Coronary Microvascular Disease

Introduction

What is Coronary Microvascular Disease?

Coronary microvascular disease (CMVD) is a group of disorders. It affects the tiny arteries feeding the heart (coronary vasculature), making them lose the capacity to accommodate blood flow (contraction and dilation to meet the oxygen and nutrient needs of the cardiovascular system). It is often signaled by chest pain (usually leaving an electrocardiographic signature) when the arteries narrow too much. Besides frequent spasms, there is a poor response to neurotransmitters (like acetylcholine) and other neurochemicals that open up the blood vessels.¹

In normal physiological conditions, coronary blood supply (laden with oxygen and nutrients) matches circulatory demand. The interactions of metabolic, hormonal, neuromuscular, and neurochemical factors maintain this balance in the endothelium and ensure that optimal tone of the blood vessels is achieved.²

Other names for CMVD are cardiac syndrome X, nonobstructive coronary heart disease, and microvascular angina.² It has been estimated that the condition affects about 30% of patients with angina. 

Signs and Symptoms

The condition’s clinical symptoms are usually shortness of breath during exertion, angina (chest pain), lethargy, and restlessness. However, many cases may pass as asymptomatic.³

Risk Factors

There are many factors that increase the risk of developing CMVD.¹ Some include: 

• Being assigned female at birth (AFAB) (research findings those AFAB are three times more likely though this has not been conclusively proven)
• Menopause
• Age
• Poor diet (especially those loaded with bad cholesterol)
• Hypertension 
• History of smoking
• Obesity  
• Hereditary factors (family history)
• Lipid disorders (dyslipidemia)
• Diabetes mellitus

In turn, CMVD increases the risk of heart failure, myocardial infarction (heart attacks), nonobstructive coronary artery disease, and atherosclerosis of larger blood vessels.

Diagnosis

The choice of diagnostic method boils down to the expertise of the investigator, cost, availability, and even patient preference.³ Each diagnostic method has its pros and cons; the consulting physician can recommend more than one of these tests.

Broadly speaking, they include the following methods:  

Coronary angiography

X-ray coronary angiography is often used as a confirmatory diagnosis, as it is capable of differentiating CMVD from epicardial coronary artery disease.⁴ It is an invasive method involving physical contact with tissue to be investigated that involves intravenous insertion of a probe (catheter) or a contrasting agent, which is the mainstay for diagnosis of CMVD.

Stress test

Exercise stress testing (with or without imaging) is another method for identifying CMVD in patients. The patient is typically placed on a treadmill and cardiovascular biomarkers (like heart rate and blood pressure) are monitored in response to patient activity. A positive result suggests obstructive coronary artery disease. However, the sensitivity and specificity of the test are poor.³ This limits its role in the modern-day diagnosis of CMVD.

Coronary magnetic resonance (CMR) imaging

CMR is an example of radiographic (imaging) procedures that exploit electromagnetic radiation to observe and assess blood flow through the coronary vascular space. They are important for noninvasive diagnosis of the condition. Besides CMR imaging, other noninvasive imaging tests are PET (positron emission tomography) scans and CT (computed tomography) scans.⁴

Duke Activity Status Index (DASI)

DASI comes in the form of a 12-point questionnaire that considers daily routine vis-à-vis cardiovascular fitness. It serves as a self-assessment tool useful in quickly evaluating the level of risk and the functional capacity of patients with CMVD.⁵ It is cost-effective and can easily be administered. 

Treatments

Treating the condition involves interrupting the pathways that control inflammation, abnormal contraction of coronary blood microvessels (arteries) and blood clotting (thromboses). These medications are found to be beneficial either for symptom control or for modifying the course of the disease.^1,3 They include: 

• Low-dose aspirin: It is a common blood thinner that blocks the clumping together (aggregation) of blood platelets. Higher therapeutic doses of the medication have an added advantage of pain relief. 

• Statins: These interrupt the inflammation-driven deposition of lipids (e.g. low-density cholesterol) within the microvessels by interfering with production. 

• Antianginal medications: They directly widen (dilate) the constricted blood vessels through different mechanisms ultimately improving coronary blood flow (e.g. calcium channel blockers, beta-blockers, nitrates, and ranolazine).   

• Angiotensin-converting enzyme inhibitors (e.g. quinapril): They target the reduction of cardiovascular inflammation and block the effects of the enzyme (angiotensin II) which constricts the blood vessel.

The medications, provided they are not interacting negatively, can be combined to achieve better results. 

Prevention

It is important to note that controlling blood pressure, lipids, and sugar levels (by medication or lifestyle adjustment) can go a long way in reducing symptoms. Non-drug measures of intervention include proper nutrition (balanced diet), regular exercise, avoidance of smoking, and stress and weight reduction. While such measures seem simple, they can make a huge difference in terms of preventing CMVD.   

Contacting your doctor

Coronary microvascular disease is a complex condition whose management requires the attention of a specialist. The management plan stretches from diagnosis to actual treatment and regular monitoring. It is best practice to alert your GP once you experience symptoms like chest pain or unusual breathlessness on exertion or even at rest. Medications for managing coronary microvascular disease must be taken strictly based on prescription, as they are regarded as highly potent.   

Summary

Coronary microvascular disease is a complex condition. It reflects the mismatch between coronary blood supply and the demand for oxygen and nutrients required for cardiovascular health. It can be detected by clinical presentations which can be typical, atypical, or asymptomatic. However, several invasive and noninvasive diagnostic measures are in place to guide treatment decisions. Such measures tend to differ in terms of cost and accuracy.   

Ultimately, careful consideration of the risk factors and preventive measures are important for understanding and managing the condition, given that CMVD is managed by an experienced cardiovascular specialist. Adjusting the modifiable risk factors like diet and smoke cessation, along with pharmacotherapy helps reduce symptoms, improving overall treatment outcomes.