According to a PubMed article dated Apr 24 2015, odds of ROSC decrease by 4% for every 1 hour delay between call receipt and vasopressor administration. Data was obtained from recent retrospective studies involving 1,122 patients who experienced out-of-hospital cardiac arrest. 544 patients, or 48.3%, experienced ROSC when vasopressors were administered within 10 minutes of arrest. ROSC was more associated with shockable rhythms than PEA and/or asystole. Large prospective studies are in need.