Case-Based Learning on Coronary Microvascular Dysfunction Despite Normal Angiography

Abstract

Coronary microvascular dysfunction (CMD) is increasingly recognized as a significant cause of ischemic symptoms and adverse cardiovascular events, even in patients with angiographically normal coronary arteries. This review provides a comprehensive exploration of CMD through a case-based learning approach, integrating current evidence, pathophysiological mechanisms, diagnostic strategies, and management recommendations. Emphasis is placed on the clinical relevance of CMD, risk stratification, and recent advances in therapeutic modalities, aiming to enhance practical understanding for healthcare professionals managing this challenging entity.

Introduction

Chest pain and ischemic symptoms with normal or non-obstructive coronary arteries represent a diagnostic and therapeutic dilemma in cardiology. CMD, also known as microvascular angina, is characterized by impaired coronary microvascular function resulting in myocardial ischemia without significant epicardial coronary artery stenosis. Despite its prevalence and impact, CMD remains underdiagnosed and undertreated. This article synthesizes recent research, guidelines, and clinical insights to elucidate the complexities of CMD through illustrative case-based discussions, offering evidence-based recommendations for clinicians.

Epidemiology / Disease Burden

CMD affects a substantial proportion of patients presenting with angina and non-obstructive coronary arteries (ANOCA). Epidemiological studies estimate that up to 50% of women and 30% of men with angina have normal or near-normal coronary angiograms, with CMD accounting for a large fraction. The Women’s Ischemia Syndrome Evaluation (WISE) study highlighted the high prevalence and morbidity associated with CMD, particularly in women, who are disproportionately affected. CMD is associated with persistent symptoms, diminished quality of life, increased healthcare utilization, and a higher risk of adverse cardiovascular outcomes, including heart failure and myocardial infarction, underscoring its clinical significance.

Pathophysiology

The pathophysiological basis of CMD is multifactorial, involving structural and functional abnormalities of the coronary microcirculation. Mechanisms include endothelial dysfunction, impaired vasodilation, heightened vasoconstrictive responses, and microvascular remodeling. Endothelial dysfunction leads to reduced nitric oxide bioavailability and impaired vasodilatory reserve. Additionally, microvascular inflammation, oxidative stress, and smooth muscle cell hyperreactivity contribute to impaired myocardial perfusion. These mechanisms are distinct from atherosclerotic epicardial disease, necessitating targeted diagnostic and therapeutic strategies.

Risk Factors

CMD shares several traditional cardiovascular risk factors with macrovascular coronary artery disease, including hypertension, diabetes mellitus, dyslipidemia, obesity, and smoking. However, non-traditional factors such as autoimmune diseases, systemic inflammation, and hormonal influences, particularly in women, play an important role. Psychological stress and microvascular spasm are also implicated. Genetic predisposition and microvascular rarefaction may further contribute to CMD pathogenesis. Recognizing these risk factors aids in identifying at-risk populations and tailoring preventive strategies.

Clinical Features

Patients with CMD typically present with exertional or rest angina, often indistinguishable from classic obstructive coronary artery disease. Atypical symptoms such as dyspnea, fatigue, or epigastric discomfort may also be reported. Anginal episodes are frequently recurrent and may be refractory to standard antianginal therapy. Importantly, CMD is more prevalent among women, who may exhibit subtle or non-classical symptoms, leading to misdiagnosis or under-recognition. The persistence of symptoms despite normal angiography should prompt consideration of CMD and further diagnostic evaluation.

Diagnosis

Diagnosing CMD is challenging due to the absence of obstructive lesions on conventional angiography. Non-invasive testing with stress echocardiography, cardiac magnetic resonance imaging (CMR) with perfusion, and positron emission tomography (PET) can assess myocardial perfusion and ischemia. Invasive coronary function testing remains the gold standard, involving measurement of coronary flow reserve (CFR) and microvascular resistance using guidewire-based techniques during coronary angiography. Acetylcholine or adenosine provocation helps differentiate microvascular spasm from endothelial dysfunction. A comprehensive evaluation excludes other causes of chest pain and ischemia, such as vasospastic angina or non-cardiac etiologies.

Treatment & Management

Management of CMD focuses on symptom relief, risk factor modification, and improvement of microvascular function. First-line pharmacotherapy includes beta-blockers, calcium channel blockers, and nitrates, although their efficacy may vary. Angiotensin-converting enzyme inhibitors and statins have shown benefit in improving endothelial function. Lifestyle interventions addressing weight reduction, smoking cessation, glycemic control, and exercise are pivotal. In refractory cases, novel agents such as ranolazine or ivabradine may be considered. A multidisciplinary approach involving cardiologists, primary care, and mental health professionals is often required for optimal management.

Recent Advances / Emerging Therapies

Emerging therapies for CMD focus on targeted modulation of endothelial function and microvascular tone. Novel pharmacological agents, including endothelin receptor antagonists, soluble guanylate cyclase stimulators, and agents targeting inflammation, are under investigation. Device-based therapies, such as coronary sinus reducers, have shown promise in selected patients. Advances in non-invasive imaging and the development of functional coronary angiography are enhancing diagnostic accuracy and enabling tailored therapy. Ongoing clinical trials continue to refine the therapeutic landscape, with a focus on improving long-term outcomes and quality of life for CMD patients.

Guideline Recommendations

Recent clinical guidelines emphasize the importance of considering CMD in patients with chest pain and non-obstructive coronary arteries. The 2019 ESC guidelines on chronic coronary syndromes and the 2021 AHA/ACC chest pain guidelines advocate for comprehensive diagnostic evaluation, including functional coronary assessment where available. Individualized management, risk stratification, and patient education are recommended to optimize care. Multimodality imaging and invasive testing are endorsed for definitive diagnosis in complex cases. Ongoing education for clinicians is critical to bridge the current gap in CMD recognition and management.

Conclusion

CMD represents a clinically significant, underrecognized cause of myocardial ischemia with substantial morbidity. Through a case-based lens, this review highlights the importance of understanding CMD\'s unique pathophysiology, risk factors, and clinical presentation. Accurate diagnosis and evidence-based management are essential to improve patient outcomes. Continued research and guideline development are needed to further refine diagnostic strategies and expand therapeutic options for this challenging and dynamic field.