WHAT IS SUDDEN CARDIAC ARREST?
SCA and the Crucial Role of the Bystander and CPR/AED Use
Sudden cardiac arrest (SCA) is a leading cause of death throughout the world. For many victims of SCA, there is no previous history of heart problems. Sudden cardiac arrest is often the first symptom, and can occur in outwardly healthy people with no known heart disease or other health problems. Most victims have heart disease, although they may not know it. There are numerous risk factors that contribute to cardiac arrest. They include:
- Previous heart attack: 75% of the people who die of SCA show signs of a previous heart attack.
- Coronary artery disease: 80% of SCA victims have signs of coronary artery disease. This is a condition in which the arteries that supply blood to the heart are narrowed or blocked.
- Low ejection fraction (EF): A healthy heart pumps 55% or more of its blood with each beat. People with EFs of less than 40% are at increased risk of SCA.
- Heart failure: In Heart Failure patients SCA occurs at six to nine times the rate of the general population.
- Primary electrical abnormalities of the heart or lungs.
Particularly with children and adolescents the following signs and symptoms may be precursors to SCA:
- Fainting (syncope), especially during or after exercise
- Dizziness/lightheadedness
- Excessive fatigue or shortness of breath associated with exercise
- Abnormal heart rate or rhythm (arrhythmia)
- High blood pressure
- Congenital heart abnormality
- Obesity and/or diabetes
- Family history of sudden death prior to age 50
Primary Prevention of SCA
Primary prevention treatments may be prescribed for patients seeking medical care due to SCA symptoms and/or identified risk factors. They include:
- Medications for specific heart conditions
- Implantable cardioverter defibrillator (ICD) to provide internal protection from SCA
- Interventional procedures or bypass surgery for repairing damaged or defective heart tissue
- Modification of risk factors, or making changes that promote a healthy heart such as better nutritional and exercise habits.
Secondary Prevention of SCA
Identifying high risk SCA patients and providing them with appropriate therapies has helped reduce the incidence of SCA. Yet for the thousands of people that collapse each year from SCA without prior knowledge of their risk factors, the key to survival is early bystander recognition of SCA and a strong 'chain of survival'.
The chain of survival includes immediate notification and dispatch of the local Emergency Medical System (EMS), early and high quality cardiopulmonary resuscitation (CPR), early use of an automated external defibrillator (AED), early advanced life support (ALS), immediate in-hospital care including induced hypothermia, and comprehensive cardiovascular follow up therapies.
Despite efforts to strengthen components of the chain of survival, especially CPR and more recently the use of AEDs, the survival rate for out-of-hospital cardiac arrest remains low worldwide, averaging 6% or less.
Yet many communities have succeeded in improving SCA survival rates. These programs typically include organized community lay rescuer CPR and AED programs. In addition, survival rates from witnessed ventricular fibrillation (VF) SCA ranging from 49% to 74% have been reported in lay rescuer CPR and AED programs in airports and casinos and programs involving police officers.
These successful programs had several common elements, including the training of rescuers in a planned and practiced response, rapid recognition of SCA, prompt provision of bystander CPR, and defibrillation within 5 minutes of collapse.
Further improvements to SCA survival rates have been reported since the introduction of the American Heart Association 2005 Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care that among other changes promote a higher ratio of compressions to ventilations (30:2 compared to 15:2 pre-2005 AHA guidelines). Recent advances in technology and EMS systems have also contributed to increased survival rates. Some communities have made inroads to higher survival by taking a 'systems' approach to SCA -- improving several links in the Chain of Survival simultaneously, including public awareness and layperson training, EMS use of impedance threshold devices (ITDs) to improve CPR efficiency, induced hypothermia, and rapid deployment of patients to in-hospital treatment protocols for cardiac follow up care.
Although dramatic increases in SCA survival rates have been reported in communities implementing these new strategies, many studies continue to show that a minority of victims of cardiac arrest receive bystander CPR and even fewer receive high-quality CPR despite outcomes suggesting that early CPR and AED use increases survival rates from cardiac arrest. The American Heart Association's 2005 CPR Guidelines state, "the most important determinant of survival from sudden cardiac arrest is the presence of a trained rescuer who is ready, willing, able, and equipped to act."
Immediate bystander CPR and AED use play a crucial role in saving more lives from SCA. A public health challenge exists to dramatically increase the number of bystanders who can quickly recognize a cardiac emergency and take appropriate action with the tools they need to save a life.
Research End Notes
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