Sudden cardiac arrest (SCA) is a medical emergency where the heart’s electrical system malfunctions, causing it to stop beating effectively. This abrupt cessation of blood flow to the brain and other organs leads to immediate collapse and loss of consciousness. Because approximately 90% of people who suffer an out-of-hospital cardiac arrest die, survival depends entirely on the immediate action of bystanders. When the heart stops, a rapid sequence of coordinated actions must be initiated to maximize the chance of a positive outcome. This framework of immediate response is known as the Cardiac Chain of Survival.
Defining the Cardiac Chain of Survival
The Cardiac Chain of Survival is a conceptual model linking the necessary steps for successful resuscitation from out-of-hospital cardiac arrest. Each step is dependent on the one preceding it. The five links of the adult Out-of-Hospital Cardiac Chain of Survival begin with community response and extend through definitive medical care. The sequence starts with recognition and activation of the emergency response system, followed by high-quality cardiopulmonary resuscitation (CPR) and rapid defibrillation. The chain concludes with effective advanced life support provided by emergency medical services and integrated post-cardiac arrest care and recovery.
The Immediate First Action: Recognition and Activation
The first and most immediate step in the Adult Cardiac Chain of Survival is the Recognition of Cardiac Arrest and Activation of the Emergency Response System. This action is the foundation for all subsequent life-saving interventions, as it mobilizes professional help and secures resources. The initial response requires the rescuer to first ensure the scene is safe before approaching the person who has collapsed. The rescuer must then quickly check for responsiveness by gently tapping the person and shouting, “Are you okay?”.
Simultaneously, the rescuer must check for normal breathing, which is often absent or replaced by ineffective gasping, known as agonal respirations. If the person is unresponsive and not breathing normally, cardiac arrest is presumed, and the emergency response system must be activated immediately by calling 911 or the local emergency number. This call connects the rescuer to a dispatcher who can provide guidance and send trained medical personnel to the location.
The rescuer should also send a second person to retrieve the nearest Automated External Defibrillator (AED) if one is available. If the rescuer is alone, they must prioritize the call to emergency services before beginning hands-on care.
Links 2 and 3: High-Quality CPR and Rapid Defibrillation
Once the emergency response system is activated, the next two links—High-Quality CPR and Rapid Defibrillation—must be initiated as quickly as possible to sustain life. High-Quality CPR, the second link, involves chest compressions that artificially circulate oxygenated blood to the brain and other vital organs. Compressions should be performed at a rate of 100 to 120 compressions per minute, pushing down to a depth of at least two inches (five centimeters) on an average adult. This consistent mechanical action buys time by keeping the heart and brain alive until the underlying electrical problem can be addressed.
The third link, Rapid Defibrillation, is the only definitive treatment for ventricular fibrillation, the most common electrical rhythm in sudden cardiac arrest. A portable AED is designed to deliver an electrical shock to the heart, which briefly stops all electrical activity. This momentary pause allows the heart’s natural pacemaker to potentially reset and restore a normal, effective rhythm. The device provides voice and visual prompts, guiding the rescuer through the process of applying the pads and delivering the shock when necessary.
The Importance of Time
The effectiveness of all links in the Chain of Survival is determined by the speed of their execution. Survival rates from sudden cardiac arrest decline rapidly, decreasing by approximately 7% to 10% for every minute that passes without intervention. The prompt initiation of CPR and defibrillation can double or even triple a person’s chance of survival. When bystander CPR is performed, the rate of decline in survival is slowed to about 3% to 4% per minute, extending the window for a successful outcome.