What is the significance of reversal of vertebral flow?

Significance of Reversal of Vertebral Flow

Reversal of flow in the vertebral artery most commonly indicates subclavian steal syndrome, which can cause posterior cerebral circulatory insufficiency and requires revascularization if symptomatic. 1

Clinical Significance

Pathophysiology

• Reversal of vertebral artery flow occurs primarily due to proximal subclavian artery stenosis or occlusion
• When the dominant vertebral artery is affected by subclavian obstruction, reversal of flow may reduce basilar artery perfusion and cause posterior cerebrovascular insufficiency 1
• Less commonly, reversal can occur due to vertebral artery occlusion or intrinsic anatomical defects 2

Diagnostic Value

• Detected on duplex ultrasonography as retrograde flow in the vertebral artery
• Occurs in approximately 2.5% of patients undergoing cerebrovascular duplex ultrasound 3
• Subclavian steal syndrome should be considered when posterior cerebral circulatory symptoms are aggravated by upper limb exercise 1

Clinical Patterns

• Two distinct patterns of reversal:
  1. Continuous complete reversal - Always indicates subclavian steal phenomenon
  2. Intermittent complete reversal - May indicate either subclavian steal or proximal vertebral artery occlusion 2

Clinical Manifestations

Symptomatic Presentation (Vertebral Ischemic Form)

• Symptoms typically aggravated by exercising the ipsilateral arm, which amplifies flow reversal 1
• May include:
  • Lightheadedness or syncope
  • Vertigo and ataxia
  • Diplopia
  • Motor deficits
  • Upper limb claudication
  • Posterior circulation stroke 1, 4

Asymptomatic Presentation

• Most patients with reversal of vertebral flow (approximately 75%) remain asymptomatic 3, 5
• This is because:
  • Basilar artery flow remains antegrade in about 76% of patients despite vertebral flow reversal 5
  • Collateral circulation often develops over time 6

Risk Assessment

High-Risk Indicators

• Symptomatic posterior circulation symptoms (vertebrobasilar insufficiency)
• Complete reversal of basilar artery flow (occurs in approximately 24% of patients with vertebral flow reversal) 5
• Higher ratio of time in intermittent complete reversed flow to cardiac cycle (tICRF/CC >0.30) strongly predicts posterior circulatory infarction 2
• Concomitant carotid artery stenosis (73% of patients with posterior circulation symptoms have concurrent carotid stenosis) 3
• Planned coronary artery bypass grafting using ipsilateral internal mammary artery 6, 4

Management Approach

Diagnostic Evaluation

• Duplex ultrasonography to detect flow reversal and assess carotid arteries
• Check for asymmetry between left and right arm blood pressure (>10-15 mmHg difference)
• Listen for periclavicular or infraclavicular bruit 1, 6
• Consider transcranial Doppler to evaluate basilar artery flow direction 5

Medical Management

• For asymptomatic patients:
  • Antiplatelet therapy (aspirin 75-325 mg daily)
  • Aggressive cardiovascular risk factor modification
  • Statin therapy with goal of >50% LDL-C reduction 6

Revascularization Indications

• Symptomatic patients with:
  • Vertebrobasilar insufficiency
  • Upper limb claudication or ischemia
  • TIA/stroke related to subclavian stenosis 6
• Asymptomatic patients with:
  • Planned CABG using ipsilateral internal mammary artery
  • Existing internal mammary artery graft with evidence of myocardial ischemia
  • Ipsilateral arteriovenous fistula for dialysis 6

Revascularization Options

• Endovascular approach (first-line):
  • Balloon angioplasty and stenting
  • Technical success rates: 98-100% for stenosis
  • Primary patency: 93% at 1 year, 70% at 5 years 1, 6
• Surgical approach:
  • Carotid-subclavian bypass
  • Subclavian-carotid arterial transposition
  • Primary patency: 100% at 1 year, 96% at 5 years 1, 6

Prognosis

• Symptomatic patients respond well to intervention, including subclavian artery stenting or carotid intervention 3
• Asymptomatic patients generally have favorable prognosis with rare progression to vertebral artery occlusion 3
• Regular follow-up with serial noninvasive imaging is recommended at 1 month, 6 months, and annually after intervention 6