Coronary cameral fistula: Diagnosis and direct shunt quantification by cardiac MRI (QF_SA_112)

A 71-year-old man with no known history of heart disease presented with persistent chest pain weeks after a motor vehicle accident involving air bag deployment. Physical examination was notable for a continuous murmur at the right upper sternal border. An ECG revealed RBBB without acute ST changes. A chest CT (not targeted to evaluate the coronary arteries) revealed an ill-defined, dilated and tortuous vessel along the anterior cardiac border.  

Diagnostic Techniques and Their Most Important Findings:

Cardiac MRI with time-resolved angiography revealed a large serpiginous coronary-cameral fistula (CCF) originating at the proximal right coronary artery and dividing the interatrial septum before emptying into the right atrium (Images 1 and 2). Velocity flow mapping through the fistula yielded an output of 3.3 L/min (Image 3), equaling the difference between the pulmonary arterial (7.1 L/min) and aortic (3.8 L/min) flows. The Qp/Qs was 1.86. Coronary angiography confirmed these findings, and the patient underwent surgical repair with saphenous vein grafting to the posterior descending artery and ligation of the fistula. Coronary CTA performed two months later revealed near complete thrombosis of the proximal fistula but some persistent left-right shunting to the distal fistula via small collaterals originating from other nearby vessels, including the proximal left circumflex artery, right internal mammary artery, and proximal left common carotid artery. Three months after repair, the patient was asymptomatic. 

Learning Points from this Case:

Coronary-cameral fistulas are rare, abnormal connections between the coronary arteries and cardiac chambers. CCF are commonly congenital but can be acquired via chest trauma or iatrogenic from various invasive cardiac procedures.  Congenital fistulas often arise from the right coronary artery and drain into the right heart or pulmonary arteries. Most cases of CCF are asymptomatic and detected incidentally, however surgical closure is indicated for symptoms (such as congestive heart failure, ischemia, and pulmonary hypertension) or hemodynamically significant shunting. Transthoracic echocardiography may detect dilated coronary arteries and chamber dilatation but may not define the course of serpiginous fistulas. Direct coronary arteriography identifies CCF, but assessment of fistulous connections may prove challenging on x-ray imaging due to overlapping chambers. With extremely high spatial resolution, coronary CTA is ideal for identifying the origin and complex course of CCF. Cardiac MRI is the gold-standard for shunt quantification and volumetric analysis of cardiac chamber size and function. Time-resolved angiography with interleaved stochastic trajectories (TWIST) utilizes a small bolus of contrast and obtains a series of images during transit, allowing for improved discrimination of vascular structures especially when proximate to other vessels or the blood pool. In this case, cardiac MRI identified the origin and course of a large and complex CCF and confirmed significant left-right shunting via both the Qp/Qs and direct flow analysis of the fistula itself. To our knowledge, this is the first case report of successful direct flow analysis of a coronary cameral fistula by cardiac MRI.