Background: Primary patency (PP) in trials assessing superficial femoral artery (SFA) stenting is defined as a combination of vessel patency assessed by duplex ultrasound (DUS) at the 12-month follow-up exam and freedom from revascularization of the index vessel through 12 months of follow-up. Loss of PP is thus more likely to be identified during the mandated DUS assessment. Moreover, DUS is performed within a prespecified allowed window of time for the visit that exceeds 12 months (typically by 30 days). Therefore, the time frame for detecting patency with DUS exceeds the time frame in which revascularization is captured. Survival analyses are often applied to present estimates of freedom from loss of PP, but there are no clear guidelines as to the correct method for presenting these analyses in reports from clinical trials. We aimed to analyze the implications of applying different methods in assessing freedom from loss of PP in studies assessing stenting for diseased SFA.
Methods: Data were simulated based on existing available results from SFA bare-metal nitinol stent trials published between 2009 and 2013 and summarized in a previous analysis (STROLL, SUPERB, RESILIENT, DURABILITY I, DURABILTY II, COMPLETE SFA). Six different approaches to Kaplan Meier (KM) analyses were applied based on entry criteria into and time frame of the KM model.
Results: Six KM estimates of PP were generated for each of the 10,000 simulated datasets. The average exact PP rate was 70.6%, while the average estimated KM rates using the six different methods ranged between 68.0% and 81.9%.
Conclusion: KM estimates of PP vary substantially according to the methods employed. These may lead to misrepresentation of results from clinical trials. The development of a unified approach is advocated.