OBJECTIVES: To determine if the quality of CPR had a significant interaction with the primary study intervention in the NIH PRIMED trial. DESIGN: The public access database from the NIH PRIMED trial was accessed to determine if there was an interaction between quality of CPR performance, intervention, and outcome (survival to hospital discharge with modified Rankin Score (mRS) 50%. Significant interaction was considered as p < 0.05. INTERVENTION: Standard CPR with an activated versus sham (inactivated) ITD. MEASUREMENTS AND MAIN RESULTS: Overall, 848 and 827 patients, respectively, in the active and sham-ITD groups had "acceptable" CPR quality performed (n = 1675). There was a significant interaction between the active and sham-ITD and compression rate, depth and fraction as well as their combinations. The strongest interaction was seen with all three parameters combined (unadjusted and adjusted interaction p-value, < 0.001). For all presenting rhythms, when "acceptable" quality of CPR was performed, use of an active-ITD increased survival to hospital discharge with mRS