About the saphenous vein graft patencies after coronary artery bypass surgery.

To the Editor,

We congratulate the authors for their work (1). In this study, the morphological factors affecting the long-term patency of the grafts used for revascularization in coronary artery bypass graft surgery were examined. The type of graft used for revascularization, the diameter of the target vessel, and the stenosis ratio of the target vessel effective to determine long-term patency were determined. We agree with the authors’ conclusions. No relationship between saphenous vein graft length and long-term graft patency was observed. However, for the saphenous vein, we do not agree with the authors’ conclusion. The saphenous vein is generally about 5-7 mm in diameter. In some cases, this may be even higher, especially above the knee. The mean diameter of the target coronary artery is between 1-2 mm. Because of this diameter mismatch, saphenous vein anastomosed to the coronary artery will cause stagnation because of hemodynamics. Stagnation is shown as a shaded area in Figure 1. As the length of the saphenous vein increases, the area of stagnation will increase and the graft patency will decrease (Fig. 1). Longer and wider saphenous vein grafts will cause more blood to be pooled, and the graft patency will be further imparied. Therefore, a 10-mm diameter graft is not used in femoro-popliteal bypass. Unlike the study, we do not agree that saphenous vein graft length does not affect graft patency. However, the situation is slightly different in arterial grafts. Arterial grafts have the capacity to decrease or increase their diameter over-time to match the target vessel. Therefore, arterial grafts do not have stagnation because of diameter mismatch. The length of the anastomosis is also an important factor to determine the patency of the graft because it affects the amount of rotation of the flow.

Figure 1

Demonstration of the increase in stagnated area as the length of the saphenous vein increases

The long-term patency of the saphenous vein grafts, harvested above and below the knee, is another issue. In the erect position, the venous pressure in the ankle can reach up to 150 mm Hg. Therefore, the veins harvested under the knee are adaptive to more pressure (unlike the veins harvested above the knee), and they are also more adaptive to the arterial flow. This may increase long-term patency. Thus, we believe that this parameter should also be considered.