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Magnetic resonance of vertebral steal syndrome
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A 63 year old man presented with exertional dyspnoea and fatigue. Twelve years previously he had undergone quadruple coronary artery bypass surgery. On clinical examination there were no palpable pulses in the left arm. Cardiac catheterisation performed via the right femoral artery revealed occluded native vessels and three patent saphenous vein grafts. It was not possible to identify the left internal mammary artery (LIMA) graft as the left subclavian artery was occluded.

 A gadolinium contrast enhanced magnetic resonance angiogram (MRA) was performed to identify the anatomy. Maximum intensity projection reformatting of the MRA demonstrated occlusion of the left subclavian artery (below, arrow). A phase contrast velocity map was performed after handgrip exercise, at the level of the vertebral arteries, to assess for the possibility of vertebral steal syndrome. The velocity encoded image (top right) acquired in systole, with cranial blood flow displayed as black and caudal flow white, demonstrated retrograde flow down the left vertebral artery during systole (white arrow) with normal cranial flow up the left internal carotid (black arrow) and right sided vessels. This was confirmed by the mean velocity profile over time for each artery (bottom right). Positive velocity indicates cranial flow in the right internal carotid artery (RICA), the left internal carotid artery (LICA) and the right vertebral artery (RVA). Negative velocity indicates caudal flow in the left vertebral artery (LVA). MRA also demonstrated patency of the LIMA graft (not shown).

An exercise myocardial SPECT perfusion scan documented no reversible myocardial ischaemia and the patient is currently asymptomatic with medical management. Contrast enhanced MRA with velocity mapping is a robust minimally invasive technique that should be used when subclavian artery steal syndrome is suspected.