Unusual cause of abnormal cardiac stress test

A patient with chest pain, dyspnoea and sudden tachycardia during exercise, confirmed by a cardiac stress test (cyclo-ergometry). Subsequent coronarography showed no stenosis, but abnormal connections between proximal RCA and LAD to the pulmonary trunk were observed. A contrast-enhanced, ECG-triggered CT examination was requested for further evaluation.

A contrast-enhanced ECG-triggered CT examination showed tortuous vessels around the pulmonary trunk originating from afferent branches from the right coronary artery (RCA) and multiple septal perforators from the left anterior descending artery (LAD) and one from the intercostobronchial trunk, draining in the pulmonary trunk with jets of contrast.
No signs of pulmonary hypertension (normal ratio of pulmonary trunk to ascending aorta, L/R ventricle, normal lung parenchyma). Presence of a ramus intermedius.
Calcium score of 1,7. Right dominant system. No plaques causing significant stenosis were noted.
No structural cardiac abnormalities were noted. Tricuspid aortic valve with two ostia in the right sinus of Valsalva, caudal is the RCA, cranial vessel is accessory afferent vessel.
Conclusion:
Left to right shunt due to coronary artery fistula (CAF) from the RCA & LAD in combination with a major aortopulmonary collateral artery (MAPCA) from the intercostobronchial trunk draining into the pulmonary trunk.

A.
Congenital isolated coronary arterial fistulas (CAFs) are rare and defined as a coronary artery with abnormal termination/connection either with a cardiac chamber (coronary cameral fistula) or venous structure (coronary arteriovenous fistula) in the absence of an interposed capillary bed. [1]
Classification is possible on morphology, number, vessels (and segment) of origin, site (and mode) of termination. [2] Most CAFs originate from the LCA (50%), less commonly the RCA (38%) and infrequently both (12%). [1] Associations are mitral valve disease, ASD/VSD, patent ductus arteriosus, pulmonary atresia or stenosis. [3] Acquired CAFs are mostly iatrogenic, although infrequently they are caused by vasculitis, penetrating chest trauma or as a complication of infective endocarditis. [4]

B.
Symptoms of CAFs are chest pain, dyspnoea and arrhythmia, adults being more frequently symptomatic than children.
Coronary flow into a low pressure system leads to a steal phenomenon in the myocardium, possibly causing myocardial ischaemia or infarction. Other complications include aneurysmal dilatation of the CAF with risk of rupture or thrombosis and less frequently infective endocarditis. Large left-to-right shunts can cause pulmonary arterial and biventricular dilatation. [1]

C.
Our case can be classified as complex coronary arteriovenous fistulas with termination in the pulmonary trunk with multiple vessels of origin (LCA, RCA and anomalous coronary artery). The dilated costobronchial vessel of origin can be thought of as an extracardiac systemic-to-pulmonary artery collateral vessel or isolated aortopulmonary collateral artery (IAPCA), the coronary supply from RCA & LAD fits the MAPCA definition as well, although intersegmental arteries (typical tortuous posterior hilar vessels) are absent, drainage this proximal in the pulmonary trunk is odd and most isolated MAPCA’s would have regressed. [5] Since no cardiac abnormalities were noted indicating an aetiological factor, this persistent left-to-right shunt is probably congenital. The exact aetiology remains challenging, patients history was unremarkable for patent ductus arteriosus or chronic lung disease. [6]
CT angiography is recommended to detail the complex anatomy (origin(s), diameters, course(s), supply of the lung) due to the ability to show 3D anatomy and provide multiplanar reconstructions. [7] Catheter angiography can be of additional value to assess blood flow patterns and device landing zones if endovascular treatment is considered.

D.
CAFs seldom close spontaneous (1-2%) [3]. Even in young or asymptomatic patients CAF closure is considered to avoid complications in adult life. Guidelines recommend closure of large asymptomatic CAFs as well as symptomatic small-to-medium CAFs. [8]