The Ankle Brachial Index Measurement, Calculation, and Interpretation Limitations

1
The Ankle Brachial IndexMeasurement,
Calculation, and InterpretationLimitations

• Ivan Casserly MD
• Denver VA Medical Center
• University of Colorado Hospital

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Ankle Brachial Index

• Ankle brachial index (ABI)
• Ankle brachial pressure index (ABPI)
• Ankle arm index (AAI)

3
Ankle Brachial IndexWhy should we care?

• In clinical practice
• Aids in diagnosis and assessment of patients with
  symptoms suggestive of PAD
• Role in primary prevention since PAD is a
  powerful independent predictor of CV morbidity
  and mortality regardless of symptomatic status of
  PAD.

4
Ankle Brachial IndexHow good is it at diagnosing
PAD?

• Using gold standard of DSA angiography
• gt50 stenosis in lower extremity vessel

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Ankle Brachial IndexDiagnosis of PAD
Niazi et al, Cath Cardiovasc Interv
200668788-792
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Ankle Brachial IndexRole in Primary Prevention
Low incidence of classic claudication
PAD
Claudication
Atypical Symptoms
Asymptomatic
Stable PAD
Rest Pain
Tissue Loss
CLI
7
Peripheral Arterial DiseasePrevalence

• PARTNERS Program (PAD Awareness, Risk, and
  Treatment New Resources for Survival)
• 350 Primary care sites
• Patients (n7,000)
• gt70 yrs
• 50-69 yrs with history DM or smoking
• PVD diagnosis
• ABI lt0.9
• Previous documentation
• Abnormal vasc studies
• Prior revascularization

Hirsch AT, JAMA 20012861317-1324
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Peripheral Arterial DiseasePrevalence
24
16
13
Hirsch AT, JAMA 20012861317-1324
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Peripheral Arterial DiseaseUnder-diagnosis in
Primary Care Practice / Influence of assoc.
diagnosis of CVD
10
7
6
6
Hirsch AT, JAMA 20012861317-1324
10
Peripheral Arterial DiseaseImpact of Diagnosis
on Survival
Adapted from Criqui MH, et al. N Engl J Med.
1992326381-386.
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Peripheral Arterial DiseaseImpact of Diagnosis
on Survival
Resnick et al. Circulation 2004109733-739
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Peripheral Arterial DiseaseImpact of Diagnosis
on Survival Polyvascular Disease
Adapted from PG Steg et al. JAMA.20072971197-12
06.
13
ABI and Primary PreventionAlgorithm
Doobay AV et al. Arterioscler Thromb Vasc
Biol.2005251463-1469.
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Ankle Brachial Index

• Performance
• Calculation
• Interpretation

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Ankle Brachial IndexPerformance - Equipment
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Ankle Brachial Index Performance
Hiatt WR, N Engl J Med 20013441608-1621
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Ankle Brachial IndexPerformance

• CLINICAL DEMONSTRATION

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Ankle Brachial IndexPerformance - Review

• Patient Position
• No activity for 4-5 minutes
• Supine position

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Ankle Brachial IndexPerformance Arm Pressure

• Arm
• Appropriate cuff size
• Doppler over brachial artery
• NOT STETHESCOPE (underestimate SBP)
• NOT OVER RADIAL ARTERY
• Record right AND left arm brachial pressures
• Why?

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Ankle Brachial IndexPerformance Ankle Pressure

• Cuff
• Appropriate size
• Appropriate location
• Lower leg above malleoli
• NOT OVER BULK OF CALF MUSCLES
• Doppler over DP AND PT
• NOT STETHESCOPE

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Ankle Brachial IndexCalculation

• ABI
• Numerator Ankle pressures
• Higher of the two pedal pressures
• Brachial
• Denominator Brachial pressure
• Higher of the two arm pressures
• Best reflects aortic pressure

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Ankle Brachial IndexCalculation - Rationale

• Patient
• DP 100, PT 150, Highest brachial 150

• Method 1.
• Higher of the two pressures
• ABI 150/150 1
• Sensitivity ?
• Specificity ?

• Method 2.
• Lower of the two pressures
• ABO 100/150 0.66
• Sensitivity ?
• Specificity ?

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Ankle Brachial IndexHigh versus Low Ankle
Pressure (HAP vs LAP)
Niazi et al, Cath Cardiovasc Interv
200668788-792
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Ankle Brachial IndexInterpretation

• What is a normal ABI?

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Ankle Brachial IndexInterpretation

• Normal ankle pressure is 8-15 higher than arm
  pressure
• Epidemiological studies have used ABI of 0.9 as
  cutoff of normal from abnormal for diagnosis of
  PAD.

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Ankle Brachial IndexInterpretation High ABI
Non-compressible vessels
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Ankle Brachial Index Interpretation
Hirsch AT et al, J Am Coll Cardiol
2006471239-1312
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Study

• 17 volunteers
• 1st year n10
• 2nd year n4
• 3rd year n3

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Feedback from StudyPart A Performance of ABI

• Measure ABI for right leg on patient

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Measure Right ABIFeedback Arm Measurement
N15
N2
N1
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Measure Right ABIFeedback Leg Measurement
N9
N8
N3
N1
Obtained accurate Doppler signal from DP and PT
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Feedback from StudyPart B Calculation of ABI

• Right brachial
• Left brachial
• Right PT
• Right DP
• Left PT
• Left DP

• A
• B
• C
• D
• E
• F

150mmHg 140mmHg 100mmHg 130mmHg 120mmHg 105mmHg
Right ABI D/A Left ABI E/A
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ABI Calculation Feedback

• Errors
• BrachialAnkle index
• Same leg/arm
• Right ankle/right arm
• Left ankle/left arm
• Lower brachial pressure
• Use of DP alone
• Use of PT alone

N1
34
Feedback from StudyPart C Interpretation of ABI

• A non-compressible
• B normal
• C mild
• D Moderate
• E - Severe

• ABI
• 1.6
• 1.2
• 1.0
• 0.8
• 0.4

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ABI Interpretation Feedback
N7
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Ankle Brachial Index Interpretation
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Ankle Brachial IndexLimitations

• Localization of disease
• Non-compressible ABI
• Pseudo-normal ABI
• Resting versus exercise ABI
• Role in diagnosis of critical limb ischemia (CLI)
• Hypertensive patient

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ABI and Localization of DiseaseSegmental Limb
Pressures
Brachial Upper Thigh Upper Calf Ankle Toe
Aorto-Iliac, CFA, Prox SFA Mid/distal SFA and
Popliteal Tibial Small Vessel Disease
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ABI and Localization of DiseasePulse Volume
Recordings

• Measures volume change in limb with each
  pulsation
• Volume of tissue and venous blood relatively
  constant
• Change in volume due to arterial inflow
• Cuffs inflated to 60mmHg
• Volume change presented on spectral display
• Similar to arterial pulse wave tracing
• Stenosis indicated by loss of amplitude during
  systole

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Non-Compressible ABI
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Non-Compressible ABIsRole of Toe Pressure

• Toe Pressure
• Great toe 32mHg
• 2nd toe 35mmHg
• 3rd toe 17mmHg
• 4th toe 19mmHg
• 5th toe absent

• Normal toe-brachial index gt 0.7

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Non-invasive Hemodynamic EvaluationToe Pressure
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Pseudonormal ABI
PAD
Vessel Ca 2
ABI
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Resting versus Exercise ABIExercise Testing

• Exercise
• ABI at baseline
• 2 mph at 12 grade, 5 minutes
• ABI post-exercise, 1 minute, then q 2 minutes
• Post-exercise ankle systolic pressure
• Falls gt20 from baseline
• Takes longer than 3 minutes to recover

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Resting versus Exercise ABIExercise Testing
Resting ABI
Exercise ABI
N396 symptomatic patients with PAD.
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Resting versus Exercise ABIExercise Testing

• 58 year old male
• Right buttock claudication
• Classic description

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Non-invasive Hemodynamic EvaluationExercise
Testing
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ABI in Patients with Critical Limb
IschemiaLimitation
Delete n49
ABI
Delete
49
ABI in Patients with Critical Limb
IschemiaImportance of Indication for Assessment
Ankle Pressure 140mmHg ABI 0.99 Toe Pressure
92mmHg
Right Heel
50
Popliteal and Tibial Angiography
AT
PT
Peroneal
AT
PT
Peroneal
51
Conclusions

• ABI
• Helpful in diagnosis and assessment of patients
  with symptomatic PAD
• Useful in primary prevention of CV morbidity and
  mortality, especially in asymptomatic patients or
  patients with atypical symptoms.
• Requires training in order to perform correctly
  and calculate ABI
• Has limitations that should be understood