1. Autogenous vein grafts have histological properties that make them less than ideal as vascular conduits compared to arteries, such as a lack of vasa vasorum and compliance mismatch. 2. Prosthetic grafts are more standardized but have higher risk of thrombosis and intimal hyperplasia. Various modifications aim to improve patency such as heparin bonding and venous adjuncts. 3. Surveillance of vascular grafts with duplex ultrasound is important to detect failing grafts which can be treated with thrombectomy or new bypass to preserve limb.

1. VASCULAR GRAFTS
Pradip Abraham
Stanley Medical College

2. AUTOGENOUS GRAFTS

3. History
1944 Dos Santos - segments of vein as patch
following SFA endarterectomy
1940s Kunlin - RSV for focal lesions of SFA
Linton, Darling - revived vein grafts which in the
interim had become unpopular due to poor long
term outcomes
1963 Dale - published use of RSV in fem-distal
bypass

4. Histology of vein graft
Endothelial cells -
cuboidal & lack tight
junctions
Poorly developed IEL
between intima & media,
large fenestrae
Poorly developed EEL
Thus more permeable
Sparse elastin with
more collagen, can’t
function in a pulsatile
manner like arteries
Thus compliance
mismatch - acts like a rigid
tube

5. Histology of vein graft
Adventitia - sparse
vasa vasorum
Thus maladaptive
response following
grafting
Increased
inflammatory
recruitment

6. Histological features associated with
failure
Due to aggressive hyperplastic response
1. Low endothelial cell coverage
2. Luminal stenosis
3. Thick walls
4. Sub endothelial spindle-shaped cells
5. Wall calcification

7. CONDUIT - GSV
Covered within the saphenous
fascia
Variants - duplicated systems
GSV thigh - 8%
GSV leg - 25%
Accessory GSV (outside the
fascia) = usually inadequate
diameter

8. CONDUIT - UPPER LIMB
Cephalic vein
Basilic vein
Basilic-cephalic loop
Composite grafts

9. CONDUIT - UPPER LIMB
Disadvantages
• Previous cannulations
• Multiple pathologies (webs,
stenosis, thrombus)

10. CONDUIT - SSV
Joins popliteal vein 5 cm proximal to
knee crease
Distal 2/3rd - subcutaneous adipose
Proximal 1/3rd - pierces fascia,
between two heads of
gastrocnemius
• Often can be harvested in continuity
with Giacomani
• Can be used as in situ for tibial
occlusive diseases

11. CONDUIT - SSV
Disadvantages
1. Length inadequacy (used often as
composite)
2. Difficult harvest/exposure
3. Size inadequacy

12. Other options
1.Femoral vein (Superficial Femoral vein)
• Intraabdominal reconstructions
• Offset by calf complications
• Complex harvest
2.Hypogastric artery
• Multiple distal anastomosis possible
• Conduit of choice in paediatric (less incidence of aneurysmal
dilatation)

13. Vein mapping - can identify > 60% vein
abnormalities
Warm the examination room
Prewarmed ultrasound gel
High frequency (>8MHz) probe
Cross section:
1. Compressibility
2. Wall thickening
3. Intraluminal echoes
4. Sites of thrombus
5. Intraluminal webs
6. Sclerotic walls

14. Standardised reference zones
Patient - modified
reverse Trendelenberg
If size is inadequate, pt
can stand +/- apply
tourniquet
GSV evaluated at 6
positions
Look for DVTs, valvular
incompetence

15. Critical factors for graft function
Diameter - at least 2.0 to 3.0 mm
Careful vein harvesting - avoid endothelial
injury - “no-touch”
Maintain continued continuity of vein
Ligate major branches away from vein -
promoting outward remodelling

16. Critical factors for graft function
Pedicle harvest technique - studied in CABG
Avoid over distention (small volume syringes
can cause > 700 mm Hg)
> 100 mm Hg - patchy endothelial
denudation
> 500 mm Hg - disruption of media
Increased c-fos expression - regulator of
PDGF

17. Irrigating solution
Buffered crystalloids like RL - best option (pH 6.5,
273 mOsm)
Unbuffered isotonic solutions like NS - most
damaging to endothelium
Autologous heparinised blood - conflicting
evidence, but can be used even though it might
not be superior
UF Heparin - added in solution, 4 to 10 U/mL
• Reduces fibrin deposition & formation of
microthrombi

18. Temperature
conflicting experimental evidence
room temperature solutions are probably
most practical

19. Preventing vasospasm -
Papaverine
Smooth muscle relaxation via PDE
inhibition/increased intracellular cAMP
Percutaneous periadvential injection (120
mg/L)
Other agents studied:
• GTN/verapamil combination

20. Minimally invasive harvest
Single continuous incision - wound complications in upto
~ 40% patients
Skip incisions
Endoscopic harvesting - single incision
1. Reduced wound complications
2. No difference in graft patency
3. Steep learning curve

21. Critical factors for graft function
Grafts with higher risk of failure (compared with 3.5
mm GSV graft):
1. Composite: 1.5 x risk
2. 3.0 to 3.5 mm diameter: 1.5 x risk
3. < 3.0 mm diameter: 2.4 x risk
4. Arm veins: 1.6 x risk
5. Reversed = non-reversed
PREVENT III trial

22. GRAFT
CONFIGURATIONS

23. Graft
configuration

24. Valve lysis
Lysis of valves: 15 - 30% improvement in flow rates by
15% reduction in haemodynamic resistance
Most pronounced in smaller diameter grafts
But not translated to better long-term patency rates
Valve morphology is dynamic: 60% of haemodynamically
significant valve lesions regress to < 20% within 3 months
Angioscopy - more sensitive > angiography/duplex for
valves, side branches, intraluminal pathologies

25. Complete disruption occurs in ~70
to 95% of treated valve leaflets

26. Graft failure - early
5% incidence of thrombosis within 30 days
Virchows triad:
1. Endothelial injury - manipulation
2. Hypercoagulability (~10%)
3. Reduced flow - inflow/outflow/graft stenosis
Most common cause = technical reasons (inadequate time for IH)
Open surgical revision = 90% 1-year patency rate
Endovascular management = limited value
(PREVENT III trial data)

27. Graft failure - early
Considered technical if:
1. Inadequate inflow (proximal disease, low CO
state, systemic hypotension)
2. Inadequate outflow (tibial/inframalleolar
disease, vasospasm)
3. Extrinsic causes (tunneling errors,
haematomas)
4. Intrinsic lesions in 20% (retained valve leaflet,
intimal flap, anastomotic defects, undersized
conduit = < 3.0 mm)

28. Intimal hyperplasia
Factors associated:
1. Surgical manipulation
2. Acute exposure to elevated shear and tensile
forces
Recruitment of chemokines, growth factors etc
Leads to smooth muscle cell dedifferentiation
Smooth muscle migration & proliferation

29. Intimal hyperplasia
Vein graft lesions = strong tendency to be focal
Peak incidence = 4 to 12 months post-
implantation
Stenotic-type lesions = usually at anastomotic
sites
Mid-graft stenotic lesions = usually at valve leaflet
sites
Pathology = complex, intersection of localised

30. Pathological remodelling
Normal vascular adaptive response = increase
in overall circumference as compensation
Upto 20% increase in diameter within 1st
month of implantation
Failure of this remodelling - higher risk of
failure

31. Graft atherosclerosis
4% annual loss of graft patency - long term
follow-up
Morphological changes:
1. Replacement of wall with lipid-laden
macrophages
2. Intramural calcification
3. Intramural thrombus

32. Prevention of graft failure - intraop
assessment
External appearance of graft
Distal pulse & perfusion
Continuous wave Doppler

33. Prevention of graft failure - intraop
assessment
Angiography, disadvantages include
1. Single projection & dense opacification
2. Inadequate assessment of distal anastomotic site
3. Cant differentiate structural defects from vasospasm
4. No information on haemodynamics
5. Can miss out on intraluminal webs, retained valve
leaflets etc.
6. Additional expense, time and effort
Angioscopy

34. Prevention of graft failure -
intraoperative assessment
Intraoperative flow rate < 80 ml/min = critical
threshold
• Not predictive of early failure
• Rather useful to predict intermediate & long-
term patency

35. Prevention of graft failure - intraoperative
assessment
Duplex assessment

36. Prevention of graft failure -
Duplex assessment
Low flow grafts, PSV < 45 cm/s with
1. High peripheral resistance & absent diastolic
flow had high risk of failure within 6 months
2. Low peripheral resistance & continuous
antegrade flow had intermediate risk of
failure (30% at 6 months) - consider post
systemic anticoagulation

37. Postoperative surveillance
At 1 year ~ 30% grafts have significant lesions
Secondary patency (post thrombectomy) at 1 year ~ 30%,
hence importance of detecting failing grafts
Early post op assessment, then at 1, 3, 6, 12 and 18
months, annually thereafter
History: new-onset claudication/rest pain
Pulse status
ABI reduction > 0.15 = significant

38. Preocclusive lesions

40. PROSTHETIC GRAFTS

41. Why use?
1. Previous harvesting of veins
2. Small vein caliber
3. Active infection at vein harvest site
4. Vein varicosities/thrombosis

42. Advantages
1. Highly standardised manufacturing & uniform
2. Can be stored on a shelf
3. Reasonably inexpensive
4. Widely available

43. Ideal prosthetic graft
1. Impermeable
2. Compliant
3. Biocompatible
4. Durable
5. Easy to sterilise
6. Facile to implant
7. Available in various sizes
8. Resistant to
thrombosis/infection
9. Cost effective
10.Surface electronegative

44. Properties to improve
function
1. Electronegativity - inhibits platelet aggregation
2. Porosity - increased tissue ingrowth
3. Endothelial seeding
4. Heparin bonding

45. Dacron

46. Dacron/Polyester
Polyethylene
terephthalate
Introduced by
DeBakey in 1958
Porosity - better
handling &
incorporation at the
cost of increased
bleeding complications

47. Dacron
Knitted Woven
Better compliance Difficult to handle
Larger pores Low porosity, better haemostasis
Requires pre clotting Doesn’t require pre clotting
Albumin/collagen/gelatin coated
Configurations:
thin-walled, ringed, pre cuffed
Higher risk of dilatation Nodal-fibril configuration
Most common available Prone to fraying

48. Knitted Woven
DACRON

50. Node - fibril configuration

51. ePTFE
GORE-TEX® Stretch Vascular Graft

52. ePTFE
Introduced in 1957 from
teflon fabric
Forcible expansion of
solid polymer into
nodular-fibrillar structure
70% air/ highly porous
But hydrophobic - limits
excrescence of blood

53. Commercial configurations
1. Sintered (chemical process) - Impra
2. External wrapping by non-expanded PTFE film
- Gore-Tex
No studies comparing these configurations

54. Other uses
1. Haemodialysis access
2. Visceral and renal reconstructions
3. Large-caliber venous reconstructions
(IVC/SVC/PV/IF/IJV) - externally supported
ePTFE

55. Dacron = PTFE patency
• Rychlik et al. meta-analysis 2014
• Cochrane review 2010

56. Strategies to improve
patency
1. Reduce graft thrombogenicity
2. Reduce myointimal hyperplasia
3. Venous adjuncts at anastomosis
4. Heparin bonding to the luminal surface
5. Addition of AV fistula

57. Venous adjuncts - how do they
aid?
1. Minimises expansibility mismatch (between stiff graft &
pulsatile flow of artery) at anastomotic site - reduces
mechanical injury
2. Positively affecting turbulence and shear forces
3. Venous endothelium - fibrinolytic and antiplatelet activity
4. Venous tissue enlarges at the site, less chance of IH to
occlude
5. Venous tissue easier to anastomose with small,
calcified tibial arteries

58. Miller cuff

59. Miller cuff
Disadvantages:
1. Significant turbulence at anastomotic reservoir
2. Difficulty in achieving adequate angle between
graft and recipient artery

60. Taylor patch

61. Taylor patch
Disadvantages:
1. Half the anastomosis exposed to prosthetic graft
2. Point of anastomotic constriction at triumvirate
3. Significant length of vein must be available
4. Difficult in inframalleolar location

62. Distal vein patch

63. Distal vein patch

64. Distal vein patch
Technically easier to perform, with maintenance of
advantages
Secondary patency through thrombectomy and revision of
distal anastomosis can be performed
Because when DVP bypasses fail, recipient artery rarely
thombose (unlike in other vein patch techniques)
Small vortex of turbulent flow at the heel, streamlined flow at
the toe

65. Heparin bonded grafts
End-point covalent bonding of heparin to graft maintains
bioactivity of heparin
Benefits (expt models):
1. Reduced platelet deposition
2. Reduced thrombus formation
3. Reduced IH at anastomotic site

67. Heparin bonded grafts
HIT has been described - few case reports
Newer grafts with covalent bonding doesn’t release
heparin into the bloodstream (c/w older ionic
bonded)
Systemic markers of haemostasis - no increase
No Ig against heparin - upto 6 weeks
Heyligers JM, Lisman T, Verhagen HJ, et al. J Vasc Surg. 2008;47:324–329

68. Spiral laminar flow grafts

69. Distal AV fistula
Spatchula (common ostium AVF at distal
anastomosis)
Common ostium AVF to DVP bypass
AVF using PTFE from target artery to
corresponding vein
Reduces outflow resistance
Increases flow velocity

70. Patchula

71. Medical therapy

72. Graft surveillance
Criteria for failing graft: PSV > 300 cm/s
PSV ratio > 3.5
Mid-graft PSV < 45 cm/s
Can consider Warfarin for low velocity grafts

73. Graft thrombosis
Revision of failed graft = often more complex
with increased morbidity when compared to
intervention for assisted primary patency
Therefore, ROUTINE SURVEILLANCE to pick
up failing graft

74. Graft thrombosis
1. If no symptoms of rest pain/tissue loss/gangrene -
thrombolysis can be attempted. Underlying lesion
could be unmasked - ? Further interventions
2. If CLTI - exploration - open thrombectomy/new
bypass
• Consider 2 week threshold for failure of thrombolysis
• Consider outflow vessel, conduit for new bypass

76. Graft infection
Lower extremity bypass: 1 - 6%
Abdominal aorta: 0.5 to 2%
Amputation rates: 10 to 70%
Mortality rates: upto 20%

77. Graft infection
Most common organisms:
Staphylococcus aureus
Staphylococcus epidermidis

78. Graft infection
Risk factors
1. Reoperative procedure
2. Females
3. Diabetes
4. Active infection at the time of surgery

79. Infection rates
Dacron = ePTFE
Roll S, Muller-Nordhorn J, Keil T, et al. Dacron vs. PTFE as bypass materials in peripheral
vascular surgery–systematic review and meta-analysis. BMC Surg. 2008;8:22.

80. Management
Blood cultures
Broad spectrum antibiotics
Review culture report
Imaging - CT, USG, MRI, gallium scanning,
labelled WBC

81. Imaging findings
Perigraft air
Fluid or soft-tissue attenuation
Pseudo aneurysm formation

82. Management
Pseudomonas & MRSA = especially virulent - require
removal
If graft thromboses with good collaterals = excision alone
Revascularisation options= in-situ or extra-anatomical
bypass
Conduits= autogenous, cryopreserved, rifampicin-soaked
prosthetic
MRSA +ve = decolonisation prior to surgery

83. VECTRA® Vascular Access Grafts

84. Silver Graft
• Polyester
• Warp-knitted
• Double-velour
• Impregnated
with polygelin

85. ePTFE
GORE-TEX® Stretch Vascular Graft

86. AlboGraft® Polyester Vascular Graft

87. IMPRA® Vascular Grafts

88. BIOLOGIC GRAFTS

89. Biografts
Allografts/homografts: same species
Xenografts/heterografts: another species
When autogenous grafts = unavailable,
prosthetic grafts are contraindicated (e.g
infected fields)
Potentially can be used “off-the-shelf”

90. Fresh vascular allografts
High rates of thrombosis and aneurysms
Highly immunogenic
Logistic issues, availability, storage
This led to new techniques to improve outcomes
1. Preservation techniques
2. Modification techniques

91. Cryopreservation
Concept of vapour pressure gradient
Cryoprotectants = chemicals to reduce this gradient
Dimethylsuloxide 10% to 20% dilution
Multiple freezing protocols (e.g rate at 5 degree
C/second)
Storage from - 102 to - 196 degrees C
Additives - chondroitin sulfate
E.g - CSV, CFV

92. Cryopreservation
Reduced endothelial function & collagen
synthesis
Gross histology maintained
Accumulates LDL at accelerated rate
No major effect on elasticity, contractility,
compliance & mechanical buffering function
Triggers significant immune response - related
to thrombosis and aneurysmal degeneration

93. Cryopreservation
Immunosuppression has been tried - AZA, low
dose cyclophosphamide, prednisolone
Others - antiplatelets, warfarin, vasodilators
Allosensitization - may interfere with future
organ transplantation (e.g use off CFFV
allografts for hemodialysis access)

94. Enzymatic digestion
Type of structural modification
Early experience with ficin, resultant collagenous
skeleton obtained
Tanning (with dialdehyde starch) - to cross link
collagen
Sterilized
Stored in proprietary solution
E.g - BCA, BMV, HUV

96. Thank you