Ankle Brachial Index Measurement: What is it and why measure it

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Ankle Brachial Index Measurement What is it and
why measure it?
Mary OConnor Cardiovascular Medical Science
Liason Bristol Myers Squibb Guinness
Storehouse 31st March 2006
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Ankle Brachial Index Measurement

• Non-invasive, rapid, quantitative measurement for
  assessing the arterial circulation
• 95 sensitivity, 99 specific
• An ABI 0.90 is diagnostic of PAD
• Permits stratification of the severity of PAD
• Assess disease progression
• Predict cardiovascular and cerebrovascular
  mortality

Mohler, E. Arch Intern Med. 2003 2306-2314
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How is Ankle-Brachial Index (ABI) measured?
ABI

• Measure ankle and brachial systolic pressures
  with Doppler
• Use highest arm and each ankle pressures1,2

1. TASC Working Group. Int Angiol 2000 19
(suppl) 5-34. 2. Vascular Disease Foundation,
2003. Available athttp//www.vdf.org/ABI.htm.
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Ankle Brachial Index Measurement
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Calculation of the of Ankle Brachial Index

• Pre-Procedure
• Position Resting supine 5 minutes prior to the
  measurement
• Allay anxiety explain procedure and
  reassure patient
• Equipment
• Handheld Doppler 5-10 MHz
• Ultrasound gel
• Sphygomanometer anaeroid or mercury

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Measurement of the Ankle Brachial Index

• Arms
• Place BP cuff on arm, Palpate the brachial pulse
• Apply ultrasound gel
• Angle the doppler probe between 45-65 angle
• Inflate the BP cuff until signal abolished
• Deflate slowly until signal returns
• Record the pressure at which signal returns,
  then deflate cuff completely
• Take the highest of the 2 systolic brachial
  pressures

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Measurement of the Ankle Brachial Index

• Legs
• Place cuff around leg just above the ankle
• Locate and record both the Posterior Tibial and
  Dorsalis Pedis systolic pressures in each limb
• Repeat the procedure as for arms
• Take the highest ankle systolic pressure in
  each limb for the ABI ratio

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ABI measurement

• Brachial Systolic blood pressure
• Right 156/88 mmHg
• Left 160/92 mmHg
• Right leg
• DP 160 mmHg
• PT 154 mmHg
• 160/160 1.00
• Left leg
• DP 96 mmHg
• PT 100 mmHg
• 100/160 0.63
• The lowest ABI between both legs is
• the ABI that stratifies the patients risk

Right 156 mmHg
Left 160 mmHg
DP 96 mmHg PT 100 mm Hg
DP 160 mm Hg PT 154 mmHg
Diagnosis moderate PAD in left leg
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How is Ankle-Brachial Index (ABI) measured?
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Interpretation of ABI

• Normal ABI 0.91 1.30
• An ABI 0.90 is diagnostic of PAD
• Mild PAD 0.70- 0.90
• Moderate PAD 0.41-0.69
• Severe PAD or Critical Limb Ischaemia 0.4
• Non-compressible 1.31

Hiatt, WR. NEJM. 2001 344 1608-1621
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Limitations of the ABI Measurement

• Non-compressible arteries ABI values ? 1.311
• Refer for other noninvasive testing
• Bilateral brachial pressures
• Difference of 20mmHg indicates arterial disease
  in upper extremity2
• Inability to localise arterial lesion accurately

1. Weitz et al. Circulation. 1996 94
3026-3049 2. Ollin JW. www.svmb.org/medpro/cme/p1/
cme_part1.html 2000
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ABI to Monitor Disease Progression

• Changes in ABI /- 0.15 indicate disease
  re/progression1
• An improved ABI suggest enhanced perfusion via
  collateral vessels
• A deterioration in ABI suggests disease
  progression or decreased perfusion secondary to
  revascularization procedure problems

1. Mohler, E. Arch Intern Med. 2003 163
2306-2314
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ABI to Assess Functional Capacity

• Decreasing ABI values are independently
  associated with impaired lower extremity
  functioning1, 2
• Lower ABI scores are associated with
• Slower walking velocity1, 2
• fewer blocks walked per week1,2
• Lower hip abduction force2
• Lower knee extension force2

1. MeDermott et al, Circulation. 2000
1011007-1012 2. Vogt et al, Journal Am Geriatric
Society. 1994 42 923-929
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Peripheral Arterial Disease

• Peripheral Arterial Disease is a manifestation of
  systemic atherosclerosis in which the arterial
  lumen of the lower extremities becomes
  progressively occluded by atherosclerotic plaque1
  
• it may be symptomatic or asymptomatic
• It is a distinct atherothrombotic syndrome

1. Criqui et al. In Fowkes FGR, ed.
Epideminiology of Peripheral Vascular Disease.
New York, NY Springer-Verlag 199185096
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5-year natural history of PAD
100 patientswith claudication who do notseek
medical advice
100 patients with asymptomatic PAD
100 patients diagnosedwith claudication
Local Events
Systemic Events
Worsening claudication25 patients
10 to 20 non-fatal MIs or strokes
PLUS
Surgical revascularization 10 patients
30 deaths
CHD 15 Other cardiovascular and
cerebrovascular 5 Non-cardiovascular 10
Major amputation 2 patients
Dormandy JA. Hosp Update 1991April314318.
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Symptomatic PAD

• 10 year mortality for Patients with large vessel
  PAD
• The risk of all cause mortality and death from
  CHD is more than 3 and 6 times respectively
  greater than in patients with no PAD1
• 3 fold excess cardiovascular morbidity at
  baseline compared with control subjects of the
  same sex2

1. Criqui et al. N Eng J Med. 1992 326
381-386 2. Criqui et al. Drugs. 1991 42 (supp
5) 16-21
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Asymptomatic PAD

• Asymptomatic PAD associated with an increased
  risk of
• atherothrombotic events ( MI and Stroke)1, 2
• Impaired lower extremity functioning3
• Internal artery carotid stenosis4, 5
• Patients with asymptomatic PAD have a risk factor
  and co-moribidity profile comparable to that of
  symptomatic patients1

1. Hooi et al. Scand J Prim Health Care. 1998
16 177-182 2. Criqui et al. Vasc Med.
1998 3 241-245 3. McDermott et al. Circulation.
2000 101 1007-1012. 4. Simons et
al. J Vasc Surg. 1999 30 519-525 5. House et
al. Cardiovascular Surgery. 1999 7 44-49
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Risk of death is increased in patients with both
symptomatic and asymptomatic PAD
100
Normal subjects
75
Asymptomatic PAD
50
Survival ( of patients)
Symptomatic PAD
25
Severe symptomatic PAD
0
0
2
4
6
8
10
12
Year
Kaplan-Meier survival curves based on mortality
from all causes.Large-vessel PAD.
Criqui MH et al. N Engl J Med 1992 326 381-386.
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ABI as a Predictor of Cardiovascular Morbidity
and/or Mortality

• Reduced ABI is a significant independent
  predictor of cardiovascular and coronary
  mortality
• Prognosis varies with multiple risk factors
  and/or severity of disease

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ABI inverse relationship with 5-year risk of
cardiovascular events and death
10.2 relative risk increaseper 0.1 decrease in
ABPI (p 0.041)
Risk relative to ABPI
Dormandy JA, Creager MA. Cerebrovasc Dis
19999(Suppl 1)1128 (Abstr 4).
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There is a strong two way association
betweendecreased ABI and increased risk for
cardiovascular death1
70
60
All-cause mortality CVD mortality
50
40
Percent ()

30

20

10
0
lt0.60 (n25)
1.0-lt1.10 (n980)
0.90-lt1.0 (n195)
0.60-lt0.70 (n21)
0.70-lt0.80 (n40)
0.80-lt0.90 (n130)
Mean participant follow-up 8.3 years
Baseline ABI
Resnick HE et al. Circulation 2004 109
733-739.
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Atherothrombosis is a Systemic Disease Increase
for Myocardial Infarction and Stroke as a
Function of ABI Measurement1
2.5
x 2.2
2.0


1.5

1.0
1.0
0.8
0.6
0.4
0.2
Ankle-brachial index (ABI) index

• Shelley, E. Dept of Health Children 2004

Dormandy JA, Creager MA. Cerebrovasc Dis
19999(Suppl 1)1128
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Referral to a Vascular Surgeon

• Primary Care Team
• Not confident of making the diagnosis
• Lack the resources to initiate monitor best
  medical practice
• Unacceptable symptoms despite a trial and
  adherence to best medical practice
• Weak or absent femoral pulses
• All Diabetic Patients
• Urgent
• Critical Limb Ischaemia/ Rest Pain
• Ulceration or Gangrene
• Suspected AAA / TIA / Amaurosis Fugax

Burns et al, BMJ, 2003 326 584-588
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Ankle Brachial Index Measurement-Key Learning
Points

• ABI measurement
• single most valuable test for assessing the
  arterial circulation
• Simple, portable, inexpensive, non-invasive,
  rapid, quantitative measurement
• An ABI 0.90 is diagnostic of PAD
• Permits stratification of the severity of PAD
• Predicts cardiovascular and cerebrovascular
  mortality
• Should ideally be performed in the primary care
  setting