Abstract & Commentary
Synopsis: The static temporal pattern of overall survival in EMS-treated out-of-hospital cardiac arrest is the result of a balance between improved EMS services and several patient factors associated with decreased probability of survival.
Source: Rea TD, et al. Circulation. 2003;107:2780-2785.
Rea and colleagues report a longitudinal survey of cardiac arrests in King County, Wash, (excluding the city of Seattle) from 1977 to 2001. The year 1977 was the year in which paramedic services were introduced in this area. The study area has a 2-tiered emergency medical services (EMS) response system. Fire engines and/or basic life support (BLS) units staffed by regular fireman provide the first tier. Paramedic-staffed advanced life support (ALS) units provide the second tier. BLS defibrillation was introduced in the late 1970s and became operational throughout the county by 1986. A program of dispatcher-assisted telephone bystander cardiopulmonary resuscitation (CPR) was initiated in 1982.
During the entire study period, the EMS treated 12,591 persons with out-of-hospital cardiac arrests. Of these, 4775 persons had witnessed ventricular fibrillation caused by heart disease. The average age, the intervals for BLS and ALS response, and the proportions who were women, were treated with citizen CPR, were defibrillated by BLS, and had arrested before EMS arrival all increased over time. The average defibrillation response interval and the proportions who were witnessed and who presented in ventricular fibrillation decreased over the study period. There was a decrease in the proportion of patients with cardiac arrest in private residences and an increase in the proportion of cardiac arrests in either nursing homes or nonhospital medical facilities. Several factors were associated with the probability of survival. For the group of patients with witnessed ventricular fibrillation, increasing age, arrest before EMS arrival, and longer intervals for BLS, ALS, and defibrillation were all associated with decreased survival. Location of the arrest in a public place and bystander CPR were associated with improved survival. When patients with all rhythms at time of cardiac arrest were analyzed, female gender, arrest in a nursing home, and arrest before arrival were strongly associated with a poor outcome. Survival was improved for a witnessed arrest, for an arrest in a public place, and when the presenting rhythm was ventricular fibrillation. Rea et al constructed several models that adjusted for changes in the overall EMS system and in the clinical characteristics such as age, gender, and location that were independent of the EMS system. Overall survival for witnessed ventricular fibrillation improved somewhat from 1977 to 1981 to 34.4% in 1986-1989 but since then has remained relatively flat. For all cardiac arrests, the crude survival rate has actually decreased. Between 1977 and 1981, 17.5% of cardiac arrest victims survived, but during the period of 1998 to 2001 survival was only 15.7%. The decrease in survival was accounted for by changes in age, gender, witness status, the presenting rhythm, and the frequency of arrest before EMS arrival.
Rea et al conclude that the static temporal pattern of overall survival in EMS-treated out-of-hospital cardiac arrest is the result of a balance between improved EMS services and several patient factors associated with decreased probability of survival. The latter factors are beyond EMS control and may represent overall population trends. Although improvements in EMS services through more widespread availability of public access defibrillation, changes in CPR, and communication may enhance survival in selected individuals, the overall mortality may change little.
Comment by John DiMarco, MD, PhD
This longitudinal study from a region with perhaps the best emergency medical system in the country adds important data. As treatments for coronary artery disease and heart failure have improved, those suffering an out-of-hospital cardiac arrest are likely to be older, of female gender, and in a nursing home or nonhospital medical facility. As a result, a larger proportion of cardiac arrest victims are now found to be in rhythms other than ventricular fibrillation. These rhythms, which include asystole and pulseless electrical activity, are associated with a much worse prognosis since they usually cannot be reversed simply by electrical defibrillation. Although in some settings, like casinos and airports, survival to hospital discharge is excellent, these patients do not typify the average cardiac arrest victim.
The changes in the demographics of sudden cardiac death demonstrates the triumph of cardiovascular medicine in that we can now delay or postpone progression of cardiovascular disease. However, this raises new problems as the typical cardiac arrest victim is now older and more likely to have severe underlying cardiac and noncardiac disease. Devoting increased resources to try to improve survival further in locales like Kings County, Wash, where mature EMS systems are already in place, may not prove cost-effective. Rather, low-cost innovations that can target improving outcome in the decreasing number of highly salvageable patients seem most promising.
Dr. DiMarco, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville, is on the Editorial Board of Clinical Cardiology Alert.