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The Ankle Brachial Index Measurement, Calculation, and Interpretation Limitations

The Ankle Brachial Index Measurement, Calculation, and Interpretation Limitations. Ivan Casserly MD Denver VA Medical Center University of Colorado Hospital. Ankle Brachial Index. Ankle brachial index (ABI) Ankle brachial pressure index (ABPI) Ankle arm index (AAI).

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The Ankle Brachial Index Measurement, Calculation, and Interpretation Limitations

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  1. The Ankle Brachial IndexMeasurement, Calculation, and InterpretationLimitations Ivan Casserly MD Denver VA Medical Center University of Colorado Hospital

  2. 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 • >50% stenosis in lower extremity vessel

  5. Ankle Brachial IndexDiagnosis of PAD Niazi et al, Cath Cardiovasc Interv 2006;68:788-792

  6. Ankle Brachial IndexRole in Primary Prevention – Low incidence of classic claudication PAD Asymptomatic Atypical Symptoms Claudication 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 (n=~7,000) • >70 yrs • 50-69 yrs with history DM or smoking • PVD diagnosis • ABI <0.9 • Previous documentation • Abnormal vasc studies • Prior revascularization Hirsch AT, JAMA 2001;286:1317-1324

  8. Peripheral Arterial DiseasePrevalence 24% 16% 13% Hirsch AT, JAMA 2001;286:1317-1324

  9. Peripheral Arterial DiseaseUnder-diagnosis in Primary Care Practice / Influence of assoc. diagnosis of CVD 10% 7% 6% 6% Hirsch AT, JAMA 2001;286:1317-1324

  10. 1.00 Normal Subjects 0.75 Asymptomatic PAD Survival 0.50 Symptomatic PAD Severe Symptomatic PAD 0.25 0.00 0 2 4 8 10 6 12 Year Peripheral Arterial DiseaseImpact of Diagnosis on Survival Adapted from Criqui MH, et al. N Engl J Med. 1992;326:381-386.

  11. Peripheral Arterial DiseaseImpact of Diagnosis on Survival Resnick et al. Circulation2004;109;733-739

  12. Peripheral Arterial DiseaseImpact of Diagnosis on Survival – Polyvascular Disease Adapted from PG Steg et al. JAMA.2007;297:1197-1206.

  13. ABI and Primary PreventionAlgorithm Doobay AV et al. Arterioscler Thromb Vasc Biol.2005;25:1463-1469.

  14. Ankle Brachial Index • Performance • Calculation • Interpretation

  15. Ankle Brachial IndexPerformance - Equipment

  16. Ankle Brachial Index Performance Hiatt WR, N Engl J Med 2001;344:1608-1621

  17. Ankle Brachial IndexPerformance • CLINICAL DEMONSTRATION

  18. Ankle Brachial IndexPerformance - Review • Patient Position • No activity for 4-5 minutes • Supine position

  19. 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?

  20. 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

  21. 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

  22. 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 ↓ Ankle Brachial IndexCalculation - Rationale • Patient • DP 100, PT 150, Highest brachial 150

  23. Ankle Brachial IndexHigh versus Low Ankle Pressure (HAP vs LAP) Niazi et al, Cath Cardiovasc Interv 2006;68:788-792

  24. Ankle Brachial IndexInterpretation • What is a normal ABI?

  25. 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.

  26. Ankle Brachial IndexInterpretation – High ABI – Non-compressible vessels

  27. Ankle Brachial Index Interpretation Hirsch AT et al, J Am Coll Cardiol 2006;47:1239-1312

  28. Study • 17 volunteers • 1st year n=10 • 2nd year n=4 • 3rd year n=3

  29. Measure ABI for right leg on patient Feedback from StudyPart A – Performance of ABI

  30. Measure Right ABIFeedback – Arm Measurement N=15 N=2 N=1

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

  32. Right brachial Left brachial Right PT Right DP Left PT Left DP A B C D E F Feedback from StudyPart B – Calculation of ABI 150mmHg 140mmHg 100mmHg 130mmHg 120mmHg 105mmHg Right ABI = D/A Left ABI = E/A

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

  34. A – non-compressible B – normal C – mild D – Moderate E - Severe Feedback from StudyPart C – Interpretation of ABI • ABI • 1.6 • 1.2 • 1.0 • 0.8 • 0.4

  35. ABI Interpretation Feedback N=7

  36. Ankle Brachial Index Interpretation

  37. 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

  38. 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

  39. 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 ABI and Localization of DiseasePulse Volume Recordings

  40. Non-Compressible ABI

  41. 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 > 0.7

  42. Non-invasive Hemodynamic EvaluationToe Pressure

  43. Pseudonormal ABI PAD Vessel Ca 2+ ABI

  44. 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 >20% from baseline Takes longer than 3 minutes to recover Resting versus Exercise ABIExercise Testing

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

  46. 58 year old male Right buttock claudication Classic description Resting versus Exercise ABIExercise Testing

  47. Non-invasive Hemodynamic EvaluationExercise Testing

  48. ABI in Patients with Critical Limb IschemiaLimitation Delete n=49 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

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