Coronary Microvascular Dysfunction in Patients with Non-Obstructive Coronary Arteries: Current Gaps and Future Directions

Coronary microvascular disease in women: epidemiology, mechanisms, evaluation, and treatment

Coronary microvascular dysfunction (CMD) involves functional or structural abnormalities of the coronary microvasculature resulting in dysregulation of coronary blood flow (CBF) in response to myocardial oxygen demand. This perfusion mismatch causes myocardial ischemia, which manifests in patients as microvascular angina (MVA). CMD can be diagnosed non-invasively via multiple imaging techniques or invasively using coronary function testing (CFT), which assists in determining the specific mechanisms involving endothelium-independent and dependent epicardial and microcirculation domains. Unlike traditional coronary artery disease (CAD), CMD can often occur in patients without obstructive atherosclerotic epicardial disease, which can make the diagnosis of CMD difficult. Moreover, MVA due to CMD is more prevalent in women and carries increased risk of future cardiovascular events. Successful treatment of symptomatic CMD is often patient-specific risk factor and endotype targeted. This article aims to review newly identified mechanisms and novel treatment strategies for managing CMD, and outline sex-specific differences in the presentation and pathophysiology of the disease.

The diagnosis and treatment of women with recurrent cardiac ischemia and normal coronary arteries

Cardiac disease is the leading cause of death in women. Among women with recurrent chest pain, abnormal electrocardiograms, and/or stress tests who undergo coronary angiography, as many as 50% have normal or <50% coronary artery obstructive disease. Pharmacologic stress assessment of coronary artery flow reserve in these women frequently demonstrates an inability to increase blood flow to >2.5 times normal flow. Contributory factors include abnormal epicardial or microvascular reactivity, microvascular remodeling or rarefaction, autonomic dysfunction, or coronary plaque rupture/erosion. Assessment is necessary of serum biomarkers and coronary artery flow reserve, fractional flow reserve, microvascular resistance, and epicardial/microvascular spasm. Aggressive treatment of women with positive tests is necessary because these women have an increased incidence of recurrent chest pain, repeated hospitalizations and coronary angiograms, and cardiac death.

Clinical Significance and Influencing Factors of Microvascular Tissue Reperfusion After Macrovascular Recanalization

The relevance of impaired microvascular tissue reperfusion despite successful macrovascular angiographic reperfusion (no-reflow) in acute ischemic stroke (AIS) remains controversial. In this study, we aimed to investigate the impact of tissue optimal reperfusion (TOR) and its influencing factors. From December 1, 2020 to December 1, 2021, AIS patients with successful recanalization (modified Thrombolysis in Cerebral Infarction score [mTICI] ≥ 2b) after mechanical thrombectomy (MT) were retrospectively reviewed. Computed tomography perfusion was performed before and after MT. Successful reperfusion was assessed by TOR, defined as > 90% reduction of the Tmax > 6 s lesion volumes between baseline and early follow-up perfusion profiles. The impact of TOR on functional outcomes after successful recanalization and influencing factors for TOR were both investigated. Sixty-three patients were included, including 44 cases in the TOR group and 19 cases in the non-TOR group. The TOR group had a higher rate of favorable outcome (aOR 4.366, 95%CI 1.159-16.445, p = 0.030) and NIHSS improvement (aOR 5.089, 95%CI 1.340-19.322, p = 0.017) than the non-TOR group. Multivariable logistic regression showed baseline glucose (OR 0.648, 95%CI 0.492-0.854, p = 0.002) and mTICI 2c/3 (OR 10.984, 95%CI 2.220-54.343, p = 0.003) predicted TOR in model 1; in model 2, postoperative glucose (OR 0.468, 95%CI 0.278-0.787, p = 0.004) and mTICI 2c/3 (OR 9.436, 95%CI 1.889-47.144, p = 0.006) were predictive. TOR was strongly associated with good functional outcomes after successful recanalization of MT. Higher mTICI grade and lower perioperative glucose level may predict microvascular tissue reperfusion.

Global trend and future landscape of coronary microcirculation: A bibliometric and visualized analysis from 1990 to 2021

Background

Coronary microcirculation has a fundamental role in the regulation of coronary blood flow in response to cardiac requirements, which has aroused wide concerns in basic science and clinical cardiovascular research. We aimed to analyze coronary microcirculation-associated literatures over 30 years and provide insightful information on the evolutionary path, frontier research hotspots, and future developmental trends.

Methods

Publications were retrieved from the Web of Science Core Collection (WoSCC). VOSviewer was used to perform co-occurrence analyses for countries, institutions, authors, and keywords and to generate visualized collaboration maps. CiteSpace was used to visualize the knowledge map derived from reference co-citation analysis, burst references, and keywords detection.

Results

This analysis was performed based on 11,702 publications including 9981 articles and 1721 reviews. The United States and Harvard University ranked at the top among all the countries and institutions. The majority of articles were published in Circulation, and it also was the most co-cited journal. Thematic hotspots and frontiers were focused on coronary microvascular dysfunction, magnetic resonance imaging, fractional flow reserve, STEMI, and heart failure. Additionally, keywords burst and co-occurrence cluster analysis showed that management, microvascular dysfunction, microvascular obstruction, prognostic value, outcomes, and guidelines were current knowledge gaps and future directions.

Conclusions

Coronary microcirculation presented a research hotspot relevant wide spectrum of cardiovascular diseases. Definite diagnostics and prognostics are particularly valued. The protection of cardiovascular events that influence clinical outcomes should be an insightful concern in the future. Multidisciplinary collaborations will provide significant advances for the development of coronary microcirculation.

Coronary functional assessment in non-obstructive coronary artery disease: Present situation and future direction

Non-obstructive coronary artery disease (CAD), which is defined as coronary stenosis <50%, has been increasingly recognized as an emerging entity in clinical practice. Vasomotion abnormality and coronary microvascular dysfunction are two major mechanisms contributing to the occur of angina with non-obstructive CAD. Although routine coronary functional assessment is limited due to several disadvantages, functional evaluation can help to understand the pathophysiological mechanism and/or to exclude specific etiologies. In this review, we summarized the potential mechanisms involved in ischemia with non-obstructive coronary arteries (INOCA) and myocardial infarction with non-obstructive coronary arteries (MINOCA), the two major form of non-obstructive CAD. Additionally, we reviewed currently available functional assessment indices and their use in non-obstructive CAD. Furthermore, we speculated that novel technique combined anatomic and physiologic parameters might provide more individualized therapeutic choice for patients with non-obstructive CAD.

Non-obstructive Plaque and Treatment of INOCA: More to Be Learned

PURPOSE OF REVIEW

A significant proportion of patients evaluated for chest pain have ischemia with non-obstructive coronary artery disease (INOCA). Studies have shown INOCA is associated with increased risk of major adverse cardiac events and significant burden on the health care system.

RECENT FINDINGS

While there is scarce scientific evidence on management of INOCA, the CorMicA trial showed that stratified medical therapy based on the type of INOCA improved patients' symptoms and quality of life. There are multiple ongoing trials, including Women's IschemiA Trial to Reduce Events in Non-ObstRuctIve CORonary Artery Disease (WARRIOR trial), assessing the benefit of intensive medical therapy versus usual care for this increasingly recognized clinical entity. In this review, we discuss the definition of INOCA, epidemiology and risk factors, pathophysiology, and management as well as the current knowledge gaps and ongoing clinical trials in this arena.