A cardiac arrest is a sudden event where the heart stops beating effectively. Within minutes, the lack of oxygenated blood supply to the brain and other vital organs begins to cause irreversible damage. Two primary interventions offer the best chance of survival: Cardiopulmonary Resuscitation (CPR) and the Automated External Defibrillator (AED). These tools are the foundation of the “Chain of Survival,” and while both are necessary, the timing and sequence of their application are often misunderstood.
Understanding CPR and AED Function
CPR is a mechanical action designed to manually circulate blood and oxygen to the brain and heart until the underlying electrical problem can be fixed. Chest compressions create a temporary, artificial circulation by squeezing the heart between the sternum and the spine, pushing blood out to the rest of the body. Trained rescuers couple this with rescue breaths to deliver oxygen to the lungs.
The Automated External Defibrillator addresses the electrical chaos within the heart that often causes sudden cardiac arrest, specifically ventricular fibrillation. This condition is characterized by disorganized electrical activity that makes the heart quiver instead of pump. The AED delivers a controlled electrical shock to briefly stop all electrical activity, allowing the heart’s natural pacemaker to potentially reset into a normal, perfusing rhythm.
The Priority Rule: Immediate CPR and Rapid AED Deployment
When a person collapses and is unresponsive with abnormal or absent breathing, the first action for a lay rescuer is to assume cardiac arrest and immediately begin CPR. This step ensures that whatever oxygen remains in the bloodstream is circulated to the brain and heart without delay. The contemporary guidelines emphasize that CPR should not be postponed while waiting for an AED to arrive.
The AED should be retrieved and applied as quickly as possible, ideally by a second rescuer who is alerted while the first rescuer starts chest compressions. CPR is started before the AED is ready, but the AED is utilized as soon as it is available. Once the device is brought to the scene, the rescuer must power it on, attach the electrode pads to the patient’s bare chest, and follow the device’s prompts. The AED analyzes the heart rhythm and advises whether a shock is necessary.
The “CPR gap” is the time when chest compressions are paused, and minimizing this gap is directly linked to better survival outcomes. Every second without compressions causes blood pressure to drop significantly, making subsequent defibrillation attempts less likely to succeed. Starting CPR immediately provides a baseline level of circulation that buys time for the AED to be set up and deployed.
Maximizing Effectiveness: Minimizing Pauses
The transition from CPR to AED use must be seamless to maintain the highest possible quality of resuscitation. If multiple rescuers are present, one person should continue chest compressions at a rate of 100 to 120 beats per minute while the other prepares and applies the AED pads. Pads should be placed on the upper right chest and the lower left side, avoiding any interruption to compressions until the AED is ready to analyze the rhythm.
The only acceptable pause in chest compressions is the brief moment required for the AED to analyze the heart rhythm and, if advised, to deliver an electrical shock. The American Heart Association recommends keeping this hands-off time under 10 seconds to prevent a major drop in blood flow. Once the pads are connected, the rescuer must clear the patient with a loud “Hands Off” command before pressing the analyze or shock button, ensuring no one is touching the victim during electrical delivery.
Modern AEDs are designed to guide the rescuer through this process with clear voice prompts and visual cues. If the AED advises a shock, the rescuer should press the button, and then immediately resume compressions once the shock is delivered. Some advanced techniques, such as continuing compressions while the AED charges, minimize the pause in circulation.
Post-Shock Care and Next Steps
The delivery of an electrical shock does not guarantee the heart will immediately resume a normal rhythm. Therefore, the most important action immediately following a shock is to instantly restart CPR, beginning with chest compressions. This continuation helps circulate the blood and oxygen, providing the heart muscle with the energy and flow it needs to potentially organize its rhythm.
The rescuer should continue CPR for a two-minute cycle, which is the standard interval programmed into the AED. Following this period, the AED prompts the rescuer to stop compressions so it can re-analyze the heart rhythm and determine if another shock is required. This cycle should be repeated until Emergency Medical Services (EMS) personnel arrive to take over care, or until the person shows definitive signs of life. The AED must remain turned on and the pads should not be removed, as the device is necessary for ongoing monitoring and guidance.