Digital Ankle Brachial Index (ABI) as a Screening Tool in Detecting Peripheral Arterial Disease
Condition: Peripheral Artery Disease; Amputation; Smoking; Diabetes; Hypercholesterolemia; Hypertension
MeSH terms: Peripheral Arterial Disease; Peripheral Vascular Diseases; Hypercholesterolemia
Study type: Interventional

Summary: 
      Peripheral artery disease (PAD) affects 8-18 million in the US and is an economic burden,
      currently estimated to be greater than cancer and heart disease. Older age (> 65 years),
      smoking, diabetes and kidney diseases are some risk factors associated with PAD and are known
      to have increased morbidity and mortality.Early detection is critical for mitigating PAD
      progression. Ankle-brachial index (ABI) testing is recommended by the US Preventative
      Services Task Force as an affordable and effective screening tool for evaluating PAD risk.

      QuantaFlo™ (Semler Scientific, Inc.) is a novel, noninvasive, 510K FDA approved digital
      device that is used as a screening tool to measure ABI of patients at risk of PAD. This
      single center prospective clinical trial will evaluate the sensitivity and specificity of
      digital ABI in detecting PAD using color Doppler ultrasound and 'gold standard' angiography
      as reference. Specifically in patient undergoing dialysis and who cannot undergo ABI using
      pressure cuffs dialysis grafts/ fistulae in the arms, we will evaluate the value of digital
      ABI in detecting PAD.
    

Detailed description: 
      Peripheral artery disease (PAD) affects 8-18 million in the US and is an economic burden,
      currently estimated to be greater than cancer and heart disease. Older age (> 65 years),
      smoking, diabetes and kidney diseases are some risk factors associated with PAD and are known
      to have increased morbidity and mortality. PAD progression directly results in claudication,
      impaired walking, and amputation. Amputation is not benign - impacts are physical and
      emotional. Recovery from amputation involves long-term rehabilitation. The American Heart
      Association (AHA) in 2016 guidelines suggests an algorithm for diagnosis and management of
      PAD. They recommend a collaborative multidisciplinary team approach between the primary care
      physician and specialists including; a diabetologists/ endocrinologist, smoking cessation
      expert, hypertension and lipid specialist, interventional radiologist, vascular surgeon,
      orthopedist, neurologist, wound healing expert, and/or others for 'the greatest chance of
      providing optimal care for the patient with PAD'.

      Early detection is critical for mitigating PAD progression. Ankle-brachial index (ABI)
      testing is recommended by the US Preventative Services Task Force as an affordable and
      effective screening tool for evaluating PAD risk. ABI testing is especially useful in primary
      care settings allowing for earlier diagnosis and treatment. Several ABI methods are used;
      classically this test uses a device for measuring blood pressure with an inflatable cuff, and
      blood pressure measurements are taken at the upper arm and the ankle; healthcare providers
      have used a doppler probe to detect audible systolic pressure signals within the arteries -
      Doppler ABI. Barriers to implementation include; time required to conduct tests, training and
      required technical skills. Hence, Doppler-based ABI in primary care has been limited.
      Recently designed oscillometric (manual or digital with automatic electronic calculation of
      blood pressure) and photophlethysmographic devices are now available. However current
      guidelines do not endorse the use of these newer devices but recommend the hand-held doppler
      technique.

      Digital ABI is noninvasive, automated ABI using pulsatile blood volume changes -
      plethysmography, irrespective of vessel compressibility. The QuantaFlo™ (Semler Scientific,
      Inc.) is an innovative, 510K FDA approved device that provides bilateral, non-invasive
      physiologic studies of upper and lower extremity arteries using volume plethysmography of the
      posterior tibial and anterior tibial/dorsalis pedis arterial distributions. QuantaFlo™ uses
      an optical sensor attached onto a digit in the hand and feet to assess extremity blood
      volume. It then displays a signal, directly related to blood volume, on a Volume
      Plethysmography Chart used to calculate PAD probability. This test is easy to use and
      portable, delivering fast, accurate results in ~5 minutes; an attractive option in primary
      care settings. While maintaining accuracy, results comparing digital methods to Doppler show
      concordance above 90%. The American Medical Association (AMA) concluded, "Evaluation of the
      digits in both legs with volume plethysmography is appropriate for this code provided that an
      ankle/brachial index (ABI) be performed." QuantaFlo™ meets both of these standards.

      ABI ≤ 0.9 has been used as the criterion for diagnosing PAD based on ACC/AHA guidelines for
      the management of patients with PAD ; the cutoff value of ABPI ≤0.9 it has been reported that
      the sensitivity of diagnosing PAD was 83% to 85% and a specificity of 95% to 100% [5]. ABI
      has been validated against lower extremity contrast angiography obtaining high sensitivity
      (85%-95%) and specificity (90%-100%), for diagnosing PAD . Many studies have reported more
      than 95% of sensitivity and specificity of colour duplex ultrasound scan in detecting a
      significant stenosis of the arteries .

      QuantaFlo™ (Semler Scientific, Inc.) is a novel, noninvasive, 510K FDA approved digital
      device that is used as a screening tool to measure ABI of patients at risk of PAD. This
      single center prospective clinical trial will evaluate the sensitivity and specificity of
      digital ABI in detecting PAD using color Doppler ultrasound and 'gold standard' angiography
      as reference. Specifically in patient undergoing dialysis and who cannot undergo ABI using
      pressure cuffs dialysis grafts/ fistulae in the arms, we will evaluate the value of digital
      ABI in detecting PAD.
    

Intervention name(s): ABI using QuantaFlo™
Intervention type(s): Device
Intervention description(s): Perform Digital ABI:
Will be performed by the nurse/medical assistant with training to perform this test
The patient will be placed in the supine position, with the arms and legs at the same level as the heart, for a minimum of 5 minutes before measurement.
The optical sensor (similar to a pulse oximeter) will be placed sequentially in the fingers of the hands and feet: Right and left hand fingers and then right and left feet toes.
Usually each digit takes about 15 seconds to obtain a waveform
At the end of 60 seconds, an automated digital ABI will be generated.
Clinical course: If based on Screening questionnaire and digital ABI, I. Patient is diagnosed with PAD- the referring physician and patient will receive a phone call about the same. He/ she will then be advised any further testing/ referral to IR clinic.
II. There is no evidence of PAD- no further action will be taken. The patient will be informed of the same.
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Prevention
Keywords: ankle brachial index; peripheral arterial disease