When an automated external defibrillator (AED) delivers a shock during sudden cardiac arrest, the immediate hope is for the patient to regain consciousness or begin moving. It is common, however, for the patient to remain unresponsive and still lack normal breathing after the energy delivery. This lack of response does not signify failure but signals the necessity to proceed immediately to the next phase of the resuscitation protocol. The standardized, time-sensitive sequence of actions that follow a shock are designed to maximize blood flow to the brain and heart while preparing for the AED’s next analysis.
The Immediate Next Step: Resume Compressions
The most important action after a defibrillation shock, if the patient remains unresponsive, is to restart chest compressions without delay. Prolonged pauses in cardiopulmonary resuscitation (CPR) allow pressure within the chest to drop significantly, halting blood flow to vital organs. Guidelines stress that the pause between shock delivery and the resumption of compressions should be less than ten seconds. Starting compressions instantly helps circulate oxygenated blood and metabolic fuel that remains in the system.
Rescuers must focus on delivering high-quality CPR. High-quality compressions are defined by specific metrics for both rate and depth. The compression rate should be between 100 and 120 pushes per minute. For an adult patient, the compression depth should be at least two inches (five centimeters), but should not exceed 2.4 inches (six centimeters).
The technique also requires the rescuer to allow the chest to fully recoil after each compression. Full chest recoil permits the heart to refill with blood before the next push, which is essential for maintaining coronary perfusion pressure. Rescuers should avoid leaning on the chest during the relaxation phase to ensure this complete elastic recoil. If the rescuer is trained and willing, chest compressions are combined with rescue breaths at a ratio of 30 compressions to two breaths for an adult patient without an advanced airway.
Two-Minute Cycle and Reanalysis
The immediate resumption of compressions marks the beginning of the next two-minute cycle of CPR. This two-minute interval is a standardized period during which continuous, uninterrupted CPR is performed to circulate blood. The AED will often provide voice prompts and a metronome feature to help the rescuer maintain the correct rate and rhythm throughout this period. During this time, the AED is actively monitoring the patient’s heart rhythm through the attached electrode pads.
At the end of the two-minute cycle, the AED automatically initiates a re-analysis of the heart’s electrical activity, known as a rhythm check. The device will instruct all rescuers to stand clear of the patient to prevent interference with the electrical reading. This analysis pause, which should be kept as brief as possible, determines the next course of action. If the heart is still in a shockable rhythm, the AED will advise a second shock, and the rescuer will follow the prompts to deliver it.
If the AED determines the rhythm is non-shockable, such as a flat line (asystole) or pulseless electrical activity (PEA), it will advise “No Shock Advised.” In either case—whether a shock is delivered or not advised—the rescuer is immediately instructed to resume the two-minute cycle of chest compressions. This repeating process of CPR, analysis, and shock (if advised) continues until professional emergency medical services (EMS) arrive.
Maintaining Quality CPR and Handover
During prolonged resuscitation, maintaining the quality of chest compressions becomes increasingly difficult due to rescuer fatigue. To combat the decline in compression effectiveness, rescuers should switch roles, or “compressors,” approximately every two minutes, coinciding with the AED’s rhythm check. Switching rescuers ensures that the compressions remain within the optimal rate and depth parameters, which directly impacts the patient’s chances of survival.
Effective communication with the 911 dispatcher is important for coordinating the arrival of professional help. Once EMS professionals arrive, a concise and organized handover of care is necessary, often while compressions are still ongoing. The incoming team requires specific pieces of information to guide their advanced care immediately.
Handover Information
The information provided to EMS should include:
- The estimated time the cardiac arrest occurred.
- Whether the arrest was witnessed.
- How long bystander CPR has been administered.
- The total number of shocks delivered by the AED.
- The patient’s rhythm findings (shockable or non-shockable).
This coordinated transfer of information and care ensures that bystander efforts are continued seamlessly by the medical team.