Defibrillation is a medical procedure that delivers a controlled electrical shock to the heart to correct certain life-threatening abnormal heart rhythms. This intervention aims to restore the heart’s natural, effective pumping action. It is a component of emergency medical care for individuals experiencing sudden cardiac arrest, a condition where the heart abruptly stops functioning. The electrical current momentarily stops the disorganized electrical activity, allowing the heart’s inherent pacemaker to reset to a normal rhythm.
Rhythms Requiring Defibrillation
Defibrillation is specifically effective for two types of chaotic heart rhythms: ventricular fibrillation (VF) and pulseless ventricular tachycardia (pVT). Ventricular fibrillation occurs when the heart’s lower chambers, the ventricles, quiver rapidly and chaotically instead of contracting in a coordinated manner. This disorganized electrical activity prevents the heart from effectively pumping blood to the body, leading to immediate loss of consciousness and cardiac arrest.
Pulseless ventricular tachycardia involves the ventricles beating extremely fast, over 180 beats per minute, but without generating a detectable pulse because they do not have enough time to fill with blood. Both VF and pVT are life-threatening conditions that result in insufficient blood flow to vital organs. Defibrillation works for these rhythms because they represent disorganized electrical activity that can be “reset” by the electrical shock, allowing the heart’s natural pacemaker to re-establish a normal, coordinated rhythm.
Rhythms Where Defibrillation Is Not Effective
Defibrillation is not a universal treatment for all forms of cardiac arrest. Two common rhythms where it is ineffective are asystole and pulseless electrical activity (PEA). Asystole is often referred to as “flatline” because it indicates a complete absence of electrical activity in the heart. In this state, there is no electrical signal to reset, making defibrillation futile.
Pulseless electrical activity (PEA) is characterized by organized or semi-organized electrical activity on an electrocardiogram, but without a palpable pulse. In PEA, the heart’s electrical system is working, but the mechanical pumping function is insufficient to circulate blood effectively. This can be due to various underlying issues, such as severe blood loss or blockages, rather than an electrical disorganization that a shock could correct. Since the problem is not a chaotic electrical signal that needs to be stopped, defibrillation does not address the root cause and is not an appropriate treatment.
The Urgency of Defibrillation
For shockable rhythms like ventricular fibrillation and pulseless ventricular tachycardia, time is an important factor. Every minute that passes without defibrillation significantly reduces the chance of survival. Survival rates can drop by approximately 7-10% per minute without intervention.
This resetting of the heart’s electrical system is most successful when performed within the first few minutes of cardiac arrest. Alongside rapid defibrillation, high-quality cardiopulmonary resuscitation (CPR) is also important. CPR helps maintain some blood flow and oxygen to the brain and other organs until a defibrillator can be used, thereby improving the chances of a successful outcome.