Which of the following statements about the evaluation of arterial substitutes are correct?

C. Patency figures should be derived from life table calculations.

D. Primary patency is the best indicator of the natural history of an arterial substitute.

DISCUSSION: Patency is the most important variable in the evaluation of the clinical effectiveness of an arterial substitute, and it should always be derived from life table calculations. Both primary and secondary graft patency are important. Primary patency is the best indicator of the natural history of a graft. A graft remains primarily patent as long as it has not thrombosed or had any graft- or anastomosis-directed procedures. Grafts are considered to be secondarily patent if patency has been restored after an episode of thrombosis or if, in order to maintain patency, operation on a patent graft is directed toward the graft itself or its anastomoses.