Charles G Brown, MD, FACEP* The Multicenter High-Dose Epinephrine Study Group Study objectives: The effect of automated defibrillation provided by basic emergency medical technician (EMT) firstresponder units on the time intervals to other critical interventions in the management of out-of-hospital cardiac arrests is unknown. The purpose of this study was to define and compare elapsed time intervals to basic CPR, paramedic arrival, initial countershock, endotracheal intubation, IV access, and initial adrenergic drug therapy in first-responder automated defibrillation/paramedic versus basic EMT/paramedic emergency medical services systems. Design: Prospectively collected data from a 15-month multicenter study of out-of-hospital, nontraumatic cardiac arrests were analyzed. The mean time intervals to critical therapeutic interventions between first-responder automated defibrillation/ paramedic and basic EMT/paramedic groups were compared using the Student's t-test with Bonferroni correction. Setting: Three first-responder automated defibrillation/ paramedic and three basic EMT/paramedic urban emergency medical services systems. Participants: 1,578 patients with out-of-hospital cardiac arrest. Interventions: The first-responder automated defibrillation/ paramedic group received initial ECG analysis and/or automated countershock by first-responder/EMTs; the basic EMT/paramedic group received initial ECG analysis and/or manual countershock by paramedics. Results: Elapsed time intervals in minutes +SD for firstresponder automated defibrillation/paramedic versus basic EMT/paramedic groups, respectively, were as follows: Collapse to CPR, 4.3 +3.9 versus 5.4 +5.2 (P= .017); collapse to countershock, 10.7 +5.9 versus 13.0 +6.0 (P= .017); collapse to paramedic arrival, 13.0 + 5.4 versus 10.3 + 6.1 (P= .0001); paramedic arrival to IV access, 5.1 _+3.9 versus 7.0 +5.0 AUGUST 1993 22:8 ANNALS OF EMER6ENCY MEDICINE