A new method of intraoperative hydraulic impedance measurement provides valuable prognostic information about infrainguinal graft patency

Purpose: Prognostic information about graft outcome, obtained by using a ne w method for intraoperafive measurement of vascular impedance, was evaluate d. Methods: Hydraulic impedance was measured in 136 infrainguinal bypass graft s that were entered into a multicenter trial. Seventy femoropopliteal and 6 6 femorocrural polytetrafluoroethylene (PTFE) grafts were used. The arteria l impedance measurement involved a silicon bypass graft temporarily inserte d between the proximal and distal anastomoses sites. A flowmeter probe and a pressure transducer were incorporated into the tube. The digitally stored waveforms were subjected to a fast Fourier transformation and both input ( Z(x)) and characteristic (Z(0)) impedances, as well as phase relations, wer e computed and related to graft outcome after 3 years. Results Significant prognostic information for both popliteal and crural gr afts was provided by means of the phase angle of the first harmonic. Primar y and secondary patency rates for popliteal bypasses were 45% +/- 1% and 65 % +/- 2% for phase angles greater than -40 degrees (n = 57) and 37% +/- 1% and 40% +/- 1% for phase angles less than -40 degrees (n = 13, (Pprim) = no t significant, (Psec) < 0.01). For crural grafts, the secondary patency rat es were 49% +/- 1% and 61% +/- 2% for phase angles greater than -40 degrees (n = 53) and 15% +/- 1% and 0% for phase angles less than -40 degrees (n = 13, P < .01). All crural bypass grafts with phase angles less than -40 deg rees occluded within 16 months. Steady flow resistance, as well as Z(x), an d Z(0), failed to indicate a significant relation to graft prognosis. Conclusion: This method provides reliable prognostic information regarding graft patency and opens hydraulic impedance measurement to clinical surgery . The phase lag between flow and pressure curves, as expressed by the phase angle of the first harmonic, provides significant prognostic information.