Coronary Artery Fistula

Coronary artery anomalies include anomalies of origin, termination, structure or course. Coronary artery fistulae (CAF) are classified as abnormalities of termination and are considered a major congenital anomaly.

A coronary artery fistula involves a sizable communication between a coronary artery, bypassing the myocardial capillary bed and entering either a chamber of the heart (coronary-cameral fistula)[1] or any segment of the systemic or pulmonary circulation (coronary arteriovenous fistula). The pathophysiology of these lesions is identical, and they are often collectively termed coronary arterial-venous fistulae (CAVFs). A coronary artery connection to the pulmonary artery (coronary-pulmonary artery fistula) may also be considered under this grouping; however, if a named coronary artery arises directly from the pulmonary trunk with absence of a direct aortic connection, this is classified as an anomalous origin of the coronary artery from the pulmonary artery.[2]

Maude Abbott published the first pathological account of this condition in 1908. The first successful surgical closure of a coronary fistula was performed in 1947 by Bjork and Crafoord in a patient with a preoperative diagnosis of patent ductus arteriosus.

Most coronary artery fistulas are small, do not cause any symptoms, and are clinically undetectable until echocardiography or coronary arteriography is performed for an unrelated cause; they usually do not cause any complications and can spontaneously resolve. However, larger fistulae are usually 3 times the size of a normal caliber of a coronary artery and may or may not cause symptoms or complications.

Small fistulas usually do not cause any hemodynamic compromise. However, the larger fistulae can cause coronary artery steal phenomenon, which leads to ischemia of the segment of the myocardium perfused by the coronary artery. The pathophysiologic mechanism of coronary artery fistula is myocardial stealing or reduction in myocardial blood flow distal to the site of the coronary artery fistula connection. The mechanism is related to the diastolic pressure gradient and runoff from the coronary vasculature to a low-pressure receiving cavity. If the fistula is large, the intracoronary diastolic perfusion pressure progressively diminishes.[3]

The coronary vessel attempts to compensate by progressive enlargement of the ostia and feeding artery. Eventually, myocardium beyond the site of the fistula's origin is at risk for ischemia, which is most frequently evident in association with increased myocardial oxygen demand during exercise or activity. Over time, the coronary artery leading to the fistulous tract progressively dilates, which, in turn, may progress to frank aneurysm formation, intimal ulceration, medial degeneration, intimal rupture, atherosclerotic deposition, calcification, side-branch obstruction, mural thrombosis, and, rarely, rupture.

The factors that determine the hemodynamic significance of the fistulous connection include the size of the communication, the resistance of the recipient chamber, and the potential for development of myocardial ischemia. Occasionally, high-output congestive heart failure has been described.

Coronary artery fistulae may mimic the physiology of various heart lesions. Fistulae that drain (1) to the systemic veins or right atrium have a physiology similar to an atrial septal defect; (2) to the pulmonary arteries have physiology similar to a patent ductus arteriosus, (3) to the left atrium do not cause a left to right shunt but do cause a volume load similar to mitral regurgitation; and (4) to the left ventricle have physiology similar to that of aortic insufficiency.

Anatomy

Normally, two coronary arteries arise from the root of the aorta and taper progressively as they branch to supply the myocardium. A fistula occurs if a substantive communication arises that bypasses the myocardial capillary phase and communicates with a low-pressure cardiac cavity (atria or ventricle) or a branch of the systemic or pulmonary systems. Direct communication between a coronary artery and one of the cardiac chambers is noted. The origin of a fistula is rarely bilateral, involving both left and right coronary artery systems. Fistulous opening into a chamber or the drainage is mostly single or, rarely, double if both coronary artery systems are involved.

Normal thin-walled vessels present at the arteriolar level may drain into the cardiac cavity (arteriosinusoidal vessels) and venous communications (thebesian veins) to the right atrium. These small vessels do not steal significant nutrient flow and do not constitute fistulous connections. Fistulae can be small or large, dilated or ectatic, and tend to enlarge over time. Often, the limits of what constitutes a fistula and what constitutes a normal vessel are debated.

Major sites of origin of the fistulae are from the right coronary artery (40-60%), left anterior descending (30-60%), circumflex and a combination thereof. Most fistulae terminate in a venous chamber or vessel and, only rarely, into the left ventricle or the pericardium. The major sites of termination include the right side of the heart (90%), left ventricle, left atrium and the coronary sinus. The most frequent sites of termination in the right side of the heart, in descending order, are the right ventricle, right atrium, and pulmonary vasculature.

In the setting of cardiac outflow obstruction such as pulmonary atresia with intact septum, the term coronary-sinusoidal connections is preferred. In this setting, epicardial coronary blood may flow to and fro during the cardiac cycle. In systole, right ventricular flow decompresses via coronary-sinusoidal connections to the aorta in a reverse direction, while in diastole, the aorta perfuses the coronary artery in a normal antegrade fashion. This contrasts with coronary arteriovenous fistulae in the absence of outflow obstruction, in which coronary steal is the primary pathophysiologic problem. In pulmonary atresia and coronary-sinusoidal connections, myocardial ischemia, necrosis, fibrosis, and systemic desaturation may occur. Areas of coronary stenosis and/or interruption of the coronary system may complicate this abnormality.

Coronary fistula communications can be congenital and acquired. Congenital coronary artery fistulae may occur as an isolated finding or may appear in the context of other congenital cardiac anomalies or structural heart defects, most frequently in critical pulmonary stenosis or atresia with an intact interventricular septum and in pulmonary artery branch stenosis, tetralogy of Fallot, coarctation of the aorta, hypoplastic left heart syndrome, and aortic atresia.

Acquired coronary artery fistula may rarely arise as a consequence of trauma such as a gun shot wound or a stab wound. They can also occur after cardiac surgery or invasive cardiac catheterization with percutaneous transluminal coronary angioplasty, pacemaker implantation, or endomyocardial biopsy.

Embryology

Coronary artery fistulae are thought to arise as a persistence of sinusoidal connections between the lumens of the primitive tubular heart that supply myocardial blood flow in the early embryologic period. Coronary artery fistulae occur in the absence of any outflow obstruction. Another explanation may be faulty development of the distal branches of the coronary artery rectiform vascular network.

When these channels persist in association with outflow obstruction (eg, pulmonary atresia), they are a variant form of fistulae termed coronary-sinusoidal connections. Associated syndromes most often associated with coronary-sinusoidal connections include pulmonary atresia or stenosis with an intact ventricular septum.

Most coronary artery fistulae are congenital and may be found in patients with structurally normal hearts. A specific variant form of coronary artery fistula (coronary-sinusoidal connection) that occur in association with congenital heart disease arise most often in association with severe right or left ventricular outflow obstruction, such as pulmonary atresia with intact ventricular septum or aortic atresia with hypoplastic left heart syndrome. In outflow obstructions, the fistula serve to decompresses the ventricle in a retrograde flow fashion.

Rarely, acquired forms of coronary artery fistula may occur as a result of septal myectomy in association with hypertrophic cardiomyopathy, muscle bundle resection in operative repair of tetralogy of Fallot, as a complication of radiofrequency ablation of accessory pathways, penetrating or nonpenetrating trauma, endomyocardial biopsy, permanent pacemaker implantation, or as a complication of coronary arterial procedures.

United States statistics

The prevalence of coronary artery fistulas was thought to be 0.05-0.25% of the population, based on findings in standard coronary angiography studies. However, coronary computed tomography (CT) angiography has been found to detect more coronary artery fistulas,[4, 5] with the prevalence found to be 0.9%.[6, 7] Approximately 50% of pediatric coronary vasculature anomalies are coronary artery fistulae.

Race-, sex-, and age-related demographics

No race or sex predilection is noted.

Coronary artery fistula may present in patients at any age but is usually suspected early in childhood when a murmur is detected in an asymptomatic child or with symptoms of congestive heart failure. Older children with murmurs may present with symptoms of coronary insufficiency. In a multicenter review, appreciably more problems related to operative risks and postoperative complications occurred after age 20 years.[8]

Results of both transcatheter and surgical approaches indicate a good prognosis. Approximately 4% of patients may require additional surgery for recurrence. Life expectancy is considered normal. However, risk of degenerative atherosclerotic disease may be higher if ectasia and dilatation of the coronary artery persist or progress. In young surgical patients, anticipate the involution of the dilated segment of the feeding vessel; this is not the case in adults.

Morbidity/mortality

Fistula-related complications are present in 11% of patients younger than 20 years and in 35% of patients older than 20 years.

Fistulae can be associated with the following complications:

• Myocardial ischemia

• Mitral valve papillary muscle rupture from chronic ischemia

• Ischemic cardiomyopathy

• Congestive heart failure from volume overload

• Bacterial endocarditis

• Sudden cardiac death

• Secondary aortic valve disease

• Secondary mitral valve disease

• Premature atherosclerosis

Small fistulas remain clinically silent and are recognized at routine echocardiography and autopsy. In the small fistulas, the myocardial blood supply is not compromised enough to cause symptoms. Spontaneous closure usually occurs; however, some can dilate over time.

Larger fistulae progressively enlarge over time, and complications, such as congestive heart failure, myocardial infarction, arrhythmias, infectious endocarditis, aneurysm formation, rupture, and death, are more likely to arise in older patients. Spontaneous closure has been rarely reported in the setting of large fistulas.

The mortality rate related to surgical repair of coronary artery fistula typically ranges from 0-4%. Variations that may increase surgical risk include the presence of giant aneurysms and a right coronary artery–to–left ventricle fistula. Complications of surgery include myocardial ischemia and/or infarction (reported in 3% of patients) and coronary artery fistula recurrence (4% of patients).

Complications

Complications of surgery include myocardial ischemia and/or infarction (reported in 3% of patients) and recurrence of the fistula (4% of patients).

Major complications associated with transcatheter embolization relate to manipulation of stabilizing catheters and wires in the coronary vasculature and may include coronary artery spasm, ventricular dysrhythmias, and perforation. Inappropriate positioning or proximal extension of occlusive coils or devices may result in obstruction of side branches and muscle loss. Intimal dissection of the coronary artery or thrombosis also may occur. However, morbidity and mortality rates generally are considered to be low.

Most children with small coronary artery fistulae (CAF) are asymptomatic, and continuous murmur may be audible on routine examinations if the fistulae are moderate to large in size. In infants, angina may be recognized by symptoms such as irritability, diaphoresis, pallor, tachypnea, and tachycardia. Most infants present at age 2-3 months after the pulmonary vascular resistance has decreased with heart failure symptoms, such as tiredness during feeding, tachypnea and excessive diaphoresis during feeds, wheezing, episodic pallor, and failure to thrive. Thus, in infancy, they can present with signs of low-output congestive heart failure.

Older patients may present with signs of low-output congestive heart failure, arrhythmias, syncope, chest pain, and, rarely, endocarditis. Patients with large fistulae may present with high-output congestive heart failure, although rarely. In older patients, symptoms may include the following:

• Dyspnea on exertion

• Angina

• Fatigue

• Palpitations

Most patients are asymptomatic, especially when the fistulas are small. Note the following:

• A coronary artery fistula is suspected following detection of a continuous murmur upon routine examination. Upon clinical examination, the murmur is suggestive of patent ductus arteriosus but is heard lower on the sternal border than usual; thus, the location is often atypical for a patent ductus arteriosus. In addition, the murmur may have an unusual diastolic accentuation, and the continuous murmur of a coronary artery fistula often peaks in mid-to-late diastole, which is uncharacteristic of the systolic accentuation in a patient with patent ductus arteriosus.

• If the fistula connects to the left ventricle, only an early diastolic murmur may be heard, as little coronary flow is evident during the period of systole.

• Some patients with fistulae with a large shunt may present with signs of congestive heart failure and angina.

• Wide pulse pressure and collapsing pulse may be noted.

• The apex beat is diffuse with a palpable or audible third heart sound (S3) gallop in a large fistula. Heart sounds are often reduced in intensity.

• A holosystolic murmur of mitral valve insufficiency is audible at the apex.

Cardiac enzyme levels may be elevated in patients with coronary artery fistulae (CAF).

In addition, brain natriuretic peptide levels may be elevated in cases with heart failure.

Chest radiography

Chest radiography findings are generally normal in cases of coronary artery fistulae, except in the presence of significant shunt flow, at which time cardiomegaly may be evident. In addition, pulmonary venous congestion and interstitial edema may be seen.

Electrocardiography

Electrocardiography (ECG) findings are usually normal. However, in some cases, ECG can reveal changes in the setting of larger fistulas. ECG may reveal the effects of volume load on the left ventricle and left atrium. Rarely, in the presence of coronary steal, ischemic changes and/or arrhythmias may be evident.

Echocardiography

Echocardiography is helpful in diagnosing most fistulae and may reveal the following:

• Left atrial and left ventricular enlargement as a result of significant shunt flow or decreased regional or global dysfunction as a result of myocardial ischemia

• Dilatation of the coronary artery: The feeding coronary artery often appears enlarged, ectatic, and tortuous.

• High-volume flow: This may be detected by color-flow imaging at the origin or along the length of the vessel

• Drainage of the fistula: Carefully seek the site of drainage; often, it is evident as a disturbed flow signal, most frequently within the right ventricle.

• Holodiastolic run-off in the descending aorta

• A squirt of color flow into a chamber without significant dilatation of the coronary artery in cases of small coronary artery fistulas

• A dilated coronary sinus, if fistula terminates in the coronary sinus

Cardiac catheterization and aortography

Cardiac catheterization remains the modality of choice for defining coronary artery patterns of structure and flow. Most frequently, intracardiac pressures are normal and shunt flow is modest. Aortography is shown in the first image below, and selective coronary arteriography is shown in the second image below.

Both studies supply the information required to manage the condition. In addition, therapeutic embolization using occlusive coils or devices may be performed via catheterization.[9]

Magnetic resonance imaging and computed tomography scanning

Reliable, complete, noninvasive 3-dimensional imaging of the coronary vasculature is advantageous. Traditionally, magnetic resonance imaging (MRI) has been a good alternative for imaging proximal coronary abnormalities, and newer imaging sequences have provided improved anatomic imaging as well as indices of coronary flow and function. Spatial resolution is often limiting, and the distal course and insertion of the fistulous connection may not be well imaged.

Multidetector row computed tomography (MDCT) cardiac imaging has provided excellent distal coronary artery and side branch imaging. Imaging of an entire 3-dimensional volume and the heart can be acquired within 20 seconds, with better temporal and spatial resolution than MR. Several authors now advocate consideration of MDCT in imaging of coronary anomalies (as is shown in the image below).[10]

In a preoperative study, Shi et al found that dual-source computed tomography (DSCT) enabled accurate assessment of morphological features, quantitative features, and associated coronary artery lesions among 34 patients with coronary artery fistula. They used DSCT to morphologically and quantitatively analyze CAF, and they found that DSCT was as accurate as surgery (R = 0.95-0.98, P < 0.001). With DSCT, they identified 15 patients with left-sided CAF, 9 with right-sided CAF, and 10 with bilateral CAF, and they found that drainage was most commonly in the main pulmonary artery (41.2%).[11]

A retrospective study by Lim et al suggested that CT angiography is useful in detecting coronary artery fistulae. The study included 6341 patients who underwent coronary CT angiography; coronary artery fistulae were found in 56 patients (0.9%), a higher percentage, according to the investigators, than has generally been found using conventional angiography. Moreover, CT angiography found coronary artery fistulae to lead most commonly to the pulmonary artery, rather than, as conventional angiography has indicated, to the ventricle.[6]

Nuclear imaging

Stress thallium studies may be used to document areas of myocardial ischemia before and after operative repair.

In childhood, most patients with coronary artery fistulae (CAF) are asymptomatic; however, some patients may present with symptoms of dyspnea on exertion, increased fatigability, and, possibly, signs of high-output congestive heart failure. Rarely, patients may present with angina,[12] palpitations, or signs of exercise-related coronary insufficiency. Direct medical treatment for symptomatic relief can be used until investigations and operative repair can be performed. Spontaneous closure may occur in small fistulae. Small fistulous connections in the asymptomatic patient may be monitored.[13] Most lesions enlarge progressively and warrant operative repair, either by transcatheter or surgical techniques.

Endocarditis and other complications are risks, and patients should be monitored for the same. In older individuals, the fistulae can rarely get obstructed with progressive atherosclerosis and cause resolution of symptoms.

Diagnostic cardiac catheterization should be performed initially with or without additional therapeutic intervention. Initial diagnostic catheterization should both define hemodynamic significance of the lesion and provide detailed angiographic assessment of the anatomy of the abnormality, in particular, the origin, course, regional narrowings, and the nature of the insertion.[14]

Procedural options can be optimized by careful identification of the number of fistulous connections, nature of feeding vessel or vessels, sites of drainage, and quantification of myocardium at risk for injury or loss and the hemodynamic shunt related to the fistula (ie, Qp:Qs). The goal of treatment is the obliteration of fistulae, while preserving normal coronary blood flow. The risk of presence of fistula should be balanced with the risk of complications with procedures to occlude the fistula.

Therapeutic transcatheter embolization

Indications

In view of the natural progression in larger fistulae to dilate over time, with progressively increasing risk of thrombosis, endocarditis, or rupture, the general advice is to close all but the small fistulous connections. In borderline situations, provide close echocardiographic or angiographic follow-up imaging to identify enlargement of feeding vessel in asymptomatic patients. Patients with large fistulae, multiple openings, or significantly aneurysmal dilatation may not be optimal candidates for transcatheter closure.

Technique

Transcatheter embolization techniques using coils (as is shown in the image below), bags, or other devices can be performed on an outpatient basis at the time of diagnostic studies or later, and may obviate the need for cardiac surgical intervention.

Generally, the course of the fistulous tract is delineated angiographically, selectively catheterized, and wired along its entire length. A delivery catheter or sheath is then positioned antegradely or retrogradely along the stabilizing wire for delivery of a suitable occlusive coil or device. The occlusive device is positioned so as to minimize myocardial muscle loss or injury. Often multiple devices or coils may be required for effective occlusion.

The transcatheter approach is, frequently, a fairly complicated intervention and requires an experienced operator and interventional specialist with expertise in both coronary arteriography and embolization techniques. Embolization often requires complicated catheter manipulation, as well as selection of various catheters and wires.

Results

To date, the literature has primarily provided only case reports and reports of small series. Results have been comparable to surgery without associated morbidities of cardiopulmonary bypass and/or sternotomy.

In a retrospective analysis of all patients with coronary artery fistula diagnosed between 1993 and 2014 (N=194), Christmann et al found that treatment was indicated in 10 patients (5.2%) and treated 6 of these patients via a catheter interventional approach. Five days after interventional closure, one patient showed a significant residual shunt through the fistula, thereby necessitating surgical removal of the device and closure of coronary artery fistula. At a median follow-up of 7 years, the other five patients who were treated with a catheter interventional approach showed successfully closed coronary artery fistula without thrombosis of the coronary artery.[15]

Cardiac surgical intervention

Indications

Indications for surgical intervention are the same as in embolization (see above). Some fistulae are unsuitable for the transcatheter approach and preferably are addressed surgically. These coronary artery fistulae may include fistulae with multiple connections, circuitous routes, and acute angulations that make catheter positioning difficult or impossible.

Techniques

Surgical repair usually is approached via a median sternotomy and cardiopulmonary bypass. Identify the feeding vessel and delineate its course and site of insertion. Identify the site of presumed fistulous drainage prior to institution of the cardiopulmonary bypass. Transesophageal echocardiographic imaging has been very useful in assisting in the location of fistulous tract insertion.

A typical procedure includes opening the chamber into which the fistula drains, identifying the fistula, and closing the site of drainage with a patch or suture. If the fistula enters the ventricle or if the feeding vessel is large, the coronary artery is opened, and the opening to the fistula is closed with a running suture. The arteriotomy is closed. Large aneurysms may require excision. Rarely, when the fistula is an end artery, it may be ligated with or without bypass.

Most patients should anticipate no restrictions on activity; however, patients who wish to compete in athletic endeavors should undergo stress testing and may be at marginally increased risk for dysrhythmias and sudden death.

Provide follow-up care after hospital discharge to check for evidence of ischemia or recurrence of coronary artery fistulae (CAF). Individuals who have undergone coronary surgical interventions and, particularly, patients who have sustained cardiac muscle loss should have ongoing cardiac follow-up monitoring that may include stress studies and repeat angiography as needed.

Patients treated surgically and with transcatheter techniques should receive maintenance doses of antiplatelet agents and, perhaps, an anticoagulant regime for the first 6 months postoperatively, until the operative surface has undergone endothelialization. Patients with persisting aneurysmal dilatations may benefit from prolonged antiplatelet agents.

Patients remain at risk for development of endocarditis until the flow is stopped and should receive antibiotic prophylaxis for any dental, gastrointestinal tract, and urologic procedures if associated with a cyanotic heart disease.

The primary therapeutic approach to coronary artery fistula (CAF) is interventional catheterization or surgery. Although medical therapy is seldom indicated, patients may require symptomatic treatment of congestive heart failure and/or coronary insufficiency until definitive treatment can be performed.

All patients should have good oral hygiene because they are at risk for endocarditis. Antibiotics for endocarditis prophylaxis are no longer required for isolated coronary artery fistulas before performing procedures that may cause bacteremia. However, endocarditis prophylaxis is indicated in the setting of a cyanotic congenital heart disease. For more information, see Antibiotic Prophylactic Regimens for Endocarditis. Guidelines for antibiotic prophylaxis in cardiac surgery have been established.[16, 17]