Multimodality imaging of a left main coronary artery-to-pulmonary artery fistula

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A coronary arterial fistula (CAF) is a connection between a coronary artery and a cardiac chamber or a great vessel, occurring in about 0.002% of the general population.1 It usually originates from the left anterior descending artery (LAD) and drains into the main pulmonary artery.2 CAFs do not usually cause symptoms or complications, especially when small and in young individuals.3
A 17-year-old young man was referred to our institute to achieve certification for standard physical activity. The transthoracic echocardiogram (TTE) showed a color-Doppler abnormality consisting of a thin flow draining into the main pulmonary trunk, immediately above the pulmonary valve plain. Pulsed wave Doppler revealed a continuous flow throughout the cardiac cycle predominantly in diastole, suggestive of coronary artery flow. In order to confirm the presence of congenital coronary fistula, coronary computed tomography (CT) was performed. As a result, a little branch of LAD-to-main pulmonary trunk fistula was found. The CAF was very thin and extremely tortuous, coiling around the pulmonary artery before draining into the pulmonary artery. The risk of steal phenomena from the main vessels has been excluded by stress myocardial perfusion scintigraphy, which ruled out any type of ischemic alterations (Fig. 1).
Currently, controversial debate exists with regard to whether or not to treat patients with incidentally detected fistula. CAFs are usually asymptomatic in the first two decades, especially when small. Later symptoms can occur, prevalently angina.4,5 Patients with moderate/severe symptoms and large shunts are usually treated with percutaneous embolization or surgical ligation, whereas conservative management is recommended in the case of small flows and mild/no symptoms.1,2
Before deciding on the most appropriate management of the CAF, we studied the coronary anomaly anatomically and fuctionally. The standard TTE detected the shunt on the pulmonary trunk, suggesting a coronary artery flow. Subsequently, CT identified morphologically the CAF, finding the origin in the proximal LAD and the drainage point in the pulmonary artery. Finally, stress scintigraphy was helpful to stratify the functional impact of CAF: abnormalities of ECG and on myocardial perfusion were excluded; symptoms did not appear. Then, we decided to follow the patient clinically, performing periodical medical visits with ECG and echocardiogram.
Despite the radiation burden due to sequential CT scans and scintigraphy in a young patient with suspected CAF, we suggest a multimodality imaging approach as management of this kind of patient. A standard TTE is the first step to suppose the presence of CAF, followed by a more accurate anatomical and functional classification of the lesion, using coronary CT and stress perfusion myocardial scintigraphy. Anyway, a risk/benefit evaluation regarding radiation exposure in young individuals is mandatory.

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