Coronary artery fistula

Associate Editor-in-Chief: Keri Shafer, M.D. [mailto:kshafer@bidmc.harvard.edu]

Overview
Coronary artery fistula is any abnormal communication through which coronary artery blood is shunted into a cardiac chamber, great vessel, or other vascular structure without first passing through the myocardial capillary bed. The number, origin, and course of the arteries is otherwise normal.

About 25% of fistulas are not associated with any other type of anomaly. The most common associated congenital anomaly is pulmonic or aortic valve atresia with or without a VSD.

Epidemiology and Demographics
The incidence in angiographic studies is .08% to .3% (usually an incidental finding at the time of angiography for another problem), but is important to know that the total incidence is unclear because many coronary artery fistulas are small and undetected in life. It is often still a postmortem diagnosis, in which 15% of coronary artery anomalies are coronary artery fistulas.

Anatomy
The coronary artery fistula can terminate in:
 * 1) Any of the cardiac chambers
 * 2) Thebesian veins that empty into the cardiac chambers
 * 3) The coronary sinus
 * 4) The SVC
 * 5) The pulmonary veins
 * 6) The mediastinal vessels

Incidental fistulas are more likely to be multiple. If the coronary artery fistula is originated from the left coronary artery, is less likely to terminate in the RV.

Symptomatic fistulas from case reports are more likely to be single, require surgery, cause chest pain, result in a continuous murmur, and drain into the RA or RV.

Fistulas may enter as a single vessel or as a plexus with multiple small entry sites, the fistulous opening may occur at the end of a main vessel or one of its branches or in the middle of the vessel forming a side-to-side anastomosis.

Progressive dilatation of the fistulous connection can occur due to the effect of increasing flow through the vessel over time, rather than a defect in the vessel wall.

Etiology & Pathophysiology
Most coronary artery fistulas are congenital in origin. They occur at week 6 to 8 as a result of a defect in the coalescence of endothelial lined blood islands.

Acquired coronary artery fistulas are rare. They are caused by:


 * 1) Gunshot wounds and shrapnel
 * 2) Stab wounds
 * 3) Inadvertent placement of an SVG graft to a coronary vein
 * 4) Secondary to large atherosclerotic coronary aneurysms
 * 5) As a complication of acute MI
 * 6) Repeated endomyocardial biopsies in transplant patients with a fistula to the RV.

When the coronary fistula connects to a right-sided chamber or vessel (RA, RV, or PA), there is a left-to-right shunt with increased flow delivered to the pulmonary circulation and ultimately to the left heart.

The left-to-right shunt is usually small with a 1.5:1 ratio, not infrequently the magnitude of the shunt is so small as to not be quantifiable by oximetry, indicator dilution methods etc.

Large fistulas draining into the LA or the LV can cause volume overload similar to that caused by aortic insufficiency.

Patients with coronary artery fistulas can experience myocardial infarction in the absence of other coronary artery pathology. This can because the fistula competes for flow with the normal circulation.

Since the coronary circulation often has a higher resistance to flow there can be coronary steal, and effect can be visualized on thallium scanning.

Using electromagnetic flow probes, studies have shown a 2.5 fold increase in flow to the distal vessel when the fistula is occluded.

Symptoms and the scintigraphic abnormality may disappear with ligation.

Natural History

 * Highly variable. Many patients remain asymptomatic, others develop symptoms after a long asymptomatic period.


 * Spontaneous closure can occur in infancy, but is unusual in adulthood.


 * Those that are due to endomyocardial biopsy have been shown sometimes to close spontaneously.


 * MI and bacterial endocarditis are rare.

Symptoms

 * CHF occurs in about 20% of these patients, usually with fistulas draining into the RV or RA.
 * Those draining into the left side of the heart cause dyspnea, fatigue or ischemia.
 * There is no good relationship between the size of the fistula and symptoms.

Heart

 * The most common physical finding is a continuous murmur.
 * If the fistula is connected to the pulmonary artery, then the murmur will be best heard in the left 2nd or 3rd interspace.
 * With fistulas draining into the RA, the murmur is best heard to the right of the sternum.
 * Fistulas draining into the RV or LA are best heard at the lower left sternal border or subxyphoid areas. Usually the diastolic component is louder in a fistula to the RV because the decreasing size of the hole during systolic contraction, and the systolic component is louder when connected to the PA or the atria.
 * Fistulas to the LV are least likely to cause a murmur.

Electrocardiogram

 * May show chamber enlargement

Chest X Ray

 * Chest x-ray may show cardiomegaly and increased pulmonary vasculature.

Echocardiography or Ultrasound

 * A coronary artery fistula can be visualized on ECHO as an enlarged lumen arising from the aortic root or in a more distal location, with continuous or turbulent flow. Angiographic confirmation is usually necessary.

Indications for Surgery

 * Surgery is necessary for the management of symptomatic fistulas. Murmurs are more frequent in those with symptoms and in those who ultimately require surgery.

Surgical Outcomes

 * Mortality rate of 0-1.7% in surgical series.


 * Most have an improvement in symptoms postoperatively.

Recent Research
In the March 2010 Circulation article titled “Predictors of Long-Term Adverse Outcomes in Patients With Congenital Coronary Artery Fistulae”, Valente et al discuss long-term outcomes of patients with treated and untreated coronary artery fistula (CAF) closure. Specifically, investigation was directed at whether or not clinical and angiographic features associated with CAF closure (symptomatic heart failure, angina and myocardial infarction) predict adverse outcomes.

Data
76 CAF patients who underwent diagnostic cardiac catheterization at Children’s Hospital Boston from 1959-2008 were studied. 20% of these patients suffered additional congenital heart disease.

64 patients underwent surgical closure (44 witnessed transcatheter closure and 20 underwent surgical repair). 3 of these patients underwent a second intervention (repeat surgery was performed on 1 of the patients and 2 patients underwent a second transcatheter closure). 1 of the 44 transcatheter closure patients went in for a repeat procedure for residual fistula.

12 patients experienced no intervention.

Major Complications
11 patients (15%) experienced symptomatic cardiomyopathy, coronary thrombosis and MI.

Predictors of adverse outcome
Both angiographic and clinical features were predictive of adverse outcome.


 * 1) Angiographic predictors Drainage of CAF into the coronary sinus (P<0.001)
 * 2) Clinical predictors *Hyperlipidemia (P<0.001) *Systemic hypertension (P<0.001) *Older age at diagnosis (P<0.001) *Diabetes (P=0.05) *Tobacco use (P=0.006)

Long-term complications
The investigators conclude that long-term complications of CAF closure may include:
 * Myocardial infarction (MI)
 * Coronary thrombosis
 * Cardiomyopathy

Further considerations
Long-term anticoagulation is suggested as treatment for the high-risk CAF that drain into the coronary sinus. This condition is likely to be associated with long-term morbidities after closure.

Acknowledgements
The content on this page was first contributed by Dr. Leida Perez