Each year, more than 350,000 Americans experience a sudden, out-of-hospital loss of electrical function in the heart, called cardiac arrest. Where heart attack is caused by a blockage in the heart that, in turn, causes death of cardiac muscle, cardiac arrest happens when the heart’s electrical system ceases to work the way it should. But before you can understand the different ways to treat cardiac arrest, it is important to understand how the heart works in the first place.
A Single Heartbeat
Like many functions inside the body, the heart operates using electrical pulses. The whole process starts in the sinoatrial node of the heart, also known as the heart’s natural pacemaker. This electrical pulse spreads throughout the heart causing the muscle to contract, filling the ventricles with blood. The atrioventricular node slows the electrical pulse just enough so the ventricles can perform this important function. A pathway of fibers, known as the His-Purkinje Network, sends the impulse into the walls of the ventricles and cause them to contract, sending blood out of the heart and into the rest of the body. The entire process repeats itself over and over, thousands of times a day, more than 42 million times per year. However, illness, electrolyte imbalances, medications, or other conditions can cause the heart to begin quivering rather than regularly beating, a condition known as arrhythmia. In these instances, medical intervention through the use of electrical shock directly to the heart is the key to survival. The method used for this electrical shock will vary depending on the type of arrhythmia, where the patient is located and who is attempting to intervene on their behalf.
When a Defibrillator is Useful
Defibrillators come in all shapes and types. The fully automatic Automated External Defibrillator (AED) is designed for the lay person to use on behalf of someone who is experiencing sudden cardiac arrest while the manual defibrillator is designed for use inside the hospital by medical personnel. Both rely on the administration of electrical shock to the outside of the body to restore a normal heart beat in a person that is experiencing sudden cardiac arrest. However, there are only certain heart rhythms that are considered “shockable.” Also known as ventricular fibrillation and pulseless ventricular tachycardia, these shockable rhythms can be corrected using an external electrical shock. While many defibrillators include pacing functions to bring the heart back into normal rhythm, defibrillators are used in emergency situations where there is no time for surgical intervention.
When a Pacemaker is Useful
Even though a pacemaker performs many of the same functions as a defibrillator, the main difference between them is that the pacemaker is an implantable device that administers shocks directly to the heart when necessary and without intervention from anyone else. Doctors implant the pacemaker into the patient’s chest where it uses electrical pulses to keep the heart beating normally. If the heart is too slow, the pacemaker can speed up the heartbeat. If it is too fast, it can slow it down. If the heart begins to quiver, rather than beat, it can re-coordinate the chambers of the heart, getting it beating in a normal fashion again.
Both defibrillators and pacemakers are helpful in restoring the heart’s normal heart beat. Although one can be used externally and the other must be implanted, both devices perform similar functions in keeping a person alive in spite of cardiac arrest.