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Validation of a new and specific intraoperative measurement of vein graft resistance
L B Schwartz1, M Belkin, M C Donaldson
1Department of Surgery, University of Chicago, Ill, USA.
Insights
Longitudinal impedance (ZL) measurement predicts bypass graft success. This conduit-specific measure is independent of outflow conditions, offering a better predictor of infrainguinal vein graft patency.
Area of Science:
- Vascular Surgery
- Biomedical Engineering
- Hemodynamics
Background:
- Bypass graft origin and quality are crucial for successful reconstruction.
- Current intraoperative hemodynamic assessments (flow, pressure gradients, resistance) are limited as they include outflow bed characteristics.
- A method to specifically measure conduit resistance is needed.
Purpose of the Study:
- To evaluate longitudinal impedance (ZL) as a measure of conduit-specific resistance.
- To assess the potential of ZL in predicting the outcome of infrainguinal vascular reconstructions.
Main Methods:
- Longitudinal impedance (ZL) was measured intraoperatively in 73 infrainguinal autologous vein reconstructions.
- Measurements included blood flow (Q) and pressure gradients (delta P) before and after papaverine-induced vasodilation.
- ZL was calculated using Fourier transformation of pressure and flow waveforms.
Main Results:
- Integral of ZL remained constant during vasodilation, indicating conduit-specific resistance.
- Primary patency was significantly associated with decreased integral of ZL (p = 0.0001).
- Integral of ZL > 47 x 10(3) dyne.cm-5 predicted primary graft failure with 90% accuracy.
Conclusions:
- Intraoperative integral of ZL measurement is independent of outflow conditions, reflecting conduit resistance.
- Preliminary data suggest integral of ZL predicts short-term primary patency in infrainguinal vein grafts.
- Integral of ZL is the first hemodynamic measurement specific to the conduit, potentially improving graft patency prediction.
Purpose:
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 (delta P), 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 delta P (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 (Q). After Fourier transformation, ZL was calculated as delta P/Q at each harmonic and total ZL (integral of ZL) was defined as the integral of moduli from 0 to 4 Hz.
Results:
All hemodynamic variables were significantly 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 of ZL, 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 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 integral of ZL (p = 0.0001), but not with baseline or papaverine-stimulated delta P, Q, delta P/Q, or R integral of ZL > 47 x 10(3) dyne.cm-5 predicted primary failure with 90% positive and negative predictive value.
Conclusions:
Intraoperative measurement of integral 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 integral of ZL is predictive of short-term primary patency. integral of 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.