This clinical trial examined whether a strategy of rescue shocks as soon as possible after arrival or a strategy of doing 3 minutes of CPR before rescue shocks improved survival after cardiac arrest.  A separate portion of this trial examined whether using a device that decreased pressure in the chest during CPR would improve survival.

ROC PRIMED stands for the Resuscitation Outcomes Consortium Prehospital Resuscitation using an IMpedance valve and Early versus Delayed (ROC PRIMED) study. This clinical trial examined the usefulness of two resuscitation strategies for patients who suffer cardiac arrest, when the heart abruptly stops, outside of a hospital setting. 

One strategy looked at when to analyze the patient’s heart rhythm to determine whether defibrillation is needed, comparing two strategies known as Analyze Early and Analyze Later. Some EMS providers perform cardiopulmonary resuscitation (CPR) for 30-90 seconds before analyzing the heart's rhythm, and, if necessary, defibrillate to restore the heart to its normal rhythm (Analyze Early). Other EMS providers perform CPR for three minutes before analyzing the heart rhythm (Analyze Later) and defibrillate if necessary.

There is evidence that the longer CPR duration helps oxygenated blood circulate more, which may prime the heart to receive the most benefit from defibrillation. Other studies suggest that delivering defibrillation sooner might be more helpful. The ROC PRIMED study found both to be equally beneficial, with no improvement or decline in patient survival rates.

Image previewThe other strategy in ROC PRIMED looked at the use of an impedance threshold device (ITD), to help improve blood flow during CPR given by EMS providers. An ITD, also known as an impedance valve, is a small, hard plastic device about the size of a fist that is attached to the face mask or breathing tube during CPR administered by EMS providers. Although the device is attached to the face mask or breathing tube during CPR, it is not intended to help with breathing. Instead, it is designed to increase the degree of negative intrathoracic pressure during decompression of the chest.

Some previous smaller studies on humans and in animal models showed short-term improvement in blood flow in patients who went into cardiac arrest when an ITD was used. However, in this study, the use of the ITD did not appear to improve or decrease patient survival rates.


Aufderheide TP, Kudenchuk PJ, Hedges JR, Nichol G, Kerber RE, Dorian P, Davis DP, Idris AH, Callaway CW, Emerson S, Stiell IG, Terndrup TE; ROC Investigators. Resuscitation Outcomes Consortium (ROC) PRIMED cardiac arrest trial methods part 1: rationale and methodology for the impedance threshold device (ITD) protocol. Resuscitation. 2008 Aug;78(2):179-85.

Stiell IG, Callaway C, Davis D, Terndrup T, Powell J, Cook A, Kudenchuk PJ, Daya M, Kerber R, Idris A, Morrison LJ, Aufderheide T; ROC Investigators. Resuscitation Outcomes Consortium (ROC) PRIMED cardiac arrest trial methods part 2: rationale and methodology for "Analyze Later vs. Analyze Early" protocol. Resuscitation. 2008 Aug;78(2): 186-95.

View the NHLBI Questions and Answers about ROC PRIMED 

View the NHLBI's "Study on Resuscitation Methods for Cardiac Arrest" Press Release