the ankle brachial index measurement, calculation, and interpretation limitations ivan casserly md...
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The Ankle Brachial IndexThe Ankle Brachial IndexMeasurement, Calculation, and InterpretationMeasurement, Calculation, and Interpretation
LimitationsLimitations
Ivan Casserly MDIvan Casserly MD
Denver VA Medical CenterDenver VA Medical CenterUniversity of Colorado HospitalUniversity of Colorado Hospital
Ankle Brachial IndexAnkle Brachial Index
• Ankle brachial index (ABI)Ankle brachial index (ABI)
• Ankle brachial pressure index (ABPI)Ankle brachial pressure index (ABPI)
• Ankle arm index (AAI)Ankle arm index (AAI)
Ankle Brachial IndexAnkle Brachial IndexWhy should we care?Why should we care?
• In clinical practiceIn clinical practice
– Aids in diagnosis and assessment of patients with Aids in diagnosis and assessment of patients with symptoms suggestive of PADsymptoms suggestive of PAD
– Role in primary prevention since PAD is a powerful Role in primary prevention since PAD is a powerful independent predictor of CV morbidity and mortality independent predictor of CV morbidity and mortality regardless of symptomatic status of PAD. regardless of symptomatic status of PAD.
Ankle Brachial IndexAnkle Brachial IndexHow good is it at diagnosing PAD?How good is it at diagnosing PAD?
• Using gold standard of DSA angiography Using gold standard of DSA angiography
– >50% stenosis in lower extremity vessel >50% stenosis in lower extremity vessel
Ankle Brachial IndexAnkle Brachial IndexDiagnosis of PAD Diagnosis of PAD
0
10
20
30
40
50
60
70
80
90
Sensitivity Specificity Accuracy
HAP
Niazi et al, Cath Cardiovasc Interv 2006;68:788-792
Ankle Brachial IndexAnkle Brachial IndexRole in Primary Prevention – Low incidence of classic claudicationRole in Primary Prevention – Low incidence of classic claudication
PADPAD
ClaudicationClaudicationAtypical SymptomsAtypical SymptomsAsymptomaticAsymptomatic
StableStablePADPAD Rest PainRest Pain Tissue LossTissue Loss
CLI
Peripheral Arterial DiseasePeripheral Arterial DiseasePrevalencePrevalence
• PARTNERS Program (PAD Awareness, Risk, and Treatment: PARTNERS Program (PAD Awareness, Risk, and Treatment: New Resources for Survival)New Resources for Survival)
– 350 Primary care sites 350 Primary care sites – Patients (n=~7,000)Patients (n=~7,000)
• >70 yrs >70 yrs • 50-69 yrs with history DM or smoking50-69 yrs with history DM or smoking
– PVD diagnosisPVD diagnosis• ABI <0.9ABI <0.9• Previous documentationPrevious documentation• Abnormal vasc studiesAbnormal vasc studies• Prior revascularizationPrior revascularization
Hirsch AT, JAMA 2001;286:1317-1324Hirsch AT, JAMA 2001;286:1317-1324
Peripheral Arterial DiseasePeripheral Arterial DiseasePrevalencePrevalence
0
5
10
15
20
25
%
PVD CVD PVD + CVD
13%
24%
16%
Hirsch AT, JAMA 2001;286:1317-1324Hirsch AT, JAMA 2001;286:1317-1324
Peripheral Arterial DiseasePeripheral Arterial DiseaseUnder-diagnosis in Primary Care Practice / Influence of assoc. diagnosis of CVDUnder-diagnosis in Primary Care Practice / Influence of assoc. diagnosis of CVD
0
2
4
6
8
10
12
%
PVD PVD + CVD
New
Prior7%
6% 6%
10%
Hirsch AT, JAMA 2001;286:1317-1324Hirsch AT, JAMA 2001;286:1317-1324
Adapted from Criqui MH, et al. N Engl J Med. 1992;326:381-386.Adapted from Criqui MH, et al. N Engl J Med. 1992;326:381-386.
Normal Subjects
Asymptomatic PAD
Symptomatic PAD
Severe Symptomatic PAD Su
rviv
al
Year
1.00
1210864200.00
0.25
0.50
0.75
Peripheral Arterial DiseasePeripheral Arterial DiseaseImpact of Diagnosis on Survival Impact of Diagnosis on Survival
Resnick et al. CirculationResnick et al. Circulation 2004;109;733-7392004;109;733-739
Peripheral Arterial DiseasePeripheral Arterial DiseaseImpact of Diagnosis on SurvivalImpact of Diagnosis on Survival
Peripheral Arterial DiseasePeripheral Arterial DiseaseImpact of Diagnosis on Survival – Polyvascular DiseaseImpact of Diagnosis on Survival – Polyvascular Disease
0
5
10
15
20
25
30
All-cause Mortality CV death Nonfatal MI CV death, MI,stroke, or
hospitalization
%
PAD alone PAD +CVD PAD + CHD PAD + CHD + CVD
Adapted from PG Steg et al. JAMA.2007;297:1197-1206.
ABI and Primary PreventionABI and Primary PreventionAlgorithmAlgorithm
Doobay AV et al. Arterioscler Thromb Vasc Biol.2005;25:1463-1469.
Ankle Brachial IndexAnkle Brachial Index
• PerformancePerformance
• CalculationCalculation
• InterpretationInterpretation
Ankle Brachial IndexAnkle Brachial IndexPerformance - EquipmentPerformance - Equipment
Ankle Brachial Index Ankle Brachial Index PerformancePerformance
Hiatt WR, N Engl J Med 2001;344:1608-1621
Ankle Brachial IndexAnkle Brachial IndexPerformancePerformance
• CLINICAL DEMONSTRATIONCLINICAL DEMONSTRATION
Ankle Brachial IndexAnkle Brachial IndexPerformance - ReviewPerformance - Review
• Patient PositionPatient Position
– No activity for 4-5 minutesNo activity for 4-5 minutes
– Supine positionSupine position
Ankle Brachial IndexAnkle Brachial IndexPerformance – Arm PressurePerformance – Arm Pressure
• Arm Arm
– Appropriate cuff sizeAppropriate cuff size
– Doppler over brachial arteryDoppler over brachial artery
• NOT STETHESCOPE (underestimate SBP)NOT STETHESCOPE (underestimate SBP)
• NOT OVER RADIAL ARTERYNOT OVER RADIAL ARTERY
– Record right AND left arm brachial pressuresRecord right AND left arm brachial pressures
• Why?Why?
Ankle Brachial IndexAnkle Brachial IndexPerformance – Ankle PressurePerformance – Ankle Pressure
• CuffCuff
– Appropriate sizeAppropriate size
– Appropriate locationAppropriate location
• Lower leg above malleoliLower leg above malleoli
• NOT OVER BULK OF CALF MUSCLESNOT OVER BULK OF CALF MUSCLES
• Doppler over DP AND PTDoppler over DP AND PT
– NOT STETHESCOPENOT STETHESCOPE
Ankle Brachial IndexAnkle Brachial IndexCalculationCalculation
• ABIABI
– Numerator – Ankle pressuresNumerator – Ankle pressures
• Higher of the two pedal pressuresHigher of the two pedal pressures
• BrachialBrachial
– Denominator – Brachial pressureDenominator – Brachial pressure
– Higher of the two arm pressuresHigher of the two arm pressures
– Best reflects aortic pressureBest reflects aortic pressure
Ankle Brachial IndexAnkle Brachial IndexCalculation - RationaleCalculation - Rationale
• Method 1. Method 1.
– Higher of the two Higher of the two pressurespressures
– ABI 150/150 = 1ABI 150/150 = 1
• Sensitivity ↓Sensitivity ↓
• Specificity ↑Specificity ↑
• Method 2. Method 2.
– Lower of the two Lower of the two pressurespressures
– ABO 100/150 = 0.66ABO 100/150 = 0.66
• Sensitivity ↑Sensitivity ↑
• Specificity ↓Specificity ↓
• PatientPatient
– DP 100, PT 150, Highest brachial 150DP 100, PT 150, Highest brachial 150
Ankle Brachial IndexAnkle Brachial IndexHigh versus Low Ankle Pressure (HAP vs LAP) High versus Low Ankle Pressure (HAP vs LAP)
0
10
20
30
40
50
60
70
80
90
Sensitivity Specificity Accuracy
HAP
LAP
Niazi et al, Cath Cardiovasc Interv 2006;68:788-792
Ankle Brachial IndexAnkle Brachial IndexInterpretationInterpretation
• What is a normal ABI?What is a normal ABI?
Ankle Brachial IndexAnkle Brachial IndexInterpretationInterpretation
• Normal ankle pressure is 8-15% higher than arm Normal ankle pressure is 8-15% higher than arm pressurepressure
• Epidemiological studies have used ABI of 0.9 as cutoff Epidemiological studies have used ABI of 0.9 as cutoff of normal from abnormal for diagnosis of PAD. of normal from abnormal for diagnosis of PAD.
Ankle Brachial IndexAnkle Brachial IndexInterpretation – High ABI – Non-compressible vessels Interpretation – High ABI – Non-compressible vessels
Ankle Brachial Index Ankle Brachial Index InterpretationInterpretation
ABI Interpretation >1.3 Non-compresssible 1.00 - 1.29 Normal 0.91 - 0.99 Equivocal 0.41 - 0.90 Mild-to-moderate PVD 0.00 - 0.40 Severe PVD
Hirsch AT et al, J Am Coll Cardiol 2006;47:1239-1312
StudyStudy
• 17 volunteers17 volunteers
– 11stst year n=10 year n=10
– 22ndnd year n=4 year n=4
– 33rdrd year n=3 year n=3
Feedback from StudyFeedback from StudyPart A – Performance of ABIPart A – Performance of ABI
• Measure ABI for right leg on Measure ABI for right leg on patientpatient
Measure Right ABIMeasure Right ABIFeedback – Arm MeasurementFeedback – Arm Measurement
0
20
40
60
80
100
%
Cuff size Rt and Lt Brachial Doppler
Correct
N=1N=2
N=15
Measure Right ABIMeasure Right ABIFeedback – Leg MeasurementFeedback – Leg Measurement
0
20
40
60
80
100
%
Cuff size CuffLocation
DP and PT Doppler*
Correct
N=1N=3
N=8N=9
* Obtained accurate Doppler signal from DP and PT
Feedback from StudyFeedback from StudyPart B – Calculation of ABIPart B – Calculation of ABI
• Right brachialRight brachial
• Left brachialLeft brachial
• Right PTRight PT
• Right DPRight DP
• Left PTLeft PT
• Left DPLeft DP
• AA
• BB
• CC
• DD
• EE
• FF
150mmHg150mmHg
140mmHg140mmHg
100mmHg100mmHg
130mmHg130mmHg
120mmHg120mmHg
105mmHg105mmHg
Right ABI = D/ALeft ABI = E/A
ABI Calculation ABI Calculation FeedbackFeedback
• ErrorsErrors
– Brachial:Ankle indexBrachial:Ankle index
– Same leg/armSame leg/arm
• Right ankle/right armRight ankle/right arm
• Left ankle/left armLeft ankle/left arm
– Lower brachial pressureLower brachial pressure
– Use of DP aloneUse of DP alone
– Use of PT aloneUse of PT alone
0
20
40
60
80
100
%
ABI calculation
Correct
N=1
Feedback from StudyFeedback from StudyPart C – Interpretation of ABIPart C – Interpretation of ABI
• A – non-compressibleA – non-compressible
• B – normalB – normal
• C – mildC – mild
• D – ModerateD – Moderate
• E - SevereE - Severe
• ABIABI
– 1.61.6
– 1.21.2
– 1.01.0
– 0.80.8
– 0.40.4
ABI Interpretation ABI Interpretation FeedbackFeedback
0
20
40
60
80
100
%
ABIinterpretation
Correct
N=7
Ankle Brachial Index Ankle Brachial Index InterpretationInterpretation
ABI Interpretation >1.3 Non-compresssible 1.00 - 1.29 Normal 0.91 - 0.99 Equivocal 0.41 - 0.90 Mild-to-moderate PVD 0.00 - 0.40 Severe PVD
Ankle Brachial IndexAnkle Brachial IndexLimitationsLimitations
• Localization of diseaseLocalization of disease
• Non-compressible ABINon-compressible ABI
• Pseudo-normal ABIPseudo-normal ABI
• Resting versus exercise ABIResting versus exercise ABI
• Role in diagnosis of critical limb ischemia (CLI)Role in diagnosis of critical limb ischemia (CLI)
• Hypertensive patientHypertensive patient
ABI and Localization of DiseaseABI and Localization of DiseaseSegmental Limb PressuresSegmental Limb Pressures
BrachialBrachial
Upper ThighUpper Thigh
Upper CalfUpper Calf
AnkleAnkle
ToeToe
Aorto-Iliac, CFA, Prox SFAAorto-Iliac, CFA, Prox SFA
Mid/distal SFA and PoplitealMid/distal SFA and Popliteal
TibialTibial
Small Vessel DiseaseSmall Vessel Disease
ABI and Localization of DiseaseABI and Localization of DiseasePulse Volume RecordingsPulse Volume Recordings
• Measures volume change in Measures volume change in limb with each pulsationlimb with each pulsation
• Volume of tissue and venous Volume of tissue and venous blood relatively constantblood relatively constant
• Change in volume due to Change in volume due to arterial inflowarterial inflow
• Cuffs inflated to ~60mmHgCuffs inflated to ~60mmHg
• Volume change presented on Volume change presented on spectral displayspectral display
• Similar to arterial pulse wave Similar to arterial pulse wave tracingtracing
• Stenosis indicated by loss of Stenosis indicated by loss of amplitude during systoleamplitude during systole
Non-Compressible ABINon-Compressible ABI
Non-Compressible ABIsNon-Compressible ABIsRole of Toe PressureRole of Toe Pressure
• Toe Pressure Toe Pressure
– Great toeGreat toe 32mHg32mHg
– 22ndnd toe toe 35mmHg35mmHg
– 33rdrd toe toe17mmHg17mmHg
– 44thth toe toe 19mmHg19mmHg
– 55thth toe toe absentabsent
•Normal toe-brachial index > 0.7Normal toe-brachial index > 0.7
Non-invasive Hemodynamic EvaluationNon-invasive Hemodynamic EvaluationToe PressureToe Pressure
Pseudonormal ABIPseudonormal ABI
PAD
Vessel Ca 2+
ABI
Resting versus Exercise ABIResting versus Exercise ABIExercise TestingExercise Testing
• Exercise Exercise
– ABI at baselineABI at baseline
– 2 mph at 12% grade, 5 2 mph at 12% grade, 5 minutesminutes
– ABI post-exercise, 1 minute, ABI post-exercise, 1 minute, then q 2 minutesthen q 2 minutes
• Post-exercise ankle systolic Post-exercise ankle systolic pressure pressure
– Falls >20% from baselineFalls >20% from baseline
– Takes longer than 3 minutes Takes longer than 3 minutes to recoverto recover
Resting versus Exercise ABIResting versus Exercise ABIExercise TestingExercise Testing
0
20
40
60
80
100
%
Normal Abnormal Non-compressible
ABI
0
20
40
60
80
100
%
ExerciseNormal
ExerciesAbnormal
Resting ABIResting ABI Exercise ABIExercise ABI
N=396 symptomatic patients with PAD.N=396 symptomatic patients with PAD.
Resting versus Exercise ABIResting versus Exercise ABIExercise TestingExercise Testing
• 58 year old male58 year old male
• Right buttock claudicationRight buttock claudication
– Classic descriptionClassic description
Non-invasive Hemodynamic EvaluationNon-invasive Hemodynamic EvaluationExercise TestingExercise Testing
Delete
Delete n=49
ABI in Patients with Critical Limb IschemiaABI in Patients with Critical Limb IschemiaLimitationLimitation
ABIABI
ABI in Patients with Critical Limb IschemiaABI in Patients with Critical Limb IschemiaImportance of Indication for AssessmentImportance of Indication for Assessment
Lower Extremities Test DEC 14,2005@14:00 SEGMENTAL LIMB PRESSURE (mm Hg) PVR (CATEGORY-AMPLITUDE) RIGHT LEFT RIGHT LEFT RESTING LEVELS 142 138 BRACHIAL 1-92 1-49 160 170 THIGH 1-50 1-50 152 150 CALF 1-60 1-78 140 (0.99) 160 (1.13) ANKLE 2-16 1-35 TM 2.5 2-26 2-21 92 110 TOE 5.0
Right HeelRight Heel
Ankle Pressure 140mmHgABI 0.99Toe Pressure 92mmHg
Popliteal and Tibial AngiographyPopliteal and Tibial Angiography
ATAT
ATAT
PTPT
PTPT
PeronealPeroneal
PeronealPeroneal
ConclusionsConclusions
• ABI ABI
– Helpful in diagnosis and assessment of patients Helpful in diagnosis and assessment of patients with symptomatic PADwith symptomatic PAD
– Useful in primary prevention of CV morbidity and Useful in primary prevention of CV morbidity and mortality, especially in asymptomatic patients or mortality, especially in asymptomatic patients or patients with atypical symptoms. patients with atypical symptoms.
– Requires training in order to perform correctly and Requires training in order to perform correctly and calculate ABIcalculate ABI
– Has limitations that should be understoodHas limitations that should be understood