Why do grafts clot despite access blood flow surveillance?

To look in more detail at those grafts that clot despite access blood flow (ABF) surveillance and the outcome of radiological thrombectomy in those grafts.

Retrospective review was carried out of all polytetrafluoroethylene grafts that clotted from September 1, 1998 to October 30, 2000. During this period, each graft had ABF measured monthly and was referred for prophylactic angioplasty if flow fell below 600 ml/min or by 25%.

Thirty-one of 62 monitored grafts clotted (0.44 episodes per patient per month). Five were surgically thrombectomized and 19 were radiologically thrombectomized. The last available ABF prior to graft thrombosis averaged 804 +/- 108 ml/min and ranged from 215 to 2497 ml/min. Nine of the 23 grafts failed to trigger either of the ABF criteria prior to initial thrombosis. All but one of the 17 grafts thrombolysed radiologically showed evidence of significant (>50%) venous stenoses, though additional lesions were found in nine. Thrombolysis was successful in 14 grafts, with ABF rising from 693 +/- 96 to 941 +/- 135 ml/min (p <0.05). Six additional grafts reclotted and were lost (6-month graft survival 37%).

(1) A significant proportion (40%) of graft thromboses that occur despite ABF surveillance occur in grafts with preserved ABF (>600 ml/min); (2) over 70% can be successfully thrombectomized/angioplastied with about 35% long-term (6 months) survival.