Relationship Between Preoperative Duplex Vein Mapping and Intraoperative Longitudinal Impedance in Infrainguinal Vein Grafts

The importance of favorable vein size, resistance, and impedance for the sustained success of infrainguinal vein grafting procedures has repeatedly been demonstrated. Estimating these properties preoperatively, however, has been problematic. Ultrasonic vein mapping is a reliable technique for measuring vein diameters at venous pressures, but it is unknown whether these data accurately assess the resistive potential of the conduit in the arterial circulation. The purpose of this study was to compare vein diameter measured preoperatively with vein graft longitudinal impedance measured intraoperatively. Patients who had undergone both preoperative vein mapping and intraoperative impedance studies at the time of infrainguinal bypass were included (December 1995-April 1999). Vein mapping was performed using B-mode ultrasound with a 10 MHz probe. The dimensions of the specific vein segment used for reconstruction were tabulated and its mean diameter (DÌ„) was calculated. At the time of operation, following reconstruction, transgraft blood pressure gradient (δP) and blood flow (Q) waveforms were recorded by using digital data acquisition. Longitudinal impedance (Z_L) was calculated as δP/Q at each harmonic following Fourier transformation and the area under the curve from 0 to 4 Hz designated as ∫Z_L. Twenty-three bypasses in 22 patients were studied (DÌ„ = 3.5 ±0.2 mm, range 1.6-5.5 mm; ∫Z_L= 37 ±4 x 10³ dyne cm^-5, range 13-95 X 10³ dyne cm^-5). DÌ„ significantly correlated with ∫Z_L (slope = -0.454, p < 0.05), albeit with a fairly low correlation coefficient (r² = 0.23). DÌ„ > 3.6 mm was predictive of graft patency at 12 months (DÌ„ > 3.6 mm 100% vs DÌ„ < 3.6 mm 57 ±20%; p = 0.02). Larger veins identified by preoperative mapping have, in general, more favorable intraoperative resistive characteristics as defined by a lower JZL. However, some veins thought to have small diameters (< 3.6 mm) may still demonstrate sufficiently low ∫Z_L when grafted to remain patent.