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The Ankle Brachial Index Measurement, Calculation, and Interpretation Limitations Ivan Casserly MD Denver VA Medical Center University of Colorado Hospital.

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Presentation on theme: "The Ankle Brachial Index Measurement, Calculation, and Interpretation Limitations Ivan Casserly MD Denver VA Medical Center University of Colorado Hospital."— Presentation transcript:

1 The Ankle Brachial Index Measurement, Calculation, and Interpretation Limitations Ivan Casserly MD Denver VA Medical Center University of Colorado Hospital

2 Ankle 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)

3 Ankle Brachial Index Why should we care? In clinical practiceIn 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 Index How good is it at diagnosing PAD? Using gold standard of DSA angiographyUsing gold standard of DSA angiography –>50% stenosis in lower extremity vessel

5 Ankle Brachial Index Diagnosis of PAD Niazi et al, Cath Cardiovasc Interv 2006;68:

6 Ankle Brachial Index Role in Primary Prevention – Low incidence of classic claudication PAD Claudication Atypical Symptoms Asymptomatic StablePAD Rest Pain Tissue Loss CLI

7 Peripheral Arterial Disease Prevalence PARTNERS Program (PAD Awareness, Risk, and Treatment: New Resources for Survival)PARTNERS Program (PAD Awareness, Risk, and Treatment: New Resources for Survival) –350 Primary care sites –Patients (n=~7,000) >70 yrs>70 yrs yrs with history DM or smoking50-69 yrs with history DM or smoking –PVD diagnosis ABI <0.9ABI <0.9 Previous documentationPrevious documentation Abnormal vasc studiesAbnormal vasc studies Prior revascularizationPrior revascularization Hirsch AT, JAMA 2001;286:

8 Peripheral Arterial Disease Prevalence 13% 24% 16% Hirsch AT, JAMA 2001;286:

9 Peripheral Arterial Disease Under-diagnosis in Primary Care Practice / Influence of assoc. diagnosis of CVD 7% 6% 10% Hirsch AT, JAMA 2001;286:

10 Adapted from Criqui MH, et al. N Engl J Med. 1992;326: Normal Subjects Asymptomatic PAD Symptomatic PAD Severe Symptomatic PAD Survival Year Peripheral Arterial Disease Impact of Diagnosis on Survival

11 Resnick et al. Circulation 2004;109; Peripheral Arterial Disease Impact of Diagnosis on Survival

12 Peripheral Arterial Disease Impact of Diagnosis on Survival – Polyvascular Disease Adapted from PG Steg et al. JAMA.2007;297:

13 ABI and Primary Prevention Algorithm Doobay AV et al. Arterioscler Thromb Vasc Biol.2005;25:

14 Ankle Brachial Index PerformancePerformance CalculationCalculation InterpretationInterpretation

15 Ankle Brachial Index Performance - Equipment

16 Ankle Brachial Index Performance Hiatt WR, N Engl J Med 2001;344:

17 Ankle Brachial Index Performance CLINICAL DEMONSTRATIONCLINICAL DEMONSTRATION

18 Ankle Brachial Index Performance - Review Patient PositionPatient Position –No activity for 4-5 minutes –Supine position

19 Ankle Brachial Index Performance – Arm Pressure ArmArm –Appropriate cuff size –Doppler over brachial artery NOT STETHESCOPE (underestimate SBP)NOT STETHESCOPE (underestimate SBP) NOT OVER RADIAL ARTERYNOT OVER RADIAL ARTERY –Record right AND left arm brachial pressures Why?Why?

20 Ankle Brachial Index Performance – Ankle Pressure CuffCuff –Appropriate size –Appropriate 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 STETHESCOPE

21 Ankle Brachial Index Calculation ABIABI –Numerator – Ankle pressures Higher of the two pedal pressuresHigher of the two pedal pressures BrachialBrachial –Denominator – Brachial pressure –Higher of the two arm pressures –Best reflects aortic pressure

22 Ankle Brachial Index Calculation - Rationale Method 1.Method 1. –Higher of the two pressures –ABI 150/150 = 1 Sensitivity ↓Sensitivity ↓ Specificity ↑Specificity ↑ Method 2.Method 2. –Lower of the two pressures –ABO 100/150 = 0.66 Sensitivity ↑Sensitivity ↑ Specificity ↓Specificity ↓ PatientPatient –DP 100, PT 150, Highest brachial 150

23 Ankle Brachial Index High versus Low Ankle Pressure (HAP vs LAP) Niazi et al, Cath Cardiovasc Interv 2006;68:

24 Ankle Brachial Index Interpretation What is a normal ABI?What is a normal ABI?

25 Ankle Brachial Index Interpretation Normal ankle pressure is 8-15% higher than arm pressureNormal 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.Epidemiological studies have used ABI of 0.9 as cutoff of normal from abnormal for diagnosis of PAD.

26 Ankle Brachial Index Interpretation – High ABI – Non-compressible vessels

27 Ankle Brachial Index Interpretation Hirsch AT et al, J Am Coll Cardiol 2006;47:

28 Study 17 volunteers17 volunteers –1 st year n=10 –2 nd year n=4 –3 rd year n=3

29 Feedback from Study Part A – Performance of ABI Measure ABI for right leg on patientMeasure ABI for right leg on patient

30 Measure Right ABI Feedback – Arm Measurement N=1 N=2 N=15

31 Measure Right ABI Feedback – Leg Measurement N=1 N=3 N=8 N=9 * Obtained accurate Doppler signal from DP and PT

32 Feedback from Study Part B – Calculation of ABI Right brachialRight brachial Left brachialLeft brachial Right PTRight PT Right DPRight DP Left PTLeft PT Left DPLeft DP A B C D E F 150mmHg140mmHg100mmHg130mmHg120mmHg105mmHg Right ABI = D/A Left ABI = E/A

33 ABI Calculation Feedback ErrorsErrors –Brachial:Ankle index –Same leg/arm Right ankle/right armRight ankle/right arm Left ankle/left armLeft ankle/left arm –Lower brachial pressure –Use of DP alone –Use of PT alone N=1

34 Feedback from Study Part C – Interpretation of ABI A – non-compressibleA – non-compressible B – normalB – normal C – mildC – mild D – ModerateD – Moderate E - SevereE - Severe ABIABI –1.6 –1.2 –1.0 –0.8 –0.4

35 ABI Interpretation Feedback N=7

36 Ankle Brachial Index Interpretation

37 Ankle Brachial Index Limitations 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

38 ABI and Localization of Disease Segmental Limb Pressures Brachial Upper Thigh Upper Calf AnkleToe Aorto-Iliac, CFA, Prox SFA Mid/distal SFA and Popliteal Tibial Small Vessel Disease

39 ABI and Localization of Disease Pulse Volume Recordings Measures volume change in limb with each pulsationMeasures volume change in limb with each pulsation Volume of tissue and venous blood relatively constantVolume of tissue and venous blood relatively constant Change in volume due to arterial inflowChange in volume due to arterial inflow Cuffs inflated to ~60mmHgCuffs inflated to ~60mmHg Volume change presented on spectral displayVolume change presented on spectral display Similar to arterial pulse wave tracingSimilar to arterial pulse wave tracing Stenosis indicated by loss of amplitude during systoleStenosis indicated by loss of amplitude during systole

40 Non-Compressible ABI

41 Non-Compressible ABIs Role of Toe Pressure Toe PressureToe Pressure –Great toe32mHg –2 nd toe 35mmHg –3 rd toe17mmHg –4 th toe 19mmHg –5 th toe absent Normal toe-brachial index > 0.7Normal toe-brachial index > 0.7

42 Non-invasive Hemodynamic Evaluation Toe Pressure

43 Pseudonormal ABI PAD Vessel Ca 2+ ABI

44 Resting versus Exercise ABI Exercise Testing ExerciseExercise –ABI at baseline –2 mph at 12% grade, 5 minutes –ABI post-exercise, 1 minute, then q 2 minutes Post-exercise ankle systolic pressurePost-exercise ankle systolic pressure –Falls >20% from baseline –Takes longer than 3 minutes to recover

45 Resting versus Exercise ABI Exercise Testing Resting ABI Exercise ABI N=396 symptomatic patients with PAD.

46 Resting versus Exercise ABI Exercise Testing 58 year old male58 year old male Right buttock claudicationRight buttock claudication –Classic description

47 Non-invasive Hemodynamic Evaluation Exercise Testing

48 Delete Delete n=49 ABI in Patients with Critical Limb Ischemia Limitation ABI

49 ABI in Patients with Critical Limb Ischemia Importance of Indication for Assessment Right Heel Ankle Pressure 140mmHg ABI 0.99 Toe Pressure 92mmHg

50 Popliteal and Tibial Angiography AT AT PT PT Peroneal Peroneal

51 Conclusions ABIABI –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


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