ABI Testing After Normal CTA: Limited Role

Diagnostic Hierarchy and Limitations

• The American Heart Association recommends CTA is reserved for highly symptomatic patients in whom revascularization is being considered, not as a first-line diagnostic tool 1, 2
• Anatomic imaging, such as CTA, shows vessel stenosis but does not assess hemodynamic significance or functional impairment, according to the American College of Cardiology 1
• A normal CTA demonstrates no significant anatomic stenosis, but this does not exclude functionally significant PAD, as stated by the American Heart Association 1

Specific Clinical Scenarios Requiring ABI Despite Normal CTA

• The American College of Cardiology recommends that patients with exertional non-joint-related leg symptoms and normal or borderline resting ABI should undergo exercise treadmill ABI testing to evaluate for PAD (Class I Recommendation) 1, 2
• Exercise ABI is critical for differentiating arterial claudication from pseudoclaudication when resting studies are normal, according to the Journal of the American College of Cardiology 3
• When ABI is >1.40, the American Heart Association recommends measuring toe-brachial index (TBI) (Class I recommendation) 1, 2, 4

Practical Algorithm

• The American Heart Association recommends performing resting ABI bilaterally when CTA is normal but symptoms persist, and if ABI >1.40, measure TBI 1, 2
• Exercise treadmill ABI testing is recommended for symptomatic patients with normal/borderline resting ABI, with a decrease in post-exercise ABI of >20% or absolute decrease >0.15 suggesting PAD, according to the Journal of the American College of Cardiology 3

Critical Pitfalls to Avoid

• The American College of Cardiology advises not to assume normal CTA excludes PAD, as CTA shows anatomy, not hemodynamics, and functional stenosis may exist without significant anatomic narrowing 1
• The American Heart Association recommends not to skip exercise ABI testing in symptomatic patients, as resting studies can miss exercise-induced ischemia 1, 2
• The American College of Cardiology advises not to rely on ABI alone in diabetic or elderly patients, and to use TBI when ABI >1.40 due to medial arterial calcification 1, 2, 4

ABI Testing for Lower Extremity Wounds

Indications for ABI Testing

• The American College of Cardiology recommends ABI testing as a first-line test for patients with suspected lower extremity PAD, defined as individuals with exertional leg symptoms, age ≥70 years, or age 50-69 years with a history of smoking or diabetes 5, 6
• ABI should be performed in patients with history or physical examination findings suggestive of PAD to establish the diagnosis, according to the American College of Cardiology 6, 7
• ABI measurement is reasonable in patients at increased risk of PAD even without history or physical examination findings suggestive of PAD, as recommended by the American College of Cardiology 6, 7

Limitations of ABI in Wound Assessment

• ABI may be normal in nearly one-quarter of patients with chronic limb-threatening ischemia, making it unreliable as the sole assessment tool, with a strength of evidence based on clinical guidelines from the American College of Cardiology 8
• The concordance between ABI and toe pressure/toe-brachial index among patients with chronic limb-threatening ischemia is poor, with only 58% of patients who meet criteria for abnormal toe pressures presenting with abnormal ABIs, according to the American College of Cardiology 8
• ABI may not be accurate when systolic blood pressure cannot be abolished by inflation of an air-filled blood pressure cuff (noncompressible pedal arteries), as occurs in some diabetic or elderly individuals, as noted by the American College of Cardiology 9

Comprehensive Vascular Assessment Approach

• For optimal wound assessment, a comprehensive approach is recommended, including initial ABI measurement for all patients with lower extremity wounds, with a strength of evidence based on clinical guidelines from the American College of Cardiology 8
• Additional testing, such as toe-brachial index (TBI), should be measured when ABI is >1.40 due to noncompressible vessels, as recommended by the American College of Cardiology and Circulation 6, 10
• Perfusion assessment measures, such as TcPO2 and SPP, can predict wound healing potential, with a TcPO2 >30 mm Hg or an SPP >40 mm Hg, according to Circulation 10