Hemodynamic effects of venous valves in aorto-coronary bypass grafts

Pressure trap created by vein valve closure and its role in graft stenosis

“…These investigators also suggested that the augmentation occurs becauseof the increase in forward flow and prevention of reverseflow. 15,[20][21][22] His obvious that the reported augmentation of flow occurs because of the 7 1 4 Thubrikar, Robicsek, Fowler pressure trap, that is, with the valve closed there is greater pressure in the distal vein segment to drive the flow through the distal vascular bed and hence to augment the forward flow. These investigators did have the pressure trap occurring in their experiments, but it went unnoticed.…”

“…Overall patency of vein graft has been described by several investigators.f 8,10,18,19 For graft patency the flow through the graft is thought to be an important parameter. An initial flow rate of greater than 45 ml/rnin is thought to be important to keep the graft patent, whereas an initial flow rate of less than 20 ml/rnin is thought to lead to graft occlusion.18 Singh14 has suggested that the presence of the vein valve may cause sluggish velocity of blood flow and thereby lead to graft stenosis, whereas several others have claimed that the presence of the vein valve may in fact augment the forward flow to the myocardium and thereby offer an advantage over the vein graft without the valve 1 5, 20-22 The focus of the majority of studies in the past has been blood flow through the vein valve,6,IS, 18,[20][21][22][23][24][25] and in this regard the present study offers new information on the function of the vein valve.…”

Improving Patency of Coronary Conduits "Valveless" Veins and/or Arterial Grafts

“…Relatively little considerations were given to the role of existing reversed venous valves in the long saphenous vein, their interference with flow, and their thrombolytics potentials. 4,5 Since the "exceptional" long-term patency of ITAs was documented by Lytle et al in 1980, 6,7 attention of surgeons turned toward the usage of bilateral ITAs 8 and other arterial bypasses. Different arterial conduits were popularized, assuming that they will respond sim-ilarly, being structurally similar to ITAs and to coronary arteries.…”

“…Relatively little considerations were given to the role of existing reversed venous valves in the long saphenous vein, their interference with flow, and their thrombolytics potentials 4,5 …”