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 pressure index (ABPI)
Ankle arm index (AAI)

3. Ankle Brachial Index Why 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 Index How good is it at diagnosing PAD?
Using 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
Asymptomatic
Atypical Symptoms
Claudication
Substrate for CLI of underlying PAD.
Only 1-3% of all patients with PAD progress to CLI
Clinical pathway to CLI is variable - Prior to presentation with CLI, most patients will have been asymptomatic – perhaps related to sedentary existence, only a minority with prior claudication.
Some present with tissue loss (especially diabetics), others progress through rest pain and subsequent tissue loss.
Stable
PAD
Rest Pain
Tissue Loss
CLI

7. Peripheral Arterial Disease Prevalence
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:

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

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

10. Peripheral Arterial Disease Impact of Diagnosis on Survival
Normal Subjects
Asymptomatic PAD
Symptomatic PAD
Severe Symptomatic PAD
Survival
Year
1.00 12 10 8 6 4 2
0.00
0.25
0.50
0.75
severe symptomatic PAD had the worst prognosis: analysis of this group revealed a 15-fold increase in rates of mortality due to cardiovascular disease and CHD.
The study cited above categorized patients (n=565) into four groups: normals (n=318) and those with PAD (n=67). Evaluated were those with asymptomatic PAD (by Rose questionnaire) , those with symptomatic PAD (symptomatic and either abnormal ABI or diminished doppler flow velocities, not both) characterized by claudication, and those with PAD that was both symptomatic and severe (symptoms by Rose, and severity by both abnormal ABI and diminished doppler flow velocities).
The graph shows the survival curves for the three groups of patients compared with the normal subjects. Patients with severe symptomatic PAD had by far the worst prognosis of the three groups of patients; only one in four was still alive at the end of the 10-year follow-up period.
METHODS. We examined 565 men and women (average age, 66 years) for the presence of large-vessel peripheral arterial disease by means of two noninvasive techniques--measurement of segmental blood pressure and determination of flow velocity by Doppler ultrasound. We identified 67 subjects with the disease (11.9 percent), whom we followed prospectively for 10 years. RESULTS. Twenty-one of the 34 men (61.8 percent) and 11 of the 33 women (33.3 percent) with large-vessel peripheral arterial disease died during follow-up, as compared with 31 of the 183 men (16.9 percent) and 26 of the 225 women (11.6 percent) without evidence of peripheral arterial disease. After multivariate adjustment for age, sex, and other risk factors for cardiovascular disease, the relative risk of dying among subjects with large-vessel peripheral arterial disease as compared with those with no evidence of such disease was 3.1 (95 percent confidence interval, 1.9 to 4.9) for deaths from all causes, 5.9 (95 percent confidence interval, 3.0 to 11.4) for all deaths from cardiovascular disease, and 6.6 (95 percent confidence interval, 2.9 to 14.9) for deaths from coronary heart disease. The relative risk of death from causes other than cardiovascular disease was not significantly increased among the subjects with large-vessel peripheral arterial disease. After the exclusion of subjects who had a history of cardiovascular disease at base line, the relative risks among those with large-vessel peripheral arterial disease remained significantly elevated. Additional analyses revealed a 15-fold increase in rates of mortality due to cardiovascular disease and coronary heart disease among subjects with large-vessel peripheral arterial disease that was both severe and symptomatic. CONCLUSIONS. Patients with large-vessel peripheral arterial disease have a high risk of death from cardiovascular causes.
Adapted from Criqui MH, et al. N Engl J Med. 1992;326:
Criqui MH, Langer RD, Fronek A, et al. Mortality over a period of 10 years in patients with peripheral arterial disease. N Engl J Med. 1992;326:

11. Peripheral Arterial Disease Impact of Diagnosis on Survival
Data from the Strong Heart Study, n= Strong heart study Circ 2004;109: Only 25 patients with ABI<0.6
Background—The associations of low (0.90) and high (1.40) ankle brachial index (ABI) with risk of all-cause and
cardiovascular disease (CVD) mortality have not been examined in a population-based setting.
Methods and Results—We examined all-cause and CVD mortality in relation to low and high ABI in 4393 American
Indians in the Strong Heart Study. Participants had bilateral ABI measurements at baseline and were followed up for
years ( person-years). Cox regression was used to quantify mortality rates among participants with high
and low ABI relative to those with normal ABI (0.90 ABI 1.40). Death from all causes occurred in 1022 participants
(23.3%; 27.9 deaths per 1000 person-years), and of these, 272 (26.6%; 7.4 deaths per 1000 person-years) were
attributable to CVD. Low ABI was present in 216 participants (4.9%), and high ABI occurred in 404 (9.2%). Diabetes,
albuminuria, and hypertension occurred with greater frequency among persons with low (60.2%, 44.4%, and 50.1%) and
high (67.8%, 49.9%, and 45.1%) ABI compared with those with normal ABI (44.4%, 26.9%, and 36.5%), respectively
(P0.0001). Adjusted risk estimates for all-cause mortality were 1.69 (1.34 to 2.14) for low and 1.77 (1.48 to 2.13) for
high ABI, and estimates for CVD mortality were 2.52 (1.74 to 3.64) for low and 2.09 (1.49 to 2.94) for high ABI.
Conclusions—The association between high ABI and mortality was similar to that of low ABI and mortality, highlighting
a U-shaped association between this noninvasive measure of peripheral arterial disease and mortality risk. Our data
suggest that the upper limit of normal ABI should not exceed (Circulation. 2004;109: )
Resnick et al. Circulation 2004;109;

12. Peripheral Arterial Disease Impact of Diagnosis on Survival – Polyvascular Disease
Hospitalization events: Transient ischemic attack, unstable angina, or worsening of PAD.
Adjusted for sex and age.
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
Performance
Calculation
Interpretation

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 DEMONSTRATION

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

19. Ankle Brachial Index Performance – Arm Pressure
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 Index Performance – 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 Index Calculation
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. Ankle Brachial Index Calculation - 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 ↓

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?

25. Ankle Brachial Index Interpretation
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 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 volunteers
1st year n=10
2nd year n=4
3rd year n=3

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

30. Measure Right ABI Feedback – Arm Measurement

31. Measure Right ABI Feedback – Leg Measurement
* Obtained accurate Doppler signal from DP and PT

32. Feedback from Study Part B – Calculation of ABI
Right brachial
Left brachial
Right PT
Right DP
Left PT
Left DP
150mmHg
140mmHg
100mmHg
130mmHg
120mmHg
105mmHg A B C D E F
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. Feedback from Study Part C – Interpretation of ABI
1.6
1.2
1.0
0.8
0.4
A – non-compressible
B – normal
C – mild
D – Moderate
E - Severe

35. ABI Interpretation Feedback

36. Ankle Brachial Index Interpretation

37. Ankle Brachial Index Limitations
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 Disease Segmental Limb Pressures
Brachial
Upper Thigh
Upper Calf
Ankle
Toe
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 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

40. Non-Compressible ABI

41. Non-Compressible ABIs Role of Toe Pressure
Great toe 32mHg
2nd toe 35mmHg
3rd toe 17mmHg
4th toe 19mmHg
5th toe absent
Value of toe pressure in patients with non-compressible tibial vessels and supranormal ABI -
Normal 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
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

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 male
Right buttock claudication
Classic description

47. Non-invasive Hemodynamic Evaluation Exercise Testing

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

49. ABI in Patients with Critical Limb Ischemia Importance of Indication for Assessment
Hemodynamic findings are usually confirmatory – However exceptions exist as illustrated in this case.
Ankle Pressure 140mmHg
ABI
Toe Pressure 92mmHg
Right Heel

50. Popliteal and Tibial AngiographyAT PT
Peroneal AT
Emphasizing the point that anatomic definition is sometimes required to confirm the diagnosis. 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