Hemodynamic changes associated with bypass stenosis regression.

Objective: Ultrasound scanning is used to detect velocity increases indicative of a bypass stenosis. Subsequent examinations have shown regression of some stenotic lesions. This study examined hemodynamic changes that coincided with stenosis regression.

Methods: Duplex ultrasound scans were used to record the peak systolic velocity (PSV) and volume flow from proximal and distal segments of infrainguinal bypasses. Valve remnants or other image defects were also noted. The PSV ratio (Vr) was calculated as the PSV at a stenosis divided by the PSV proximal to the lesion. A stenosis was defined as Vr >/=2.0.

Results: An initial ultrasound scan performed 31 +/- 6 days after surgery revealed a stenosis in 68 of 565 bypasses. In six bypasses, the increased PSV (272 +/- 61 cm/s) and Vr (3.4 +/- 1.3) were sustained during the follow-up period of 8 +/- 3 months. In 27 bypasses with a PSV of 335 +/- 63 cm/s and a Vr of 4.0 +/- 1.6, the stenosis was repaired. In 35 bypasses with a PSV of 261 +/- 82 cm/s and Vr of 3.2 +/- 1.2, stenosis regression occurred with no increases in PSV observed on later scans. In this group, proximal bypass flow decreased during the follow-up interval from 247 +/- 130 mL/min to 151 +/- 135 mL/min and distal flow from 180 +/- 102 mL/min to 103 +/- 54 mL/min ( P < .05, paired t test). Ultrasound image abnormalities were noted in 4 bypasses (67%) with persistent stenoses, 14 with repaired stenoses (52%), and 10 with resolved stenoses (29%).

Conclusion: These data indicate early postoperative hyperemia is present in bypasses, demonstrating focal velocity increases. Such velocity increases may be the result of the bypass conduit acting as a flow-limiting lesion until the hyperemia subsides. As the blood flow decreases so does the PSV, giving the appearance of stenosis regression.