M8: Peripheral Arterial Disease Part 3 Flashcards
does trickle flow show reversal
no
why dont you often get a staccato waveform is the peripheral arteries
b/c of multiple branches which causes a lower resistance system
role of US in assessing bypass grafts
- assess baseline hemodynamics post revascularization
- provide info to help w/ decisions about alternative treatments
- identify correctable lesions before graft thrombosis
indication for US of arterial bypass graft and stent
post-opt follow up
new symptoms post intervention (claudication, pain, ulcer, etc)
decreased ABI >0.15 compared to previous exam
lack of pulse, rubor, cyanosis
pulsatile mass near anastomotic site/intervention site
most common location of arterial bypass grafts and stents
other common places
AO-iliac (abdo AO to unitlaterl or bilateral iliac)
AO-Fem (abdo AO to uni/bilateral FA)
AX-Fem
Fem-Fem
types of LE arterial bypass grafts
synthetic - PTFE or Dacron
autogenous - natural materials
modified biological grafts
composite - synthetic graft connected to a vein (part synthetic, part native vein)
describe autogenous LE arterial bypass grafts
vein bypass grafts…. 2 types:
In-situ (as is) vein: vein is left in original location w/ valves cut and branches ligated
reversed vein: vein is ligated, reversed and attached to arteries
veins commonly used for autogenous LE arterial bypass grafts
GSV
SSV
basilic or cephalic vein
types of modified biological grafts
human umbilical vein
cryopreserved saph vein
bovine/cow
3 types of bypass anastamoses
end - end
end to side
side to side
which type of bypass anastamosis allows flow to go both ways
end to side
describe the mechanisms of early graft failure (<30 days)
due to erros in bypass construction (poor choice of inflow or outflow vessel, retained values, clamp injury)
describe the mechanisms of late graft failure
1 month - 2 years: most commonly, intimal hyperplasia can cause a stenosis in the graft
older than 2 years: atherosclerotic plaque can cause a stenosis in the graft
general causes of graft failure
hyper coagulable disorder infection aneurysmal degeneration in older vein grafts due inability to handle high press trauma leading to thrombus thromboembolism idiopathic
describe the mechanisms of early stent failure (<30 days)
describe the mechanisms of late stent failure (> 30 days)
early: technical failures
late: re-current stenosis
common sites of graft obstruction
valve site for vein grafts
anastomoses
inflow or outflow tract
graft kink
do we obtain bilateral ABIs when assessing grafts and stents
yes
describe how you assess a bypass graft and stent
obtain TRX 2D and colour and SAG colour and spectral of:
inflow/prox native artery prox anastomosis prox graft/stent mid graft/stent distal graft/stent distal anastomosis outflow/distal native artery
if you see a stenosis in a graft or stent, in which plane(s) do you measure
TRX and SAG
describe the waveform see early post opt (first 2 months) in a stent and bypass
why is it like this
may not be triphasic and it will be low resistance
reactive hyperemia
how should spectral waveforms seen in early stent/graft assessment change with time
change from low resistance to high resistance and triphasic.. some may never become triphasic but should become high resistance
w/ a graft, what determines the severity of the stenosis
graft material
how do we assess a stenosis in a graft
do an ABI or TBI
PSV and flow direction
Vr
assess waveform patterns and changes
what is the velocity ratio
ratio of highest PSV in the stenosis (V2) divided by the PSV of a normal proximal segment
characteristic US appearance of a synthetic graft
double line wall appearance
what should the waveform of the inflow artery of a graft look like and what should the Vr be
should the body of the stent/graft appear any different
triphasic
Vr < 2.0
no, should be the same unless there was recent placement
what should the waveform of the prox anastamosis of a graft look like and what should the Vr be
may be disturbed due to bifurcating and branching
Vr < 2.0
how will a large inflow artery feeding a small diameter graft affect the Vr
it will make it higher
norm PSV and VR for the body of a graft
minimum PSV for vein grafts = 4 mm in diameter… what about for larger grafts
PSV <180 cm/s
Vr <2.0
smaller: >40-45 cm/s
larger: minimum ~35 cm/s
norm PSV and VR for the body of a stent
is there a minimum velocity for stents
< 190 cm/s
Vr <1.5
no
what should the waveform of the distal anastamosis of a graft look like and what should the Vr be
increased velocity, usually due to size change from a wider graft to a narrower artery…. also disturbed flow
Vr <3.0
what should the waveform of the outflow artery of a graft look like and what should the Vr be
velocities remain unchanged w/ waveform similar to the body of the graft/stent
Vr <2.0
significant inflow artery obstruction is indicated by what type of spectral waveform in the graft
significant outflow artery or anastomoses obstruction is indicated by what type of spectral waveform in the graft
monophasic (tardus parvus)
high resistance w/ no end-diastolic flow, or staccato
The Vr can be up to what value is the graft diameter is much smaller than the inflow vessel
up to <3.0
what PSV and Vr in the body of a graft indicate >/= 50% stenosis?
> /= 70% stenosis
> /= 50%: PSV >180 cm/s and Vr >2.0
> /= 70%: PSV >300 cm/s and Vr >3.5
what PSV and Vr in the body of a stent indicate > 50% stenosis?
> 70% stenosis
> 50%: PSV >190 cm/s and Vr >1.5
> 70%: PSV >275 cm/s and Vr >/= 3.5
a PSV of what value indicates impending vein graft failure
PSV < 40-45 cm/s throughout a normally size graft
what Vr value indicates >/= 50% stenosis at the distal anastomoses site
Vr >3.0
describe aneurysmal dilatation of the bypass or stent
focal enlargement twice the proximal arterial segment w/ possible intraluminal thrombus in the aneurysm
where can entrapment of a graft commonly occur
describe what happens
at the knee…
w/ slight leg bend normal flow is seen
w/ leg straight, no flow is detected w/ colour or spectral doppler
