Coronary Artery Fistula
December  2017

​A 34-year-old male applied for life insurance. He had no significant cardiac history or cardiovascular risk factors. Two years prior to the application he was evaluated for left side chest pain associated with shortness of breath that occurred while seated at work. 

An exercise nuclear myocardial perfusion imaging (MPI) study which showed inducible ischemia in the anterolateral wall prompted a cardiac catheterization which showed small fistulas between the left main and left anterior descending arteries and the pulmonary artery. He also had an exercise stress echocardiogram which showed no evidence of inducible ischemia. 

The case was reviewed by another interventional cardiologist who stated that these coronary artery fistulas were “too small to result in a symptomatic coronary steal syndrome.” Moreover, the atypical nature of symptoms which showed no relation to exertion and the lack of inducible ischemia on exercise stress echocardiogram made ischemia due to coronary steal unlikely. This led to a recommendation for no further intervention. Instead an investigation for non-cardiac causes of this applicant’s chest discomfort was begun.

What is a coronary artery fistula and what are the mortality implications?

A coronary artery fistula (CAF) is usually a congenital anomaly of a coronary artery such that it communicates either with a chamber of the heart (coronary-cameral fistula) or any segment of the systemic or pulmonary circulation (coronary arteriovenous fistula).Fistulas are rarely acquired due to trauma, postcardiac surgery or angioplasty. And they occur very rarely because of coronary aneurysm rupture.

In early fetal development, the primitive, loosely packed myocardium is nourished via sinusoids which communicate with the heart cavities. Persistence of these sinusoids may lead to coronary artery cameral fistulae. 

At approximately 32 days of gestation the myocardium becomes more compact and the sinusoids disappear to be replaced by a network of veins, arteries and capillaries that may have connections with other mediastinal vessels. Persistence of these connections leads to the formation of coronary artery fistulae.

CAF are present in 0.002% of the general population and are visualized in nearly 0.25% of patients undergoing catheterization. They account for 0.2-0.4% of congenital cardiac anomalies.

Approximately 50% of pediatric coronary vasculature anomalies are coronary artery fistulae. No race or sex predilection has been noted. 

Although some previous studies reported CAFs originate from the right coronary artery (RCA) in approximately 50% of cases, some authors mentioned that most CAFs originate from the left anterior descending artery (LAD). There are, however, certain predilections. More than 90% of fistulae open into right heart chambers or their connecting vessels. 

True AV fistulae to the veins themselves (coronary sinus or its major branches or the venae cava) are uncommon. Thus, about 40% connect to the right ventricle, 25% to right atrium, 15%-20% to the pulmonary artery, 7% to the coronary sinus and only 1% to the superior vena cava. Fistulas to the LV are very rare, representing about 3% of CAF.

Coronary artery fistula can present in patients at any age but may be suspected in early childhood when a murmur is detected in an asymptomatic child or when symptoms of congestive heart failure are present. Older children with murmurs may present with symptoms of coronary insufficiency. 

When CAF are small myocardial blood flow is not compromised, and the patient is usually asymptomatic. These small CAF are often discovered incidentally upon coronary angiography.

Various symptoms and signs may occur based on the type of fistula, shunt volume, site of shunt and presence of other cardiac conditions. When CAF are moderate to large, a continuous murmur may be heard on examination. In addition, there may be coronary artery steal, with resultant ischemia of the segment of myocardium distal to the fistula. This can cause chest pain, fatigue, palpitations or dyspnea. 

Increased blood flow causes the coronary artery proximal to the fistula to enlarge in a compensatory fashion.With increasing age, symptoms are more likely to appear, and the incidence of complication rises. Heart failure is the most common complication in the setting of large CAF.

Figure 1 - Viewing a Fistula

Selective left coronary artery (LCA) injection demonstrates a markedly enlarged left main (*) with normal size circumflex (CX) and left anterior descending (LAD) branches. The fistula continues across the right ventricle free wall to the atrioventricular groove where it terminates at the crux of the heart in the right atrium (straight arrow). (Reproduced from Congenital Heart Disease, Textbook of Angiocardiography)

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
The chest radiograph and electrocardiogram are normal if the shunt through the fistula is small but may show evidence of chamber enlargement or ischemia with a larger shunt and coronary artery steal. Significantly enlarged coronary arteries can be detected by two-dimensional echocardiography. 

The diagnosis of a coronary artery fistula can often be made with transthoracic two-dimensional and color Doppler echocardiography in children. In adults, however, two-dimensional transesophageal echocardiography may be more sensitive for detection of the entrance and termination site of the shunt, which is characterized by a continuous turbulent systolic and diastolic flow pattern.Coronary fistulae have also been detected noninvasively using 64-slice multidetector computed tomography. 

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 Magnetic Resonance. Several authors now advocate consideration of MDCT in imaging of coronary anomalies.

Figure 2 - Locating the fistula

MDCT 3-D volume rendering images showing the coronary fistula located between the left anterior descending (LAD) artery and the pulmonary artery.The size and anatomical features of the fistula can be reliably established during coronary angiography or with retrograde thoracic and aortic root aortography.

Natural history 
In the small fistulas, the myocardial blood supply is not compromised enough to cause symptoms, and spontaneous closure usually occurs. However, some small fistulae can dilate over time.

Large 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 fistulae.

The management of CAF in asymptomatic children is unclear and is dependent on the presence of symptoms, the clinical significance, the hemodynamic shunt dimension and the morphological appearance and characteristics of the fistula visualized with different imaging techniques.

Medical treatment for symptomatic relief is often used until investigations and operative repair can be performed. Most authors recommend CAFs be closed when there is a significant shunt flow (QP/QS=1.5:1) and/or when the patient is symptomatic. 

In a multicenter review, appreciably more problems related to operative risks and postoperative complications occurred after age 20 years.Transcatheter embolization techniques using coils, 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. 

Some fistulae are unsuitable for the transcatheter approach and are addressed surgically. A typical procedure includes a coronary artery bypass, opening the chamber into which the fistula drains, identifying the fistula and closing the abnormal communication with a patch or suture.

The main complications of CAFs are bacterial endocarditis, congestive heart failure, arrhythmia, pericardial effusion and premature atherosclerosis complicated by myocardial infarction or even sudden cardiac death. Myocardial infarction is seen rarely in cases of coronary to pulmonary artery fistulas. In a recent study, the prevalence of myocardial infarction was found to be 5%.

Results of both transcatheter and surgical approaches result in a good prognosis. Approximately 4% of patients may require additional surgery for recurrence. Life expectancy is usually considered normal. However, the risk of degenerative atherosclerotic disease may be higher if ectasia and dilatation of the coronary artery persist or progress.

Returning to the case 
It is unclear if the symptoms of this young male are related to a coronary steal syndrome because of the conflicting results of the nuclear myocardial perfusion study and the stress echocardiogram performed two years prior. Even if this fistula has been assessed as small, it involves two major coronary arteries, left main and LAD. It appears prudent to postpone and offer to reconsider with a more current evaluation of coronary artery disease including a transthoracic echocardiogram.

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