A defibrillator, particularly an Automated External Defibrillator (AED), is designed to correct chaotic electrical problems in the heart, not to restart a heart that has completely stopped beating. The definitive answer to whether you can use a defibrillator on someone with no heartbeat is generally no, because the device requires disorganized electrical activity to function. An AED delivers a controlled electrical shock intended to momentarily halt the heart’s erratic electrical signals. This allows the heart’s natural pacemaker to potentially resume a normal, effective rhythm. This process is effective only for specific types of cardiac arrest where underlying electrical chaos is present.
The Physiology of Shockable Rhythms
The electrical shock from a defibrillator is effective only against two specific shockable rhythms: Ventricular Fibrillation (V-Fib) and Pulseless Ventricular Tachycardia (V-Tach). Both involve the heart’s electrical system malfunctioning.
In V-Fib, the ventricles—the heart’s main pumping chambers—quiver rapidly and chaotically instead of contracting in a coordinated manner. This disorganized electrical activity prevents the heart from pumping blood effectively, resulting in immediate collapse and loss of pulse.
Pulseless V-Tach is an extremely fast, but somewhat organized, electrical rhythm originating in the ventricles. The rate is so accelerated that the heart chambers cannot fill with blood between beats. Consequently, no effective circulation is generated, and the patient has no palpable pulse.
The defibrillator delivers a high-energy electrical current that simultaneously depolarizes, or resets, the heart muscle cells. This momentary electrical silence clears the chaotic signals, allowing the heart’s natural pacemaker (the sinoatrial node) to take over. Interrupting the electrical malfunction allows the SA node to re-establish a normal, coordinated rhythm that restores effective blood circulation.
When Defibrillation Will Not Work
Defibrillation is ineffective against non-shockable rhythms, which represent the true “no heartbeat” scenarios. The two primary non-shockable rhythms are Asystole and Pulseless Electrical Activity (PEA).
Asystole, often shown as a flat line on an electrocardiogram (ECG), signifies a complete absence of measurable electrical activity. Since defibrillation resets chaotic signals, a shock cannot help when there are no signals to reset. Administering a shock in Asystole is useless and can potentially damage heart tissue.
In Asystole, the focus shifts entirely to mechanical intervention, specifically high-quality chest compressions, and the administration of medications like epinephrine.
PEA is complex because the heart’s electrical system produces organized signals, but the muscle does not contract strongly enough to generate a pulse or circulate blood. The ECG may show a relatively normal rhythm, but the mechanical action is absent. An electrical shock is not advised because the underlying problem is mechanical failure or an extreme physiological issue, not electrical chaos.
PEA is often caused by severe underlying conditions, such as extreme blood loss or cardiac tamponade, which must be identified and corrected. In both Asystole and PEA, continuous chest compressions manually circulate blood to the heart and brain. This buys time for advanced medical providers to address the root cause.
Immediate Response Protocols for Cardiac Arrest
When encountering an unresponsive person who is not breathing normally, the immediate response must follow a specific sequence regardless of the underlying heart rhythm. First, activate the emergency response system by calling the local emergency number. If possible, a second person should locate and retrieve an Automated External Defibrillator (AED).
While waiting for the AED, initiating high-quality cardiopulmonary resuscitation (CPR) is paramount. Chest compressions must be performed immediately, pushing hard and fast in the center of the chest at a rate of 100 to 120 compressions per minute. This mechanical action keeps oxygenated blood flowing to the brain and heart until definitive treatment is possible.
When the AED arrives, the rescuer must turn it on and follow the clear, verbal prompts. The AED analyzes the patient’s heart rhythm and determines if a shockable rhythm is present. If the device detects V-Fib or Pulseless V-Tach, it will charge and advise the user to deliver a shock.
If the AED detects a non-shockable rhythm, such as Asystole or PEA, the device will state, “No shock advised,” and prompt the rescuer to continue CPR. The AED prevents inappropriate shocks, meaning a lay rescuer does not have to distinguish between rhythms. The rescuer should continue alternating between following the AED’s instructions and performing continuous chest compressions until emergency medical services arrive.