It is a common misunderstanding that a defibrillator can restart a heart that has completely stopped beating. While defibrillators are life-saving devices, their application is specific and depends on the heart’s underlying electrical activity. Understanding their function and the specific conditions they address clarifies their role in cardiac emergencies.
How a Defibrillator Works
A defibrillator delivers a controlled electrical shock to the heart. This shock is intended to depolarize a significant portion of the heart muscle simultaneously. The goal is to interrupt chaotic electrical activity and allow the heart’s natural pacemaker to reset and re-establish a normal, coordinated rhythm. It essentially “reboots” the heart’s electrical system, much like restarting a computer.
The device does not generate a heartbeat from scratch. Instead, it aims to synchronize the disorganized electrical signals that prevent the heart from pumping blood effectively. If there is no electrical activity present, there is nothing for the defibrillator to reset.
Heart Rhythms a Defibrillator Addresses
Defibrillators are specifically designed to treat certain life-threatening cardiac arrhythmias where there is electrical activity, but it is disorganized and ineffective. The two primary “shockable” rhythms are ventricular fibrillation (VF) and pulseless ventricular tachycardia (PVT).
Ventricular fibrillation occurs when the heart’s electrical signals become chaotic, causing the ventricles to quiver uselessly instead of contracting to pump blood. This disorganized electrical activity means the heart cannot circulate blood to the body. Pulseless ventricular tachycardia is characterized by a very rapid, but ineffective, electrical rhythm originating in the ventricles, where the heart beats too fast to effectively pump blood, resulting in no detectable pulse. In both conditions, electrical activity is present but uncoordinated, making defibrillation effective.
When a Defibrillator is Not Used
A defibrillator is ineffective and therefore not used when the heart has no electrical activity at all, a condition known as asystole. Asystole is commonly referred to as a “flatline” on an electrocardiogram (ECG) monitor, indicating a complete absence of electrical impulses. Since a defibrillator works by resetting chaotic electrical activity, it cannot “jump-start” a heart that has no electrical activity.
Attempting to shock a heart in asystole provides no benefit and can potentially cause further harm to the heart muscle. Therefore, in cases of asystole, medical professionals focus on other interventions rather than defibrillation.
Immediate Actions for a Stopped Heart
When someone collapses and appears to have a stopped heart, immediate action is necessary. The first step is to call for emergency medical services (e.g., 911 or equivalent local emergency number). Early activation of the emergency response system significantly improves the chances of survival.
Simultaneously, starting cardiopulmonary resuscitation (CPR) without delay is essential. CPR involves chest compressions to manually circulate blood and oxygen to the brain and other vital organs. CPR helps to maintain partial blood flow, extending the window of opportunity for professional medical intervention and potentially delaying tissue death. High-quality chest compressions, at a rate of 100 to 120 per minute and a depth of 2 to 2.4 inches (5 to 6 cm) for adults, should be performed. CPR should continue until emergency medical professionals arrive and can take over or a defibrillator becomes available and advises a shock.