Biomarkers of Coronary Microvascular Function Beyond Conventional Cardiac Injury Markers

Abstract

Coronary microvascular dysfunction (CMD) represents a critical yet often overlooked contributor to myocardial ischemia, especially in patients without obstructive coronary artery disease. While conventional cardiac injury biomarkers such as troponins and creatine kinase-MB have established roles in acute coronary syndromes, they lack specificity for microvascular pathology. This review explores novel and emerging biomarkers that reflect coronary microvascular function, delving into their mechanistic underpinnings, clinical relevance, and potential diagnostic and therapeutic implications. The article synthesizes recent evidence and guideline perspectives, offering a comprehensive resource for clinicians aiming to enhance the precision of CMD detection and management.

Introduction

Coronary microvascular dysfunction is increasingly recognized as a significant cause of myocardial ischemia and angina, especially among individuals with non-obstructive coronary arteries. Traditional cardiac injury markers, such as high-sensitivity troponins, primarily indicate myocyte necrosis and are insensitive to subtle microvascular changes. This limitation has driven a growing interest in identifying alternative biomarkers that better reflect the state of the coronary microcirculation. A nuanced understanding of these markers can improve diagnostic accuracy, guide management, and potentially enable tailored therapies for patients with CMD.

Epidemiology / Disease Burden

CMD is prevalent among patients presenting with symptoms of ischemia but lacking significant epicardial stenosis, a scenario described as ischemia with non-obstructive coronary arteries (INOCA). Epidemiological studies estimate that CMD affects up to 50% of women and 30% of men with anginal symptoms and non-obstructive coronary arteries. The burden is substantial, with CMD linked to adverse cardiovascular outcomes, including heart failure with preserved ejection fraction (HFpEF), recurrent hospitalizations, and reduced quality of life. The under-recognition and under-diagnosis of CMD contribute to a significant, yet modifiable, healthcare gap.

Pathophysiology

The central mechanism in CMD is impaired regulation of coronary microvascular tone, resulting from endothelial dysfunction, smooth muscle cell abnormalities, and microvascular remodeling. This leads to inadequate myocardial perfusion during increased oxygen demand. Inflammation, oxidative stress, and neurohormonal activation contribute to microvascular injury and dysfunction. Unlike epicardial atherosclerosis, CMD may occur without overt plaque formation, making its detection challenging with standard imaging and biomarker strategies. The pathophysiological complexity underscores the need for biomarkers that specifically mirror microvascular health rather than gross myocardial necrosis.

Risk Factors

Risk factors for CMD overlap substantially with those for atherosclerotic cardiovascular disease but with distinct patterns. Female sex, especially post-menopause, is a well-recognized risk factor, as are metabolic syndrome, diabetes mellitus, hypertension, dyslipidemia, and systemic inflammatory conditions such as rheumatoid arthritis. Additionally, chronic kidney disease, obesity, and psychosocial stress contribute to microvascular dysfunction. Certain genetic polymorphisms and epigenetic factors are emerging as potential contributors to CMD susceptibility, although further research is required to elucidate their clinical significance.

Clinical Features

Patients with CMD commonly present with exertional or rest angina, dyspnea, and signs of myocardial ischemia despite angiographically normal coronary arteries. The symptom burden may be disproportionate to findings on non-invasive stress testing. Importantly, CMD is associated with a higher prevalence of atypical chest pain, particularly among women. The clinical course can be chronic and relapsing, with substantial impact on functional status and quality of life. CMD also portends higher risk for adverse outcomes, including microvascular angina, arrhythmias, and progression to heart failure.

Diagnosis

Diagnosis of CMD is challenging due to the limitations of conventional biomarkers. Cardiac troponins and CK-MB remain insensitive to microvascular injury unless significant myocyte necrosis occurs. Emerging biomarkers of microvascular function include: (1) Endothelial biomarkers such as asymmetric dimethylarginine (ADMA), a marker of impaired nitric oxide production; (2) Inflammatory markers like high-sensitivity C-reactive protein (hsCRP) and interleukin-6, which reflect microvascular inflammation; (3) MicroRNAs, such as miR-126 and miR-133a, associated with endothelial integrity and vascular remodeling; (4) Natriuretic peptides (e.g., NT-proBNP), which may reflect microvascular stress even in the absence of overt heart failure; (5) Circulating progenitor cells and markers of endothelial repair. Functional assessments, such as coronary flow reserve (CFR) and index of microvascular resistance (IMR), supplement biomarker data but require specialized imaging. The integration of these biomarkers holds promise for a more accurate and practical diagnostic approach.

Treatment & Management

Management of CMD focuses on symptomatic relief, risk factor modification, and addressing underlying endothelial dysfunction. Pharmacological strategies include beta-blockers, calcium channel blockers, and long-acting nitrates, although their efficacy may be variable. Statins and angiotensin-converting enzyme inhibitors target endothelial health and reduce inflammation. Emerging data support the use of anti-inflammatory agents, such as colchicine, in selected patients. Lifestyle interventions diet, exercise, and weight management are cornerstone therapies. Close monitoring and reassessment are essential, given the chronic and fluctuating nature of CMD. Personalized medicine approaches, guided by biomarker profiles, are increasingly advocated to optimize therapy.

Recent Advances / Emerging Therapies

Recent advances in CMD research have spotlighted novel and more sensitive biomarkers. Proteomic and metabolomic analyses have identified candidate markers, such as lipoprotein-associated phospholipase A2, galectin-3, and growth differentiation factor-15 (GDF-15), linked to microvascular inflammation and remodeling. MicroRNA signatures and circulating endothelial microparticles are emerging as both diagnostic and potentially therapeutic targets. Therapies modulating these biomarkers such as SGLT2 inhibitors and GLP-1 receptor agonists are under investigation for their vascular protective effects beyond glycemic control. Advances in non-invasive imaging, including positron emission tomography (PET) and cardiac magnetic resonance (CMR), allow for more precise correlation of biomarker profiles with microvascular function.

Guideline Recommendations

Recent guidelines from major cardiology societies acknowledge the importance of CMD and recommend considering microvascular function in patients with persistent angina and non-obstructive coronary arteries. The use of conventional cardiac biomarkers remains standard, but there is increasing recognition of the need for more specific markers. Current recommendations advocate for a multimodal diagnostic strategy that integrates clinical assessment, imaging, and emerging biomarkers where available. Ongoing clinical trials are expected to inform future guideline updates regarding the clinical utility of novel biomarkers in CMD diagnosis and management.

Conclusion

CMD is a prevalent and clinically impactful entity that demands greater diagnostic precision than afforded by conventional cardiac injury markers alone. Emerging biomarkers reflecting endothelial dysfunction, inflammation, and microvascular remodeling offer enhanced specificity and open new avenues for risk stratification and personalized therapy. Continued research and guideline evolution are essential to integrate these advances into routine clinical practice, ultimately improving outcomes for patients with coronary microvascular dysfunction.