Diagnosis and evaluation of peripheral artery disease

www.tasc-2-pad.org
Diagnosis and evaluation
of peripheral artery disease
Noninvasive vascular laboratory and imaging techniques
Based on the Inter-Society Consensus
Edited by Dr Denis Clement
University Hospital, Ghent, Belgium
Supported by an educational grant from Otsuka Pharmaceutical Co. Ltd.
Otsuka Pharmaceutical Co.Ltd. was not involved in the development of this pocket guide
and in no way influenced its contents.
CONTENTS
Introduction
4
Noninvasive vascular laboratory
6
Segmental limb systolic measurement
7
Segmental plethysmography or pulse
volume recordings
10
Toe pressures and the toe-brachial index
12
Doppler velocity wave form analysis
13
Imaging techniques
16
Angiography
16
Color-assisted duplex ultrasonography
18
Magnetic resonance angiography
19
Computed tomography angiography
22
Summary – a comparison of different
imaging techniques
24
References
26
3
Introduction
Initial diagnosis of peripheral artery disease (PAD) typically
relies on patient history and physical examination of
the patient.1
Two types of techniques are used for the assessment of
a patient with PAD:
1.
The noninvasive vascular laboratory
2.
Imaging techniques (some techniques, for example
If PAD is suspected, a number of tests need to be
duplex ultrasonography, are regarded as integral
performed to detect the presence of atherosclerosis,
components of the vascular laboratory)
as well as to localize areas of stenosis and to estimate
the degree of the stenosis.
Diagnostic testing for PAD must be:
The use of these techniques in patients with lower
extremity PAD will allow the clinician to:
Objectively establish the presence of the lower
Accurate
extremity PAD diagnosis
Inexpensive
Quantitatively assess the severity of disease
Widely accessible
Localize lesions to specific limb arterial segments
Easy to perform
Determine the temporal progression of disease
Preferably noninvasive
Determine patients’ response to therapy
Patients with PAD have differing levels of disease severity
In this pocket guide, the strengths and limitations of the
and risk factors, which will necessitate different,
techniques will be reviewed.
individualized management strategies to control the
disease. Consequently, a detailed assessment is needed
4
to develop a suitable treatment plan for the individual patient.2
5
Noninvasive vascular laboratory
The routine evaluation of patients with PAD can include
a referral to the vascular laboratory. Noninvasive
hemodynamic measurements can provide an initial
assessment of the location and severity of the arterial
disease. These tests can be repeated over time to follow
The main noninvasive vascular
laboratory tests are1:
Ankle-brachial systolic pressure index (ABI).
For more information on the ABI please refer
to the pocket guide on management of
intermittent claudication
disease progression.
Segmental limb systolic pressure (SLP)
measurement
The noninvasive vascular laboratory provides a
powerful set of tools that can objectively assess the
status of lower extremity arterial disease and facilitate
Segmental plethysmography or pulse volume
recordings (PVRs)
the creation of a therapeutic plan.
Toe pressures and the toe-brachial index (TBI)
Vital information can be obtained through the
Doppler velocity wave form analysis
combined use of physiological noninvasive data
and imaging studies. This information can be used
to determine the overall treatment pathway and,
Segmental limb systolic pressure
measurement
in particular, the choice of interventional approach.
SLP measurements are widely used to detect and
segmentally localize hemodynamically significant large-vessel
occlusive lesions in the major arteries of the lower extremities.
Segmental pressure measurements are obtained in the
6
thigh and calf in the same fashion as ankle pressure.
7
In contrast to ankle brachial index (ABI) studies, the SLP
analysis is able to accurately determine the location of
individual arterial stenoses.3
A sphygmomanometer cuff is placed at a given level with
a Doppler probe over one of the pedal arteries, and the
systolic pressure in the major arteries under the cuff is
Limitations of SLP measurements include1:
Nondetection of isolated moderate stenoses (usually
iliac) that produce little or no pressure gradient at rest
Falsely elevated pressures in patients with diabetes
calcified, incompressible arteries
measured (Figure 1). The location of occlusive lesions
The inability to differentiate between arterial stenosis
is apparent from the pressure gradients between the
and occlusion
different cuffs.
Figure 1. Segmental limb systolic pressure (SLP)
measurement
150
Brachial
150
Typically, a gradient of 20 mmHg
or between adjacent segments
indicates an underlying arterial
stenosis3,4
Gradients between the lower thigh and upper
150
150
110
146
108
100
62
84
calf cuffs identify a distal superficial femoral or
popliteal arterial stenosis
Gradients between the upper and lower calf
cuffs identify infrapopliteal disease
8
0.54
ABI
0.44
9
Segmental plethysmography or pulse
volume recordings
The PVR technique is useful as an initial diagnostic
For this technique, cuffs are placed around the leg at
and to assess limb perfusion after revascularization
selected locations and connected to a plethysmograph –
procedures, and it can predict risk of critical limb
an instrument that detects and graphically records
ischemia and amputation.3
test for patients with suspected lower extremity PAD
changes in limb volume. Normally, a single, large thigh cuff
is used along with regular-sized calf and ankle cuffs, plus
a brachial cuff that reflects the undampened cardiac
Figure 2. Pulse volume recordings (PVRs) in a healthy
individual (left) and in a patient with PAD (right)
contribution to arterial pulsatility.
Once the cuff is inflated to 60–65 mmHg – a pressure
Healthy individual
sufficient to detect volume changes without resulting in
Upper thigh
Upper thigh
Lower thigh
Lower thigh
Calf
Calf
Ankle
Ankle
Patient with PAD
arterial occlusion – PVRs are obtained (Figure 2).
Compared with angiography, SLP and PVR measurements
alone have an accuracy of 85% in detecting and localizing
significant occlusive lesions.1 However, when used
together, the accuracy approaches 95%. Consequently,
these two diagnostic methods are commonly used
together when evaluating PAD.1
In the presence of arterial disease, the slope of the waveforms flattens, the pulse
width widens, and the dicrotic notch is lost
10
11
Toe pressures and the toe-brachial index
Patients with long-standing diabetes, renal failure and
other disorders with vascular calcification can develop
incompressible tibial arteries, resulting in false high
systolic pressures.
Noncompressible measurements are defined as a highly
False-positive results with TBI are unusual. The main
limitation is that in patients with diabetes it may be
impossible to measure toe pressure in the first and
second toes due to inflammatory lesions, ulceration
or loss of tissue.
Doppler velocity wave form analysis
elevated ankle pressure (e.g. ≥250 mmHg) or ankle-
Arterial flow velocity can be assessed using a continuous
brachial index (ABI) >1.40. In this situation, measurement
wave Doppler at multiple sites in the peripheral circulation.
of toe pressures provides an accurate measurement of
distal limb systolic pressures in vessels that do not typically
become noncompressible.
A special small occlusion cuff is used proximally on the first
or second toe with a flow sensor, such as that used for
digital plethysmography.
The normal Doppler velocity
waveform is triphasic (Figure 3),
with each component corresponding
to different phases of arterial flow5:
Rapid forward flow reaching a peak during systole
Transient reversal of flow during early diastole
Toe pressure is normally approximately
30 mmHg less than ankle pressure
Low forward flow during late diastole
An abnormal TBI is <0.70
12
13
The flow-reversal component, a result of high peripheral
Figure 3. Left: Doppler velocity waveforms
vascular resistance, is absent in the presence of
Tight 7x
hemodynamically significant stenosis.4
Therefore, the Doppler waveforms transition from the
Significant 3x
normal triphasic pattern to a biphasic and, ultimately,
monophasic appearance in patients with significant PAD.1
While the test is operator-dependent, it provides another
means to detect PAD in patients with calcified tibial arteries.
4x
“Arterial flow velocity can be
assessed using a continuous wave
Right: Anatomic chart used to record position of stenoses, showing three
Doppler at multiple sites”
stenoses with velocity increases of 7x, 4x and 3x compared with adjacent
unaffected arteries
14
15
Imaging techniques
Limitations of angiography1:
Imaging is used to identify arterial lesions suitable for
revascularization with either an endovascular or open
surgical technique.
Risks associated with invasive procedures,
notably those related to vascular access
(e.g., bleeding, infection and vessel disruption)
The currently available techniques
for imaging are1:
Development of atheroemboli
Risk of severe reaction to contrast medium (0.1%)
Angiography
Nephrotoxicity of iodinated contrast agents
Color-assisted duplex ultrasonography
Risk of complications severe enough to alter
Magnetic resonance angiography (MRA)
Computed tomography angiography (CTA)
patient management (0.7%)
Mortality risk (0.16%)
Access site complications (i.e. pseudoaneurysm,
Angiography
arteriovenous fistula and hematoma)
Significant expense
Angiography is considered as the reference standard for
evaluating PAD, and is the most readily available and
widely used imaging technique. However, its use is
associated with a number of drawbacks.
16
17
Color-assisted duplex ultrasonography
Color-assisted duplex ultrasonography is especially
Color-assisted duplex imaging has been proposed as
helpful in determining the location of disease and in
a better alternative to angiography.
delineating between stenotic and occlusive lesions,
Compared with angiography, color-assisted duplex
an added benefit when preparing for an intervention.4
ultrasonography1:
Is completely safe
Magnetic resonance angiography
Is less expensive
MRA has become the preferred imaging technique for the
diagnosis and treatment planning of patients with PAD in
Can provide most of the essential anatomic
information plus some functional information
(e.g., velocity gradients across stenoses)
The lower extremity arterial tree can be visualized, with
the extent and degree of lesions accurately assessed
and arterial velocities measured.
Disadvantages of the technique include:
Lengthy examinations
many centers.1 It is useful for treatment planning prior to
intervention and in assessing suitability of lesions for
endovascular approaches.
The main advantage of MRA is its ability to provide rapid
high-resolution three-dimensional (3D) imaging of the entire
abdomen, pelvis and lower extremities in one setting.1
Furthermore, image volumes can be rotated and assessed
in an infinite number of planes.
Variability of skill of the technologist
Crural arteries are challenging to image in their entirety
18
19
Figure 4. An example of a gadolinium-enhanced MRA
A recent advance in this technique is the development
of gadolinium contrast-based MRA (CE-MRA), which
has replaced noncontrast MRA for the assessment of
peripheral vessels, as it provides rapid imaging with better
artifact-free images (Figure 4).1
CE-MRA has been shown to have better discriminatory
power than color-guided duplex ultrasound for the
diagnosis of PAD.
The limitations of CE-MRA are1:
The high magnetic field strength, which excludes
its use for patients with, e.g. defibrillators,
spinal cord stimulators, intracerebral shunts,
and cochlear implants
Cannot be used for patients affected by
claustrophobia and patients who are not
amenable to sedation (<5%)
Signal loss in the presence of stents; however,
20
Reproduced with permission from Dr. Michael R Jaff, Massachusetts General
this depends strongly on the metallic alloy,
Hospital, Boston, MA, USA
e.g., nitinol stents produce minimal artifact
21
Computed tomography angiography
Improvements in image resolution and scan times, and the
Multislice MDCTA enables fast imaging of the lower
advent of 64-channel ‘multidetector’ scanners, have driven
extremity and abdomen in a single breath-hold at sub-
the widespread adoption of the multidetector CTA
millimeter isotropic voxel resolution.
(MDCTA) for the initial diagnostic evaluation and treatment
planning of PAD (Figure 5).
Figure 5. An example of a CTA showing a patent right
femoropopliteal artery bypass graft and focal stenosis
of the left superficial femoral artery
The major limitations of MDCTA
include1:
The use of iodinated contrast (approximately
120 mL/exam)
Radiation exposure
The presence of calcium
Calcium can cause a ‘blooming artifact’ and can preclude
assessment of segments with substantive calcium.
Stented segments can also cause significant artifact and
may preclude adequate evaluation. However, the ability
to evaluate vessel wall lumen in stented and calcified
segments is dependent on the technique (window/level,
reconstruction kernel, and type of image [e.g. maximum
Reproduced with permission from Dr Michael R Jaff, Massachusetts General
Hospital, Boston, MA, USA
22
intensity projection versus multiplanar reformation]).
23
Moderate risk
Contrast
nephropathy
Radiation
exposure
Relative risk
and
complications
Widespread
Moderate
Availability
Moderate
Widespread
X-ray
contrast
angiography
MDCTA
Modality
MRA
Duplex
Hemodynamic
information
True 3D imaging
modality; infinite
planes and
orientations can
be constructed
Plaque morphology
from proximal
segments with
additional sequences
Calcium does not
cause artifact
Strengths
Rapid imaging
Sub-millimeter voxel
resolution
3D volumetric
information from
axial slices
Plaque morphology
‘Established
modality’
Strengths
MDCTA: Multidetector computed tomography angiography; MRA: magnetic resonance angiography.
None
None
High risk
Access site
complications
Contrast
nephropathy
Radiation
exposure
Availability
Modality
Relative risk
and
complications
Operator-dependent
and time-consuming
to image both lower
extremities
Calcified segments
are difficult to
assess
Stents cause
artifact but alloys
such as nitinol
produce minimal
artifact
Weaknesses
Calcium causes
‘blooming artifact’
Stented segments
difficult to visualize
2D images
Limited planes
Imaging pedal
vessels and
collaterals in the
setting of occlusion
requires prolonged
imaging and
substantial radiation
Weaknesses
None
Intracranial devices,
spinal stimulators,
pace-makers,
cochlear implants
and intracranial clips
and shunts are
absolute
contradications
Contraindications
Renal insufficiency
Contrast allergy
Renal insufficiency
Contrast allergy
Contraindications
Summary – a comparison of different imaging techniques
24
25
References
1. Norgren L, Hiatt WR, et al.; TASC II Working Group. Inter-Society Consensus for the Management
of Peripheral Arterial Disease (TASC II). Eur J Vasc Endovasc Surg 2007; 33(Suppl 1): S1–75.*
2. Collins R, et al. Duplex ultrasonography, magnetic resonance angiography, and computed
tomography angiography for diagnosis and assessment of symptomatic, lower limb peripheral
arterial disease: systematic review. BMJ 2007; 334: 1257–1261.
3. Hirsch AT, et al. ACC/AHA 2005 Practice Guidelines for the management of patients
with peripheral arterial disease (lower extremity, renal, mesenteric, and abdominal aortic).
J Am Coll Cardiol 2006; 47: 1239–1312.
4. Begelman SM, Jaff MR. Noninvasive diagnostic strategies for peripheral arterial disease.
Cleve Clin J Med 2006; 73(Suppl 4): S22–29.
5. Donnelly R, et al. ABC of arterial and venous disease. Non-invasive methods of arterial and
venous assessment. BMJ 2000; 320: 698–701.
*Also published as follows:
J Vasc Surg 2007; 45(Suppl S): S5–67.
Eur J Vasc Endovasc Surg 2007; 33(Suppl 1): S1–75.
Int Angiol 2007; 26(2): 8–157.
26
TASC
II
Inter-Society Consensus
for the Management of PAD
This pocket guide is one of a series of booklets designed
to present the TASC II guidelines in a quick reference format.
You can find pocket guides on other topics covered in the
TASC II guidelines on the TASC II website: www.tasc-2-pad.org
© 2008 Discovery London and TASC II. All rights reserved.