Surveillance of Bypass Grafts

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Surveillance of Bypass Grafts

• W. Kent Williamson, M.D.

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Graft Failure

• 5 causes
• Inflow
• Outflow
• Conduit quality
• Hypercoaguable state
• Technical

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Graft Failure

• Most common cause intimal hyperplasia (accounts
  for 75 of failures (Szilagi)
• Life table analysis of vein graft patency
  demonstrates 15 to 20 overall improvement in
  patency with duplex surveillance

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Graft Failure

• Critical stenosis is thought to be gt 70 -- this
  is debated by some
• Surveillance for prosthetic grafts has yet to be
  defined

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The failing graft

• Grafts that thrombose and require thrombectomy
  before revision have about a 11 1 year patency
  on average
• Goal is to detect grafts at risk before thrombosis

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The failing graft

• 20 to 30 of all vein grafts will eventually
  develop hemodynmically significant stenosis
  within the first year! (Mills, Bandyk)
• Revision of grafts offers 96 1 year patency and
  88 at 2 years

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The failing graft essentials of surveillance

• 30 of failing grafts may be detected on Hx PE
  (claud, ulcers, loss of pulses, ABI)
• Up to 70 of gt 70 vein grafts stenoses are not
  associated with a drop in ABI (Bandyk, Veith,
  Mills)

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Failing graft time course

• Incidence of graft stenosis is highest in first
  month (10 15 of all grafts)
• Rate 1 per year thereafter, up to 18 months
• Rate 4 / year after 18 months

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Failing graft time course

• 25 of grafts that require revision are detected
  within the first month of implantation
• 75 of lesions requiring revision occur within
  the first year

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Proposed Surveillance Scheme

• Pre discharge
• 6 weeks
• Every three months first year
• Every 6 months thereafter

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Location of graft stenosis

• Likely at areas of flow disturbance especially
  at valve sites
• In review of 10 studies, 25 of in situ and 20
  of RSVG get stenosis

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Location of graft stenosis

• Location of stenosis incidence
• Inflow 10
• Prox Anast 23
• Midgraft 44
• Distal Anast 15
• Outflow 10

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Definition of critical stenosis by DU

• High velocity criteria (HVC) PSV gt 200cm/s or
  ratio gt 2 (PSV max/ PSV prox)
• Low velocity criteria lt 40 cm / sec

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Risk Categories

• I immediate hosp repair
• PSV gt 300
• VR gt 3.5
• Low GFV lt 40 cm/sec
• ABI drop gt 0.15

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Risk Categories

• II Repair within 2 weeks
• PSV gt 300
• Vr gt 3.5
• ABI change
• No low GFV

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Risk Categories

• III (54 progress to Cat I or II, 23 regress
  to cat IV over 2 years, 23 no change)
• PSV gt 300 cm / s
• Vr gt 2.0
• ABI lt 0.15 change
• No low flow (no psv lt 45 cm/sec)

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Risk Categories

• IV low risk
• PSV lt 200 cm/sec
• Vr lt 2.0
• ABI lt0.15 change
• No low flow

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Graft Surveillance in Ax Bifem

• 120 pts studied 1996 to 2001
• Mean Axillary PSV 93 to 129 cm/sec
• Mean midgraft and distal PSV was lower in grafts
  about to thrombose (84 vs 112 cm/s and 89 vs 127
  cm/sec)
• Mean mid graft velocity of 80 cm/sec or less was
  sole predictor of graft failure

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Graft Surveillance in Ax Bifem

• Velocities vary widely within and among axillary
  femoral grafts
• Patent SFA does not appear to be required to
  improve patency (resistance)
• High PSV in a prosthetic graft does not
  necessarily predict impending graft failure

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Graft Surveillance in Ax Bifem

• PSV will tend to fall as you move down from prox
  anastomosis --- PSV will settle down over a
  distance of 10 graft diameters (i.e. 8 cm in an
  8mm graft)

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CASES