Screening for Early Coronary Reserve Abnormalities Using Functional Stress Responses

Abstract

Early coronary reserve abnormalities often precede overt coronary artery disease (CAD), representing a critical window for intervention to prevent adverse cardiac events. Functional stress testing offers a non-invasive approach to unmask subclinical coronary dysfunction by assessing myocardial perfusion and vascular reactivity under physiological or pharmacological stress. This review synthesizes recent evidence on the use of stress-based modalities for early detection of coronary reserve deficits, discusses the mechanistic underpinnings, and highlights clinical implications for risk stratification and management in at-risk populations.

Introduction

Coronary reserve describes the capacity of coronary circulation to increase blood flow in response to increased myocardial demand. Impairment of this reserve, often termed coronary microvascular dysfunction (CMD), can occur even in the absence of obstructive coronary lesions and is linked to adverse cardiovascular outcomes. Early detection of coronary reserve abnormalities is crucial, as it can facilitate timely intervention and may improve long-term prognosis in patients at risk of CAD. Functional stress responses—elicited by exercise or pharmacological agents—provide valuable diagnostic information about both epicardial and microvascular coronary function.

Epidemiology / Disease Burden

The prevalence of early coronary reserve abnormalities is underestimated due to the subclinical nature of the condition. Population-based studies suggest that up to 50% of patients with chest pain and non-obstructive coronary arteries exhibit evidence of CMD or impaired coronary flow reserve (CFR). Notably, women and patients with traditional cardiovascular risk factors such as hypertension, diabetes, and dyslipidemia are disproportionately affected. The burden of CMD is further amplified by its association with increased risk of heart failure with preserved ejection fraction (HFpEF) and adverse cardiovascular events, emphasizing the need for robust screening strategies.

Pathophysiology

Coronary reserve primarily reflects the ability of the coronary vasculature to dilate in response to increased metabolic demands. Underlying mechanisms of impaired reserve include endothelial dysfunction, microvascular remodeling, and heightened vasoconstrictive responses. These changes may be driven by oxidative stress, inflammation, and metabolic derangements. The dysfunction can manifest as reduced CFR, typically defined as a blunted increase in coronary blood flow during stress compared to rest. This pathophysiology underpins the rationale for utilizing stress-based diagnostic modalities, which can reveal abnormalities not evident under resting conditions.

Risk Factors

Traditional cardiovascular risk factors are closely linked to early coronary reserve abnormalities. Hypertension leads to microvascular remodeling and increased arterial stiffness, while diabetes promotes endothelial dysfunction and microvascular rarefaction. Hyperlipidemia fosters a pro-inflammatory milieu, further impairing endothelial function. Other contributing factors include obesity, sedentary lifestyle, smoking, and chronic inflammatory states. Non-traditional risk factors, such as autoimmune diseases and chronic kidney disease, are increasingly recognized as contributors to CMD and impaired vasodilatory reserve.

Clinical Features

Patients with early coronary reserve abnormalities may present with atypical chest pain, exertional dyspnea, or angina-like symptoms despite the absence of obstructive CAD on angiography. In some cases, silent myocardial ischemia occurs, particularly in high-risk populations such as diabetics. The clinical presentation is often subtle, necessitating a high index of suspicion, especially in women and patients with multiple risk factors. Recurrent hospitalizations for chest pain with non-obstructive findings should prompt consideration of underlying CMD.

Diagnosis

Functional stress testing is the cornerstone for detecting early coronary reserve abnormalities. Modalities include stress echocardiography, positron emission tomography (PET), cardiac magnetic resonance imaging (MRI), and single-photon emission computed tomography (SPECT), each offering unique advantages. PET is considered the gold standard for quantitative assessment of CFR, while stress echocardiography enables real-time evaluation of wall motion abnormalities. Pharmacological agents such as adenosine, dipyridamole, or regadenoson are commonly used to induce coronary vasodilation, revealing subclinical deficits. Invasive coronary flow measurements using Doppler or thermodilution techniques are reserved for selected cases. Importantly, the integration of functional data with clinical risk stratification enhances diagnostic accuracy and prognostic value.

Treatment & Management

Management of early coronary reserve abnormalities focuses on aggressive risk factor modification and optimization of medical therapy. Pharmacologic interventions include antiplatelet agents, statins, angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, and beta-blockers, all of which have demonstrated benefits in improving endothelial function and reducing cardiovascular events. Lifestyle interventions—targeting weight loss, physical activity, smoking cessation, and dietary modification—are foundational. In patients with persistent symptoms, nitrates or calcium channel blockers may be considered to alleviate vasospasm. Regular follow-up and repeat functional assessment can guide therapy and monitor progression.

Recent Advances / Emerging Therapies

Recent advances in imaging technology and biomarker research have expanded the diagnostic and therapeutic landscape for early coronary reserve abnormalities. Novel PET tracers, high-resolution cardiac MRI, and integration of artificial intelligence into image interpretation are enhancing the sensitivity and specificity of screening modalities. Research into endothelial-derived microparticles, circulating microRNAs, and inflammatory markers holds promise for non-invasive risk stratification. Therapeutically, agents targeting microvascular inflammation, oxidative stress, and endothelial repair are under investigation. Clinical trials evaluating the impact of SGLT2 inhibitors and GLP-1 receptor agonists on microvascular function are underway, potentially offering new avenues for management.

Guideline Recommendations

Current guidelines from major cardiology societies underscore the importance of functional assessment in patients with suspected microvascular dysfunction, particularly when non-obstructive CAD is identified. The American College of Cardiology (ACC) and European Society of Cardiology (ESC) recommend the use of stress testing in symptomatic individuals with intermediate pre-test probability of CAD. Emphasis is placed on individualized risk assessment and the incorporation of advanced imaging techniques when available. Guideline-directed therapy for risk factor modification and symptom relief remains the mainstay of management, with regular reassessment to tailor interventions.

Conclusion

Early identification of coronary reserve abnormalities using functional stress responses is pivotal for optimizing cardiovascular outcomes in at-risk populations. Advances in diagnostic modalities and an improved understanding of underlying mechanisms have enabled more accurate detection and risk stratification. Integration of evidence-based therapies and emerging interventions holds promise for further reducing the burden of CMD and its associated complications. Continued research and adherence to guideline-based practices will be essential in refining screening strategies and improving patient care.