Coronary artery fistula is defined as any abnormal luminal connection between 1 or both coronary arteries and the cardiac chambers or great vessels.¹ Coronary artery fistulae (CAFs) are a rare entity, found in 1 out of 50,000 live births and in 1 of 500 patients undergoing coronary angiography.² They may be congenital or acquired and, clinically, can range from completely asymptomatic to florid congestive heart failure and ischemia with electrocardiogram (ECG) changes and other typical presenting complaints.

In the majority of cases, CAFs are isolated, but they can be associated with other anomalies in 20% to 45% of cases. Common associated anomalies include tetralogy of Fallot, atrial septal defect, patent ductus arteriosus, and ventricular septal defect. CAFs are an important component of pulmonary atresia with intact ventricular septum, as they can provide the only blood supply to areas of the left ventricle.³

Acquired CAFs can be a consequence of surgical or percutaneous intervention, trauma, or infection. Most cases are congenital malformations, although an increased incidence of CAF to the right ventricle has been observed in the heart transplant population due to repeated endomyocardial biopsy.⁴ The presence of a CAF places the patient at increased risk of bacterial endocarditis, myocardial ischemia, arrhythmias, coronary aneurysm with or without rupture, coronary atherosclerosis, and hypervolemic chamber overload.⁵

Coronary artery fistulas are classified according to the Congenital Heart Surgery Nomenclature and Database Project completed in 2000, which incorporates the prior angiographic classification schema of Sakakibara et al⁶ along with the etiology of the lesion (acquired vs congenital), vessel of origin, and site of drainage.² In the era of percutaneous treatment, the morphology of the fistulous connection is also important to recognize. The condition was first treated in 1947 with surgical ligation, and in 1990, 2 separate groups first described transcatheter embolization of large coronary fistulas using both coils and detachable balloons.^7,8 There is a paucity of clinical data supporting any particular treatment modality, although outcomes are favorable with both percutaneous and open surgical techniques.^9-12 Current management favors catheter-based closure of these anomalies unless open fistula closure is to be performed as an adjunct to surgical correction of associated anomalies.

There are no clear guidelines regarding patient selection for fistula closure. Most authors agree that all symptomatic patients should be treated. There is no clear consensus regarding the management of asymptomatic patients. Criteria for closure of asymptomatic fistulae include presence of a systolic murmur, presence of a continuous murmur, and Qp/Qs >2.0 as a cutoff for significance, whereas others propose a shunt fraction greater than 1.5. Some groups recommend closure of fistulas >1.5 mm.¹³ Other authors have endorsed closure of all large fistulas to prevent future endocarditis¹⁴ or atherosclerosis.¹³ Some small fistulas in young patients will spontaneously close, and in low-risk cases, follow-up angiography could be considered.

In any case, anatomic considerations must inform the decision to pursue percutaneous fistula closure. The fistula should be accessible and safe to embolize. No large branches that could be inadvertently embolized should be near the fistula, and the neck should be narrow enough to be closed by available devices. Major contraindications to catheter-based closure include very young age or coronary arteries too small to catheterize, a large and wide-based fistula, multiple fistulas, a distal fistula, adjacent myocardial branches, and the need for other surgical repairs.⁵

Devices include the following:

1. 
   

   Coils (0.010-, 0.012-, 0.014-, 0.018-, 0.021-, and 0.035-inch diameters)

   
   
   
   
   1. 
      

      Pushable

      
      
   2. 
      

      Detachable

   
   
2. 
   

   Vascular plugs

   
   
3. 
   

   Septal occluders (atrial septal defect, ventricular septal defect)

   
   
4. 
   

   Duct occluders (patent ductus arteriosus)

Wang et al¹⁰ recently published a review of percutaneous treatment of CAF in 54 patients, including their technical approach. After selective coronary angiography, they selected a site within the fistula that was favorable to device occlusion. Optimal sites for occlusion include acute vessel curves¹⁵ or sites where the vessel narrows but that are far from normal coronary artery branches. Arterial side access to the fistula was attempted first in all cases, using a 2.5-Fr microcatheter in some cases to help navigate through difficult tortuosities.

In cases that had a more favorable occlusion site on the venous side or in which the device delivery catheter could not reach the occlusion site from the arterial side, an atrioventricular (AV) loop technique was used. After arterial catheterization, the guide wire was threaded through the fistula to the superior vena cava or pulmonary artery. The wire was then snared and exteriorized. The venous end of the wire then was used to place a 6- or 7-Fr delivery sheath into position. This technique was used in 21 of 32 patients, of whom 2 patients developed moderate or severe tricuspid regurgitation. When the AV loop technique was not used, no tricuspid regurgitation was reported. Other cases were approached from a more straightforward transvenous or transarterial approach.¹⁰ The Boston Children’s Hospital group used an AV loop method in all patients, and reported no resulting tricuspid regurgitation.¹²

Distal angiography should then be performed to identify any distal coronary side branches near the site of occlusion. If present, a detachable device should be used. In these cases, the authors deployed the device for 10 to 15 minutes under 12-lead ECG surveillance prior to releasing the device.¹⁰ Completion angiography was performed, followed by placement of additional devices if needed. Only 3 of 32 patients needed an additional device.

Acute myocardial infarction due to extension of thrombosis from the fistula has been reported following surgical and transcatheter coronary fistula closure.^10,16-18 In cases with a large residual cul-de-sac or a giant coronary artery aneurysm that has not been excluded from the arterial circulation, Wang et al¹⁰ recommend attempting to close the inflow to fistula or aneurysm, followed by dual antiplatelet therapy or therapeutic anticoagulation to prevent subsequent myocardial infarction due to progression of fistula thrombosis, again paying close attention to nearby normal coronary branch vessels.

The choice of a specific transcatheter device for the endovascular management of a CAF is traditionally predicated on considerations of both anatomic and physiologic characteristics of the individual lesion.

Relevant anatomic features that are commonly factored into device selection include the length, diameter, and morphology of the aberrant fistulous tract between the afferent and efferent vessels and the size of the parent vessel supplying the lesion and the vessel draining the fistula. In terms of the physiologic variables that warrant evaluation when planning therapy, flow through the fistula, perfusion of tissue by the feeding artery and its branches distal to the shunt, and perfusion of the tissue subtended by the vessel draining the fistula are all important to assess.

Coils

A variety of transcatheter agents have been used successfully to occlude coronary fistulas. Embolization coils are clearly the most traditional and versatile type of device employed. Their transcatheter placement is the most common embolization technique reported in the medical literature. Coils are available in multiple different configurations from simple cylindrical forms to a variety of preformed geometric shapes to amorphous strands ideal for packing. They are manufactured in multiple different coil diameters and lengths out of a wide variety of metallic (eg, platinum, nitinol, stainless steel) and nonmetallic (polymeric) materials of different diameters (0.010, 0.012, 0.014, 0.018, 0.021, and 0.035 inches).

The method of transcatheter deployment is typically classified as either pushable or detachable. Pushable coils are loaded into the delivery catheter from a cartridge and then advanced by means of a guide wire, usually of the same gauge, or a dedicated coil pusher. Once the coil segment is introduced to the target position at the catheter tip, it is either deployed by further guide wire advancement or injected using a syringe. In either case, the coil is not able to be repositioned or retrieved once it is outside the delivery catheter. Of course, a dedicated coil retriever, snare, or forceps can be subsequently used to retrieve a malpositioned coil, but this requires skill and time.

Detachable coils are a more recent advancement and allow the coil to be test placed before it is finally deployed. The coil and pushing “wire” are essentially one until a detach mechanism is activated and the distal coil becomes disconnected from the proximal delivery segment. Until the coil is detached, it may be advanced and withdrawn from the catheter multiple times until the desired morphology is achieved. There are many proprietary methods to allow detachment when the interventionalist is satisfied with the coil’s appearance. These include mechanical (eg, ball and claw, screw), electrical, radiofrequency, and other methods.

Irrespective of the particular type of delivery mechanism, coils are also selected based on a variety of anatomic factors, including the diameter and shape of the vessel tract and parking space or length available to deposit a coil pack.

The size of the coil is chosen to allow for an oversize of 15% to 30% depending on the target vessel diameter. This allows for some margin of tolerance in providing the necessary friction and interference fit between the coil and vessel wall. Ideally, this will prevent coil migration while providing a stable coil configuration to the coil matrix. A tight coil nest or pack promotes an accelerated tempo of vessel occlusion. If the coil is too oversized, it cannot reach its preformed shape and elongates into a sinusoidal strand that is not as effective.

The fundamental coil element may be supplemented with attached fibers or other supplemental agents to promote thrombus formation. Recently, coils with hydrogel polymeric jackets have been introduced. Once deployed, the polymeric coating swells to effectively enlarge the coil diameter so it occupies more space, filling in gaps in the coil matrix to facilitate vessel occlusion. Predictably, technologic developments will continue to contribute to coil use by providing new adjunctive features that will increase the efficiency of vessel occlusion.

The coil length is another variable to consider before selecting a devise. The labeled nominal length on coil package is the length of the device measured in its unconstrained or reconfigured shape. Depending on the diameter of the target vessel or fistula tract and the degree of coil oversizing based on the flow and critical importance of downstream tissue at risk from coil migration, the length of the deployed coil can be reasonably estimated. This calculus, however, takes operator experience to anticipate any elongation beyond the nominal length secondary to variable degrees of oversizing. Suffice it to say, this is not an exact science, and one should factor in a generous margin of error when selecting a coil length to match the available parking space.

Vascular Plugs

Vascular plugs are typically self-expanding nitinol mesh devices with or without a fabric covering that are placed via a catheter to occlude a blood vessel. Similar to embolization coils, vascular plugs come in a variety of sizes and designs depending on the target anatomy and the manufacturer.

The Amplatzer Vascular Plug (St. Jude Medical Inc., Saint Paul, MN) is the modern day prototype of the vascular plug. It was specifically designed for occlusion of arteries or veins within the peripheral vasculature. More recently, the original design has been modified to address specific anatomic challenges, and currently, there are 2 other devices in addition to the initial Amplatzer Vascular Plug—the Amplatzer Vascular Plug II and Amplatzer Vascular Plug 4. The plugs should be distinguished from the Amplatzer occluders, which are a family of devices comprised of 2 nitinol disks with or without a polyester fabric cover that are used to permanently occlude septal defects within the heart.

The original Amplatzer Vascular Plug is a cylindrical nitinol mesh with proximal and distal radiopaque markers. The proximal marker has a microscrew that attaches the plug to a 135-cm nitinol delivery wire. The plug comes in 7 sizes from 4 to 16 mm in diameter in 2-mm intervals.