MEASUREMENT OF VASCULAR INPUT IMPEDANCE IN INFRAINGUINAL VEIN GRAFTS

The purpose of this investigation was to measure vascular input impeda nce in infrainguinal vein grafts and assess the importance of clinical and hemodynamic parameters in predicting graft patency. Fifty-seven p atients undergoing infrainguinal vein bypass grafting for limb salvage (n = 40) or claudication (n = 17) were prospectively studied. At the time of revascularization, simultaneously acquired intraluminal pressu re and blood flow waveforms were digitized at 200 Hz and subjected to Fourier transformation in near real-time. Input impedance was calculat ed at baseline (immediately after unclamping) and after stimulation wi th either papaverine or completion arteriography. Resistance (R(in)) w as calculated as mean pressure divided by mean blood flow ((Q) over ba r). Characteristic impedance (Z(0)) was calculated as the mean of harm onics 3-10. Intraoperative data acquisition required approximately 5 m in, utilized the completion angiography cannula already in place, and was uncomplicated in all patients. Stimulation with either papaverine or arteriography resulted in increased (Q) over bar (72 +/- 7 to 146 /- 11 ml/min, p < 0.001), decreased R(in) (126 +/- 13 to 52 +/- 4 x 10 (3) dyne . s . cm(-5), p < 0.001), and slightly decreased Z(0) (18 +/- 2 to 15 +/- 1, p = 0.002). After a mean follow-up of 20 months, the 2 -year primary patency, secondary patency, limb salvage, and survival r ates were 61 +/- 8%, 74 +/- 7%, 76 +/- 6%, and 86 +/- 6%, respectively . Primary patency was not associated with any of the clinical variable s studied including age, sex, smoking history, history of previous vas cular surgery, hypertension, coronary artery disease, diabetes mellitu s, creatinine, indication for revascularization (claudication versus l imb salvage), anesthesia (general versus regional), or level of distal anastomosis (popliteal versus infrapopliteal). Furthermore, there was no association between primary patency and baseline (Q) over bar, bas eline R(in), or stimulated Z(0). However, using univariate analysis, p atency was positively associated with decreased stimulated R(in) (p = 0.002), elevated stimulated (Q) over bar (p = 0.006), and decreased ba seline Z(0) (p = 0.02). Multiple regression analysis identified stimul ated R(in) as the only independent predictor of primary patency (p = 0 .002). Stimulated R(in) greater than or equal to 50 x 10(3) dyne . s . cm(-5) was 71% sensitive and 65% specific for graft failure. It is co ncluded that 1) vascular input impedance can be simply and reliably me asured in the operating room, and 2) elevated stimulated R(in) is an i ndependent predictor of primary patency.