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This review article describes the natural course of infrainguinal bypasses, duplex ultrasound flow characteristics of stenosed vein bypasses, and the clinical relevance of duplex surveillance of infrainguinal vein bypasses. Among multiple factors bypass patency rates and limb salvage rates are influenced by the surgical technics of revascularization, graft material, localisation of the distal anastomosis, distal run-off, time interval between detection of bypass stenosis and revision. Preliminary duplex ultrasound criteria of a bypass dysfunction are a distal flow velocity < 45 cm/s, a bypass flow < 25 ml/min, a reduction of the inner diameter < 3 mm. The intrastenotic mean systolic peak velocity and the peak velocity ratio (PVR) are suitable for the grading of bypass stenoses. A vein bypass stenosis > 70% shows an intrastenotic mean peak velocity of 250 cm/s and a PVR > 3.3, a severe stenosis shows a mean peak velocity of 360 cm/s and a PVR > 7.2.

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