Primary graft patency

Primary graft patency measures how long a graft remains open without an intervention that terminates the primary-patency endpoint. It concerns the history since the original reconstruction, not merely whether a bypass graft is open on today’s image. Under the 1997 reporting standard, work confined to disease beyond the graft and its anastomosis can be an exception; an intervention on the graft to prevent its failure is not.^[ref]

For an explicit time-to-event model, define $T_p$ as the first qualifying loss of primary patency. Its survival function isOpening a narrowed but still patent graft by a qualifying preventive procedure can end primary graft patency even though blood never stopped flowing. Later rescue does not put that same graft back into the original primary-patency history. Assisted primary graft patency and secondary graft patency answer different questions about preserving or restoring function.

An original five-graft example demonstrates the denominator. All enter follow-up together. One has a qualifying intervention at month 2, another is last observed event-free at month 3, and a third occludes at month 4; the other two remain event-free through month 4. The Kaplan–Meier estimator givesThe graft patency risk set falls after both the first endpoint and the later right censoring. The censored graft is neither declared a failure nor assumed patent indefinitely. Interpreting this estimate requires an appropriate independent-censoring assumption.

A report should identify the original procedure date, qualifying interventions, documented occlusions and observation limits. A status image alone cannot reconstruct every earlier event. Primary graft patency is therefore most informative alongside the intervention history and separately defined clinical outcomes, rather than as an unexplained percentage.