Hemodynamic characteristics of failing infrainguinal in situ vein bypass

The successful follow-up of distal arterial reconstructions for the identification of the failing bypass in the postoperative period hinges on a knowledge of the natural history of flow characteristics in these reconstructions. Over a 4-year period resting and hyperemic bypass flow, fistula flow, conduit diameter, and distal peak systolic velocity of 350 in situ bypasses were measured serially. B-mode ultrasound imaging of the entire bypass was performed to identify specific stenoses. Measurements were performed 5 to 9 days after operation, every 2 months for the first year, and every 6 months thereafter. Distal bypass flow less than 25 ml/min, a ratio of hyperemic/resting distal bypass flow less than 2.5, and vein size less than or equal to 3.0 mm inner diameter all correlated with bypass stenosis (greater than 50%) or occlusion (p less than 0.01). Contrary to previous studies, a distal peak systolic velocity of less than 45 cm/sec did not correlate with bypass stenosis or occlusion. A low distal peak systolic velocity did correlate with bypass stenosis or occlusion in bypasses larger than or equal to 3.5 mm inner diameter (p less than 0.03). However, no combination of these factors was able to accurately predict preocclusive stenosis or occlusion. Distal bypass flow was highest initially but reached a plateau 6 to 12 months after operation. Fistula flow, although very high initially, showed marked decrement with time.