Effective hemodynamic diameter: An intrinsic property of vein grafts with predictive value for patency

Introduction: Conduit size and quality are major determinants of the long-t erm success of infrainguinal autologous vein grafting. However, accurate me asurement of the internal diameter of vein grafts is difficult given their variable wall thickness and taper. The purpose of this study was to define the "effective" internal diameter of a vein graft according to its hemodyna mic properties and to determine its significance for graft patency. Methods: Sixty infrainguinal bypass grafts performed on 57 patients were ev aluated intraoperatively. Proximal and distal graft pressure and blood flow (Q(meas)) were measured with fluid-filled catheter transduction and ultras onic transit-time flowimetry, respectively, after unclamping. Waveforms wer e recorded digitally at 200 Hz under baseline conditions and after stimulat ion with 60 mg of papaverine. According to Fourier transformation of the me asured pressure gradient (Delta P), the Womersley solution for fluid flow i n a straight rigid tube was used to calculate theoretical flow waveforms (Q (calc)) for a range of graft diameters. The theoretical waveforms were then compared with the measured flow waveforms and the best-fit diameter chosen as the "effective hemodynamic diameter" (EHD). Only grafts in which the co rrelation coefficient of Q(calc) versus Q(meas) was more than 0.90 were acc epted (n = 47) to assure validity of the hemodynamic model. After a mean fo llow-up of 12.5 months (range, 0.1-43.9 months), patency was determined by the Life table method. Hemodynamic and clinical variables were tabulated, a nd their effect on patency determined the use of univariate and multivariat e Cox regression. Results: Mean EHD was 4.1 +/- 0.1 Nm with a range of 2.5 to 5.7 mm. Adminis tration of papaverine caused profound changes in Delta P (+78% +/- 17%) and Q(meas) (+71% +/- 12%) as expected, but had no effect on EHD (+0.05% +/- 0 .1%). Univariate regression identified five variables associated with decre ased secondary patency (P < .10): low EHD, conduit source other than the gr eater saphenous vein, high baseline Delta P-mean, female sex, and redo oper ation. Of these, onlJ low EHD was significant after multivariate analysis ( P = .03). Patency of small diameter grafts (EHD < 3.6 mm; n = ii) was compa red with patency of larger grafts (EHD > 3.6 mm; n = 36) to test a frequent ly espoused clinical guideline. Grafts with an EHD less than 3.6 mm exhibit ed significantly lower secondary patency compared with larger grafts (P = . 0001). The positive and negative predictive values for an EHD less than 3.6 mm for secondary graft failure for grafts with at least 1 year follow-up n ;ere 86% and 88%, respectively. Conclusion: An EHD is a unique parameter that quantifies conduit size and h as a significant impact on vein graft patency. An EHD less than 3.6 mm port ends graft failure.