How to Interpret Ankle-Brachial Index (ABI) Waveforms | medmastery (2023)

Master how to interpret audible and analog waveforms at all stages of peripheral arterial disease.

Elizabeth Tenny, BS RVT RDCS

7m reading


Shelley Jacobs, PhD

Peer Reviewers:

Franz Wiesbauer, MD Internist MPH

Last updateFebruary 26, 2021

During an automated ankle-brachial index (ABI) test, ABI rates are calculated and included in the patient report. While the waveforms are only audible when Doppler is used during a manual ABI, the Doppler probe from an automated ABI machine also provides analog waveforms, which form an important component of the report.

Understanding how to interpret the audible and analog waveforms from an automated ABI machine is especially important in circumstances where ABI rates are inaccurate and irrelevant. For example, some vessels are so calcified that they resist compression and falsely elevate the ABI.

How to place the Doppler probe

Before we discuss how to interpret audible and analog waveforms, let's review how to position the Doppler probe when performing an ABI. Pulse sounds (for example, audible waveforms) and analog waveforms are qualitative data produced by the Doppler probe. The sound is crucial, but it is not recorded. Only analog waveforms are recorded and their quality depends on the skill of the person using the Doppler probe.

It is easy to make a healthy vessel appear diseased, but it is not easy to make a diseased vessel appear healthy. In other words, audible and analog waveforms can overestimate the presence of disease if technique is poor.

Good technique comes with practice and experience. Ideally, the pen is held at 45° (or less) to the vessel or skin and is aimed at the heart. The more perpendicular you are to the vessel, the more you will overestimate the severity of the disease.

Figure 1. Good technique for a Doppler probe is to hold the pen at 45° or less to the vessel or skin and point it toward the heart.

(Video) Interpreting ankle brachial index (ABI) waveforms

How to avoid waveform artifacts

Artifacts can appear in analog waveforms as multiple spikes and tiny pits. Artifacts are errors, not true peaks and valleys, and can make it difficult to classify waveforms.

There are two reasons why artifacts can be introduced:

  1. The user has a shaky hand.
  2. There is interference with the venous flow.

One tip to avoid interfering with venous flow is to gently press the vein with the probe. Since the vein has less pressure, it will collapse. Venous flow will stop and allow a clear arterial Doppler reading without artifacts.

Figure 2. An artifact in a waveform appears as many small spikes and pits, which can make waveforms difficult to interpret and classify.

How to interpret audible and analog waveforms

In general, waveforms consisting of two peaks and one pit are ideal and are considered normal. These are called triphasic waveforms.

As peripheral arterial disease (PAD) worsens from mild to severe, the waveforms change. First, they decrease the number of peaks and valleys, then they develop rounded upsweeps or humpbacked peaks (for example, broad peaks without valleys), and finally all peaks and valleys disappear.

There are five stages of waveform degradation that occur with worsening PAD:

  1. Biphasic (mild)
  2. Weak biphasic (moderate)
  3. High single phase (moderate)
  4. Single phase buffered (bass)
  5. Absent (critical)

First, let's see what triphasic waveforms look and sound like. Next, we'll describe each stage of waveform degradation so that you can master how to interpret audible and analog waveforms in the PAD stages.

Triphasic waveforms (normal)

The healthiest waveforms are called triphasic, meaning they have two peaks and one dip that are both audible and visible. A triphasic waveform indicates that a change in the direction of blood flow is taking place, reflecting the normal flexibility of the vessel.

A triphasic waveform has a steep slope toward the highest peak; the upward movement represents an acceleration of blood flow to peak systole. The nostril is the beginning of diastole, which is the reversal of flow. The second peak is late diastole, which is a forward flow. Essentially, triphasic waveforms represent normal resting blood flow.

Figure 3. Normal triphasic ankle-brachial index (ABI) waveforms show a steep upward course to the highest peak (acceleration of blood flow during systole), a trough (reversal of flow during early diastole), and a second peak (forward flow during systole). late diastole). diastole).

With audible triphasic waveforms, you will notice three distinct sounds that follow the peak-pit-peak pattern (for example, one pit and two peaks).

Check out this short excerpt from our Ultrasound Master Class: Leg Arteries Course to listen to a normal triphasic waveform:

(Video) Understanding Ankle Brachial Pressure Index (ABPI) in Peripheral Vascular Disease

G67 Arterial USClinicalGuideArtículo8 Ch2L2 Video 1


Biphasic waveforms (light)

The walls of the arteries lose elasticity as they become diseased, which is reflected in a loss of bumps on the ABI waveforms. Audible biphasic waveforms have only two sounds, and visually (for example, in analog form) have only one peak and one trough. In particular, biphasic waveforms still have a steep upward travel to the highest peak.

The loss of the second peak can sometimes be due to an asymptomatic loss of elasticity in the artery. This is due to calcification of the wall, which is made worse by atherosclerosis and diabetes, but can also develop naturally with age. Wall calcification can become severe at a younger age in patients with diabetes.

Patients with biphasic waveforms often have symptoms of intermittent claudication. However, biphasic waveforms can also be found in patients with mild to moderate arterial insufficiency. Correlating the waveforms with the ABI rates helps to decipher the cause of the biphasic waveforms. For example, if the ABI is 1.0 and the waveform is biphasic, there may be mild calcification in the vessels, but not significant atherosclerosis. Biphasic waveforms obtained with an ABI of 0.7 indicate mild to moderate PAD.

Figure 4. Biphasic ankle-brachial index (ABI) waveforms caused by mild peripheral arterial disease (PAD) show a steep upward course, peak, and trough.

When listening to biphasic waveforms, you will only notice two distinct sounds. As long as the waveforms are multiphasic, biphasic, or triphasic (eg, not monophasic), the situation is not an immediate surgical concern.

This short video from our Ultrasound Master Class: Leg Arteries Course presents what you can expect to hear when listening to biphasic waveforms:

G67 Arterial US ClinicalGuideArtículo8 Ch2L2 Video 2


Weak (moderate) biphasic waveforms

Waveforms with a steep upward course and shallow cavities are called weak biphasic. They are found when there is moderate arterial insufficiency.

Weak biphasic waveforms are best analyzed using analog (non-audible) waveforms. Similar to biphasic waveforms, you can still expect to hear a peak and trough. But the difference with weak biphasic waveforms is that the upward motion (ie the peak) is usually higher than the trough.

(Video) Ankle Brachial Index (ABI) Test: How to Perform

Figure 5. Weak biphasic ankle-brachial index (ABI) waveforms caused by moderate peripheral arterial disease (PAD) show a steep upward course, peak, and shallow troughs.

High (moderate) single-phase waveforms

When the waveforms have no troughs but still have a peak with a strong upward movement, they are called high monophasic. These waveforms also represent moderate arterial insufficiency.

Distinguishing between strong single phase and damped single phase waveforms can be difficult. It has a subjective component that depends on the experience of the operator. Experienced traders can appreciate the strong bullish movement found with the single-phase uptrend, as opposed to the muffled waveforms seen with more severe forms of PAD.

Figure 6. High monophasic ankle-brachial index (ABI) waveforms caused by moderate peripheral arterial disease (PAD) show a steep upward course, a peak, and no trough.

When listening to strong single phase waveforms, you will only hear one sound. To see an example of what high monophasic waveforms sound like, check out this video from our Ultrasound Master Class: Leg Arteries Course:

G67 ArterialUSClinicalGuideArtículo8 Ch2L2 Video 3


Damped single-phase waveforms (bass)

Damped waveforms with a monophasic hump indicate severe PAD. There is a slow rising spike above the baseline and the upward movement is rounded, not sharp. Smoothed monophasic waveforms can be seen in non-healing ischemic ulcers.

(Video) How to perform an ankle brachial index

Figure 7. Damped monophasic ankle-brachial index (ABI) waveforms caused by severe peripheral arterial disease (PAD) show a slowly rising peak above baseline and a rounded up course.

When listening to damped monophasic waveforms, you will only hear a steady peak and flow throughout cardiac cycles.

You can hear an example of damped monophasic waveforms by watching this video from our Ultrasound Master Class: Leg Arteries Course:

G67 Arterial US ClinicalGuideArtículo8 Ch2L2 Video 4


Missing waveforms (critical)

Missing ABI waveforms are due to missing peripheral pulses. They are found in patients with rest pain and critical limb ischemia.

Figure 8. The absence of ankle-brachial index (ABI) waveforms is due to the lack of peripheral critical arterial disease (PAD) pulses.

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(Video) Ankle Brachial Index (ABI)- How to Measure and What it Means

recommended reading

  • Aboyans V, Criqui MH, Abraham P, et al. 2012. Measurement and interpretation of the ankle-brachial index: a scientific statement from the American Heart Association.Circulation.126: 2890–2909.PMID: 23159553
  • Cervin, A, Wanhainen, A, and Björck, M. 2020. Popliteal aneurysms are common among men with examined abdominal aortic aneurysms, and the prevalence correlates with the diameters of the common iliac arteries.Eur J Vasc Endovasc Surg.59: 67–72.PMID: 31757587
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What are the waveforms of ankle-brachial index? ›

Normal, triphasic ankle-brachial index (ABI) waveforms feature a sharp upstroke to the tallest peak (blood flow acceleration during systole), a pit (reversal of flow during early diastole), and a second peak (forward flow during late diastole).

How to interpret ABPI results? ›

How should I interpret ankle brachial pressure index (ABPI) results?
  1. Less than 0.5 suggests severe arterial disease. ...
  2. Greater than 0.5 to less than 0.8 suggests the presence of arterial disease or mixed arterial/venous disease. ...
  3. Between 0.8 and 1.3 suggests no evidence of significant arterial disease.

What is the difference between monophasic and biphasic Doppler waveforms? ›

biphasic which occurs in more distal blood vessels as the result of ventricular systole and the elasticity of the blood vessels; monophasic which occurs when the flow of blood is no longer pulsatile. All three types of blood flow occur in healthy subjects.

What is a normal waveform for a lower extremity artery? ›

The Doppler waveform of the lower extremity arteries at rest is classified as a high pulsatility waveform and is characterized by a triphasic flow pattern [9].

What is monophasic waveform? ›

A monophasic waveform has slow, blunted antegrade systolic flow, which continues into diastole. Monophasic arterial waveforms are always abnormal and are often seen downstream from stenoses or in collateral vessels formed around the occlusive disease.

What ankle-brachial index value indicates arterial insufficiency? ›

Health care providers calculate ABI by dividing the blood pressure in an artery of the ankle by the blood pressure in an artery of the arm. The result is the ABI. If this ratio is less than 0.9, it may mean that a person has peripheral artery disease (PAD) in the blood vessels in his or her legs.

What is a positive ankle-brachial index? ›

What does a high ankle-brachial index mean? An ABI ratio higher than 1.4 could mean the blood vessels in your limbs are stiff because of advanced age or diabetes. Researchers have found that people with an ankle-brachial index higher than 1.4 had twice the risk of cardiovascular death.

What does an ABI value of 0.70 indicate? ›

The ABI is calculated as the higher pressure at the ankle divided by the higher of the left and right arm pressures. An ABI ratio above 0.90 is normal, 0.71-0.90 indicates mild obstruction, 0.41-0.70 indicates moderate obstruction, and <0.40 indicates severe obstruction.

What do these ABI results indicate? ›

The ankle-brachial index test compares the blood pressure measured at the ankle with the blood pressure measured at the arm. A low ankle-brachial index number can indicate narrowing or blockage of the arteries in the legs. Ankle-brachial index testing might be done before and right after walking on a treadmill.

What does an ABI value tell you about your patient's venous insufficiency? ›

Abnormal or unhealthy ABI values are 0.9 or lower and 1.41 and higher. These values indicate that you have different blood pressure levels at the two points of measurement, and thus that you have a high possibility of having narrowed arteries, blood clots, or venous insufficiency.

What is an abnormal ABI reading? ›


PAD is graded as mild to moderate if the ABI is between 0.4 and 0.9, and an ABI less than 0.40 is suggestive of severe PAD [19]. An ABI value greater than 1.3 is also considered abnormal, suggestive of non-compressible vessels.

What does biphasic waveform indicate? ›

Biphasic waveform indicates mild to moderate disease and monophasic flow indicates significant disease. Duplex scanning can be added to further localize occlusive disease. Some practitioners choose to perform pulse volume recordings (PVR) instead of or in addition to arterial Doppler.

What does a biphasic waveform mean? ›

The biphasic type describes a two-phase Doppler waveform with an extension of the reverse flow phase during the whole diastole and the disappearance of the forward flow phase during diastole, in comparison with the triphasic type. Tri- and biphasic types are considered normal.

Why is monophasic better than biphasic? ›

Although monophasic and biphasic machines are successful in performing defibrillation, the latter is considered a better option. They are more convenient, accurate, effective, and cost less and are able to prevent further damage to the heart.

What is a good arterial line waveform? ›

Normal wave: 1-2 Oscillations before returning to baseline is deemed normal. Over-dampened: Air bubbles, kinks, clots, spasms, stopcock closed/loose connections, or no volume or low pressure in pressure bag and tubing. This can underestimate systolic pressure and/or overestimate diastolic pressure.

What is a normal waveform? ›

Most waves of 8 Hz and higher frequencies are normal findings in the EEG of an awake adult. Waves with a frequency of 7 Hz or less often are classified as abnormal in awake adults, although they normally can be seen in children or in adults who are asleep.

What is a low resistance waveform? ›

Low-resistance spectral waveforms are characterized by a slower increase in flow velocity with the onset of systole and a gradual decrease in velocity during diastole with continued forward flow throughout the cardiac cycle (Fig. 39.4B).

How do you know if its monophasic or biphasic? ›

The main difference between monophasic and biphasic shock delivery is that a monophasic electrical current moves in a single direction while a biphasic current is bidirectional (moving in a straight line and then reversing its direction).

What is blunted waveform? ›

Blunted waveforms were characterized by the absence of the characteristic peak of the systolic signal and the elevated end-diastolic flow velocity (fig. 1).

Is monophasic waveform normal? ›

Monophasic has most commonly been used to describe abnormal waveforms with a single phase found distal to a hemodynamically significant arterial obstruction,18,25 but has also been employed to characterize abnormal blood flow proximal to a significant obstruction and from normal extremities following exercise and ...

What is the hallmark symptom of peripheral arterial insufficiency? ›

The most characteristic symptom of PAD is claudication which is a pain in the lower extremity muscles brought on by walking and relieved with rest. Although claudication has traditionally been described as cramping pain, some patients report leg fatigue, weakness, pressure, or aching.

What are normal and abnormal ABI values? ›

Normal cut-off values for ABI are between 0.9 and 1.4. An abnormal ankle-brachial index- below 0.9-is a powerful independent marker of cardiovascular risk.

What are normal ankle-brachial index values? ›

A normal ABI value is 1.10 to 1.40. This is because among individuals without PAD, lower extremity arterial pressures increase with greater distance from the heart, due to increasing impedance with increasing arterial taper, resulting in higher systolic pressures at the ankle compared with the brachial arteries.

What does ABI of 0.5 mean? ›

On the other hand, an ABI of 0.5 means that only 50% of the blood is reaching the ankles, and 50% is blocked by PAD.

What is a safe ABI for compression? ›

Normal ABI will range from 0.9-1.3; 0.5-0.8 indicates no significant PAD or mild PAD; < 0.5 indicates severe PAD or critical ischemia, in which case compression therapy is contraindicated. If the ABI is > 1.3, the result is unreliable and those patients should also be evaluated before considering compression.

What does ABI 1.4 mean? ›

ABI values and what they mean: 1.0 - 1.4 - could indicate calcification in the vessels. . 9 - 1.4 - normal range - no treatment is necessary.

What is the measurement and interpretation of the ankle-brachial index? ›

The ankle-brachial index (ABI) is the ratio of the systolic blood pressure (SBP) measured at the ankle to that measured at the brachial artery. Originally described by Winsor1 in 1950, this index was initially proposed for the noninvasive diagnosis of lower-extremity peripheral artery disease (PAD).

What is normal toe pressure on ABI? ›

In general, a toe pressure of 70 to 110 mmHg or TBI > 0.5 to 0.75 is considered normal and anything below is diagnostic of PAD. A toe pressure lower than 30 mmHg or TBI < 0.2 is considered severely ischemic and diagnostic of critical limb ischemia (CLI).

How do you test for poor circulation in your legs? ›

Arterial Doppler Ultrasound

A Doppler ultrasound uses sound waves to produce images that highlight blood flow in the leg arteries. This test detects and evaluates any blockages caused by plaque buildup.

What is the treatment for blocked arteries in the legs? ›

A graft is used to redirect blood flow around a blocked or narrowed artery. A graft can be a blood vessel from another part of the body or a synthetic substitute. In some cases, angioplasty or surgery may be necessary to treat peripheral artery disease that's causing claudication: Angioplasty and stent placement.

Is arterial insufficiency the same as venous insufficiency? ›

Venous insufficiency refers to a breakdown in the flow of blood in our veins, while arterial insufficiency stems from poor circulation in the arteries. Left untreated, both conditions may lead to slow-healing wounds on the leg.

What are the expected assessment findings in chronic venous insufficiency? ›

Initial evaluation begins in the office setting with a thorough history and physical examination. Typical symptoms of venous insufficiency include aching, pain, tightness, skin irritation, pruritus, heaviness, tingling, muscle cramps, and cosmetically unsatisfying varicose veins.

What is ABI with intermittent claudication? ›

Introduction: The Ankle-Brachial Index (ABI) makes it possible to identify patients with peripheral artery disease (PAD). Intermittent claudication (IC) is the first major symptom of PAD, although many patients with an ABI ≤ 0.9 do not exhibit IC, and the range of ABI among those who do have IC is very variable.

How do you read the toe brachial index? ›

Calculating toe brachial pressure index

Divide the toe's systolic pressure by the brachial systolic pressure in the arm with the higher pressure. A toe brachial pressure index (TBPI) less than 0.64 warrants further evaluation and testing.

How do you interpret toe brachial index? ›

A TBI value less than 0.5 suggests proximal arterial disease of moderate severity, while an index less than 0.2 and toe pressures less than 30 mm Hg are consistent with critical ischemia and poor potential for healing.

What does high blood pressure in ankle mean? ›

It has been recognized for some time that systolic pressures at the level of the ankles can also be elevated in comparison to pressures measured in the arm. This is usually attributed to calcification of the arteries, which prevents arterial compression and results in a falsely elevated pressure measurement.

What is the difference between triphasic and biphasic? ›

The aim of this review was to compare biphasic with triphasic oral contraceptive pills. Our a priori hypotheses were that biphasic and triphasic pills have similar contraceptive efficacy but that triphasic oral contraceptives cause fewer side effects, give better cycle control, and have higher continuation rates.

What is normal triphasic waveform pattern? ›

The normal (“triphasic”) Doppler velocity waveform is made up of three components which correspond to different phases of arterial flow: rapid antegrade flow reaching a peak during systole, transient reversal of flow during early diastole, and slow antegrade flow during late diastole.

What is biphasic and triphasic? ›

Biphasic pills provide in succession 2 estrogen-progestagen combinations in increasing doses. Triphasic pills provide a continuous dose of estrogen combined with a progressively increased dose of progestagen from week to week.

What does an ABI value of 1.4 to indicate? ›

A normal ankle-brachial index is between 1.0 and 1.4. Normal. Stiff blood vessels in your limbs may be from advanced age, diabetes or calcification. Borderline.

What are normal values for ABI? ›

A normal ABI value is 1.10 to 1.40. This is because among individuals without PAD, lower extremity arterial pressures increase with greater distance from the heart, due to increasing impedance with increasing arterial taper, resulting in higher systolic pressures at the ankle compared with the brachial arteries.

Which ankle-brachial index value indicates noncompressible arteries? ›

The ankle-brachial index (ABI) provides objective data about arterial perfusion of the lower limbs. The ABI refers to the ankle to arm systolic blood pressure ratio; a normal ABI is 1.0–1.4. ABI values above 1.4 indicate noncompressible arteries.

Why is ankle pressure higher than brachial pressure? ›

It has been recognized for some time that systolic pressures at the level of the ankles can also be elevated in comparison to pressures measured in the arm. This is usually attributed to calcification of the arteries, which prevents arterial compression and results in a falsely elevated pressure measurement.

What is an ABI with toe pressures? ›

Toe/Ankle Pressure (TBI/ABI) have proven to be an accurate option for the diagnosis of PAD in patients at risk for falsely elevated ankle-brachial index (ABI) values, as vessels in the toes are usually not affected by calcification. The procedure is similar to an ABI test but requires small cuffs and a sensitive probe.

What does it mean when an ABI is non compressible? ›

However, the ABI may be unreliable and termed 'non-compressible' when the infrapopliteal arteries cannot be compressed by a blood pressure cuff.

What does an ABI of 0.8 mean? ›

If blood flow is normal in the lower extremities, the pressure at the ankle should equal or be slightly higher than that in the arm with an ABI of 1.0 or more. An ABI less than 0.9 indicates LEAD.


1. Performing a manual ankle-brachial index (ABI)
2. Interpreting duplex waveforms
3. Ankle–Brachial Index: Everything You Need to Know
(Medical Centric)
4. How to measure Ankle-Brachial Pressure Index (ABPI)
5. Peripheral artery disease: Ankle Brachial Index
(Dr. Andras Fazakas)
6. Bilateral Lower Extremity Pressures and Waveforms - Case Study


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