A PROSPECTIVE-STUDY OF THE DETERMINANTS OF VEIN GRAFT FLOW VELOCITY -IMPLICATIONS FOR GRAFT SURVEILLANCE

Purpose: Serial monitoring of vein graft peak systolic flow velocity ( PSFV) has been endorsed as a technique for vein graft surveillance wit h low values (<45 cm/sec) considered a marker for impending graft fail ure. Optimal application of this method requires an understanding of t he factors affecting PSFV in normal grafts. A prospective evaluation o f 46 consecutive elective infrainguinal vein grafts (6 popliteal/29 ti bial/11 pedal) was undertaken to assess the major determinants of PSFV . Methods: Factors recorded for each patient included vein graft diame ter (VGD), measured outflow resistance (MOR), conduit length, outflow level (popliteal/tibial/pedal), inflow level (femoral/popliteal), syst olic blood pressure, cardiac ejection fraction, the presence of a pate nt plantar arch, and Society for Vascular Surgery/International Societ y for Cardiovascular Surgery resistance scoring. MOR was measured by o ccluding graft inflow and infusing saline solution through a proximal graft cannula at 60 cc/min while simultaneously recording the pressure at the distal anastomosis via a separate cannula. MOR was calculated by dividing the resultant pressure by the infusion rate. MORs were exp ressed in resistance units and were measured before and after the infu sion of papaverine (MOR((PAP))). PSFVs and VGDs were measured 4 to 6 c m from the distal anastomosis 3 weeks after surgery with duplex scanni ng (60 degree angle with midstream sample volume). Results: PSFVs rang ed from 22 to 148 cm/sec and averaged 83.4 +/- 4.8 cm/sec. Pedal bypas s grafts had significantly lower PSFVs (64 +/- 10 vs 89.5 +/- 5 cm/sec ,p = 0.02) and significantly higher MOR((PAP))s (0.86 +/- 0.15 vs 0.51 +/- 0.05 resistance units, p = 0.05) than bypasses to the popliteal/t ibial level. When subjected to univariate analysis the factors correla ting with PSFV were MOR (r = -0.59, p = 0.0001), MOR((PAP)) (r = -0.69 , p = 0.0001) VGD (r = -0.31, p = 0.06), the Society for Vascular Surg ery/International Society for Cardiovascular Surgery score (r = -0.35, p = 0.04), inflow level (r = -0.47, p = 0.002), and outflow level (r = -0.35, p = 0.03). When subjected to multiple regression analysis, on ly MOR((PAP)) (r(2) = 0.51, p = 0.001) and VGD (r(2) = 0.14, p = 0.001 ) contributed significantly to the overall model (r(2) = 0.65, P = 0.0 001) with MOR((PAP)) eliminating the effect of the other variables. Th e multiple regression model predicts PSFV as follows: PSFV = 176 + VGD ((mm))(-11.7) + MOR((PAP))(-63.4). Conclusions: Clinically successful and, hemodynamically normal vein grafts have widely variable, yet pred ictable flow characteristics that are influenced primarily by outflow resistance and VGD. This wide variability suggests that no single lowe r threshold value for PSFV is universally applicable in identifying al l grafts at risk for failure. Detection of focal areas of flow acceler ation within the graft may be more accurate in identifying grafts at r isk for failure.