= Assisted primary graft patency
<Assisted primary graft patency> credits maintenance of an open graft by interventions performed before it occludes. The distinction is temporal: assistance preserves uninterrupted patency, whereas successful reopening after an occlusion belongs to <secondary graft patency>. The 1997 reporting standard introduced this distinction explicitly when revising how preventive graft procedures were counted.<Recommended standards for reports dealing with lower extremity ischemia: Revised version by Robert B. Rutherford and others>[Printed p. 525, assisted-primary-patency discussion]{ref}
A qualifying preventive intervention can end <primary graft patency> without ending <assisted primary graft patency>. Thus the two endpoints measure different aspects of durability: the former concerns performance without that assistance, while the latter also credits preservation work. They should share a stated time origin and compatible rules before their curves are compared.
Consider an original four-graft cohort. At month 2, one graft undergoes a preventive procedure while still open. At month 3, a different graft occludes, then is successfully reopened at month 4. The other two remain open without procedures. With complete follow-up to month 4, primary patency is $2/4$, assisted primary patency is $3/4$, and secondary patency is $4/4$, assuming the restoration qualifies for the original reconstruction’s secondary endpoint. The reopened graft does not regain an uninterrupted assisted-primary history.
Surveillance influences what is observed and when assistance is undertaken. A narrowing may be detected before occlusion, so reports need their detection and intervention rules. A high assisted-primary proportion can coexist with many preventive procedures; it is not a measure of low procedural burden. Conversely, two cohorts with different surveillance intensity are not made directly comparable merely by using the same endpoint name.
With incomplete follow-up, <survival analysis> uses a <graft patency risk set> rather than treating every graft as observed to the final study date. Clinical interpretation also requires the separately measured consequences for tissue function and the patient. Preserving a conduit is an important intermediate outcome, not a complete description of benefit.
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