Termination Based on Event Accrual in Per Protocol Versus Intention to Treat in the ROCKET AF Trial

Background In event‐driven clinical trials, study termination is based on accrual of a target number of primary efficacy events. For noninferiority trials in which superiority is conditionally examined, the ideal cohort in which to track event accrual is unclear. We used data from the ROCKET AF (Rivaroxaban Once Daily Oral Direct Factor Xa Inhibition Compared With Vitamin K Antagonism for Prevention of Stroke and Embolism Trial in Atrial Fibrillation) trial to determine the effect of primary efficacy‐event tracking in the per‐protocol cohort during the on‐treatment period versus the intention‐to‐treat (ITT) cohort during the ITT period. Methods and Results ROCKET AF was terminated after accruing 429 primary efficacy events (stroke or systemic embolism) in the per‐protocol cohort during the on‐treatment period for noninferiority. We identified the date on which 429 events occurred in the ITT cohort during the ITT period. We performed noninferiority and superiority analyses based on hypothetical study termination on this date. ROCKET AF would have terminated 226 days earlier if events were tracked during the ITT period. Similar to the main trial findings, rivaroxaban would have met noninferiority versus warfarin for the primary efficacy end point (hazard ratio [HR], 0.77; 95% CI, 0.62–0.96; P<0.001). In contrast to the main trial findings, rivaroxaban would have met superiority for the primary efficacy end point (HR, 0.82; 95% CI, 0.68–0.99; P=0.038). In both termination scenarios, rivaroxaban was associated with a lower risk of intracranial hemorrhage and similar risk of other safety end points. Conclusions Clinical trial termination based on event accrual in the ITT cohort versus the per‐protocol cohort may have important implications on trial results depending on rates of study drug discontinuation and event rates off treatment.