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GRAFT SURVEILLANCE AND PREOPERATIVE VEIN MAPPING FOR BYPASS SURGERY
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GRAFT GRAFT
AB
Figure 14.17 An example of graft entrapment. A: A vein graft is running between two muscles in the lower thigh, and a moderate stenosis is seen (arrow). B: During leg flexion the graft is compressed between the muscles, causing a virtual occlusion (arrow).
ENTRAPMENTS OF GRAFTS
Entrapment of grafts can occur around the knee level, especially where in situ vein grafts run from superficial to deep, through a tunnel in the muscles. In this situation, normal flow may be recorded with the leg extended, but mild to moderate flexion of the knee joint produces pinching of the graft between muscle groups, causing a temporary steno- sis (Fig. 14.17). Conversely, some grafts become temporarily obstructed during full knee extension. This is a relatively rare problem, but it will be seen from time to time in a busy laboratory. If the prob- lem is significant, the muscle can be divided or the graft re-routed.
ARTERIOVENOUS FISTULAS
Arteriovenous fistulas occur in in situ vein grafts where there has been incomplete ligation of a long saphenous vein side branch, allowing blood to short-circuit from the graft directly into the venous system (Fig. 14.18). Arteriovenous fistulas are characterized by hyperemic or high-volume flow in the graft proximal to the fistula, with an area of marked color flow disturbance at the site of the fistula (Fig. 14.19). Spectral Doppler also demonstrates turbulent high-volume flow with a low-resistance waveform at this site. The veins lead- ing from the fistula also demonstrate a high-volume flow pattern. Flow in the graft distal to the fistula
V
G
An arteriogram demonstrates an arteriovenous fistula (arrow) between a vein graft (G)
and the venous system (V).
Figure 14.18
is usually lower in volume and more pulsatile. In some circumstances, the graft below the site of the fistula may be totally occluded. Arteriovenous fistulas can be ligated or embolized. It is useful to