Cardiac Arrest Trial Cut Short

Researchers in a major EMS cardiac arrest study pulled the plug after finding no apparent benefit to a pair of interventions being tested--including, surprisingly, use of an impedance threshold device during CPR.

Assessing results from around 11,500 patients included to date, the independent board monitoring data in the Resuscitation Outcomes Consortium's ROC PRIMED trial recommended ending enrollment, deciding that continuing the study was unlikely to change the results.

ROC PRIMED (for Prehospital Resuscitation using an Impedance valve and Early versus Delayed) examined a pair of EMS resuscitation strategies to increase blood flow during cardiac arrest. One of these was use of an ITD--a small plastic device designed to enhance changes in intrathoracic pressures during CPR, thus improving circulation.

In earlier animal and smaller human studies, ITDs were shown to increase blood flow to the heart and raise blood pressure, and were linked to improved short-term outcomes without adverse effects. In the ROC PRIMED trial, however, using ITDs during CPR did not significantly improve or reduce survival rates for cardiac arrest patients.

"We were surprised," says Myron Weisfeldt, MD, director of the Department of Medicine at the Johns Hopkins University School of Medicine and chair of the ROC Steering Committee. "Most of us thought that hemodynamically, they were pretty impressive, and the evidence that improving hemodynamics improves outcome is pretty good. We thought this device would have a beneficial effect."

Why it didn't bears further scrutiny. With such a large study population, it may be that the device worked well for certain subgroups of patients and less well for others, creating a net wash when they were considered together.

"Certainly, a device put on toward the end of resuscitation is not highly likely to save people's lives," Weisfeldt notes. "It might be that with patients who had the device put on promptly, or who had better quality CPR, we might see a better result. There are also groups among those people we try to resuscitate who just have a very unlikely possibility of survival. Until we do the analysis we won't know, but we are going to look at those things very carefully."

The other aspect of ROC PRIMED contrasted the results of performing different durations of CPR before assessing the heart rhythm for possible defibrillation. It compared "early" assessment, in which the rhythm was checked as soon as providers could analyze it (after around 30-90 seconds of CPR), to "delayed" assessment, in which they performed three minutes of CPR first. Both patient groups then received defibrillation as indicated. These strategies appeared equally effective in terms of outcomes.

That's good enough news for EMS systems, which shouldn't have to change their resuscitation protocols on this point. But on the ITD issue, where it leaves us isn't exactly clear.

The American Heart Association gives the ITD a Class IIa recommendation for increasing blood flow and short-term survival rates in cardiac arrest patients. That makes it the most highly recommended CPR adjunct in the 2005 guidelines. Advanced Circulatory Systems, which makes the only ITD on the market, the ResQPOD, provides supporting data for it at www.advancedcirculatory.com.

With that support, and given that the ROC PRIMED monitoring board had no concerns about the safety of any of the interventions being tested--neither early nor delayed assessment nor use of an ITD caused any harm to patients--it's likely premature to abandon ITDs until the data can be further analyzed. Chiefs and medical directors will have to weigh all the evidence and make their own best calls.

"There was nothing in the study to suggest the device was harmful, and the AHA was quite positive about it," says Weisfeldt. "I think individual EMS directors and physicians doing resuscitation will have to make their own decisions based on the sum of the evidence."