Coronary artery fistulas are sizable pathologic connections between the coronary artery and the cardiac cavity or a venous vessel. Fistulas are seen in 0.1% of patients who undergo coronary angiography. The mean age for the diagnosis of coronary artery fistula is 32±14 years.¹

Case Presentation
A 62-year-old woman presented to the emergency department with difficulty in speech, deviation of the mouth, and right upper-limb weakness. The symptoms began about 90 minutes earlier, upon her waking up in the morning. Her medical history included hypertension and recurrent chest pain associated with exertion but no shortness of breath, orthopnea, or paroxysmal nocturnal dyspnea. Recent exercise and nuclear stress test results showed no evidence of ischemia. Her daily medications included aspirin 325 mg, atenolol 50 mg, and hydrochlorothiazide 25 mg.

Physical examination showed the patient was alert and in no distress. Her pulse rate was normal and blood pressure slightly elevated at 131/91 mm Hg. Cardiovascular examination was unremarkable. Neurologic examination revealed dysarthria, right facial weakness, and right hemiparesis. The right plantar reflex was up-going. A diagnosis of acute cerebrovascular accident was made based on the clinical findings.

A noncontrast computed tomography (CT) scan of the brain showed multiple old bilateral lacunar infarcts but no evidence of an acute intracranial event. Electrocardiogram (ECG) showed sinus bradycardia with left ventricular hypertrophy. Cardiomegaly was evident on chest x-ray.

 Because the brain CT scan did not show acute pathology, the patient was given tissue-type plasminogen activator and was admitted to the intensive care unit for observation. Her speech improved gradually, and after 24 hours of observation she was transferred to the stroke unit. Clopidogrel (Plavix) was added to her daily aspirin regimen.

Carotid artery Doppler imaging and transthoracic echocardiogram were performed, revealing minimal stenosis in both carotid arteries and an ejection fraction of 50% to 55%, with mild-to-moderate mitral regurgitation.

The next day, the patient complained of palpitations. Her heart rate was 77 beats/min and irregular. Repeat ECG showed atrial fibrillation. She converted back to sinus rhythm after a few hours. She refused to take any anticoagulant medication.

Transesophageal echocardiogram (TEE) was performed to rule out valvular vegetations and atrial appendage thrombus, revealing a sessile atheroma at the aortic root, left atrial dilatation, and a tubular structure with prominent diastolic flow originating in the left coronary artery and terminating in the right atrium near the superior vena cava (Figure 1). A differential diagnosis of coronary artery aneurysm or coronary artery fistula was proposed.

Following the TEE findings, cardiac catheterization was performed, revealing nonobstructive coronary artery disease; left main coronary artery aneurysm with abnormal shunting to the right atrium through an anomalous branch (Figure 2); normal right-sided pressures; mild mitral regurgitation; mild aortic insufficiency; and normal left ventricular systolic function, with an ejection fraction of 60%. A fistula was diagnosed between the left main coronary artery and the right atrium. Treatment with coiling or surgery was offered to the patient, but she refused any invasive intervention. The patient was discharged with a prescription for aspirin and clopidogrel and was advised to follow up with the cardiology clinic.

Discussion
Pathophysiology
Fistulas communicate between the coronary arteries and one of the cardiac chambers (coronary–cameral fistulas) or between the arteries and other vessels (coronary artery arteriovenous malformations). Coronary artery fistulas are often caused by deviations from normal embryologic development. They may also be acquired from trauma (eg, stab or gunshot wounds, blunt trauma), or from invasive cardiac procedures, such as a pacemaker implantation, endomyocardial biopsy, or percutaneous transluminal coronary angioplasty.

The resultant physiologic derangement depends on the sites of origin and termination of the abnormal connection, which determine the pressure, resistance, and size of the connection. The major sites of origin are the right coronary artery, left anterior descending artery, and circumflex coronary arteries. The major termination sites for fistulas originating from the right or left coronary arteries are the pulmonary artery, right atrium, right ventricle, left ventricle, left atrium, and coronary sinus.¹ The volume of the shunt varies, depending on the size of the fistula and the differences between the systemic resistance and the resistance in the terminating vessel or chamber.²

Symptoms and signs
Most coronary artery fistulas are small and, therefore, myocardial blood flow is not compromised.² Coronary artery steal may occur, however, with resultant ischemia of the segment of myocardium perfused by the coronary artery distal to the fistula, and with the coronary artery proximal to the fistula enlarging in a compensatory fashion.

Most patients are asymptomatic, but some present with symptoms, such as recurrent chest pain, shortness of breath, or palpitations. Clinical examination is usually normal. Coronary artery fistula should be suspected when a continuous murmur is detected during a routine physical examination. Clinically, the murmur is suggestive of a patent ductus arteriosus (PDA) but is heard lower on the sternal border than usual; thus, the location of the murmur often is atypical.

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 a PDA. Some patients who have fistulas with a large shunt may present with signs of congestive heart failure and angina. The differential diagnosis of a coronary artery fistula is listed in Table 1.

Diagnosis
The chest x-ray and ECG findings 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. Color Doppler TEE is useful for diagnosing and determining the precise location of a fistula.³ Contrast-enhanced electron beam CT is a reliable method to diagnose coronary artery fistulas and other coronary anomalies.⁴ Cardiac catheterization is necessary for accurate definition of coronary artery anatomy, flow, and structural abnormalities.⁵ Usually, the intracardiac pressures are normal, and the shunt flow is modest. Aortography or selective coronary arteriography supplies the information required to manage the condition.

Treatment
Complications of untreated coronary artery fistulas are summarized in Table 2. Clinically silent coronary fistulas that are hemodynamically insignificant and are not associated with abnormal findings may not require treatment. Fistulas that are large and hemodynamically significant should be closed. Because smaller fistulas tend to increase in size with age,² it is recommended that elective closure be performed in children, even in those who are asymptomatic.⁶ 

Therapeutic options include transcatheter closure and surgery. The preferred approach will depend on the anatomy of the fistula, the presence or absence of any associated defects, and the experience of the interventional cardiologists and surgeons. Most patients will benefit from transcatheter closure.⁷ In this procedure, therapeutic embolization is performed using occlusive coils or devices during cardiac catheterization.

Surgical methods of closure are generally not associated with mortality, and morbidity is low; long-term prognosis is excellent and most patients remain asymptomatic.^8,9 Surgery involves median sternotomy with epicardial or endocardial ligation.

Conclusion
Coronary artery fistula is a rare entity and can be difficult to diagnose. Most fistulas are asymptomatic and follow a benign course. Symptomatic patients with large fistulas need aggressive approach to diagnosis. We recommend accurate assessment of the size and the shunt gradient to ensure appropriate management.

References
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2. Lopez-Candales A, Kumar V. Coronary artery to left ventricle fistula. Cardiovasc Ultrasound. 2005; 3:35-40.

3. Vitarelli A, De Curtis G, Conde Y, et al. Assessment of congenital coronary artery fistulas by transesophageal color Doppler echocardiography. Am J Med. 2002; 113:127-133.

4. Ropers D, Moshage W, Daniel WG, et al. Visualization of coronary artery anomalies and their anatomic course by contrast-enhanced electron beam tomography and three-dimensional reconstruction. Am J Cardiol. 2001; 87:193-197.

5. Gowda RM, Vasavada BC, Khan IA. Coronary artery fistulas: clinical and therapeutic considerations. Int J Cardiol. 2006; 107:7-10.

6. Farooki ZQ, Nowlen T, Hakimi M, et al. Congenital coronary artery fistulae: a review of 18 cases with special emphasis on spontaneous closure. Pediatr Cardiol. 1993; 14:208-213.

7. Armsby LR, Keane JF, Sherwood MC, et al. Management of coronary artery fistulae. Patient selection and results of transcatheter closure. J Am Coll Cardiol. 2002; 39:1026-1032.

8. Sunder KR, Balakrishnan KG, Tharakan JA, et al. Coronary artery fistula in children and adults: a review of 25 cases with long-term observations. Int J Cardiol. 1997; 58:47-53.

9. Chen Y, Belboul A, Roberts D. The surgical management of congenital coronary artery fistula. Coron Artery Dis. 1994; 5: 995-1000.