When an Automated External Defibrillator (AED) delivers a shock, the goal is to stop the chaotic electrical activity, such as ventricular fibrillation, and allow the heart’s natural pacemaker to restart a normal rhythm. If the patient remains unresponsive after the shock, it means the heart’s electrical system has not yet been successfully reset. This moment requires immediate, focused action to maintain the patient’s oxygen supply and blood flow to the brain and other vital organs. The response is not to pause and assess, but to instantly transition to the next phase of life support as directed by the device.
Immediate Resumption of CPR
The instant the AED shock is delivered, you must transition back to performing high-quality cardiopulmonary resuscitation (CPR) without delay. Minimizing the time between the shock and the resumption of compressions—known as the “hands-off” time—is important for patient survival. Even a brief pause allows the pressure that drives blood to the heart and brain to drop significantly. Guidelines recommend keeping this pause under ten seconds to maximize the effectiveness of the CPR cycle.
This next phase of CPR will last for a programmed two-minute cycle, during which the AED will provide voice prompts and a metronome to guide your compressions. You should aim for a rate of 100 to 120 compressions per minute, pushing down at least two inches (five to six centimeters) on the center of the chest. Allowing the chest to fully recoil between compressions is equally important, as this enables the heart to refill with blood. If you are trained in rescue breathing, deliver two breaths for every 30 compressions, maintaining the 30:2 ratio throughout the two-minute interval.
Assessing the AED’s Prompt and Rationale
The two-minute period of chest compressions is a deliberate strategy to circulate oxygenated blood, which helps improve the heart’s metabolic state and increases the chances that the next shock will be effective. At the conclusion of this period, the AED will automatically announce that it is re-analyzing the heart rhythm and instruct everyone to stand clear. This analysis determines the heart’s electrical status after the period of circulatory support you provided.
The AED will then provide one of two possible outcomes. If the heart is still in a shockable rhythm, such as ventricular fibrillation (VF) or pulseless ventricular tachycardia (pVT), the device will advise another shock. Conversely, if the rhythm has converted to a non-shockable rhythm, or if the heart has stopped completely (asystole), the device will state “No Shock Advised.” In either case, whether a shock is delivered or not, you must continue CPR immediately after the analysis is complete.
Addressing Potential Equipment Failure
When the shock is delivered but the patient’s condition does not change, it is important to consider if the equipment itself is functioning optimally. Defibrillation can be ineffective if the electrical current does not pass correctly through the heart tissue. One common cause is poor contact between the electrode pads and the skin, which can happen if the patient is wet or excessively hairy, or if the pads are not firmly adhered.
During the two-minute CPR interval, a rescuer can quickly check the AED pads and cables to ensure they are firmly connected to both the patient and the machine. If there is visible moisture beneath the pads, drying the area and applying new pads, if available, can improve conductivity. Other potential issues include a low battery or expired pads, usually indicated by a warning light or message on the AED itself. Addressing these technical factors during the CPR cycle helps ensure that the next analysis and potential shock are delivered at maximum effectiveness.
Sustaining the Resuscitation Effort
The process of two minutes of high-quality CPR followed by an AED analysis and potential shock is a continuous loop that must be sustained until professional help arrives. The vast majority of patients remain pulseless for over two minutes following a shock, emphasizing the need for uninterrupted CPR. If a second rescuer is available, they should switch roles every two minutes, coinciding with the AED’s analysis cycle, to prevent fatigue and maintain the quality and depth of chest compressions.
This coordinated effort maximizes the patient’s chance of survival by minimizing interruptions to blood flow. When emergency medical services (EMS) personnel take over, clearly communicate the actions you have taken, including the number of shocks administered and any troubleshooting steps performed. This information is valuable for the incoming medical team to transition seamlessly into advanced life support protocols.