Functional Coronary Angiography (FCA) - Advantages, Procedure, and Uses

Introduction

Various diagnostic tests, invasive and non-invasive, are used to diagnose cardiovascular diseases. A traditional coronary angiogram is one of them, which has been used for years. All these tests help identify the problems, for example, stenosis or narrowing of blood vessels due to blockages but fail to provide characteristics of such blockages. Hence, microcirculatory dysfunction, a very crucial component of cardiovascular diseases, is often ignored. To circumvent such problems, there was the advent of functional coronary angiography. It not only helps identify the source of blockage or problems but also provides flow-limiting characteristics of the identified source of problems.

What Is Functional Coronary Angiography (FCA)?

Also known as the coronary reactivity test (CRT), functional coronary angiography is a diagnostic test used to assess microcirculation of the coronary arteries (blood vessels of the heart). It also helps in the response of blood vessels to various medications. It is primarily used in patients with INOCA.

What Does INOCA Stand For?

INOCA stands for ischemia with no obstructive coronary arteries. It is a medical condition in which patients present with various signs and symptoms associated with heart disease but, on examination, do not show significant blockage of the coronary blood vessels. The signs and symptoms include -

• Chest pain.

• Chest tightness.

• Chest pain radiating to the neck, shoulders, arm, and back.

• Fatigue.

• Dyspnea (shortness of breath).

The symptoms resemble angina with blockage in the larger coronary blood vessels.

Ischemia with no obstructive coronary arteries, or INOCA, involves an imbalance in the supply and demand of oxygen to the heart tissue, and it is associated with two significant mechanisms which include-

1. Microvascular Dysfunction - Microvascular dysfunction occurs due to microvascular diseases, which are diseases of the small blood vessels. Women are more likely to experience microvascular dysfunction. Risk factors for microvascular dysfunction are similar to those of atherosclerosis, and they include-

• Tobacco abuse.

• Hypertension (high blood pressure).

• Dyslipidemia (abnormal cholesterol levels, triglycerides, low-density lipoproteins or bad cholesterol, and high-density lipoproteins or good cholesterol).

2. Vasospastic Disorders - Vasospastic disorders are medical conditions in which the small blood vessels experience spasms that limit blood flow. Vasospasm in the coronary blood vessels can be consistent, leading to myocardial infarction (heart attack), or transient, leading to Prinzmetal angina. Also known as vasospastic angina, Prinzmetal angina is a rare and severe variant of chest pain and is characterized by pain in the chest, during the night or early morning, while people are resting or awake.

What Advantage Does the Functional Coronary Angiogram Have Over Traditional Coronary Angiograms?

Traditional coronary angiography has been used to check the presence or absence of coronary stenosis, but it does not provide information on flow-limiting characteristics of stenosis or narrowings. On the contrary, functional coronary angiograms have been expanded to interrogate coronary microcirculation and provide information on microvascular resistance. Typically, functional coronary angiography works by combining information obtained with a three-dimensional reconstruction of the coronary arteries. Therefore it generates information on the locations of the stenoses and helps assess whether they are flow-limiting.

Which Drugs Are Used in a Functional Coronary Angiography Test (FCA)?

Functional coronary angiography test or coronary reactivity test consists of the following drugs -

• Adenosine - Adenosine, when injected into the coronary blood vessels, helps widen the smaller blood vessels of the heart. This aids in measuring blood flow.

• Acetylcholine - The drug acetylcholine helps in the dilation or widening of the larger blood vessels.

• Nitroglycerin - Nitroglycerine significantly reduces pulmonary vascular pressure, intraventricular pressure, and cardiac output. It also enhances myocardial perfusion (heart tissue perfusion) by reducing the oxygen demand and tension within the heart walls.

How Is Functional Coronary Angiography Performed?

• One week before the test, the cardiologist conducts pre-procedural tests. They include chest x-rays, blood work, and electrocardiogram scans (EKG or ECG).

• The patient is advised to avoid drinking fluids and eating food for at least two hours before the procedure. Caffeine consumption should be halted 24 hours before the exam.

• If the patient is on medication such as blood thinners, for example, Warfarin or Aspirin, doctors advise stopping the medication before the procedure.

• Patients are also advised to temporarily halt beta-blockers, calcium channel blockers, and angiotensin receptor blockers 48 hours before the test.

• An intravenous line (IV) is inserted in the arm, allowing the cardiologist to administer various drugs into the blood vessels slowly.

• The test is performed in a specialized room called the catheterization ward.

• The test is typically conducted within 60 to 90 minutes.

• After the exam, the catheters are removed, and firm pressure is applied to stop bleeding.

• The patient is advised to rest until the sedative wears off.

What Are the Other Uses of Functional Coronary Angiography?

A functional coronary angiography helps identify microvascular dysfunction much better than a traditional coronary angiogram. INOCA is not the only disease that is identified by vascular dysfunction. There are other medical conditions associated with the dysfunction of the microvasculature. Hence, it can be employed for the following conditions as well -

• Heart Failure With Preserved Ejection Fraction (HFpEF): It is a clinical condition associated with the signs and symptoms of heart failure. It occurs because of elevated left ventricular pressure, although the ejection fraction of the left ventricle is almost normal. The ejection fraction is a numerical value that accounts for the blood the lower left heart chamber pumps out with each heartbeat.

• ST-Elevation Myocardial Infarction: Otherwise known as STEMI, it is a type of heart attack associated with higher mortality risk and complications. It accounts for at least 40 percent of the heart attacks recorded yearly. It is a time-sensitive heart condition, and survival depends only on timely treatment.

• Angina With Post Percutaneous Coronary Intervention: Percutaneous coronary intervention, formerly known as angioplasty, is a procedure used to place a small device called a stent in the blood vessels to increase the width of its lumen. When patients have an angioplasty but still show signs and symptoms of angina or chest pain, it indicates an underlying disease. Since a stent is supposed to improve blood flow, it is necessary to understand the flow characteristics of the blocked blood vessels when it fails to aid the patient. Hence, a functional coronary angiography can help identify and aid such situations.

Conclusion

With various invasive and non-invasive diagnostic tests available today, it is easier to make an early diagnosis in patients with cardiovascular diseases. Although numerous methods are available today, these methods do not provide the flow characteristics of the blood vessels impacted by stenosis or other conditions. This makes it challenging to identify heart disease in patients who lack the early signs and symptoms, especially in the case of ischemia with no obstructive coronary arteries. It is a new technique with limited research but considering its advantages; it can prove to be a highly credible diagnostic test for assessing cardiovascular diseases.