The first treatment involves using a device called the Impedance Threshold Device (ITD). The ITD is a small hard plastic device about the size of a fist that is attached to the face mask or airway tube used during CPR (cardiopulmonary resuscitation). The ITD provides increased blood flow back to the heart during chest compressions until the heart starts beating on its own again. The other treatment involves the amount of CPR given before the emergency medical services (EMS) providers first look at the heart rhythm to determine if a shock is needed. A person would receive either about 30 seconds of chest compressions or about 3 minutes of compressions before checking the heart rhythm. Giving some compressions before checking the heart rhythm increases the blood being circulated to the body. Researchers do not know how many compressions before the rhythm check are necessary to save more lives. Depending on the circumstances of the cardiac arrest a person may receive only one of these treatments or both of these treatments. The purpose of the research study is to determine if more people live when either the real ITD is used or if additional CPR is given before looking at the heart rhythm the first time. This study is being conducted in 9 different areas throughout the United States and Canada by the Resuscitation Outcomes Consortium (ROC). About 15,000 patients will be enrolled in this research study.
Inclusion Criteria: - All persons of local age of consent or older who suffer non-traumatic cardiopulmonary arrest outside of the hospital in the study communities with defibrillation and/or delivery of chest compressions provided by emergency medical service (EMS) providers dispatched to the scene and do not meet any of the exclusion criteria. Exclusion Criteria: Common: - Do not attempt resuscitation (DNAR) orders - Blunt, penetrating, or burn-related injury - Patients with exsanguinations - Known prisoners - Known pregnancy - Non-ROC EMS agency/provider For Analyzing Late versus Early - EMS-witnessed arrests - Non-EMS rhythm analysis (AED placed by police or lay responder is an exclusion but CPR by lay or other non-EMS responders is not) For ITD: - Tracheostomy present - CPR performed with the mechanical compression "Autopulse" device.