Ankle Brachial Index Measurement:
What is it and why measure it?
Mary O’Connor
Cardiovascular Medical Science Liason
Bristol Myers Squibb
Guinness Storehouse
31st March 2006
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
How is Ankle-Brachial Index (ABI)
measured?
ABI =
Ankle systolic pressure
Brachial systolic pressure
Measure ankle and brachial systolic pressures with
Doppler
1,2
Use highest arm and each ankle pressures
1. TASC Working Group. Int Angiol 2000; 19 (suppl): 5-34.
2. Vascular Disease Foundation, 2003. Available at:http://www.vdf.org/ABI.htm.
Ankle Brachial Index Measurement
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
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
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
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
Right
Left
156 mmHg
160 mmHg
– Left leg:
DP: 96 mmHg
PT: 100 mmHg
100/160 = 0.63
The lowest ABI between both legs is
the ABI that stratifies the patient’s risk
Diagnosis:
moderate PAD in left leg
DP: 160 mm Hg
PT: 154 mmHg
DP: 96 mmHg
PT: 100 mm Hg
How is Ankle-Brachial Index (ABI)
measured?
Right
side
156
Measurements
Left side
Brachial Systolic Blood
Pressure
160
160
Dorsalis Pedis
96
154
Posterior Tibialis
100
160
160
Highest each ankle pressure
Highest Brachial Pressure
100
160
1.0
ABI
0.63
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
Limitations of the ABI Measurement
Non-compressible arteries: ABI values  1.31
1
Refer for other noninvasive testing
Bilateral brachial pressures
– Difference of 20mmHg indicates arterial disease
in upper extremity
2
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
ABI to Monitor Disease Progression
Changes in ABI +/- 0.15 indicate disease
re/progression
1
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
ABI to Assess Functional Capacity
Decreasing ABI values are independently
associated with impaired lower extremity
functioning
1, 2
Lower ABI scores are associated with
– Slower walking velocity ,
– fewer blocks walked per week
– Lower hip abduction force
– Lower knee extension force
1 2
2
2
1. MeDermott et al, Circulation. 2000; 101:1007-1012
2. Vogt et al, Journal Am Geriatric Society. 1994; 42: 923-929
1,2
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 plaque
it may be symptomatic or asymptomatic
1
It is a distinct atherothrombotic syndrome
1. Criqui et al. In: Fowkes FGR, ed. Epideminiology of Peripheral Vascular Disease. New York, NY: Springer-Verlag; 1991:85096
5-year natural history of PAD
100 patients
with claudication who do not
seek medical advice
100 patients
with asymptomatic PAD
Local Events
Worsening claudication
25 patients
100 patients
diagnosed
with claudication
Surgical revascularization
10 patients
Major amputation
2 patients
Dormandy JA. Hosp Update 1991;April:314–318.
Systemic Events
10 to 20 non-fatal MIs or strokes
PLUS
30 deaths:
• CHD 15
• Other cardiovascular
and cerebrovascular 5
• Non-cardiovascular 10
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 PAD
1
3 fold excess cardiovascular morbidity at baseline
compared with control subjects of the same sex
2
1. Criqui et al. N Eng J Med. 1992; 326: 381-386
2. Criqui et al. Drugs. 1991; 42 (supp 5): 16-21
Asymptomatic PAD
Asymptomatic PAD associated with an increased
risk of
– atherothrombotic events ( MI and Stroke)
– Impaired lower extremity functioning
– Internal artery carotid stenosis
Patients with asymptomatic PAD have a risk factor
and co-moribidity profile comparable to that of
symptomatic patients
1, 2
3
4, 5
1
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
Risk of death is increased in patients with
both symptomatic and asymptomatic PAD
Survival (% of patients)
100
Normal subjects*
75
Asymptomatic PAD†
50
Symptomatic PAD†
Severe symptomatic PAD†
25
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.
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
ABI – inverse relationship with 5-year
risk of cardiovascular events and death
Risk relative to ABPI
2.5
10.2% relative risk
increase
per 0.1 decrease in ABPI
(p = 0.041)
2.0
1.5
1.0
0.0
0.2
0.4
0.6
0.8
ABPI
Dormandy JA, Creager MA. Cerebrovasc Dis 1999;9(Suppl 1):1–128 (Abstr 4).
1.0
There is a strong two way association between
decreased ABI and increased risk for cardiovascular death1
70
60
Percent (%)
All-cause mortality
50
CVD mortality
40
30
20
10
0
Baseline ABI*
Resnick HE et al. Circulation 2004; 109: 733-739.
*Mean participant follow-up 8.3 years
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
•
Dormandy JA, Creager MA. Cerebrovasc Dis 1999;9(Suppl 1):1–128
Shelley, E. Dept of Health & Children 2004
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
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