What is the management for PAD with normal ABI and reduced TBI?

Management of PAD with Normal ABI and Reduced TBI

Patients with normal ABI but reduced TBI should receive guideline-directed medical therapy (GDMT) for PAD including antiplatelet therapy, statin therapy, risk factor modification, and consideration for revascularization if symptoms are severe or there is critical limb ischemia.

Diagnostic Significance

A normal ankle-brachial index (ABI) with reduced toe-brachial index (TBI) represents a specific diagnostic pattern that indicates peripheral artery disease (PAD) that may be missed by ABI testing alone:

• TBI ≤0.70 is diagnostic of PAD even when ABI is normal (1.00-1.40) 1
• This pattern is particularly common in patients with:
  • Diabetes mellitus 1, 2
  • Chronic kidney disease (CKD) 2, 3
  • Patients on hemodialysis 3

Why This Happens

• Noncompressible tibial arteries due to medial arterial calcification can result in falsely normal or elevated ABI readings despite significant PAD 1, 4
• Digital arteries (measured in TBI) are rarely noncompressible, making TBI more reliable in these patients 1
• Research shows that 20.5% of patients referred with suspected PAD have low TBI but normal ABI 5

Management Algorithm

1. Medical Therapy (First-line for all patients)

• Antiplatelet therapy: Clopidogrel 75 mg daily to reduce the rate of MI and stroke 6
• Lipid management: High-intensity statin therapy regardless of baseline LDL levels 4
• Blood pressure control: Target <130/80 mmHg 4
• Diabetes management: Target HbA1c <7% 4

2. Lifestyle Modifications

• Structured exercise program:
  • Supervised exercise training (SET): 30-45 minute sessions, 3-5 times/week for at least 12 weeks 4
  • Home-based exercise training when SET is not available 4
• Smoking cessation if applicable 4

3. Additional Diagnostic Evaluation

• Anatomic assessment if symptoms are significant:
  • Duplex ultrasound (first-line imaging) 1
  • CTA or MRA if revascularization is being considered 1
  • Invasive angiography only for patients with critical limb ischemia (CLI) or lifestyle-limiting claudication with inadequate response to medical therapy 1

4. Revascularization Considerations

• Consider revascularization when:
  • Toe pressure <30 mmHg 4
  • TcPO₂ <30 mmHg 4
  • Presence of nonhealing wounds or gangrene 1
  • Lifestyle-limiting claudication despite adequate medical therapy 1

Special Considerations

• Diabetic patients: More likely to have ischemia (toe pressure <60 mmHg) than non-diabetic patients with PAD 7
• Patients on dialysis: 7.3 times increased likelihood of having PAD compared to patients not on dialysis 7
• Asymptomatic patients: Up to 68.7% of patients with PAD on hemodialysis may have no lower limb symptoms 3, warranting careful evaluation

Pitfalls to Avoid

1. Relying solely on ABI: Research shows that 43% of symptomatic PAD patients with significant stenosis (≥50%) on duplex ultrasound had normal/inconclusive resting ABIs 2

2. Missing asymptomatic disease: In patients with type 1 diabetes, studies suggest examining every 3 asymptomatic patients with normal pulses to unmask one case of PAD 8

3. Overlooking comorbidities: Patients with low TBI but normal ABI have similar rates of cardiovascular comorbidities as those with low ABI, indicating increased cardiovascular risk 5

4. Delaying treatment: Early identification and treatment may prevent lower limb amputation, cardiovascular events, and death 3