Validation of a new and specific intraoperative measurement of vein graft resistance

AbstractPurpose: Clinical studies have revealed that the most important predictor of successful bypass grafting is the origin and quality of the bypass conduit. Attempts at intraoperative evaluation of the hemodynamic properties of the conduit, including assessment of blood flow (Q), pressure gradients (ΔP), and resistance (R), have not been useful. This is because each of these parameters measures the characteristics of the graft plus the outflow bed. To date, no specific measurement of the resistive properties of the conduit only is available. The purpose of this investigation was to evaluate longitudinal impedance (ZL) as a measure of conduit-specific resistance and to evaluate its potential in predicting the outcome of infrainguinal vascular reconstructions.Methods: ZL was measured during surgery in 73 infrainguinal autologous vein reconstructions performed in 68 patients in two separate institutions over a 21-month period. Vein graft ultrasonic transit time Q and ΔP (from proximal to distal anastomosis) were measured at baseline and after maximal peripheral vasodilatation with an intraarterial injection of papaverine 30 mg. Waveforms were recorded for 10 seconds at 200 Hz using a digital acquisition system. R was calculated as proximal mean pressure divided by mean blood flow (Q̄). After Fourier transformation, ZL was calculated as ΔP/Q at each harmonic and total ZL (∫ZL) was defined as the integral of moduli from 0 to 4 Hz.Results: All hemodynamic variables were significantly affected by papaverine vasodilatation (ΔP̄, 3.9 ± 0.5 vs 6.3 ± 0.8 mm Hg; Q, 78.2 ± 7.0 vs 126 ± 11 ml/min; R, 134 ± 17 vs 72.7 ± 6.2 × 103 dyne · sec · cm−5; p < 0.0001), except ∫ZL, which remained constant (31.1 ± 2.8 vs 30.8 ± 2.8 × 103 dyne · cm−5; p = NS). After follow-up of 1 week to 17 months (median, 5 months), the 1-year primary, primary-assisted, and secondary patency rates were 72% ± 7%, 77% ± 6%, and 81% ± 6%, respectively. Using Cox analysis, primary patency was significantly associated with decreased ∫ZL (p = 0.0001), but not with baseline or papaverine-stimulated ΔP̄, Q̄, ΔP̄/Q̄, or R. ∫ZL > 47 × 103 dyne · cm−5 predicted primary failure with 90% positive and negative predictive value.Conclusions: Intraoperative measurement of ∫ZL in infrainguinal vein grafts is independent of outflow conditions (that is, does not change with papaverine), and hence describes the resistive properties of the conduit only. In addition, these preliminary data suggest that ∫ZL is predictive of short-term primary patency. ∫ZL is the first available hemodynamic measurement that is conduit-specific and may therefore be a better predictor of graft patency than currently available methods