Ankle Brachial index Flashcards
What kind of test is a Ankle Brachial index test?
Non invasive physiologic test that compares the systolic pressure at the ankle to the systolic pressure of the brachial artery
What kind of doppler waveform is used with ABI tests?
CW doppler waveforms are recorded to support the pressure data
During a ABI test, when an arterial lumen is narrowed to a critical level, what happens?
The distal arterial flow and pressure significantly increase
What is the ABI protocol?
- Wrap cuffs on the ankle and upper arms
- Should be placed snug and “straight” rather than “angled”
How should we place the ankle and arm cuffs for ABI protocols?
0-12 cm bladder (width) 2-3 cm above the medial malleolus
How do we obtain the posterior tibial artery signal? 7 step by step
- Obtain signal posterior to the medial malleolus
- Angle 45-60 degrees, pointing the probe towards the heart, with enough pressure to keep the probe in place without compressing the artery
- Record PTA signal
- Inflate the cuff 20-30 mmHg above the last audible signal
- Slowly deflate cuff (2-4 mmHg/ second)
- Systolic pressure is recorded in mmHg at the first audible signal
- Ensure the doppler pulse continues after the first pulse to confirm it is an actual signal and not an artifact
What is the problem with each of these images?
- Doppler probe is positioned over the artery at 90 degrees X
- Doppler probe is positioned to far distal to the medial malleolus X
- Doppler probe is in a good position over the PTA with a good angle and parallel to the long axis of the artery
What are we getting here?
Posterior tibial artery
When sampling the pedis artery (DPA) we need to avoid sampling to close to the toes why?
You will likely be listening to the plantar arch or digital vessel
When sampling the DPA if the signal is dampened, retrograde or absent what do we do?
Move to the anterior ankle area and search for the ATA signal
What do we do if we can’t locate the DPA or the ATA signal?
Find the peroneal artery (PerA) slightly anterior to the lateral malleolus
What procedure does this represent?
DPA
Where doe we obtain the bilateral brachial (BrA) Pressures?
On the radial artery
If the brachial pressure differs >20mmHg or if the waveforms are different, what do we examine? Why?
- The vertebral arteries to check flow direction.
- Retrograde vertebral flow on the same side as the lower brachial indicates subclavian steal syndrome
How do we calculate ABI?
Pedal pressure / Highest brachial pulse
In terms of ABI, what is the normal drop from heart to distal lower extremity?
10 mmHg
In terms of ABI, corresponding increase in the amplitude of pulses distally, results from what?
Increased peripheral resistance and elastic recoil?
In terms of ABI, Normal resting ankle systolic pressures are usually what?
The same or slightly higher than the brachial pressure
IF ABI appears abnormal, what should be done?
Higher brachial should be measured again
During ABI, At the ankle the PRA usually has higher pressure than what?
The ATA and DPA
What is the average ABI supine?
1.1
What is the normal ABI normally?
Usually >0.9 but values will differ in each lab
Label the chart
Falsely high ABIs will occur in patient with what?
Medical calcifications (5-10% too high)
ABI’s >1.3 toe pressures (PPG) should be done why? And what is the normal toe/ brachial pressure?
- For accuracy
- > 0.75
Systolic pressure is invalid and must rely on what?
Pulse waveforms and toe pressures
What are indications that the artery is calcified? 3
- Doppler signal does not reappear at a clearly defined pressure
- Pulse amplitude increases with further cuff deflation
- Artifactually elevated pressure may not correspond with the pulse waveform
ABI’s >1.3 mmHg occurs when? 2
- Diabetic patients
- Patients on steroid therapy for renal disease
What is important to understand in terms of level of pressure measurement?
It is determined by cuff position and NOT by the site of doppler interrogation
Placing the cuff too high on the calf does what?
Does not give an accurate reading on ankle pressure
What are some limitations of ABI? 6
- Falsely increased pressures from calcified vessels, you can rely on a low pressure recording but not a high one
- Significant lesions with developed collateral circulation resulting in normal distal pressures and waveforms at rest
- Extensive bandaging or casts which cannot be removed
- Areas of trauma, surgery, ulceration, or graft placement that the pressure cuff should not compress
- Acute DVT in the lower extremities should not have pressure cuffs inflated over their thrombus
- Pressure measurements are usually not permitted on ipsilateral side of mastectomy or AVG/ AVF (arteriovenous graft/ Arteriovenous fistula
In terms of exercise stress testing, what is acceptable for exercising for a symptomatic patient?
Treadmill walking is acceptable for exercising a symptomatic patient with suspected PAD, especially when the ABI is in the normal range
Post- exercise ABI’s are used to assess what?
Functional impairment
Exercise stress testing assesses what?
Whether walking limitations and induced pain is secondary to nonvascular conditions, such as MSK or cardio pulmonary disease
What is the protocol for Exercise stress testing? 4
- Measure pre-exercise BP and ABI’s
- Patient walks on the treadmill at 10% grade and speed of 2 mph for 5 minutes or until claudication or other restrictions occur.
- Remeasure the BPs and ABIs within the first minute post exercise
- Measure BPs and ABIs every 2 minutes, until the ankle pressure returns to within 10 mmHg of the baseline pressure or for 6 -12 minutes
What are limitations for exercise stress testing? 4
- Chest pain
- Arrythmias
- Post MI/ cardiac procedure and not cleared by cardiologist
- Hypertension greater than 180 mmHg
What would normal ABI stress testing look like?
- Little or no decrease in ankle BP after 5 minutes of exercise
- Decrease in post- exercise systolic pressure should be <20% of the resting pressure and should return to baseline within 3 minutes after exercise
Filling in the diagnostic criteria post treadmill exercise BP and ABI’s and recovery times
What does abnormal recovery Exercise stress test look like? 2
- Immediate decrease from baseline in post-exercise ankle BP indicates significant arterial obstruction
- Severity of the disease is also related to the distance a patient can walk and the absolute pressure drop
