Coronary Arteriovenous Fistula

Excerpt

Coronary arteriovenous fistula (CAVF) is a rare form of congenital heart disease. However, it is the most common type of congenital coronary artery anomalies..An arteriovenous fistula is an abnormal conduit between the artery and vein, typically bypassing the capillaries in between. When present between the coronary artery and cardiac chambers, it is called a coronary cameral fistula. The fistula can also be present between a coronary artery and another adjacent vessel from pulmonary or systemic circulation. A patent fistula provides a low resistance flow, shunting the blood directly from an artery into a vein, cardiac chamber, or another low-pressure vessel like the pulmonary artery. Patients with CAVF can develop symptoms at birth or a later age, depending on the type of fistula and the presence of collateral circulation. Studies have reported an association between ventricular arrhythmias and sudden cardiac death syndromes in young adults and athletes in certain types of coronary anomalies like the anomalous origin of the left coronary artery from the pulmonary artery (ALCAPA). Exertional dyspnea and angina pectoris from myocardial ischemia or endocardial fibrosis are the predominant symptoms in adults. Typically, these patients have extensive collateral formation.

Human coronary circulation comprises of two main epicardial coronary arteries. They arise from the coronary ostia located in the coronary sinus of Valsalva situated just above the aortic valve cusps. The aortic valve is tricuspid and consists of the right coronary cusp, left coronary cusp, and noncoronary cusp. The left coronary artery (LCA) originates from the left coronary sinus and branches into the left circumflex and the left anterior descending artery (LAD). The left circumflex artery supplies the anterolateral and posterolateral left ventricular walls. The left anterior descending artery supplies the anterior septum, the anterior free wall at the base and mid cavity level, apical septum, anterior wall, and apical cap. The right coronary artery (RCA) arises from the anterior aortic sinus or the right coronary sinus. It supplies the right atrium, right ventricle, sinoatrial (SA) node, and atrioventricular (AV) node. The posterior descending artery, a branch of RCA, provides blood supply to the inferior septum, the inferior free wall, and posterior left ventricular segments. The right coronary artery dominant variant is 80%.

The right coronary artery is the most common site of origin for CAVFs, found in approximately 50% of patients. Other sites include the left anterior descending artery in 35% to 40%, the left circumflex artery in 5% to 20%, and both coronary arteries in 5%. Approximately 90% of the fistulas drain into the low-pressure venous circulation. The most common drainage sites are the right ventricle 41%, right atrium 26%, pulmonary artery 17%, coronary sinus 7%, left atrium 26%, left ventricle 3%, and superior vena cava 1%.

A coronary arteriovenous fistula may lead to coronary artery dilatation due to increased flow, hyperkinetic pulmonary artery hypertension due to the large left to right shunt, congestive heart failure, myocardial ischemia from coronary steal phenomenon and thrombosis or aneurysm of fistula.