B52-15 The Fainting Arm - Inter-Arm Blood Pressure Discrepancy Revealing Left Subclavian Steal Syndrome

Abstract Introduction Subclavian Steal Syndrome (SSS) occurs when the proximal subclavian artery stenosis (before the origin of the vertebral artery) causes retrograde blood flow in the ipsilateral vertebral artery, “stealing” blood from the posterior cerebral circulation to supply the arm. We present a patient with SSS and patent carotid arteries which would have been overlooked by attributing symptoms solely to vasovagal or orthostatic causes. Case Report A woman in her sixties with past medical history of hypertension and hypercholesterolemia developed sudden onset dizziness and diaphoresis while drying her hair with the episode lasting for about 10 minutes. She reported no loss of consciousness and had no chest pain or focal weakness or visual disturbances. Physical examination was unremarkable except for faint left radial pulse (1+) and a strong right radial pulse (3+). BP measurements were 94/70 mm Hg in the left arm and 113/78 mmHg in the right arm. EKG, Chest Xray and blood work were unrevealing. CT angiography showed moderate - severe narrowing at the origin of the left subclavian artery and patent carotid arteries. Duplex ultrasound demonstrated a high-grade stenosis of the proximal subclavian artery on the left, with color aliasing and spectral broadening. The ipsilateral vertebral artery showed bidirectional flow with intermittent systolic reversal, consistent with partial/latent subclavian steal physiology. The contralateral vertebral artery had anterograde flow at rest. Interarm systolic BP difference measured 40 mmHg. The patient eventually underwent endovascular revascularization with complete resolution of symptoms. Discussion and learning objectives Anatomically, ostial subclavian stenoses are heavily calcified and may behave differently from more distal lesions; ostial location can affect procedural planning and the likelihood of durable stent patency. CTA provides precise anatomical mapping necessary while duplex ultrasound is required to demonstrate vertebral flow reversal and to quantify flow velocities. Management of symptomatic SSS commonly begins with endovascular approaches—angioplasty with selective stent placement. These procedures are less invasive than open surgery and have favorable early symptomatic outcomes, though ostial disease and heavy calcification may affect longterm durability and the need for reintervention. Surgical bypass remains an option when endovascular therapy is not feasible or has failed. This case emphasizes the high diagnostic yield of routinely measuring BP in both arms in patients with dizziness, syncope or neurological complaints. A marked interarm BP difference and ipsilateral pulse diminution localizes the lesion to the proximal subclavian artery and should prompt vascular imaging rather than attributing symptoms solely to vasovagal or orthostatic causes. This abstract is funded by: Self