cTnAAbs) and natriuretic peptides during the treatment protocol in children with hypoplastic left heart syndrome (HLHS).

METHODS

In a prospective study, we had 18 consecutive children with HLHS, for whom serum samples were analysed before the Norwood operation, before the bidirectional Glenn (BDG) operation, at the age of one year and before total cavo-pulmonary connection (TCPC). In addition, we performed a cross-sectional study in 22 children examined before TCPC. Controls comprised 34 healthy children.

RESULTS

In the prospective study, troponin I was positive in eight children before the Norwood operation. At the next follow-up, six children were positive. Thereafter, in all samples, cTnI was negative. Serum levels of natriuretic peptides decreased during the treatment protocol but remained higher than in controls throughout the study. In the cross-sectional study, cTnI levels were negative, but levels of natriuretic peptides were higher than in controls. Levels of cTnI and natriuretic peptides showed no correlation with oxygen saturation or haemoglobin concentration. Autoantibodies against cardiac troponin appeared in one patient but not in the control children.

CONCLUSIONS

Cardiac TnI release is common before Norwood and BDG operations; then during the treatment protocol for HLHS, cTnI release resolves and serum levels of natriuretic peptides decrease. This may reflect a reduction of volume overload of the right ventricle during the surgical programme.

Cardiac biomarkers in the intensive care unit

Cardiac biomarkers (CB) were first developed for assisting the diagnosis of cardiac events, especially acute myocardial infarction. The discoveries of other CB, the better understanding of cardiac disease process and the advancement in detection technology has pushed the applications of CB beyond the 'diagnosis' boundary. Not only the measurements of CB are more sensitive, the applications have now covered staging of cardiac disease, timing of cardiac events and prognostication. Further, CB have made their way to the intensive care setting where their uses are not just confined to cardiac related areas. With the better understanding of the CB properties, CB can now help detecting various acute processes such as pulmonary embolism, sepsis-related myocardial depression, acute heart failure, renal failure and acute lung injury. This article discusses the properties and the uses of common CB, with special reference to the intensive care setting. The potential utility of "multimarkers" approach and microRNA as the future CB are also briefly discussed.

The Human Protein Atlas as a proteomic resource for biomarker discovery

The analysis of tissue-specific expression at both the gene and protein levels is vital for understanding human biology and disease. Antibody-based proteomics provides a strategy for the systematic generation of antibodies against all human proteins to combine with protein profiling in tissues and cells using tissue microarrays, immunohistochemistry and immunofluorescence. The Human Protein Atlas project was launched in 2003 with the aim of creating a map of protein expression patterns in normal cells, tissues and cancer. At present, 11,200 unique proteins corresponding to over 50% of all human protein-encoding genes have been analysed. All protein expression data, including underlying high-resolution images, are published on the free and publically available Human Protein Atlas portal (http://www.proteinatlas.org). This database provides an important source of information for numerous biomedical research projects, including biomarker discovery efforts. Moreover, the global analysis of how our genome is expressed at the protein level has provided basic knowledge on the ubiquitous expression of a large proportion of our proteins and revealed the paucity of cell- and tissue-type-specific proteins.

Predictive value of predischarge spectral tissue doppler echocardiography and n-terminal pro-B-type natriuretic peptide in patients hospitalized with acute heart failure

BACKGROUND

Admission for an acute heart failure (HF) confers an extremely poor prognosis. We aimed at finding out whether simultaneous assessment of multiple plasma-based biomarkers and Doppler echocardiography could provide complementary information and thus enable clinicians to stratify risk more effectively among patients hospitalized with acute HF; hence, untoward events after discharge avoided.

METHODS

A comprehensive echocardiographic study and measurements of cardiac troponin I (cTnI), N-terminal pro-B-type natriuretic protein (NT-proBNP), and high-sensitivity C-reactive protein (hsCRP) were conducted in 87 patients with symptomatic de novo acute HF or decompensation of chronic HF. Major adverse cardiac events (MACE) regarding cardiac death or hospitalization with worsening HF during a median follow-up period of 191 days were determined.

RESULTS

According to the univariate analysis, echocardiographic variables left atrial volume, left atrial volume index, pulmonary artery systolic pressure, E/E' ratio, and the concentrations of NT-proBNP were significantly related to clinical outcomes (all P-values < 0.05). Cox proportional hazard analysis identified two independent prognostic predictors of MACE: E/E' ratio and NT-proBNP. Moreover, the combining of plasma level of NT-proBNP with E/E' ratio provided independent and additional prognostic value in identifying high-risk acute HF patients.

CONCLUSIONS

These findings reinforce the necessity of combining the heart hemodynamic variable E/E' ratio and plasma-based neurohormonal biomarker NT-proBNP when clinicians attempt to define the individual risk of patients hospitalized with acute HF.