Discussion:
When a fistula drains into the right side of the heart, the volume
overload is occurring there, as well as in the pulmonary vascular bed,
left atrium, and left ventricle. When the fistula drains into the left
atrium or ventricle, volume overloading takes place in these chambers,
but pulmonary blood flow does not dramatically increase. The size of the
shunt is determined by the size of the fistula and the pressure
difference between the coronary artery and the chamber into which the
fistula drains. Most patients display no symptoms, especially during the
first two decades of life, and are referred for testing due to an
asymptomatic murmur; however, older patients may experience dyspnea or
angina and occasionally arrhythmias. Complications that may arise
include ‘theft’ from the adjacent myocardium, which can lead to
myocardial infarction (MI), thrombosis and embolism, heart failure,
atrial fibrillation, rupture, endocarditis/endarteritis, and even sudden
death [4,5]. When diagnosing an AV shunt, CXR and EKG do not
generally have significant value [6]. When the initial EKG is
normal, treadmill or nuclear stress tests often reveal ischemic changes.
2D Doppler echocardiography and TEE may also show the site of drainage,
but it is difficult to understand the detailed anatomy using these
techniques. [4,5,6] Cardiac MRA is limited because the information
regarding the origin and drainage site of the fistula are less clear in
comparison with those observed with CTA and conventional angiography
[7]. Previously, cardiac catheterization was the first-line modality
for diagnosing CAFs and was thought to have the highest efficiency for
detailing the anatomy, size, origin, course, and presence of any
stenosis and/or drainage; however, more recent studies have shown that
CTA actually produces the best results. It has been demonstrated that
the exact 3D course of the artery is difficult to obtain by conventional
angiography, the drainage sites may not be as well visualized, and the
invasive nature yields a higher mortality rate than CTA [7]. CTA is
a relatively new imaging tool that was introduced 20 years ago for
non-invasive cardiac imaging, and with the introduction of
multi-detector computed tomography (MDCT), many problems related to
image quality have been resolved [8]. CTA can produce high quality
images that clearly delineate the cardiac chambers and coronary arteries
and veins [5], in addition to having a shorter acquisition time and
higher spatiotemporal resolution. The multiplanar reformation clearly
demonstrates the sites of origin and termination of abnormal blood
vessels, and 3D data provide a more precise overview of the heart, its
vascular anatomy, and information pertaining to the diagnosis of
coexistent abnormalities as compared with left heart catheterization
[7]. However, limitations include less hemodynamic information,
which we speculate to be the rationale for its failure to detect the
fistula in our case.
According to the 2008 ACC/AHA guidelines, all large fistulas and
small-to-moderate fistulas associated with myocardial ischemia,
systolic/diastolic dysfunction, or ventricular dilation should undergo
closure irrespective of the symptoms of lack thereof [9]. Patients
diagnosed with CAFs should be educated prior to treatment. In contrast
to patients with acquired heart disease, those with CAFs or adult
congenital heart disease (ACHD) may have never experienced ”normal”
function. Cardiopulmonary exercise testing provides an objective
assessment and has been shown to possess prognostic value for a wide
variety of congenital conditions. There exist conflicting arguments
regarding physical activity in these patients, with some suggesting
restricted exercise, which will inevitably lead to a greater prevalence
of obesity and other forms of heart disease. The most recent guidelines
recommend safe exercise in patients across the spectrum of CAF severity,
being individualized depending on patient clinical status. Self-directed
activity is usually at 40−60% of the maximal exercise capacity, whereas
fitness training occurs at 60−80% [9]. The treatment options for
CAFs include surgery or catheter closure [5]. The main surgical
options are epicardial fistula mobilization with ligation or division,
arteriotomy of the dilated proximal coronary artery with suturing close
to the fistula origin, and exposure of the fistulous connection and
closure by direct suture or autologous pericardial patch. However,
surgery is associated with a morbidity and mortality rate ranging from
0−6%, and there is a risk of MI and recurrence of the fistula [10].
Catheter closure is considered an effective and safe alternative, with
the aim of occluding the fistula artery as distally and close to its
termination point as possible to avoid occlusion of the branches
supplying the normal myocardium [10]. There are many tools available
for closure, including occlusion coils, detachable balloons, and
deployable stents and balloons. The techniques and tools used for
catheter closure are influenced by several different factors such as the
morphology of the feeding arteries, patient age, and location of the
fistula [10]. With catheter closure techniques, complete occlusion
of the fistula may be achieved in >95% of patients. In the
remaining patients, either further procedures are required to close the
fistulas or conservative management can be undertaken if the residual
fistulas are small [11]. Selection of percutaneous or surgical
management is influenced by the anatomy and physiology of the CAF.
Indications for surgical management are large, symptomatic, and/or
tortuous fistulas with or without multiple communications and drainage;
whereas, percutaneous transcatheter closure is considered when the
origin of the fistula is in the proximal portion of the feeding coronary
artery, is non-tortuous, or is in an older patient with high
preoperative risk [7]. After closure, these patients should be
placed on Coumadin, with a goal therapeutic INR of 2.5 for 6−12 months;
and should be on anti-platelet drugs indefinitely.
Conclusions: The present case illustrated a rare CAF, in which
the drainage is into the left circulation. CAFs are only detected in
0.05−0.25% of patients who undergo coronary angiography and left-sided
drainage is seen in a mere 10% of these cases. Although current
literature states that CTA is the first-line modality for the detection
of CAFs and provides a more precise overview of the heart, its vascular
anatomy and information pertaining to coexisting abnormalities via 3D
data, we found that conventional angiography was able to detect the
fistula when CTA was not. Further research should be elicited to
directly compare the sensitivity and specificity of coronary angiography
with that of CTA for the detection of CAFs.