The coronary artery to sinus connection effectively creates a sizable left to right shunt, with the high pressure left coronary artery circulation preferentially flowing into the low pressure venous sinus, with vastly increased flow as a result, leading to profound dilation and tortuosity of the left coronary system. The relatively small caliber of the mid to distal LAD is due to steal phenomenon, which can cause diffuse subendocardial ischemia within the left ventricle.

Dilation of the pulmonary trunk relative to the aorta is due to the established left to right shunt.

ECG gated post cardiac CT with left and right heart contrast is the optimal test to accurately assess coronary artery and venous anatomy in multiple planes, to facilitate planning and workup of these cases.

Follow up cardiac MRI with contrast may be helpful to quantify the shunt, assess right heart dilation and function and detect the volume of chronic myocardial ischemia caused by steal.