Multivariable Analysis - Effect Modifiers In addition to variables described in the Outcomes subsection, the multivariable analysis will include the following potential effect modifiers: Data Source (VSE2 vs. VSE1 study), Study Center (4), group (VSE vs, control), cardiac arrest cause (cardiac vs. non-cardiac), area of cardiac arrest occurrence (monitored vs. non-monitored), initial cardiac arrest rhythm (shockable vs. non-shockable) atropine use (yes vs. no), prescribed total dose of sodium bicarbonate, cardiac arrest occurrence on holiday vs. working day; Cardiac arrest occurrence at night (23:00-07:00) vs. morning-to-late evening (07:00-23:00), total dose of epinephrine during CPR, and therapeutic hypothermia (use vs. no use).