Chapter 14 - Ultrasound Assessment of Arterial Bypass Grafts

proximal and distal anastomosis may exhibit ____

turbulence (velocity changes)

_____ may be present as outflow artery may have small caliber

slight increase in PSV

Primary goal of duplex examination is to…

document anatomic and hemodynamic characteristics of bypass graft and adjacent vessels

Abnormal waveforms may suggest…

pathology proximal and distal to bypass graft

What incidental findings must you document during duplex exam?

venous thrombosis, dilated lymph nodes, hematoma, seroma, abscesses

• length, width, depth, color, doppler

At the inflow artery, the previously blocked artery may have ______ waveform due to hyperemia

monophasic

Pitfalls of duplex exam

• obesity

• deeply placed grafts - lower frequency

• dressings, skin staples, and sutures can limit access

Normal walls of a INSITU vein graft should appear as…

smooth and uniform

(prosthetic) PTFE grafts have a distinctive…

double line appearance of graft wall

Retained valves

• valve remnants that remain due to incomplete valve removal

• larger remnants → stenosis

• bright echoes

myointimal hyperplasia

rapid proliferation of cells into intimal layer → stenosis

• can occur along bypass conduit

• occurs at: sustained injury or vein sinus

other grayscale findings:

• dissections

• intimal flaps

• aneurysms

• pseudoaneurysms

• hematomas

Color flow imaging of grafts

• indicates mild changes in flow profiles

• aliasing in stenosis

Normal bypass should demonstrate ______

multiphasic waveforms with sharp upstroke and narrow systolic peak

Reversal component may be absent in _____

early postoperative period (monophasic due to hyperemia of stenotic vessel)

forward flow in diastole may indicate…

hyperemia or fistula

distal stenosis = scanning proximal

blunted, monophasic with no diastolic flow, abnormally high resistance

Proximal stenosis = scanning distal

continuous diastole flow and prolonged rise to peak systole

• energy losses across stenosis → lower velocities distally

normal velocities

below 150 cm/s

PSV ____ are considered abnormal

>180 cm/s

PSV with velocity ratio of 2

> 50% (PSV 180-300 cm/s)

PSV velocity ratio of 3.5

>75% stenosis (>300 cm/s)

Arteriovenous Fistula

abnormal connection between artery and vein

• occurs when branch of GSV is left unligated

• can be diverted into deep system

Doppler spectrum proximal to fistula

low resistance with continuous flow in diastole

Doppler spectrum distal to fistula

little to no diastolic flow

Mean Graft Flow Velocity (GFV)

calculated by averaging 3-4 PSV values in non-stenotic graft segments

GFV <40cm/s

large graft diameters or with limited outflow

decrease in GFV >30 cm/s

pending graft failure