Four-dimensional magnetic resonance flow analysis clarifies paradoxical symptoms in a patient with aortic bypass and retrograde flow mimicking subclavian steal.

We present the case of a 39-year-old physically active male amateur hockey player with a history of preductal coarctation of the aorta repaired at the age of 10 years with an ascending-to-descending aortic conduit. He presented with neurological symptoms, which were present at rest but paradoxically resolved with physical exertion, including left upper extremity weakness, dizziness, visual changes, and facial tingling. A 2008 echocardiogram demonstrated a bicuspid aortic valve with moderate regurgitation and a mildly to moderately dilated and hypertrophied left ventricle with ejection fraction of 50%. A 2009 carotid Doppler ultrasound examination demonstrated high-velocity retrograde flow in the left vertebral artery, which reduced on exertion. Stenosis of the subclavian artery, and thus subclavian steal, which has been shown to cause neurological symptoms, was ruled out by a 2010 arteriogram.1 A recent magnetic resonance imaging (MRI) evaluation (in 2011) demonstrated worsening (moderate to severe) aortic insufficiency with a clearly visible asymmetrical diastolic flow jet (Figure 1, white arrows), mild decrease of left ventricular ejection fraction, and a patent aortic bypass conduit. To further interrogate the paradoxical reversal of neurological symptoms on exertion, we performed flow-sensitive 4D MRI.2 The aim was to evaluate time-resolved 3D blood flow during rest and exertion with full volumetric coverage of the entire aorta, bypass conduit, and supra-aortic vessels (1.5-Tesla MRI; Siemens, Erlangen, Germany; velocity sensitivity 150 cm/s, spatial resolution 2.6 2.6 3.2 mm, temporal resolution 38 ms, ECG gating, respiratory navigator gating, scan time 20 minutes). Flow-sensitive 4D MRI was performed after administration of intravascular gadolinium contrast agent (Ablavar; Lantheus Medical Imaging, North Billerica, MA; dose 0.03 mmol/kg) at rest. Imaging was repeated after administration of 1.5 mg of atropine intravenously in an attempt to evaluate the effect of exercise on aortic hemodynamics. A moderate increase in heart rate was achieved (from 45 bpm to 67–71 bpm). The study was approved by the institutional review board, and informed consent was obtained from the patient. To visualize blood flow in 3D, we calculated time-resolved path lines depicting the direction and temporal evolution of flow through the entire thoracic aorta, conduit, and 3 supraaortic branches.3 4D flow data were also used to retrospectively quantify retrograde fraction (retrograde flow divided by antegrade flow) at several locations in the vessels.