A 68-year-old man comes to the emergency department due to severe dizziness while playing tennis an hour ago. He says that he had a spinning sensation accompanied by nausea and vomiting; the symptoms have now subsided. The patient has had brief episodes of dizziness in the past, especially when performing vigorous work with his arms. He has also experienced heaviness and fatigue of the left arm with exertion. The patient has a history of hypertension, hyperlipidemia, and type 2 diabetes mellitus. Blood pressure is 140/90 mm Hg on the right arm and 100/74 mm Hg on the left, and pulse is 82/min and regular. A systolic bruit is present at the base of the neck just above the clavicle on the left side. Cardiac auscultation discloses a fourth heart sound. There is no extremity weakness or sensory loss. Which of the following is the most likely cause of this patient's symptoms?
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This patient likely has subclavian steal syndrome due to severe atherosclerosis of the left subclavian artery proximal to the origin of the vertebral artery. Significant stenosis or occlusion leads to decreased pressure in the distal subclavian artery and reversal ("steal") of blood flow in the ipsilateral vertebral artery. The left subclavian artery is more commonly affected than the right, likely due to sharper curvature and more turbulent blood flow (leading to atherosclerosis).
Most patients with subclavian artery stenosis are asymptomatic. When symptomatic, patients most commonly have symptoms of ischemia in the affected upper extremity (eg, pain, fatigue, paresthesias). Less commonly, patients with concurrent atherosclerosis of the circle of Willis may develop symptoms of vertebrobasilar ischemia (eg, dizziness, ataxia, dysequilibrium). Exercising the affected upper extremity causes arterial vasodilation and a further lowering of distal pressure, which may exacerbate vertebrobasilar symptoms. Physical examination often demonstrates a significantly lower brachial systolic blood pressure (eg, >15 mm Hg) in the affected arm and a systolic bruit in the supraclavicular fossa on the affected side. A fourth heart sound may be present due to left ventricular hypertrophy from systemic hypertension.
Diagnosis is typically made by Doppler ultrasound or magnetic resonance angiography. Treatment involves lifestyle management (eg, lipid-lowering interventions, smoking cessation) and sometimes stent placement.
(Choice A) Coronary artery atherosclerosis typically causes chest pain or dyspnea with exertion (eg, stable angina). Transient dizziness with exertion would be unusual.
(Choice B) Internal carotid artery stenosis can be asymptomatic (eg, due to collateral circulation) or may cause transient symptoms of ocular or cerebral ischemia (eg, amaurosis fugax, limb weakness). Dizziness and dysequilibrium are more consistent with vertebrobasilar (eg, cerebellar) ischemia.
(Choice C) Aortic coarctation is a usually congenital narrowing of the aortic arch typically just distal to the origin of the left subclavian artery. Patients typically have headaches, epistaxis, and lower (not upper) extremity claudication. Hypertension is usually present in the bilateral upper extremities.
(Choice E) Vertebral artery stenosis can cause symptoms of dizziness or dysequilibrium; however, symptoms of arm ischemia or a blood pressure difference in the upper extremities is not expected.
Educational objective:
Subclavian steal syndrome occurs due to stenosis or occlusion of the proximal subclavian artery, leading to reversal of blood flow in the ipsilateral vertebral artery. Patients are often asymptomatic but may have symptoms of upper extremity ischemia (eg, pain, fatigue, paresthesias) or vertebrobasilar insufficiency (eg, dizziness, ataxia, dysequilibrium) that are worsened by upper extremity exercise.