Defibrillation is a medical procedure that uses an electrical shock to address certain life-threatening heart rhythms. This intervention is often depicted in media, but its appropriate application is frequently misunderstood, particularly concerning a condition known as asystole. The question of whether defibrillation is used for asystole is a fundamental one in emergency medical care.
Asystole: The Flatline Rhythm
Asystole, commonly referred to as “flatline,” signifies a complete absence of electrical and mechanical activity in the heart. This condition is the most severe form of cardiac arrest, as the heart is not pumping blood.
Defibrillation is ineffective for asystole because the heart muscle is electrically silent, meaning there is no chaotic electrical activity to reset. Delivering an electrical shock would have no beneficial effect. In fact, attempting to defibrillate a patient in asystole can be harmful, potentially causing damage to the heart.
Defibrillation: How It Works
Defibrillation delivers a controlled electrical shock to the heart. Its primary purpose is to stop abnormal, chaotic electrical activity, allowing the heart’s natural pacemaker to resume a normal, organized rhythm. This process can be likened to rebooting a computer.
The electrical current from a defibrillator momentarily depolarizes a large portion of the heart muscle. This brief, induced electrical silence allows the heart’s natural electrical system to re-establish a coordinated beat. Defibrillation is a time-sensitive intervention, as its effectiveness decreases with each passing minute after the onset of dangerous heart rhythms.
Treating Asystole
When a patient presents with asystole, medical interventions focus on restarting the heart’s electrical activity rather than shocking it. High-quality cardiopulmonary resuscitation (CPR) is the cornerstone of treatment. Continuous chest compressions are important for maintaining blood flow to the brain and heart, and interruptions to CPR should be minimized.
Specific medications are also administered to support resuscitation efforts. Epinephrine, a vasopressor, is given every 3 to 5 minutes to increase blood flow to the heart and brain. This medication works by causing vasoconstriction, which helps to improve perfusion during cardiac arrest. While epinephrine is a primary drug for asystole, some authorities question its overall clinical effectiveness in improving long-term survival.
Medical professionals also actively search for and treat any reversible causes that might have led to the asystole. These causes are often remembered using mnemonics like the “H’s and T’s.”
Reversible Causes (H’s and T’s)
- H’s: Hypovolemia (low blood volume), Hypoxia (lack of oxygen), Hydrogen ion (acidosis), Hypo/hyperkalemia (electrolyte imbalances), and Hypothermia (low body temperature).
- T’s: Tension pneumothorax, Cardiac tamponade, Toxins, and Thrombosis (coronary or pulmonary).
Addressing these underlying issues is important, as correcting them can sometimes lead to the return of spontaneous circulation.
When Defibrillation is Applied
Defibrillation is specifically indicated for two types of life-threatening heart rhythms: ventricular fibrillation (VF) and pulseless ventricular tachycardia (pVT). In ventricular fibrillation, the heart’s lower chambers (ventricles) quiver erratically and chaotically instead of contracting effectively, rendering the heart ineffective at pumping blood.
Pulseless ventricular tachycardia occurs when the ventricles beat very rapidly but without producing a pulse. While the electrical activity is more organized than in VF, the extreme speed prevents the heart chambers from filling properly. In both VF and pVT, the heart has abnormal electrical activity that defibrillation can interrupt and reset, offering a chance for the heart’s natural rhythm to restart.