Discussion
Congenital CAFs occur with equal frequency in both sexes, there is no research to suggest a correlation to ethnicity. In the general population, the occurrence of coronary anomalies ranges from 0.2% to 1.2%, with CAFs constituting 0.002% of these cases. Among CAFs, solitary fistulas are more prevalent, and approximately 75% of incidentally discovered CAFs exhibit no clinical symptoms. (1)
The RV serves as the most common drainage site for CAFs, representing 34.9% of reported cases. The RA and the PA rank as the second most frequent drainage sites, each comprising 27% of cases, followed by the left ventricle at 6.3%. The coronary sinus accounts for 3.2% of cases, and lastly, the left atrium makes up 1.6% of occurrences. (7)
The most common types of CAFs have a congenital etiology. Anomalies in the coronary arteries can arise from various sources, including the persistence of rudimentary embryonic coronary arterial structures, disruptions in normal development or atrophy processes, and misplacement of connections within an otherwise typical coronary artery. (1,8)
CAFs can be classified based on their size: small, medium, or large, depending on whether the fistula diameter is < 1, between 1 to 2, or > 2 times the largest diameter of the coronary vessel that does not supply the coronary fistula. They can also be categorized according to the drainage site: coronary-cameral fistula (the most common), coronary-to-pulmonary artery fistula, coronary artery-to-coronary sinus, and coronary artery-to-bronchial artery fistula. (2,9) A shunt from left to right (coronary artery to right vessels or chambers) leads to an ongoing flow throughout the entire cardiac cycle, driven by the lower pressure within the right structure (vessel or chamber) in comparison to the myocardial capillaries or arterioles. This often gives rise to a volume overload on the right side, although this pathophysiological mechanism can also involve chambers on the left side. (1)
Symptoms typically arise around age 18, with dyspnea being the primary symptom, accompanied by fatigue, congestive heart failure and pulmonary hypertension. Possible complications encompass coronary artery dilation, aneurysm formation, intimal ulceration, medial degeneration, intimal rupture, atherosclerotic deposition, calcification, side-branch obstruction, mural thrombosis, and rupture. Notably, angina pectoris is rare without arteriosclerotic coronary artery disease. (3,4)
A characteristic physical finding in patients with CAFs is the presence of a gentle, continuous murmur. This murmur typically follows a crescendo-decrescendo pattern in both systole and diastole, with its intensity being more pronounced during diastole. (3) Depending on the location where the fistula connects to the heart, the murmur will be most audible at certain points on the chest wall. (4)
Diagnosing CAFs can be challenging. Initial assessment includes an electrocardiogram, with findings based on the fistula’s location and flow. Selective invasive coronary angiography used to be the reference standard. It enables precise visualization of the anatomy of the CAF, including fine vessels, with high temporal and spatial resolution and yields hemodynamic information. In addition, it facilitates the diagnosis and therapeutic embolization. However, conventional coronary angiography is invasive and involves risks of procedure related complications. Furthermore, it yields two-dimensional projection images, which are often limited in the delineation of the complex anatomy of abnormal communications, with reported correct diagnosis rates of 35%–50%. (5).
Selective invasive coronary angiography has been replaced by TTE, the now preferred initial assessment method. TTE can show dilated coronary arteries (coronary artery fistulas that are large and/or have a diameter greater than 3 mm) and distal drainage via color flow mapping in CAF cases. (9) However, it’s less effective for small shunts and pulmonary artery fistulas. Microbubbles enhance color Doppler signals to pinpoint CAF locations. (7) Two-dimensional echocardiography displays heart enlargement and function, but not fistula function. (4)
MDCT is a valuable alternative to echocardiography and catheter angiography for evaluating anomalies, with its increased use leading to enhanced anomaly recognition due to improved sensitivity in volumetric data acquisition and pre-procedural planning for patients with larger communications to specific heart chambers, defining fistula characteristics and assisting in treatment approach decisions, device selection, embolization predictions, and optimal fluoroscopic angle identification. (7,10)
DSCT with ECG gating provides high-resolution images in a shorter time frame through a single breath-hold, with superior temporal and spatial resolution compared to MRI. Volume-rendered images from three-dimensional CT data sets offer comprehensive views of cardiac and vascular anatomy, aiding surgical planning by clarifying anatomical complexities. The primary downside of CT lies in radiation exposure risk, which can be mitigated by modern DSCT scanners and advanced dose reduction techniques. (7,10)
The updated 2018 American College of Cardiology/American Heart Association guidelines underscore the significance of a collaborative heart team approach to assess the suitability and feasibility of CAFs closure at centers proficient in both percutaneous and surgical closure techniques. (11)
Common clinical scenarios warranting consideration for CAFs closure encompass evidence of ischemia in the feeder artery territory, arrhythmias suspected to be linked to CAFs, endarteritis, vessel rupture, cardiac chamber enlargement, and ventricular dysfunction. It’s crucial to highlight that small CAFs tend to close spontaneously over time, allowing for monitoring without intervention. In contrast, medium to large sized fistulas can expand, particularly in pediatric and young adult patients, often associated with proximal coronary artery dilation signifying prolonged high shunt flow. Medium-sized fistulas are ideally closed early to prevent further growth, as closing larger fistulas carries a heightened risk of myocardial infarction. (2)
Hyun Woo Goo’s 2021 review outlined the following as contraindications (9) for percutaneous transcatheter closure: fistulas draining near the atrioventricular annulus, extreme tortuosity, a very small patient size that complicates the procedure, as well as multiple communications and drainage sites.