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Different blood pressure in each arm: when a narrowed subclavian artery is the cause
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If the blood pressure in your right and left arms differs noticeably, the cause may be a narrowing (stenosis) or blockage (occlusion) of the subclavian artery — the vessel that carries blood to the arm and gives off a branch to the back of the brain. It is often an incidental finding without symptoms that calls for assessment and prevention rather than surgery; a procedure is considered only with certain symptoms or in specific situations.
Different blood pressure in each arm: what difference matters
A small difference in blood pressure between the arms is common. To assess it properly, measure your blood pressure at rest in both arms, one after the other, and then once more in the first arm. If on repeated measurements the systolic (top number) pressure consistently differs by more than 10–15 mmHg, it is a reason to have your arteries checked: such a difference can be a sign of a narrowed subclavian artery on the side where the pressure is lower.
From then on, measure your blood pressure in the arm where it is higher: that reading reflects your true blood pressure. If you measure it in the arm with the narrowed artery, the reading will be falsely low, and high blood pressure (hypertension) can be missed.
What is subclavian artery stenosis and “steal syndrome”?
The subclavian artery arises from the aorta (on the right, from the brachiocephalic trunk) and carries blood to the arm. It gives off the vertebral artery, which supplies the back of the brain. The most common cause of narrowing is atherosclerosis, so it often occurs together with disease of the carotid and coronary arteries and the leg arteries.
With a severe narrowing at the start of the subclavian artery, blood may reach the arm by a detour — through the vertebral artery, flowing in the reverse direction. On ultrasound this is described as retrograde (reversed) flow in the vertebral artery, or the “subclavian steal” phenomenon. This finding is common and in most people causes no symptoms; it is called subclavian steal syndrome only when it causes symptoms.
Symptoms: an arm that tires quickly, dizziness
- Weakness, fatigue or pain in the arm during use, especially when working with the arms raised
- Coldness, pallor or numbness of the hand on the side of the narrowing
- In severe cases, pain in the hand at rest, or ulcers or darkening of the skin on the fingers
- Dizziness, unsteadiness, double vision or visual disturbance that occur specifically while using the arm
- Chest pain in people who have had coronary artery bypass surgery, if the internal thoracic (mammary) artery on the same side was used for the graft
- Worsening function of a hemodialysis fistula in that arm
When it is urgent
Sudden weakness or numbness of an arm, a leg or one side of the face, facial droop, trouble speaking, sudden loss of vision or double vision, severe dizziness with unsteadiness: call an ambulance (103 in Ukraine). These may be signs of a stroke or transient ischemic attack — even if they pass within a few minutes. Do not wait for a routine appointment.
Sudden severe pain in the chest, back or abdomen, or chest pain or pressure lasting more than a few minutes or starting at rest: call an ambulance (103 in Ukraine). This may be a heart attack (including in people who have had coronary bypass surgery) or aortic dissection — especially if a difference in pulse or blood pressure between the arms has suddenly appeared.
Sudden pain, coldness, pallor, numbness or weakness of an arm: call an ambulance (103 in Ukraine). This may be an acute blockage of an arm artery. Do not warm the arm with a heating pad or hot water.
Tests: vascular ultrasound and CT angiography
The first test is duplex ultrasound of the brachiocephalic arteries (the arteries supplying the head and arms): it shows the degree of narrowing and the direction of blood flow in the vertebral artery. If the result is inconclusive or treatment is planned, CT or MR angiography is performed. Catheter angiography is done immediately before the procedure, usually during the same session.
Because the most common cause is atherosclerosis, the doctor also assesses other arteries — the carotid and coronary arteries and the leg arteries — as well as risk factors. Less often, the cause is inflammation of the artery wall (arteritis, such as Takayasu arteritis), which is investigated and treated differently from atherosclerosis.
Who needs treatment and who only needs monitoring
All patients with a narrowed subclavian artery need atherosclerosis prevention: statins, antiplatelet medicines as prescribed by the doctor, control of blood pressure and blood sugar, and stopping smoking.
If the narrowing causes no symptoms, stenting or surgery is usually not performed — even with a significant blood pressure difference between the arms or reversed flow in the vertebral artery on ultrasound. The exceptions are specific situations: planned coronary bypass surgery using the internal thoracic artery on the same side, an existing graft of this kind with signs of myocardial ischemia, or a hemodialysis fistula in that arm; less often, significant narrowing on both sides that makes accurate blood pressure measurement impossible.
Restoring blood flow is considered when the narrowing has caused a stroke or transient ischemic attack, chest pain (angina) after coronary artery bypass surgery, worsening fistula function, or symptoms that significantly interfere with daily life. Many symptoms lessen on their own over time, so patients with symptoms are monitored to check whether a procedure is still needed.
Stenting or open surgery
An endovascular procedure — balloon angioplasty, with a stent placed if needed — is performed through an arterial puncture, without an incision. It is less invasive and is often the first choice. Open surgery (subclavian-to-carotid transposition — reattaching the subclavian artery to the carotid artery — or a bypass) is considered for a long occlusion, failed stenting or specific anatomical features. There are no randomized comparisons of these methods, so the decision is made individually, together with the vascular surgery department. Any procedure on these arteries, endovascular or open, carries a risk of complications, including stroke (about 1–2% in registry data), so it is not performed without a clear indication.
After treatment: follow-up and prevention
After the procedure, atherosclerosis prevention continues and follow-up visits with ultrasound are scheduled: the artery can narrow again over time, and follow-up helps to spot this early. From time to time, measure your blood pressure in both arms: if a difference between them reappears, tell your doctor.
Frequently asked questions
What difference in blood pressure between the arms is normal?
A small difference — up to 10 mmHg — is common and usually does not matter, although it does not rule out a narrowing if you have symptoms. If on repeated measurements at rest the difference in systolic (top number) pressure consistently exceeds 10–15 mmHg, it is worth discussing an assessment of your arteries, including an ultrasound, with a doctor.
Which arm should I measure my blood pressure in if the readings differ?
First measure it in both arms. If the readings differ, from then on measure it in the arm where it is higher: that reading reflects your true blood pressure.
An ultrasound found subclavian artery stenosis, but I have no symptoms. Do I need a stent?
Usually not. Without symptoms, the narrowing is treated with medicines and control of risk factors. The exceptions are specific situations, for example planned coronary bypass surgery using the internal thoracic artery on the same side, or a hemodialysis fistula in that arm. The decision is made by a vascular surgeon.
What does “retrograde flow in the vertebral artery” mean on an ultrasound report?
Blood in the vertebral artery flows in the reverse direction — toward the arm, bypassing the narrowed subclavian artery. It is a common sign of severe narrowing, but on its own it does not mean surgery is needed: in most people it causes no symptoms.
Can subclavian artery stenosis cause dizziness?
It can, but not often: dizziness, unsteadiness or visual disturbance that occur specifically while using the arm can be a sign of steal syndrome. Dizziness more often has other causes, so it is assessed together with a neurologist. Sudden weakness, trouble speaking, facial droop, double vision, or severe dizziness with unsteadiness may be signs of a stroke: call an ambulance (103 in Ukraine).
Stenting or surgery: which is better?
There are no randomized trials comparing these methods. An endovascular procedure is less invasive and is often the first choice; open surgery is considered for a long occlusion, failed stenting or specific anatomical features. The method is chosen individually.
Book a consultation
Vascular surgeon consultation at the Shalimov Center, 30 Akademika Shalimova St, Kyiv. Booking and questions go through the contact doctor, Yurii Vahis. Patients from other cities and abroad can arrange an online consultation.