Coronary artery fistula
Synonyms and keywords: CAF, CAVF

# Overview
A 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 coronary arteries is otherwise normal.

# Anatomy
The coronary artery fistula can terminate in:
- Any of the cardiac chambers
- The vessels of Wearn that empty into the cardiac chambers
- The coronary sinus
- The SVC
- The pulmonary veins
- 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.

# Pathophysiology
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.

# Causes

## Congenital
Approximately 75% of coronary artery fistulas are congenital in origin. They develop at week 6 to 8 as a result of a defect in the coalescence of endothelial lined blood islands.

## Acquired
Acquired coronary artery fistulas occur in 25% of cases. They are caused by:
- Gunshot wounds and shrapnel
- Stab wounds
- Inadvertent placement of an SVG graft to a coronary vein
- Secondary to large atherosclerotic coronary aneurysms
- As a complication of acute MI
- Repeated endomyocardial biopsies in transplant patients with a fistula to the RV.

# 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 true incidence is unknown given that many coronary artery fistulas are small and undetected in life. Coronary artery fistula remains a postmortem diagnosis, and 15% of coronary artery anomalies are due to coronary artery fistulas.

# Natural History, Complications, Prognosis
- 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.
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 notclinical and angiographic features associated with CAF closure (symptomatic heart failure, angina and myocardial infarction) predict adverse outcomes.

## 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.
- Angiographic predictorsDrainage of CAF into the coronary sinus (P<0.001)
- 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.

# Differentiation form other Disorders
On angiography, a coronary artery fistula must be distinguished from a tumor blush, or arterial blood flow to a myxoma.

# Diagnosis

## 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.

## Physical Examination

### 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.

# Laboratory Findings

## 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.

# Treatment

## Surgery and Device Based Therapy

### 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.

# 2008 ACC/AHA Guidelines for the Management of Adults With Congenital Heart Disease (DO NOT EDIT)

## Coronary Arteriovenous Fistula (DO NOT EDIT)