Defibrillation

Defibrillation is a critical medical treatment for life-threatening cardiac arrhythmias. An arrhythmia is a disturbance in the heart's normal rhythm. Defibrillation specifically targets ventricular fibrillation (V-Fib) and non-perfusing ventricular tachycardia (V-Tach). In these states, the heart cannot pump blood effectively to the rest of the body. The treatment involves delivering a dose of electric current to the heart. This is often referred to as a counter-shock.

While the exact process is not fully understood, the mechanism is quite specific. The electrical shock causes depolarization in a large amount of the heart muscle. This sudden electrical event stops the chaotic, irregular rhythm. Once the arrhythmia is interrupted, the body's natural pacemaker can take over. This pacemaker is a part of the heart called the sinoatrial node. It works to re-establish a normal sinus rhythm. It is important to note that defibrillation cannot restart a heart in asystole. Asystole is often called a flatline. In those cases, medical professionals use cardiopulmonary resuscitation (CPR) and medication instead.

There are several different types of defibrillation devices used in medicine. Manual external defibrillators are used by healthcare professionals. These require a provider to diagnose the rhythm using an electrocardiogram. The professional must then manually determine the correct voltage and timing. These are common in hospitals and ambulances. For example, every NHS ambulance in the United Kingdom carries one. In the United States, paramedics and advanced EMTs are trained to use them.

Another type is the internal defibrillator. These are used during or after cardiac surgery, such as a heart bypass. They use round metal plates called electrodes. These plates make direct contact with the myocardium, which is the heart muscle. These are mostly used in operating rooms or during open-heart procedures in emergency rooms. There are also implantable cardioverter-defibrillators (ICDs). These are small devices implanted in a patient, similar to a pacemaker. They constantly monitor the heart and automatically deliver shocks if they detect life-threatening rhythms.

Automated external defibrillators (AEDs) are designed for a different purpose. They are portable machines meant for lay responders or bystanders. These devices can be used with little to no training. This is because they provide pre-recorded voice instructions to guide the user. The machine automatically analyzes the patient's heart rhythm. It then decides if a shock is necessary. Some AEDs are semi-automatic, requiring the user to press a button to shock. Others are fully automatic and deliver the shock on their own.

Survival rates for cardiac arrest vary depending on the setting and the heart's rhythm. In North America, survival rates for out-of-hospital cardiac arrests are often less than 10%. In a hospital setting, the rate is higher at 20%. However, the specific rhythm at the time of arrest is a major factor. People with a shockable rhythm, like V-Fib, have much better survival rates. These rates range between 21% and 50%. This is much higher than those with non-shockable rhythms like asystole or pulseless electrical activity (PEA).

To deliver electricity, the device must connect to the patient via electrodes. These electrodes use electrically conductive gel to minimize electrical resistance. This resistance is also called chest impedance. Using gel helps prevent the patient's skin from burning. Some electrodes are traditional metal paddles with insulated handles. A provider must press these against the chest with about 25 pounds of force. Other electrodes are self-adhesive pads that stick to the skin like a sticker. These pads are very common in non-hospital settings. They are easy for untrained users to apply quickly.