Coronary Arteriovenous Fistula

What is Coronary Arteriovenous Fistula?

A coronary arteriovenous fistula (CAVF) is an unusual type of inborn heart disease. Despite being rare, it is the most common inborn anomaly or unusual condition of the coronary artery. This condition is characterised by an unusual link between an artery and a vein, often skipping the small blood vessels, or capillaries, in between. When this abnormal link occurs between the coronary artery and heart chambers, it’s referred to as a coronary cameral fistula. This kind of condition can also occur between a coronary artery and another nearby vessel from the lung or body’s general circulation.

People born with CAVFs may experience symptoms at birth or later in life, depending on the specific type of fistula and if there are other nearby or supporting blood vessels present. Certain types of coronary anomalies, such as one where the left coronary artery comes from the pulmonary artery, have been linked to heart rhythm disturbances and sudden cardiac death syndromes in young adults and athletes. Adults typically experience shortness of breath and chest pain during exertion due to insufficient supply of blood to their heart tissues or scarring of the inner linings of their hearts, often due to an extensive formation of collateral blood vessels.

Our heart receives the blood it needs to function through two major arteries on its surface. These arteries begin at openings or ostia in a part of the heart known as the coronary sinus of Valsalva, located just above the three-part aortic valve. The left coronary artery begins from the left side of this sinus and splits into two parts, one of which feeds the left sides of the heart, while the other fuels the front section. The right coronary artery emerges from the right side of this sinus or the anterior aortic sinus, breathing life into the right side of the heart and some other parts. About 80% of people have more blood supplied by the right coronary artery.

Research has shown that the right coronary artery is the most common source of CAVFs, found in around half of patients. The remaining cases start from different sites in the left coronary artery, or in some cases, both coronary arteries. Almost 90% of these fistulas drain into the lower pressure venous circulation, with varying common drainage sites.

Untreated, a coronary arteriovenous fistula can lead to complications such as swollen coronary arteries due to excessive blood flow, high lung artery pressure due to a large left to right blood shift, congestive heart failure, lack of blood supply to the heart from ‘stealing’ of blood flow, and clot or widening of the fistula.

What Causes Coronary Arteriovenous Fistula?

Coronary arteriovenous fistulas (CAVF’s) can either be present from birth (congenital) or develop later in life (acquired) – with 90% being congenital. They could arise due to the continued existence of small blood vessels that nourish the fetal heart, leading to an abnormal connection between the heart’s arteries and chambers.

Further, if the natural process of eliminating the connection between the heart’s arteries and nearby vessels fails, it may result in the coronary arteriovenous fistula. These nearby vessels could be bronchial, pericardial, or mediastinal arteries, or the superior vena cava.

Acquired coronary arteriovenous fistulae, while rare, can occur due to heart trauma, certain medical procedures like placing a coronary stent or grafting a bypass for a blocked coronary artery, chest radiation, or heart diseases like heart attacks and inflammation of the heart’s blood vessels.

Risk Factors and Frequency for Coronary Arteriovenous Fistula

Krause was the first to describe a heart defect known as a coronary arteriovenous fistula (CAVF) back in 1865. This condition is quite rare, affecting only about 0.002% of the general population. It makes up 0.4% of all heart malformations and roughly half of all coronary artery anomalies. CAVF is occasionally discovered during heart catheterization procedures, occurring in about 0.25% of these cases. Most people diagnosed with this condition are over 20 years old, and symptoms tend to become more noticeable as they age. Interestingly, this condition has also been detected in about 0.06% of children who undergo echocardiograms. Importantly, there’s no preference for any race or gender with regards to who might develop CAVF.

Signs and Symptoms of Coronary Arteriovenous Fistula

A coronary arteriovenous fistula is a condition where an abnormal connection exists between a coronary artery and a vein. In some cases, small fistulas don’t cause symptoms or harm the blood supply to the heart muscle. However, large fistulas can cause issues. These can include symptoms like chest pain due to a “coronary steal” phenomenon, where blood is diverted away from the heart tissue that needs it. They can also cause an excess of blood flow to the right side of the heart, leading to volume overload.

When this happens, individuals may experience symptoms of right-sided heart failure. These symptoms include shortness of breath, swelling in the extremities, difficulty breathing when laying flat, and fainting spells. Health professionals should consider the possibility of a coronary arteriovenous fistula in patients with unexplained heart failure, especially those with a history of chest trauma, radiation to the chest, heart attacks, or heart procedures.

During a physical examination, signs of congestive heart failure might be evident. These could include increased pressure in the neck veins, a positive response to pressure over the neck veins when the liver is palpated, swelling in the feet and ankles, and fluid in the space surrounding the lungs. Listening to the patient’s chest might reveal a continuous sound from increased blood flow in the large fistula and associated blood vessels. A loud second heart sound and an early diastolic murmur (an unusual sound heard between heartbeats) in the lung area could indicate high blood pressure in the pulmonary arteries.

• Chest pain from decreased blood flow to the heart
• Shortness of breath
• Swelling in the extremities
• Difficulty breathing when laying flat
• Fainting spells
• Increased pressure in the neck veins
• Positive hepatojugular reflux
• Swelling in the feet and ankles
• Fluid accumulation around the lungs
• Continuous murmur from increased blood flow
• Loud second heart sound and early diastolic murmur

Testing for Coronary Arteriovenous Fistula

An electrocardiogram (ECG), a test that records the electrical activity of your heart, can show indicators of increased volume and strain in the left side of your heart and signs of impaired blood flow.

A chest x-ray— a test that uses a small amount of radiation to create pictures of the structures inside your chest— can reveal an enlarged heart (cardiomegaly) and fluid in the space surrounding your lungs (pleural effusion); Both of these conditions can result from congestive heart failure, a condition when your heart doesn’t pump blood as well as it should.

2D echocardiography, a type of test, uses sound waves to create a detailed picture of your heart. It’s useful for looking at the size of both the right and left sides of your heart, measuring the average pressure in the pulmonary artery (the blood vessel carrying blood from your heart to your lungs) in cases of left to right abnormal blood flow through a hole, and analyzing the performance of your heart’s main pumping chamber (the left ventricle).

Coronary angiography, a test that uses dye and special x-rays to show the insides of your coronary arteries, near the heart, remains the main method for diagnosing and treating the abnormalities with coils and devices. These tubes carry blood around the heart, and issues with them can be life-threatening.

Multidetector computed tomography, a kind of scan that uses rotating x-rays to create a 3-dimensional image of your body, is useful for visualizing the 3D anatomy for the beginning, patency, and end of abnormal vessels.

Finally, magnetic resonance imaging (MRI)— a test that uses a magnetic field and radio waves to create detailed images of the organs and tissues within your body— can confirm the diagnosis. It shows a detailed picture of your blood vessels and can help identify complications like myocardial fibrosis (scarring of heart tissue) resulting from reduced blood supply.

Treatment Options for Coronary Arteriovenous Fistula

Spontaneous healing happens in about 1% to 2% of cases. Small fistulas that don’t cause any symptoms aren’t typically treated, but instead are watched closely for any related complications. According to guidelines from the American College of Cardiology and American Heart Association, fistulas larger than 250 mm should be closed, regardless of whether they’re causing symptoms or not. Symptoms can include myocardial ischemia, arrhythmia, ventricular dysfunction, and endarteritis.

Fistula closure can be done in two ways: with a non-surgical procedure called a percutaneous transcatheter approach, or with surgery through a sternotomy. Surgery is often recommended for larger fistulas with high blood flow, fistulas that are tortuous and aneurysmal, fistulas with multiple entry and exit points, and when there’s a need for a bypass to be done at the same time.

On the other hand, patients with a fistula origin near the surface of the body, a single drain site, non-complex fistulas that are easy to reach are suitable for a non-surgical occlusion procedure. This might involve the use of coils, detachable balloons, vascular plugs, or duct occluders.

What else can Coronary Arteriovenous Fistula be?

When doctors are determining if a patient has a coronary arteriovenous fistula, a condition where the heart arteries and veins have an abnormal connection, they might contemplate other causes that might explain similar symptoms. These causes may include:

• Patent ductus arteriosus (PDA)
• Rupture of sinus of Valsalva aneurysm (SVA)
• Pulmonary arteriovenous fistula (PAVF)
• Aortopulmonary window (APW)
• Anomalous origin of the left coronary artery from the pulmonary artery (ALCAPA)
• Prolapse of the right coronary cusp with a supracristal ventricular septal defect
• Internal mammary to pulmonary artery fistula
• Systemic arteriovenous fistula

For example, PDA is a heart issue that’s present from birth when an artery connecting the heart’s major vessels doesn’t close properly. Pulmonary arteriovenous fistula is another abnormal connection between the lung artery and veins, which might cause symptoms such as difficulty breathing, and discovering this issue often happens by chance during a chest imaging procedure. APW is another rare heart condition present from birth, where there’s a defect between two major heart arteries. ALCAPA, or Bland-White-Garland syndrome, is a rare heart-related birth defect, where the left and right heart arteries communicate through extensive collateral channels.

Each of these conditions may produce symptoms similar to a coronary arteriovenous fistula, so it’s crucial for physicians to conduct comprehensive examinations to ensure an accurate diagnosis.

What to expect with Coronary Arteriovenous Fistula

Patients who have surgery typically have a good outlook, and the surgical risks are low. The ultimate outcome depends on the severity of the shunt (an abnormal connection between blood vessels) and any accompanying issues like heart failure, infection of the heart valves (endocarditis), or high blood pressure in the lungs (pulmonary hypertension).

Certain surgical complications like the coil moving into the lung artery, the vessel wall being accidentally punctured with the guidewire causing clot formation, and heart attack can lead to death and illness shortly after operation.

Research indicates that the outcomes are generally comparable whether the procedure is done via an open technique or through a less invasive procedure, like a catheter. The ACC/AHA (American College of Cardiology/American Heart Association) suggests that patients with small asymptomatic fistula (an abnormal connection between heart chambers) should have an echocardiography (an ultrasound of the heart) every 3 to 5 years to check for enlargement of the heart chambers.

Possible Complications When Diagnosed with Coronary Arteriovenous Fistula

Coronary Arteriovenous Fistulas (CAVFs) can cause a variety of complications. These include:

• Enlargement of the coronary artery
• Formation of an aneurysm in the coronary artery
• Development of atherosclerosis, a disease where plaque builds up inside the arteries
• Infective endocarditis of the fistula, an infection of the heart’s inner lining
• Endarteritis, inflammation of the innermost layer of the arteries
• Obstruction or blockage
• Mural thrombosis, a condition where a blood clot forms in the heart’s wall
• Rupture or breakage
• Ischemia, a condition where blood flow to the heart is reduced due to the coronary steal phenomenon
• Heart rhythm disorders or arrhythmias
• Congestive heart failure in cases of large shunts
• Hyperkinetic pulmonary artery hypertension with a large left to right shunt, a condition where there’s increased pressure in the lungs due to excessive blood flow from the left to right side of the heart.

Preventing Coronary Arteriovenous Fistula

Small coronary artery fistulas (CAVFs) don’t usually cause symptoms, but patients still need regular heart scans to keep an eye on them. If these are detected early, the prognosis is positive. Doctors highly recommended prompt treatment for those who need it because it can lead to excellent results. However, even if a large fistula isn’t causing any symptoms, it needs to be fixed to avoid potential complications down the line.