Longer CPR before Rhythm Analysis in Cardiac Arrest Patients

Having emergency medical services (EMS) personnel delay the initial analysis of cardiac rhythm to prolong administration of cardiopulmonary resuscitation (CPR) does not appear to improve survival outcomes for individuals who experience cardiac arrest outside the hospital. Authors of a study investigating early versus later rhythm analysis in this patient population said although 2005 guidelines from the American Heart Association-International Liaison Committee on Resuscitation (AHA-ILCOR) recommended that EMS personnel administer CPR for at least 2 minutes before first analysis of cardiac rhythm and subsequent defibrillation, their findings suggest this practice is no more beneficial than approximately 30 seconds of CPR preceding analysis [N Engl J Med. 2011;365(9):787-797]. Prior to the 2005 guidelines, it was standard practice to analyze cardiac rhythm as soon as possible and perform defibrillatory shock when indicated, and questions arose regarding the evidence used to support the 2005 recommendation. Consequently, AHA-ILCOR revised their guidelines in 2010, noting “inconsistent evidence to support or refute” delaying analysis of cardiac rhythm. At the outset of this recent analysis—a component of the Resuscitation Outcomes Consortium (ROC) PRIMED (Prehospital Resuscitation Using an Impedance Valve and Early Versus Delayed Analysis) trial—investigators wanted to add clarity to the issue of early versus later analysis. ROC PRIMED involved researchers from 10 US and Canadian university hospitals who recruited 150 regional EMS agencies to assist in this phase of the trial. To power the study sufficiently, investigators had planned to enroll 13,239 patients starting June 2007. As of November 2009, when the data and safety monitoring board suggested halting the study, 9933 eligible patients had been randomized to early (n=5290) or later (n=4643) cardiac analysis. Patient characteristics were similar between the groups, with a median age of 66.7±16.6 years in each arm. For the early-analysis group, the goal was for EMS personnel to perform 30 to 60 seconds of CPR (chest compressions and ventilations) before subjecting patients to electrocardiographic analysis compared with 3 minutes of CPR for the later-analysis group. First responders were to place the defibrillator electrodes on the patient during CPR and document when CPR was initiated and stopped. In the early-analysis group, EMS personnel executed cardiac rhythm analysis at a median of 42 seconds (targeted range, 0-60 seconds) after arrival compared with 180 seconds (targeted range, 150-210 seconds) for the later-analysis group. In both groups, 5.9% of patients survived to discharge from the hospital with a modified Rankin score ≤3, which was the study’s primary outcome (Rankin scores >3 indicate severe disability or death). No significant difference was observed between the groups on any of the secondary outcomes, which consisted of survival to discharge, survival to hospital admission, and return to spontaneous circulation on arrival at the emergency department. Both the early- and the later-analysis groups saw 53.2% of patients transported to the hospital; nearly one-quarter of patients in each group (24.6% vs 24.4%, respectively) survived to hospital admission. Overall survival was low, with 91.9% of patients in the early-analysis group and 92.0% in the later-analysis group dying prior to hospital discharge. Previous animal and clinical studies had reported that a few minutes of chest compressions prior to defibrillation improved survival compared with earlier or immediate defibrillation. According to the ROC PRIMED researchers, the theory is that the chest compressions increase myocardial perfusion, which improves the metabolic state of the cardiac myocytes and increases the likelihood of successful defibrillation. The authors examined findings from 5 studies that assessed early versus later cardiac analysis and concluded that all had limitations and lacked definitive findings. ROC PRIMED investigators did not evaluate patients whose cardiac arrest was witnessed by an EMS responder nor did they examine whether immediate analysis—without CPR—might improve survival. “We deliberately insisted on some CPR for the early-analysis group in the belief that good patient care required cardiopulmonary support while the defibrillator was being prepared,” explained the authors. When CPR is being administered, “compressions should be of high quality with minimal interruptions,” they said. The study concluded that brief CPR followed by early analysis is most likely the preferred approach for individuals whose cardiac arrest occurs outside the hospital and is not witnessed by EMS personnel. For patients who received CPR from a bystander prior to the first responders’ arrival, later analysis may be appropriate.