Hemodynamic impact of vein graft stenoses and their prediction in the vascular laboratory.

PURPOSE

We undertook this prospective evaluation to define the direct hemodynamic impact of vein graft stenoses and to correlate intraoperative hemodynamic findings with the preoperative duplex scan.

METHODS

Twelve consecutive isolated vein graft stenoses were identified in the vascular laboratory during our routine duplex scanning surveillance protocol over 10 months. Peak systolic flow velocity ratios (PSFVRs; velocity within stenosis/velocity proximal to the stenosis) at the stenoses ranged from 2.7 to 10 (mean, 5.5), and ankle-brachial indexes ranged from 0.47 to 0.94 (mean, 0.68) Preoperative arteriograms were obtained and confirmed the isolated stenoses, which radiographically ranged from 20% to 83% diameter reduction (mean, 64%). At the time of surgery the stenotic graft segment was isolated, and simultaneous pressure measurements proximal and distal to the graft stenosis were measured, along with ultrasound transit-time blood flow measurements. Pressure and flow wave forms were recorded for 10 seconds at 200 Hz and were stored on a personal computer-based digital acquisition system. The graft stenoses were then repaired with either a vein patch or short interposition graft, and the hemodynamic measurements were repeated. Fourier transformation of the pressure and flow curves was performed, and the resistance and longitudinal impedance were calculated for each graft segment.

RESULTS

Before repair, mean pressure gradients across the stenotic graft segments (delta P) ranged from 1.0 to 74.6 mm Hg (mean, 20.4 mm Hg), and vein graft flow ranged from 4.9 to 140 ml/min (mean, 45.2 ml/min). After repair of the stenotic segments, the mean pressure gradient was decreased to a mean of 1.3 mm Hg, and vein graft flow increased to a mean of 104.8 ml/min. The PSFVR recorded in the vascular laboratory correlated significantly with delta P (r = 0.71; p = 0.01) and allowed prediction of delta P as: delta P = 7.4 (PSFVR) - 19.8. PSFVR also correlated with measured resistance across the stenosis (r = 0.79; p = 0.004). Conversely, the angiographic measurement of stenosis did not correlate significantly with these parameters. The angiographic measurement of stenosis showed a moderate correlation with the PSFVR (r = 0.58; p = 0.046).

CONCLUSIONS

The PSFVR, as measured in the laboratory, is an accurate and useful indicator of the hemodynamic impact of vein graft stenosis. Revision of stenotic vein graft segments resulted in a significant improvement in graft hemodynamics.