INSONATION AND IMPEDANCE ANALYSIS IN GRAFT SURVEILLANCE

Seventy consecutive patients with infrainguinal bypass grafts entered a 1-year graft surveillance programme involving colour duplex scanning , direct graft insonation and computer-assisted impedance analysis. Gr aft patients with a positive duplex scan, high frequencies on graft in sonation or an impedance value above 0.50 subsequently underwent arter iography. Sixteen patients were excluded before the initial surveillan ce visit. The 54 remaining patients with grafts (30 vein, 24 synthetic ) underwent a total of 137 surveillance visits, with 21 grafts confirm ed to be 'at risk'. The sensitivity of an impedance value above 0.55 i n identifying these grafts was 86 per cent, rising to 95 per cent when combined with graft insonation. Duplex scanning did not identify any abnormalities in 11 grafts that were either shown by arteriography to be 'at risk' or occluded before arteriography. Impedance measurement a nd graft insonation are simple screening techniques with a high sensit ivity (when combined), which identify 'at risk' infrainguinal grafts. Positive graft insonation or an impedance value over 0.55 will identif y all 'at risk' vein grafts while minimizing the number of unnecessary arteriograms.