Out-of-Hospital Cardiac Arrest — The Solution Is Shocking
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《新英格兰医药杂志》
Sudden cardiac arrest claims 350,000 to 450,000 lives per year in the United States alone and is responsible for more than half of all deaths that are due to cardiovascular disease. Our ability to recognize patients who are at high risk for cardiac arrest has improved, but 90 percent of cases of sudden death from cardiac causes occur in patients without identified risk factors. Although the majority of cases of sudden death from cardiac causes involve patients with preexisting coronary heart disease, cardiac arrest is the first manifestation of this underlying problem in 50 percent of patients. The sudden death of an apparently healthy person has a devastating emotional effect on others.
Most victims of cardiac arrest are initially found in ventricular fibrillation (see Figure 1). Decades of experience within cardiac intensive care units have shown that immediate defibrillation is almost universally effective. Furthermore, implantable defibrillators, which detect and treat ventricular tachyarrhythmias within 20 seconds, restore sinus rhythm in more than 98 percent of episodes of ventricular tachyarrhythmia and ventricular fibrillation.
Figure 1. Episode of Sudden Death Recorded with a Holter Monitor.
The episode begins as uniform ventricular tachycardia and degenerates to ventricular fibrillation and, ultimately, asystole. The period from cardiac arrest to death is less than 10 minutes.
Sudden cardiac arrest is primarily a problem in patients outside of the hospital; in fact, approximately 80 percent of cases of sudden death from cardiac causes occur at home. The rate of success of resuscitation in patients with out-of-hospital cardiac arrest has been poor, averaging 2 to 5 percent in major urban centers. By far, the most important factor for success in resuscitation is time to treatment, in particular, defibrillation (see Figure 2). Although cardiopulmonary resuscitation (CPR), particularly chest compression, is important later in the arrest sequence, defibrillation should be the primary treatment focus within the first four minutes of ventricular fibrillation. Each minute that defibrillation is delayed reduces by 8 to 10 percent the chance of eventual hospital discharge. Resuscitation efforts initiated after eight minutes are almost always doomed to fail.
Figure 2. The Exponential Decline in the Rate of Survival after Sudden Cardiac Arrest as Time to Defibrillation Increases.
Defibrillation alone often results in successful resuscitation if delivered within four minutes of cardiac arrest.
An early attempt to organize the community response to victims of cardiovascular emergencies was the "chain of survival" process. The four links in the chain are early access to care, early initiation of CPR, rapid defibrillation, and early advanced cardiac life support. Initially, the effort focused on teaching CPR through community programs, improving activation of emergency-response systems (e.g., by telephoning 911), and training emergency medical technicians (EMTs) to provide defibrillation. However, in the absence of regional programs, prompt access to defibrillation remained problematic both in rural settings and in dense population centers. EMTs simply could not reach patients soon enough to deliver defibrillation therapy effectively.
The prospects for out-of-hospital resuscitation changed with the development of automated external defibrillators (AEDs). These units are light (<10 lb [4.5 kg]), are relatively inexpensive, require little maintenance, and facilitate use by bystanders because heart rhythms are automatically diagnosed by the devices. After minimal training, sixth-grade students' performance with AEDs in mock arrest situations is comparable to that of cardiologists. Leaders in the field envisioned using AEDs to enlist a large army of early responders with the capacity to provide prompt defibrillation, erasing the time disadvantage inherent in all but the best-designed paramedic systems.
Early efforts focused on providing AEDs and training to nonmedical, professional first responders, such as firefighters and police officers. An early study from Seattle showed that equipping first-responder units with AEDs decreased the time to defibrillation to 5.1 minutes and increased rates of survival as compared with first-responder CPR alone. Similarly, AEDs deployed in well-defined niche locations such as airplanes, airports, and casinos provided further proof of concept. AEDs were shown to be extremely dependable, and unnecessary shocks due to rhythm misdiagnosis were not observed. However, additional studies in different venues did not always reproduce these favorable results. Differences in the average response time achieved, in the willingness of nonmedical providers to respond, and in the integration of first responders with other elements of the delivery of emergency care contributed to the varying results.
Two studies in this issue of the Journal address the importance of rapid access to defibrillation. The Public Access Defibrillator Trial Investigators (pages 637–646) examined the effect of AED therapy in the hands of trained lay volunteers without a specific duty to respond. Volunteers were recruited in community units such as shopping malls and apartment complexes; the units were randomly assigned to an emergency-response system involving volunteers trained in CPR or CPR plus the use of AEDs. The use of AEDs increased survival to hospital discharge (30 survivors of 128 arrests vs. 15 of 107, P=0.03) without a decrement in the neurologic function of survivors.
Stiell et al., reporting for the Ontario Prehospital Advanced Life Support Study Group (pages 647–656), evaluated the marginal benefit of advanced-life-support training in an emergency-medical-services system previously optimized for rapid defibrillation (response time was eight minutes or less in more than 90 percent of cases). Although the rate of admission to the hospital after a cardiac arrest increased significantly from the rapid-defibrillation phase to the advanced-life-support phase, the rate of survival to hospital discharge did not increase and remained suboptimal at 5 percent. Multivariate predictors of survival included arrests witnessed by bystanders or emergency-medical-services personnel, CPR by bystanders, and rapid defibrillation (the first three links in the chain of survival), but not access to advanced life support.
Even if such exemplary programs were implemented on a widespread basis, the majority of victims of sudden death from cardiac causes — those who die at home — remain unprotected. The concept of therapy with AEDs at home, though attractive at first glance, remains unproven. In order to protect even half the victims of cardiac arrest, people with an annual risk of approximately 1 percent would require intervention. In addition to the cost implications, community-based strategies could not be used and first responders would be limited to the people available in each home.
Both studies confirm the importance of early access to defibrillation for improved survival in out-of-hospital cardiac arrest. Early-access programs are possible with strategic planning within individual communities, focused training of medical personnel, and well-motivated volunteers. Widespread implementation of these initiatives will require political resolve but would add substantially to the rescue of hearts too good to lose.
Source Information
From the Division of Cardiovascular Diseases, Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia.
Related Letters:
Advanced Cardiac Life Support
Nurok M., Stiell I. G., the OPALS Study Group , Callans D. J.(David J. Callans, M.D.)
Most victims of cardiac arrest are initially found in ventricular fibrillation (see Figure 1). Decades of experience within cardiac intensive care units have shown that immediate defibrillation is almost universally effective. Furthermore, implantable defibrillators, which detect and treat ventricular tachyarrhythmias within 20 seconds, restore sinus rhythm in more than 98 percent of episodes of ventricular tachyarrhythmia and ventricular fibrillation.
Figure 1. Episode of Sudden Death Recorded with a Holter Monitor.
The episode begins as uniform ventricular tachycardia and degenerates to ventricular fibrillation and, ultimately, asystole. The period from cardiac arrest to death is less than 10 minutes.
Sudden cardiac arrest is primarily a problem in patients outside of the hospital; in fact, approximately 80 percent of cases of sudden death from cardiac causes occur at home. The rate of success of resuscitation in patients with out-of-hospital cardiac arrest has been poor, averaging 2 to 5 percent in major urban centers. By far, the most important factor for success in resuscitation is time to treatment, in particular, defibrillation (see Figure 2). Although cardiopulmonary resuscitation (CPR), particularly chest compression, is important later in the arrest sequence, defibrillation should be the primary treatment focus within the first four minutes of ventricular fibrillation. Each minute that defibrillation is delayed reduces by 8 to 10 percent the chance of eventual hospital discharge. Resuscitation efforts initiated after eight minutes are almost always doomed to fail.
Figure 2. The Exponential Decline in the Rate of Survival after Sudden Cardiac Arrest as Time to Defibrillation Increases.
Defibrillation alone often results in successful resuscitation if delivered within four minutes of cardiac arrest.
An early attempt to organize the community response to victims of cardiovascular emergencies was the "chain of survival" process. The four links in the chain are early access to care, early initiation of CPR, rapid defibrillation, and early advanced cardiac life support. Initially, the effort focused on teaching CPR through community programs, improving activation of emergency-response systems (e.g., by telephoning 911), and training emergency medical technicians (EMTs) to provide defibrillation. However, in the absence of regional programs, prompt access to defibrillation remained problematic both in rural settings and in dense population centers. EMTs simply could not reach patients soon enough to deliver defibrillation therapy effectively.
The prospects for out-of-hospital resuscitation changed with the development of automated external defibrillators (AEDs). These units are light (<10 lb [4.5 kg]), are relatively inexpensive, require little maintenance, and facilitate use by bystanders because heart rhythms are automatically diagnosed by the devices. After minimal training, sixth-grade students' performance with AEDs in mock arrest situations is comparable to that of cardiologists. Leaders in the field envisioned using AEDs to enlist a large army of early responders with the capacity to provide prompt defibrillation, erasing the time disadvantage inherent in all but the best-designed paramedic systems.
Early efforts focused on providing AEDs and training to nonmedical, professional first responders, such as firefighters and police officers. An early study from Seattle showed that equipping first-responder units with AEDs decreased the time to defibrillation to 5.1 minutes and increased rates of survival as compared with first-responder CPR alone. Similarly, AEDs deployed in well-defined niche locations such as airplanes, airports, and casinos provided further proof of concept. AEDs were shown to be extremely dependable, and unnecessary shocks due to rhythm misdiagnosis were not observed. However, additional studies in different venues did not always reproduce these favorable results. Differences in the average response time achieved, in the willingness of nonmedical providers to respond, and in the integration of first responders with other elements of the delivery of emergency care contributed to the varying results.
Two studies in this issue of the Journal address the importance of rapid access to defibrillation. The Public Access Defibrillator Trial Investigators (pages 637–646) examined the effect of AED therapy in the hands of trained lay volunteers without a specific duty to respond. Volunteers were recruited in community units such as shopping malls and apartment complexes; the units were randomly assigned to an emergency-response system involving volunteers trained in CPR or CPR plus the use of AEDs. The use of AEDs increased survival to hospital discharge (30 survivors of 128 arrests vs. 15 of 107, P=0.03) without a decrement in the neurologic function of survivors.
Stiell et al., reporting for the Ontario Prehospital Advanced Life Support Study Group (pages 647–656), evaluated the marginal benefit of advanced-life-support training in an emergency-medical-services system previously optimized for rapid defibrillation (response time was eight minutes or less in more than 90 percent of cases). Although the rate of admission to the hospital after a cardiac arrest increased significantly from the rapid-defibrillation phase to the advanced-life-support phase, the rate of survival to hospital discharge did not increase and remained suboptimal at 5 percent. Multivariate predictors of survival included arrests witnessed by bystanders or emergency-medical-services personnel, CPR by bystanders, and rapid defibrillation (the first three links in the chain of survival), but not access to advanced life support.
Even if such exemplary programs were implemented on a widespread basis, the majority of victims of sudden death from cardiac causes — those who die at home — remain unprotected. The concept of therapy with AEDs at home, though attractive at first glance, remains unproven. In order to protect even half the victims of cardiac arrest, people with an annual risk of approximately 1 percent would require intervention. In addition to the cost implications, community-based strategies could not be used and first responders would be limited to the people available in each home.
Both studies confirm the importance of early access to defibrillation for improved survival in out-of-hospital cardiac arrest. Early-access programs are possible with strategic planning within individual communities, focused training of medical personnel, and well-motivated volunteers. Widespread implementation of these initiatives will require political resolve but would add substantially to the rescue of hearts too good to lose.
Source Information
From the Division of Cardiovascular Diseases, Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia.
Related Letters:
Advanced Cardiac Life Support
Nurok M., Stiell I. G., the OPALS Study Group , Callans D. J.(David J. Callans, M.D.)