Defibrillation is a medical procedure that uses an electrical shock to restore a normal heart rhythm during specific life-threatening cardiac emergencies. It delivers a controlled electrical pulse to stop an abnormal rhythm, allowing the heart’s natural electrical system to reset. This intervention counteracts chaotic electrical activity, enabling the heart to resume effective pumping. Defibrillation can save a life in instances of sudden cardiac arrest.
The Heart’s Electrical System
The heart, a muscular pump, relies on an intricate electrical system to coordinate its contractions and circulate blood throughout the body. At the core of this system is the sinoatrial (SA) node, often called the heart’s natural pacemaker, located in the upper right chamber (atrium). The SA node generates electrical impulses that spread across the upper chambers, causing them to contract and push blood into the lower chambers.
These electrical signals then travel to the atrioventricular (AV) node, which briefly delays the impulse, allowing the lower chambers (ventricles) to fill with blood. From the AV node, the impulses rapidly spread through specialized pathways, reaching the ventricles and causing them to contract. This synchronized electrical activity ensures the heart beats in a regular, coordinated manner, typically 60 to 100 times per minute at rest, pumping blood throughout the body.
Rhythms Requiring Defibrillation
Defibrillation is specifically indicated for certain life-threatening heart rhythms that prevent the heart from effectively pumping blood. The two primary rhythms that require defibrillation are ventricular fibrillation (VF) and pulseless ventricular tachycardia (VT). These conditions are forms of sudden cardiac arrest, meaning the heart’s electrical activity becomes so disorganized that it can no longer pump blood, leading to immediate collapse and loss of consciousness.
In ventricular fibrillation, electrical signals in the lower chambers become chaotic and uncoordinated, causing the ventricles to quiver uselessly instead of contracting in a synchronized way. This prevents any effective blood flow to the body’s organs. Similarly, in pulseless ventricular tachycardia, the ventricles beat extremely rapidly, but contractions are so fast that there is insufficient time for the chambers to fill with blood, resulting in a lack of pulse. Both conditions demand immediate defibrillation to reset the heart’s electrical activity and allow a normal rhythm to resume, which is the only definitive treatment for these rhythms.
When Defibrillation is Not Used
While defibrillation is a life-saving intervention for specific cardiac rhythms, it is not a universal treatment for all cardiac emergencies. It is ineffective and not used for conditions where there is either no electrical activity to reset or where electrical activity is organized but does not produce a pulse. Two common scenarios where defibrillation is not indicated are asystole and pulseless electrical activity (PEA).
Asystole, often referred to as a “flatline” on an electrocardiogram, signifies a complete absence of electrical activity in the heart. In this situation, there is no electrical chaos to interrupt or reset, making an electrical shock futile. Pulseless electrical activity (PEA) occurs when the heart’s electrical system shows organized activity, but the heart muscle itself does not contract effectively enough to generate a pulse. Since the problem is with mechanical contraction rather than electrical disorganization, a shock will not resolve the issue. In cases of asystole or PEA, other interventions like cardiopulmonary resuscitation (CPR) and specific medications are used to attempt to restore heart function.
Automated External Defibrillators
Automated External Defibrillators (AEDs) are portable, user-friendly devices that allow even untrained bystanders to provide life-saving defibrillation. An AED works by analyzing the heart’s electrical rhythm through electrode pads placed on the chest. If the device detects a shockable rhythm, such as ventricular fibrillation or pulseless ventricular tachycardia, it advises the user to deliver an electrical shock.
Using an AED involves turning on the device, attaching the pads to the patient’s bare chest, and then following clear voice prompts and visual instructions. The AED guides the user through the process, often instructing them to clear the patient before delivering the shock. The immediate availability and ease of use of AEDs in public spaces, combined with CPR, significantly increases the chances of survival for individuals experiencing sudden cardiac arrest. For every minute defibrillation is delayed, the chance of survival decreases by approximately 7-10%.