In out-of-hospital cardiac arrest, interrupting CPR after 30 sec, 1 or 3 minutes before checking rhythm made no difference
Stiell et al (the ROC investigators) report results of a 10-center randomized trial in the U.S. and Canada. Among 9,933 patients with out-of-hospital cardiac arrest randomized to receive either 30-60 seconds or 2 minutes of uninterrupted CPR before rhythm analysis, there were no differences in survival, or survival to discharge with good functional status (primary outcome). Six percent of patients in each group met the primary outcome (alive at discharge with Rankin = 3 or less; able to walk and toilet without assistance).
Stiell IG et al. Early versus Later Rhythm Analysis in Patients with Out-of-Hospital Cardiac Arrest. N Engl J Med 2011;365:787-797.