QuantaFlo, a Reliable Alternative to ABI Testing and Ankle Brachial Index Machines
● What is Ankle Brachial Index (ABI) technology?
● Peripheral Arterial Disease (PAD)
● First signs of PAD
● What happens when PAD gets worse?
● Who needs an ankle brachial index test?
● What is an ABI machine?
● How is the ankle brachial index test conducted?
● Measuring brachial pressure
● Measuring ankle systolic pressure
● How is the ankle brachial index calculated?
● Interpreting the ABI values
● Post-exercise ABI test for peripheral vascular disease
● Indications and contraindications of ABI vascular test
● Correlation of ankle brachial index with lower extremity function
● Abnormal ankle brachial index as marker for atherosclerosis
● Abnormal ankle brachial index as predictor of morbidity and mortality in patients with post-coronary bypass artery
● Specificity and sensitivity of ABI in the diagnosis of PAD
What is Ankle Brachial Index (ABI) technology?
Before we get into the specifics of how QuantaFlo and ankle brachial index works and dive into the various interpretation of its results, we need to first understand what ankle brachial index refers to.
The ankle brachial index study, simply put, is a vascular study used primarily to diagnose Peripheral Arterial Disease. A non-invasive vascular testing equipment — an ABI Doppler Ultrasound Machine — is used to measure a patient’s systolic pressures at the arm and the ankle. The ankle brachial index is then determined by calculating the ratio of these two systolic pressures. QuantaFlo helps us do that easily!
In other words, the ankle brachial index is the systolic pressure of a patient at the ankle divided by the systolic pressure at the arm. Based on this index, the potential and the severity of peripheral vascular disease in a patient is determined.
It might sound rather weird that a test of your ankle could help predict threatening cardio-vascular diseases. However, ABI vascular test is not only possible but also crucial as it helps your doctor test the blood flow in your arteries and foresee threatening diseases.
With a proper QuantaFlo and ABI ultrasound protocol in place, a team of doctors with the help of an ABI ultrasound machine and an ABI ultrasound CPT code conduct the test. During the process, the specialized ABI equipment bounces sound waves on the patient’s arteries to get their blood flow readings and transform those readings into images.
The accuracy and comprehensiveness of the QuantaFlow and ankle brachial index test have made it the most popular cardiovascular examination method and the most specific metric in diagnosing peripheral vascular diseases and arterial stress.
Furthermore, the ankle brachial index also helps identify the extent of damage from the disease, especially how it might be affecting a patient’s extremities. The index does have its limitations, though. For instance, the test doesn’t show where or how severe the blockage is.
Before we understand how ABI helps diagnose PAD, let’s have a look at PAD is and what causes it.
Essentially, the buildup of plaque in a person’s arteries leads to blockage in regular blood flow. The arteries carrying blood to the arms, stomach, aorta, kidneys and brain could be blocked. The arteries inside the heart could harden from the plaque leading to a cardiovascular condition called coronary artery disease.
This can also be done using QuantaFlo ABI Test.
Depending on the extent of the blockage to the peripheral arteries, the severity of PAD is determined. In case of PAD, the narrowing of the arteries could lead to the occlusion of a patient’s legs.
PAD is not the only cardiovascular disease that ankle brachial index helps predict. The index is also used to predict adverse cardiovascular events with non-traditional risk factors.
Peripheral Arterial Disease (PAD)
Due to several genetic or lifestyle reasons, there is a tendency for the arteries to harden or become narrower owing to the buildup of fats and cholesterol, among other substances.
PAD Test can also be done by QuantaFlo. This gradual building up of plaque in the wall of an artery is commonly referred to as atherosclerosis. The blockage caused by the disease hinders circulation to the stomach, brain, heart and limbs, among other parts.
If atherosclerosis is found in the peripheral arteries affecting blood flow to the limbs, that condition is known as Peripheral Arterial Disease. In most cases, patients don’t show any symptoms until there is 60 percent arterial narrowing. By that time, the condition is a lot worse than it would have been had it been diagnosed earlier with an ankle brachial index test.
In some cases, the arterial occlusion can cause smaller peripheral arteries to form. These smaller arteries spring up to allow blood to flow — collateral circulation — despite the plaque. If the plaque becomes brittle, it might break up and a blood clot might form. Such clots can be extremely dangerous, either causing further arterial narrowing or completely blocking the blood vessels.
PAD has been found to affect 20 percent Americans over the age of 60, and timely treatment is a must to prevent the situation from exacerbating. Although PAD has common symptoms, many people don’t show the symptoms for PAD. That makes an early diagnosis by using ABI test for peripheral vascular disease crucial.
First Signs Of PAD
As has been mentioned before in this guide, many people with PAD are asymptomatic or only show mild symptoms. Regardless, it’s important to know what the signs of PAD are for prompt intervention.
Some people with PAD experience claudication. This includes pain in the legs or muscle cramping while walking that disappears with rest. QuantaFlow PAD test can be a solution. The severity of claudication can range from mild discomfort to crippling pain making it difficult for patients to perform any physical activity involving their legs — such as walking or climbing the stairs.
The most common symptoms, apart from claudication, include:
· Numbness, weakness or heaviness in legs
· Burning sensation in the toes and feet
· Feeling of coldness in the lower leg or in the foot, usually in one leg
· Persistent sores on the toes, feet or legs
· Change in skin color, usually blue or pale
· Erectile Dysfunction in men
· Hair loss on legs
· Slow toenail growth
· No or weak pulse in the leg
Most people are not aware of the risks involved with PAD and hence might end up ignoring the early signs. But if left unchecked, the disease gets increasingly worse and might even cause irreversible damage.
What Happens When PAD Gets Worse?
Blockage in the blood vessels in the legs can lead to pain and discomfort, difficulty in walking, change in skin color, sores and ulcers. Some patients may experience discomfort even when they are at rest — rest pain — especially during the night. In that case, lowering the legs can ease the blood flow and provide the patient temporary relief. Using QuantaFlo can help prevent PAD.
If the flow of blood is hindered for a long period of time, PAD may cause Critical Limb Ischemia. CLI refers to a prolonged or permanent loss of circulation to the limbs leading to the formation of gangrene and persistent sores, or even worse, loss of limbs.
If someone is suffering from PAD, and not using QuantaFlo, that might also be an indication of coronary arterial disease. The plaque might rupture and the clot can hinder blood flow to your heart or your brain resulting in a heart attack or a stroke. So it is critical to identify plaque buildup to prevent damage not only to your limbs but also to your vital organs, and that’s why you need to get your ankle brachial index computed from time to time.
Who Needs An Ankle Brachial Index Test?
Most of us tend to ignore minor physical inconveniences as a part and parcel of ageing. But ignoring these signs, as we have learned above, can cause irreparable damage to our body.
So if you are experiencing any of the aforementioned symptoms, go see your doctor immediately. Even if you haven’t experienced these symptoms, you need to get regular screenings if you are:
· Older than 70 years old
· Over 50 with a history of diabetes
· Over 50 with a smoking habit
· Under 50 but suffer from obesity or high cholesterol
If you are diagnosed with PAD, the next course of action would be to formulate a treatment plan. Furthermore, getting frequent ABI vascular tests can help determine how effective the treatment has been and if modifications are necessary.
What Is An ABI Machine?
An ankle brachial index machine, or ABI vascular machine, is a broad term used by specialists to refer to the medical equipment that is used to conduct an ankle brachial index test and assess a patient’s arterial health and predict peripheral vascular disease.
ABI equipment consists of a continuous wave Doppler ultrasound, which is a noninvasive test to estimate the blood flow through blood vessels by bouncing high-frequency sound waves off circulating red blood cells. ABI equipment also includes sphygmomanometer and pressure cuffs to measure brachial and ankle systolic pressures.
ABI Doppler equipment is used to perform non-invasive ABI ultrasound of patients’ arteries to monitor the blood flow. High-frequency sound waves are bounced off of blood vessels, and the sound waves are then converted into images allowing specialists to monitor plaque buildup and blockages.
The equipment allows the specialists to analyze the blood flow in a patient’s arteries. A wide variety of ankle brachial index machines are available in the market — from the highly advanced ones used in hospitals to the more portable handheld ABI machines.
These machines are quite pricey and can cost anything from $2000 to $7000 depending on the quality of the equipment. An average ABI Doppler machine can cost up to $6000, and it comes with cuffs, a computer, the software, and other accessories. The portable ones usually cost around $2000, but you need to have a mobile printer and a laptop separately.
Among the most popular and trusted ABI Doppler equipment is Koven Smartdop XT Vascular Testing System, which supports both Doppler and automated testing. It also has an integrated touchscreen and computer, and the software allows you perform the measurements and then record them in a database for future use.
A more affordable option is the ABI Doppler System by Summit. It features an 80MHz Doppler probe and a big screen that ensures accurate readings with ease. It is also much faster than traditional ABI Doppler machines.
Another option is Quantaflo, a portable and easy to use equipment that uses digital technology to detect PAD. It is comprised of a sensor, proprietary software and a portable computer or tablet. It can detect the presence of PAD even before the patient starts showing the symptoms so that preemptive treatment and care can be administered.
With a traditional ABI machine, the doctor records the blood pressure readings and does the calculations to come up with an ankle brachial index value. However, with the Quantaflo, it is the software that does the calculation based on the blood pressure measurements recorded by the sensor. The Quantaflo is also easier to use and less time-consuming than the traditional ABI Doppler machines.
How Is The Ankle Brachial Index Test Conducted?
The ABI test for peripheral vascular disease takes about 10 to 15 minutes. The patient’s systolic brachial pressure and systolic pressure of both the ankles have to be recorded using an ABI machine. QuantaFlo can be a great option.
It’s important to determine the maximum inflation level for each patient. This helps assure that the cuff pressure at the beginning of the reading exceeds the systolic blood pressure. The cuff has to be inflated to about 20 mmHg above the patient’s expected presfsure. However, with QuantaFlo, the process is very easy!
Measuring Brachial Pressure
Once the patient has been in a supine position for about 10 minutes, the doctor wraps an inflatable cuff on their arms and attaches the cuff tubing to the sphygmomanometer. Without QuantaFlo, it is complex. S/he makes sure the cuff is on the same level as the patient’s heart. To take the right brachial systolic pressure, the doctor applies some gel in the antecubital fossa over the right brachial artery.
The transducer part of the 5- or 10-MHz handheld ABI Doppler pen probe ultrasound device is placed on the gel. The Doppler probe has to be held absolutely still. To measure the blood pressure, the doctor palpates the brachial artery and inflates the cuff rapidly — by 10 mmHg increments — to the maximum inflation level. The doctor will then deflate the cuff slowly — at 2 mmHG/second — and wait for the Doppler signal to reappear. QuantaFlo can make this process much easy.
Then s/he follows down for 10 mmHg until two subsequent beats are heard, which is the valid systolic blood pressure.
Once the pressure of the right brachial artery has been recorded, the process is repeated for the right ankle followed by the left ankle, and lastly, the left arm.
Measuring Ankle Systolic Pressure
Again, to measure the ankle systolic pressure, the doctor starts with the right leg. The right ankle cuff has to be connected to the sphygmomanometer. The ABI ultrasound gel is placed over the dorsalis pedis and posterior tibial arteries. The doctor first measures the systolic pressure at the dorsalis pedis artery. S/he moves the ABI Doppler probe until a signal is located, which can be found in the midline dorsum of the foot. QuantaFlo is surely a good option.
Once the doctor locates the strongest signal, s/he repeats the inflation and deflation process used to measure the brachial pressure on the arms. The measurement is recorded and now the systolic pressure from the posterior tibial artery has to be recorded. Using the Doppler probe again the doctor locates the PT signal posterior to the medial malleolus.
The same process is repeated as before to measure the PT systolic pressure. After that, the measurement is repeated on the other ankle.
How Is The Ankle Brachial Index Calculated?
After the systolic brachial pressures and the pressures of the ankles are measured, a patient’s ankle brachial index is calculated.
To calculate the ankle brachial index value of the systolic pressure of that particular ankle is taken, which is then divided by the higher systolic brachial pressure that has been recorded.
For normal individuals, the difference between the two systolic brachial pressures would be minimal (less than 10 mm HG). However, if the two systolic pressures are considerably different — greater than 20 mm HG — that can be an indication of axillary or subclavian arterial stenosis. This difference can usually be seen in people who are at risk of suffering from atherosclerosis. The reading could also help predict other cardiovascular events.
To put it simply, the ankle brachial index for each leg is calculated as follows:
Right ABI = Highest Right Average Ankle Pressure
Highest Brachial Pressure
Left ABI = Highest Left Average Ankle Pressure
Highest Brachial Pressure
The recorded ABI value is recorded to 2 decimal places. QuantaFlo can help with this calculation.
Interpreting The Ankle Brachial Index Values
Now that we know how to conduct a test using an ankle brachial index machine, let’s understand what the different ABI values mean.
Here is the range of numbers that can be obtained from the test and their interpretation in terms of PAD severity in each leg:
1.0–1.4: Normal ankle brachial index.
>1.4: This number points to a non-compressible calcified blood vessel. In case of elderly or diabetic patients, the blood vessels may be hardened to a point where the cuff doesn’t collapse, showing a higher signal at the cuff pressures and producing incorrect blood pressure values. Here, ABI vascular machines don’t provide correct results requiring the doctor to administer a different kind of test.
0.90 or less: This is indicative of peripheral arterial disease.
0.70–0.90: An API of 0.70 to 0.90 indicates a mild occlusion.
0.69–0.40: Points to moderate occlusion
<0.4: If the value of ABI is less than 0.40, it means that the PAD has progressed significantly in a patient and has caused severe occlusion. Here, surgical wounds are either slow to heal or don’t heal at all. If a patient has non-healing ulcers, revascularization to increase blood flow around the blocked arteries is a more suitable treatment option. In case of severe PAD, the patient will most likely be referred to a vascular specialist — a doctor who specializes in vascular diseases.
That is all about the typically performed resting ABI vascular test results. However, studies have found some discrepancy in the resting ankle brachial index’s ability to predict peripheral vascular disease and it’s accuracy in grading the severity of the disease. That has led more and more doctors to depend on post-exercise ankle brachial index test as a more reliable test for lower-extremity revascularization rates in PAD, particularly for patients that experience claudication when walking that is resolved with rest.
Post-exercise ABI Test for Peripheral Vascular Disease
If in case, you are experiencing pain in your legs when you walk and the doctor wants to conduct an ankle brachial index test, they may conduct what’s known as post-exercise ABI test. That’s done owing to the disconnect that’s caused when a patient is experiencing pain when s/he walks but the ankle brachial index is recorded for when s/he is at rest.
To conduct the test, the doctor asks the patient to walk or run on the treadmill for about five minutes, and the brachial and ankle systolic pressures are measured again. The ankle brachial index values are then calculated using the same formula.
A drop in the ABI index after the second reading indicates that there’s a significant level of PAD in the patient. Because the blood pressure may fluctuate in the process of conducting the test, doctors usually examine the right limbs first — right arm then the right leg — followed by the left leg and the left arm. The findings from the two brachial pressures from the resting and post-exercise ankle brachial index tests provide for some quality control.
A post-exercise ankle brachial index test can lead to some difference in the range of results. So apart from the test results, the doctor will also have to bear in mind the patient’s medical history and her/his symptoms to formulate an accurate course of action. It may include a change in medication or the patient’s adopting a healthier lifestyle.
Indications And Contraindications Of ABI Vascular Test
Before taking the test, it’s important to understand the indications and the contraindications of the ABI vascular test.
· The ankle brachial index can help assess the vascular risk for PAD in an asymptomatic patient.
· The index helps diagnose PAD in a symptomatic patient.
Apart from the ankle brachial index tests conducted in a primary care setting, tests conducted in emergency and trauma settings can help assess the chances of lower-extremity arterial injury in a patient. The ankle brachial indexes in such situations are as follows:
ABI<0.90: This indicates that further vascular imaging is required. In this case, an angiography is conducted for a stable patient and an operative exploration is required for an unstable one.
ABI>0.90: This indicates that the likelihood of an arterial injury is fairly low. The patient would have to undergo a series of ABI assessments to be sure or an ABI vascular study would have to be performed later on.
Despite the importance of ankle brachial index in diagnosing PAD, the test is not for everyone. Firstly, the test cannot be performed on patients who cannot remain a supine position for over 15 minutes, which is how long it normally takes to conduct the test.
Another instance where the test cannot be carried out is if the patient might suffer extreme injuries from the ankle brachial index machine, like in case of patients with venous stasis ulceration or open wounds. The test cannot be carried out for people with bilateral leg amputations or for people with hardened arteries.
Correlation Of Ankle Brachial Index With Lower Extremity Function
This correlation explains how different levels of PAD severity affect lower-extremity function in patients diagnosed with the disease. Patients who suffer from mild to moderate PAD usually suffer from lower-extremity pain when engaged in a physical activity like walking or climbing the stairs.
However, those with ankle brachial index of 0.5 or less are more likely to experience lower-extremity pain when they are resting rather than from exercise. It has been found through various studies that the ABI values correlate with the level of physical function in patients.
In a study conducted with 865 women aged over 65, it was found that patients with ankle brachial index values below 0.6 were more prone to experiencing pain and discomfort when walking. Another similar study was conducted in which physical activity of 740 patients, out of which 460 suffered from PAD, was monitored for 7 days, 6-minute walk, and 4-m walking velocity.
It was found from the study that out of those 460 patients, 33 percent had intermittent claudication. Less than 40 percent patients with ABI below 0.4 could complete the 6-minute walk. However, 95 percent patients with ABI value of 1.0 to 1.50, which is the normal ankle brachial index, completed the walk. For each additional 0.4 ABI, an increase was measured in the walking speed of the patients.
For ABI value below 0.4 patients also face the risk of ulceration, persistent sores, non-healing wounds, gangrene, and in some cases limb loss.
Abnormal Ankle Brachial Index As Marker For Atherosclerosis
The values of ABI equal to or below 0.9 and equal to or above 1.4 are abnormal ankle brachial indexes. ABI values ranging from 0.91 to 1.00 are considered borderline abnormal. An abnormal ABI in an asymptomatic person can be an indication of high risk for atherosclerosis and PAD in the future. It also means that a patient might have a higher chance of narrowing of arteries in other parts than the legs.
Abnormal Ankle Brachial Index As A Predictor Of Morbidity And Mortality In Patients With Post-Coronary Bypass Artery
Abnormal ABI is used as a prognostic indicator to foresee complications in patients undergoing coronary artery bypass surgery. Studies have also found that abnormal ABI is highly useful in long-term prognosis for patients with coronary artery bypass graft [Aboyans et al]. The study was conducted on patients with an average age of 69 followed by other people aged 44.
It was found that patients with a clinical PAD and subclinical PAD faced three times the risk of primary endpoints from coronary artery bypass graft — non-fatal acute coronary syndrome, composite of cardiovascular death, non-fatal stroke, peripheral and coronary revascularization, among others — than people without PAD. Apart from that, these patients with clinical and subclinical PAD also faced twice [HR 2.12 to 2.53] the risk of an acute coronary syndrome.
In another study, a 5-year mortality rate was studied in people with post coronary artery bypass graft [Burek et al]. It was found from the study that abnormal low ankle brachial index value of 0.9 was a strong predictor of mortality in patients who suffered from a multi-vessel cardiovascular disease.
Specificity And Sensitivity Of ABI In The Diagnosis Of PAD
Various studies have concluded that an ankle brachial index test has 95 percent more specificity and 90 percent sensitivity in diagnosing stenosis of lower-extremity arteries compared to other test methods such as angiography.
Provided that ABI is non-invasive, easy to perform and inexpensive, it is a useful tool in predicting the risk of cardiovascular disease in people. However, according to a study by Schroder et al, the high ABI was found to have a specificity of 99 percent and a sensitivity of 68 percent. Because the test doesn’t have a high enough sensitivity, it cannot be applied broadly in the population. That means that an ABI is not enough to ‘rule out’ the risk of cardiovascular diseases in a wide range of population groups.
Research has also been conducted to determine that a low ABI can look beyond the cardiovascular risk factors in people and provides a more comprehensive risk assessment. Low ABI has been found to indicate the presence of generalized atherosclerosis. It is more common in patients exposed to CV risk factors such as smoking, diabetes and hypertension. Based on several evaluated studies, it has been discovered that a low ankle pressure can independently predict cardiovascular risk given that the traditional cardiovascular risk factors have been adjusted for.
Although the ankle brachial index test has for long been considered the primary test for peripheral vascular diseases, more studies in the sector have led clinicians to look for even more efficient methods. That is owing to the many limitations of ABI test, such as the lack of a stepwise procedure and lack of training programs to familiarize doctors with ABI vascular machines.
A physician has to recognize the symptoms of PAD and refer a patient for screening. But since most patients don’t exhibit the symptoms for PAD in an early stage, they may not be referred for further vascular screening.
Major limitations for ankle brachial index testing include:
● The test can only be performed by trained vascular technicians.
● It is time-consuming.
● It can cause discomfort in patients.
● The results may not be accurate for patients who have undergone a mastectomy.
● The test doesn’t accurately find disease in smaller blood vessels of the ankle and the foot.
● The ABI vascular machine doesn’t produce accurate results for patients with hardened blood vessels.
Owing to these limitations, other screenings have been proved to be more effective in testing PAD in patients than ankle brachial index tests. QuantaFlo™, by Semler Scientific, has a few advantages that make it better than ABI testing. Among the major advantages is that patients don’t have to be referred to a special vascular lab to get tested for PAD.
Unlike ABI tests, the QuantaFlo™ test can be performed right in the primary care physician’s office. Because it doesn’t incorporate as complicated equipment as an ABI vascular machine, the test can be easily administered in less than five minutes. Apart from accurately diagnosing asymptomatic patients with PAD, the test also provides accurate results for patients who have undergone mastectomy or for patients with calcified vessels.
Aboyans V, Lacroix P, Postil A, et al. Subclinical peripheral arterial disease and incompressible ankle arteries are both long term prognostic factors in patients undergoing coronary artery bypass grafting. J Am Coll Card. 2005;46:815–20.
Burek KA, Sutton-Tyrell K, Brooks MM, et al. Prognostic importance of lower extremity arterial disease in patients undergoing coronary revascularization in the Bypass Angioplasty Revascularization Investigation (BARI) J Am Coll Cardiol. 1999;34:716–21. [PubMed]
Schroder F, Diehm N, Kareem S, et al. A modified method of ankle-brachial pressure index is far more sensitive in the detection of peripheral arterial disease. J Vasc Surg. 2006 Sep;44(3):532–36. [PubMed]