Introduction

Heart failure and heart enlargement are conditions that require specific diagnosis and monitoring. Blood biomarkers have emerged as valuable tools for evaluating these cardiac conditions. Based on current scientific evidence, the article summarises the most relevant blood biomarkers for assessing heart enlargement and heart failure. Heart failure refers to the physiological dysfunction of the heart due to its not pumping blood effectively to meet the body's needs. It often develops due to heart enlargement, as the enlarged heart struggles to function properly. Heart enlargement, more commonly termed cardiomegaly, refers to an increase in the size of the heart. Specifically, it is defined as when the transverse diameter of the cardiac silhouette is greater than or equal to 50% of the transverse diameter of the chest on imaging.¹ Heart enlargement can occur through two main mechanisms:

• Dilatation: The heart walls become lean, stretched out, and weakened, enlarging the heart chambers
• Hypertrophy: The heart walls thicken, causing the heart to become less efficient

A biomarker is an objectively measured characteristic that defines normal biological processes, pathogenic processes, or responses to therapeutic interventions related to the heart.² For heart conditions, biomarkers are typically substances found in the blood that reflect cardiac function, stress, or damage. These biomarkers are usually proteins or other molecules released by the heart muscle in response to strain, injury, or abnormal functioning. They can be measured through blood tests, providing valuable information about cardiac health without requiring more invasive procedures.³

Key blood biomarkers for heart enlargement and heart failure

• Natriuretic peptides: B-type Natriuretic Peptide (BNP) and N-terminal pro-B-type Natriuretic Peptide (NT-proBNP) are secreted in response to cardiac wall trauma. They are extensively studied and used for heart failure diagnosis and prognosis⁴
• Cardiac troponins: High-sensitivity troponin assays (hsTn) indicate heart muscle damage and are accurate in predicting heart failure⁵
• ST2 (Interleukin-1 Receptor-Like 1): This biomarker is associated with cardiac remodelling and fibrosis and has the potential to predict adverse outcomes in heart failure⁴

Natriuretic peptides

BNPs and NT-proBNPs are the most extensively studied and clinically used biomarkers for heart failure.² These cardiac-specific indicators are produced by ventricular cardiomyocytes (muscle cells making up the ventricles in your heart) in response to excessive volume or pressure strain.²

NT and BNP- people with heart failure see a large increase in proBNP levels as a compensatory mechanism.

• A worse prognosis is correlated with higher baseline BNP levels
• The Val-HEFT trial showed that the best outcome went to those whose BNP decreased the most during treatment
• The risk of dying increases by 35% for every 100 pg/ml increase in BNP

Cardiac troponins

Cardiac troponins, particularly high-sensitivity troponin assays (hsTn), have shown prognostic value in heart failure.^2,6

• High baseline troponin levels correspond to a worse prognosis, with an odds ratio of 2.5 for death within a year
• Serial measurements of hsTn during hospitalisation for acute heart failure can help risk-stratify patients for 90-day mortality and readmission
• The prognostic value of troponins is enhanced when combined with natriuretic peptides

ST2 (interleukin-1 receptor-like 1)

ST2 is a member of the interleukin-1 receptor family and has shown potential in predicting adverse outcomes in heart failure.²

• In the PRIDE study, ST2 values >0.20 ng/ml were associated with an increased risk of annual death
• ST2 works hand in hand with natriuretic peptides to enhance mortality prediction in acute and chronic heart failure

MicroRNAs

MicroRNAs (miRNAs) are currently emerging biomarkers in research, showing potential in HF diagnosis and prognosis.²

• Plasma levels of miR-302 family members, except for miR-302f, were significantly above normal in acute heart failure (AHF) patients
• miR-302b-3p demonstrated the highest area under the curve (AUC) value of 0.87, indicating strong potential as a diagnostic biomarker for AHF
• miR-302b-3p levels were significantly higher in AHF patients with left ventricular ejection fraction ≤45% and New York Heart Association (NYHA) class IV²

Other relevant biomarkers

Several other biomarkers have shown promise in evaluating heart failure and cardiac enlargement:

• Cathepsin S, platelet reactive protein-1, and interleukin-11 (IL-11) levels were above normal concentration in patients with chronic heart failure and associated with the severity of cardiac dysfunction
• Soluble ST2 receptor (sST2) has been demonstrated to be an independent indicator for detecting and diagnosing chronic heart failure
• Pregnancy-associated plasma protein-A (PAPP-A) levels may be biomarkers for identifying individuals at risk of coronary artery disease, which leads to heart failure²

Importance of biomarkers in diagnosis and management

Biomarkers play a crucial role in the diagnosis and management of heart enlargement and heart failure:

• Diagnosis: Biomarkers can help detect heart conditions early, even before symptoms appear. They provide objective evidence of cardiac injury³
• Risk stratification: Certain biomarkers can indicate the severity of the condition and help predict outcomes, allowing for more targeted treatment approaches
• Monitoring disease progression: Serial measurements of biomarkers can track how the condition is evolving
• Guiding treatment: Biomarker levels can help clinicians assess the effectiveness of treatments and make necessary adjustments³
• Prognosis: Some biomarkers strongly predict future cardiovascular events or mortality, aiding in long-term patient management
• Differential diagnosis: Biomarkers can help distinguish between different cardiac conditions, leading to more accurate diagnoses

By providing quantifiable data on cardiac function and stress, biomarkers significantly enhance the provider’s ability to make informed decisions about patient care in cases of heart enlargement and heart failure.

Comparative analysis of biomarkers

Sensitivity and specificity

• BNP and NT-proBNP have shown high sensitivity and specificity for diagnosing heart failure, with AUC values ranging from 0.67 to 0.78 during hospitalisation⁷
• High-sensitivity troponin T (hs-TnT) demonstrated superior diagnostic value compared to other cardiac biomarkers in diagnosing acute myocardial infarction within the first 3 hours of admission⁶

Combining biomarkers

A multi-marker approach may provide the most comprehensive assessment of cardiac function and prognosis in heart failure patients.^2,7 For example, combining natriuretic peptides with troponins or ST2 can enhance prognostic accuracy.

Clinical applications

Diagnosis and monitoring

• Natriuretic peptides are used for diagnosing heart failure and monitoring disease progression^2,7
• Cardiac troponins aid in diagnosing acute myocardial infarction and risk stratification in heart failure patients⁶
• Serial measurements of biomarkers can help assess treatment response and guide management decisions⁶

Risk stratification and prognosis

• Elevated levels of natriuretic peptides, troponins, and ST2 are associated with worse outcomes in heart failure patients^2,7
• Changes in biomarker levels during treatment can provide valuable prognostic information.²

FAQs

What are the most important cardiac biomarkers for heart failure?

BNPs and NT-proBNPs are the gold standard biomarkers for diagnosing and monitoring heart failure.⁵ They are released by the heart when it is stretched or under stress. Higher levels indicate a greater likelihood of heart failure.

Troponin - While primarily used to diagnose heart attacks, elevated troponin levels can also indicate heart failure, especially when used in combination with BNP/NT-proBNP.⁶

How are BNP and NT-proBNP used clinically?

BNP and NT-proBNP are used in several ways:

• To help diagnose heart failure in patients with shortness of breath or other symptoms
• To assess the severity of heart failure 
• To monitor the response to heart failure treatment
• To predict prognosis in heart failure patients

Higher levels generally indicate more severe heart failure and worse outcomes.⁵

Are there any other promising biomarkers for heart failure?

Some other biomarkers being studied include:

• Galectin-3: associated with cardiac fibrosis and remodeling5
• ST2: a marker of cardiac stress and fibrosis
• Mid-regional pro-atrial natriuretic peptide (MR-proANP): may provide additional diagnostic value in certain patients⁵

However, BNP/NT-proBNP and troponin currently remain the most clinically useful and widely available biomarkers.

What are normal and abnormal levels for these biomarkers?

Reference ranges can vary by laboratory and assay, but general guidelines include:

• BNP: <100 pg/mL is normal, >400 pg/mL suggests heart failure¹ 
• NT-proBNP: <300 pg/mL is normal, >450-1800 pg/mL (depending on age) suggests heart failure¹ 
• Troponin: Levels above the 99th percentile of the reference range suggest cardiac injury⁶ 

Are these biomarkers specific to heart failure?

While useful, these biomarkers are not 100% specific to heart failure. Levels can be affected by:

• Age
• Kidney function
• Obesity (which can lower BNP levels)
• Other cardiac conditions, like atrial fibrillation

This is why biomarkers are always interpreted in the context of clinical presentation and other diagnostic tests.⁵

Summary

While numerous biomarkers have been identified for evaluating heart enlargement and heart failure, natriuretic peptides (particularly BNP and NT-proBNP) remain the gold standard for diagnosis and prognosis. Cardiac troponins, ST2, and emerging biomarkers like microRNAs offer additional predictive value, especially when combined. Ongoing research continues to improve, a multi-marker approach may provide the most comprehensive assessment of cardiac function and prognosis in heart failure patients.