Search

Vein graft or native artery stenosis after femoro-distal revascularisation is a common cause of graft occlusion. The early detection and treatment of such stenoses offers the potential for better graft patency than salvage procedures undertaken for graft thrombosis. In the past, two criteria using duplex scanning have been used to detect grafts at risk: (a) a localised increase in the peak velocity (V2) by 100% or more in comparison to the peak velocity (V1) 2 cm upstream (i.e. V2/V1 ratio greater than 2.0), and (b) a decrease in average peak velocity to less than 45 cm s-1. Seventy-four consecutive patients with femoro-distal vein grafts have been studied with intravenous digital subtraction angiography to detect stenosis (greater than 50% diameter) and colour flow imaging using both duplex scanning criteria (a) and (b) at 1.5, 3, 6, 9 and 12 months after operation. The results show that the V2:V1 ratio greater than criterion had a sensitivity of 100% and a specificity of 83%. Stenoses in the native distal arteries were not detected. Low average peak velocity less than 45 cm s-1 had a sensitivity of 61% and a specificity of 98%. By combining both criteria the sensitivity for detecting stenoses in both the vein graft and native distal artery, became 100% and the specificity 98%.

We have conducted three in vitro experiments (using cadaver internal mammary artery as a model for crural artery), which establish the advantage of the Miller collar and Taylor patch over direct PTFE-artery anastomoses: (1) A new method of simultaneously measuring longitudinal and circumferential elasticity in human saphenous vein (n = 16) has demonstrated the latter to be anisotropic (i.e.: greater longitudinal than transverse compliance, P less than 0.002). This suggests that benefit may be gained by aligning the saphenous vein's longitudinal axis with that of the arteriotomy--a feature of both vein interposition anastomoses. (2) We have compared maximal pulsatile and constant flow across each type of anastomosis (n = 10 of each) using a flow model incorporating standard pressure, viscosity, graft and outflow vessel length, and anastomotic angle. This experiment has demonstrated loss of anastomotic reliability only in direct PTFE-artery anastomoses (i.e. no correlation between flow and vessel diameter, r = 0.04). (3) Casts of the internal anatomy of the anastomoses (n = 10 of each) have demonstrated a greater degree of oval distortion of the toe of the outflow vessel of direct PTFE-artery anastomoses than either of the other techniques (P less than 0.01). This experimental evidence suggests that both of these vein interposition techniques optimise the mechanical properties of saphenous vein and protect small arteries from anastomotic distortion. These benefits do not occur with direct PTFE-artery anastomoses.

Autologous vein from either the arm or the leg is the preferred conduit for femoro-crural grafting. Limb salvage rates using prosthetic grafts have been sufficiently disappointing for many surgeons to consider primary amputation in the absence of suitable vein. We have attempted to improve prosthetic graft patency by the creation of a compliant, wide diameter vein collar at the distal anastomosis. Thirty patients with critical ischaemia (i.e.: rest pain with distal tissue loss or doppler ankle pressure less than 40 mmHg2.3) have undergone grafting to a crural vessel in the lower third of the calf using 6 mm externally supported PTFE (IMPRA) with a vein collar (17% of all lower calf grafts, 9% of all femoro-distal procedures). Five of the grafts occluded in the peri-operative period, resulting in major amputations. Another 4 grafts occluded within 12 months of operation resulting in amputation. A further 7 grafts have occluded but not required amputation. Fourteen (47%) grafts remain patent at a mean follow-up of 13.9 months (range 1-49) with a mean graft patency of 10 months. The aim of salvage surgery is to maintain independence until death supervenes. In this series 6 (20%) patients have died during follow-up and the best possible result in the 30 patients would have been a total of 417 "amputation avoided" months. In fact 300 "amputation avoided" months were achieved. Moreover, 21 legs (70%) have avoided amputation during the patient's lifetime, or at the most recent follow-up. These results suggest that femorocrural grafting using PTFE with a vein collar is worthwhile and preferable to primary amputation in the elderly patient.