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The variation in vein graft flow velocity with luminal diameter and outflow level
M Belkin1, W C Mackey, R McLaughlin
1Department of Surgery, New England Medical Center, Tufts University School of Medicine, Boston, MA 02111.
Insights
Duplex ultrasound criteria for failing vein grafts need to account for graft diameter and outflow resistance. Flow velocity varies significantly with graft diameter in tibial and popliteal grafts, but not inframalleolar grafts.
Area of Science:
- Vascular Surgery
- Medical Imaging
- Hemodynamics
Background:
- Duplex scanning is used to monitor infrainguinal vein graft patency.
- Existing criteria for identifying failing grafts do not consider graft diameter or outflow resistance, which significantly impact flow.
Purpose of the Study:
- To prospectively examine how graft peak systolic flow velocity varies with graft diameter and outflow level in functioning infrainguinal vein grafts.
Main Methods:
- Prospective study of 68 patients with 72 functioning infrainguinal vein grafts.
- Duplex ultrasound imaging was used to record distal peak systolic flow velocity and intraluminal diameters.
- Grafts were categorized by outflow level: inframalleolar, tibial, and popliteal.
Main Results:
- Graft diameters differed significantly by outflow level (inframalleolar: 3.95 mm, tibial: 4.78 mm, popliteal: 5.65 mm).
- Peak systolic flow velocities were significantly lower in inframalleolar grafts (59.1 cm/sec) compared to tibial (77.2 cm/sec) and popliteal (71.0 cm/sec) grafts.
- Significant inverse correlations between peak systolic flow velocity and graft diameter were found in tibial (r=-0.49) and popliteal (r=-0.73) grafts, but not inframalleolar grafts (r=-0.21).
Conclusions:
- The relationship between graft diameter and flow velocity in infrainguinal vein grafts is complex and varies by outflow level.
- Current duplex ultrasound criteria for graft monitoring may need refinement to incorporate graft diameter and outflow resistance.
- Further research is needed to develop more accurate methods for assessing vein graft patency.
Abstract:
Duplex scanning has recently been used to monitor the patency of infrainguinal vein grafts. Empirically derived criteria that have been used for identifying the failing graft have never accounted for the effect of vein graft diameter or varying outflow resistance, despite the fact that they are major determinants of flow. We prospectively examined the variation in graft peak systolic flow velocity with graft diameter and outflow level in a consecutive series of 68 patients with 72 normally functioning vein grafts returning for routine follow-up. Images were obtained of vein grafts with a duplex scanner throughout their lengths, and the distal peak systolic flow velocity and intraluminal diameters were recorded. There were 15 popliteal, 26 tibial, and 21 inframalleolar grafts. The mean ankle-brachial index of inframalleolar grafts was 1.01 +/- 0.04 and did not differ significantly from tibial (0.96 +/- 0.03) or popliteal (0.93 +/- 0.06) grafts (p = 0.32). Grafts to the three outflow levels differed significantly in diameter, with inframalleolar grafts measuring 3.95 +/- 0.17 mm, tibial grafts 4.78 +/- 0.21 mm, and popliteal grafts 5.65 +/- 0.38 mm (p = 0.0001). In a similar manner inframalleolar grafts had significantly lower peak systolic flow velocities (59.1 +/- 3.4 cm/sec) than tibial (77.2 +/- 5.6 cm/sec) or popliteal (71.0 +/- 7.6 cm/sec) grafts (p = 0.04). Inframalleolar grafts did not demonstrate a significant correlation (r = -0.21, p = 0.29) between peak systolic flow velocity and graft diameter. Conversely, both tibial (r = -0.49, p = 0.005) and popliteal (r = -0.73, p = 0.002) grafts demonstrated significant inverse correlations.(ABSTRACT TRUNCATED AT 250 WORDS)