VALIDATION OF A NEW AND SPECIFIC INTRAOPERATIVE MEASUREMENT OF VEIN GRAFT RESISTANCE

Purpose: Clinical studies have revealed that the most important predic tor of successful bypass grafting is the origin and quality of the byp ass conduit. Attempts at intraoperative evaluation of the hemodynamic properties of the conduit, including assessment of blood flow (Q), pre ssure gradients (Delta P), and resistance (R), have not been useful. T his is because each of these parameters measures the characteristics o f 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 (Z(L)) a s a measure of conduit-specific resistance and to evaluate its potenti al in predicting the outcome of infrainguinal vascular reconstructions . Methods: Z(L) was measured during surgery in 73 infrainguinal autolo gous vein reconstructions performed in 68 patients in two separate ins titutions over a 21-month period. Vein graft ultrasonic transit time Q and Delta P (from proximal to distal anastomosis) were measured at ba seline and after maximal peripheral vasodilatation with an intraarteri al injection of papaverine 30 mg. Waveforms were recorded for 10 secon ds at 200 Ha using a digital acquisition system. R was calculated as p roximal mean pressure divided by mean blood flow ((Q) over bar). After Fourier transformation, Z(L) was calculated as Delta P/Q at each harm onic and total Z(L) (integral Z(L)) was defined as the integral of mod uli from 0 to 4 Ha. Results: All hemodynamic variables were significan tly affected by papaverine vasodilatation (Delta P, 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 x 10(3) dyne.sec.cm(-5); p < 0.0001), except integral Z( L), which remained constant (31.1 +/- 2.8 vs 30.8 +/- 2.8 x 10(3) dyne .cm(-5); p = NS). After follow-up of 1 week to 17 months (median, 5 mo nths), the 1-year primary, primary-assisted, and secondary patency rat es were 72% +/- 7%, 77% +/- 6%, and 81% +/- 6%, respectively. Using Co x analysis, primary patency was significantly associated with decrease d integral Z(L) (P = 0.0001), but not with baseline or papaverine-stim ulated Delta (P) over bar, (Q) over bar, Delta (P) over bar/(Q) over b ar, or R integral Z(L) > 47 x 10(3) dyne.cm(-5) predicted primary fail ure with 90% positive and negative predictive value. Conclusions: In t raoperative measurement of integral Z(L) in infrainguinal vein grafts is independent of outflow conditions (that is, does not change with pa paverine), and hence describes the resistive properties of the conduit only. In addition, these preliminary data suggest that integral Z(L) is predictive of short-term primary patency. integral Z(L) is the firs t available hemodynamic measurement that is conduit specific and may t herefore be a better predictor of graft patency than currently availab le methods.