Resuscitation Outcomes Consortium (ROC) Prehospital Resuscitation Using an Impedance Valve and Early Versus Delayed Analysis (PRIMED)

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Accession Number

Study Type
Clinical Trial

Collection Type
Open BioLINCC Study See bottom of this webpage for request information

Study Period
June 2007 - July 2010

NHLBI Division

Dataset(s) Last Updated
January 3, 2018

Primary Publication URLs
Rhythm Analysis


Commercial Use Data Restrictions No

Data Restrictions Based On Area Of Research No


The purpose of this study was to examine two different treatments during a cardiac arrest that occurs outside of the hospital and whether either or both treatments would increase the number of people who lived to hospital discharge with satisfactory functional status. The first treatment involved using a device called the Impedance Threshold Device (ITD). The other treatment involved the amount of CPR given before the emergency medical services (EMS) providers first looked at the heart rhythm to determine if a shock is needed.


Out-of-hospital cardiac arrest is a common and lethal problem with a low survival rate, leading to an estimated 330,000 deaths each year in the United States and Canada. The traditional approach to out-of-hospital cardiac arrest has been to emphasize early analysis of cardiac rhythm, with delivery of defibrillatory shocks, if indicated, as quickly as possible. It has been suggested, however, that many patients may benefit from a period of CPR before the first analysis of rhythm.

The impedance threshold device (ITD) is designed to enhance venous return and cardiac output during CPR by increasing the degree of negative intrathoracic pressure. Previous studies have suggested that the use of an ITD during CPR may improve survival rates after cardiac arrest. This effect is achieved by preventing the passive inflow of air into the chest during chest recoil between chest compressions without impeding active ventilation. The ITD has been found to improve hemodynamics, the perfusion of vital organs, and neurologically intact survival in studies in animals. The results of small, short-term clinical trials have suggested that the ITD can increase systolic blood pressure during resuscitation and improve short-term survival rates.


Subjects included adults with nontraumatic, out-of-hospital cardiac arrest being treated with resuscitative efforts by EMS personnel who were participating in the Resuscitation Outcomes Consortium (ROC). Patients were excluded from either treatment if they were incarcerated, known to be pregnant, had do-not-attempt-resuscitation orders, or had exsanguinations, severe burns, blunt, or penetrating injury. Patients were excluded from late vs. early heart rhythm analysis if EMS witnessed the arrest or if a non-EMS individual performed rhythm analysis. Patients were excluded from ITD use if they had an existing tracheostomy, or were undergoing attempted resuscitation with the use of other mechanical CPR devices. In the ITD study, 4,345 patients were assigned to sham ITD and 4,373 to active ITD, while in the early versus later rhythm analysis, 5,290 patients were assigned to early cardiac rhythm analysis, and 4,643 were assigned to later cardiac rhythm analysis. This study qualified for exception from informed consent required for emergency research.


Most patients were enrolled simultaneously in both the early analysis versus later analysis component and the active ITD versus sham ITD component of the trial.

The use of an active ITD was compared with that of a sham ITD in patients at 10 ROC sites in the United States and Canada. Patients, investigators, study coordinators, and all care providers were unaware of the treatment assignments. EMS personnel were trained in ITD function, proper use of the ITD, and all aspects of protocol implementation, with an emphasis on the optimal performance of CPR according to local guidelines. The first EMS responders to arrive at the scene of the arrest who were equipped with a randomly assigned ITD (active or sham) attached the device between the ventilation bag and face mask or between the bag and an advanced airway. Responders were encouraged to implement use of the device within 5 minutes after their arrival or as soon as clinically possible.

Each of the 10 participating ROC centers was also divided into approximately 20 clusters. All episodes of cardiac arrest in a cluster were randomly assigned to one CPR strategy; after a set period of time, ranging from 3 to 12 months, all episodes in that cluster were then assigned to the other strategy. Patients in the early-analysis group were assigned to receive 30 to 60 seconds of chest compressions and ventilations (sufficient time to place defibrillator electrodes) before electrocardiographic (ECG) analysis, and those in the late-analysis group were assigned to receive 3 minutes of chest compressions and ventilations before ECG analysis. The start and stop times for CPR were recorded by the responders, and the information was supplemented by the recording of defibrillator time.


All 10 sites halted enrollment in November 2009 when the data and safety monitoring board recommended termination because interim analysis showed that the findings were not likely to change with continuation of the study. Neither use of the ITD nor the amount of CPR given before cardiac rhythm analysis significantly improved survival with satisfactory function (i.e., a score of ≤3 on the modified Rankin scale) among patients with out-of-hospital cardiac arrest receiving standard CPR. There were also no significant differences in the secondary outcomes, including rates of return of spontaneous circulation on arrival at the emergency department, survival to hospital admission, and survival to hospital discharge (N Engl J Med. 2011; 365(9): 787-97) (N Engl J Med. 2011; 365(9): 798-806).

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