Cardiac arrest is a time-sensitive, life-threatening emergency defined by the sudden loss of consciousness, breathing, and circulation. This devastating event occurs when the heart stops pumping blood effectively, starving the brain and other organs of necessary oxygen. When monitoring a person in cardiac arrest, medical professionals observe the heart’s electrical activity, which helps determine the correct treatment. The outcome for a patient depends entirely on how quickly the specific cardiac rhythm is identified and addressed.
Defining Pulseless Electrical Activity
Pulseless Electrical Activity (PEA) is a state of cardiac arrest where organized electrical activity is visible on an electrocardiogram (ECG) monitor, yet the patient has no detectable pulse. Essentially, the heart’s electrical system is firing, but the mechanical function of the heart muscle—the contraction necessary to pump blood—is inadequate or completely absent. Because no blood is being circulated, the condition is just as severe as a complete flatline.
PEA is one of the two non-shockable rhythms, the other being Asystole, which is a complete lack of electrical activity, appearing as a flat line on the monitor. While Asystole represents both electrical and mechanical failure, PEA represents a mechanical failure despite the presence of electrical signals. The electrical impulses are not translating into a strong enough muscle contraction to generate a blood pressure or a palpable pulse, which is why the patient is considered to be in full cardiac arrest.
The Role of Defibrillation
Defibrillation is a procedure that delivers a controlled electrical shock across the chest to the heart muscle. The purpose of this shock is to momentarily depolarize, or “reset,” a large portion of the heart’s cells simultaneously. This action is intended to interrupt chaotic, disorganized rhythms, such as Ventricular Fibrillation (V-Fib) or Pulseless Ventricular Tachycardia (pulseless V-Tach).
The goal of a shock is to extinguish the multiple, uncoordinated electrical wavelets that are preventing the heart from pumping effectively. By briefly rendering the heart muscle unexcitable, the hope is that the heart’s natural pacemaker will take over and re-establish a coordinated, effective rhythm. Since PEA is already an organized, though ineffective, electrical rhythm, shocking it serves no therapeutic purpose.
Delivering an electrical current to a heart that already has an organized rhythm will not restore mechanical function, which is the root of the problem in PEA. Therefore, PEA is categorized as a “non-shockable” rhythm in all emergency cardiac protocols. The electrical issue that defibrillation fixes is not present in PEA.
Treatment Strategy for PEA
The management of PEA focuses on two main pillars: continuous, high-quality Cardiopulmonary Resuscitation (CPR) and the immediate search for and reversal of the underlying cause. Chest compressions must be initiated immediately to maintain some blood flow to the brain and heart until the cause of the arrest can be identified. Simultaneously, medications like epinephrine (adrenaline) are administered to stimulate the heart and improve blood pressure through its vasoconstrictive effects.
The central strategy of treating PEA is correcting the physiological problem that caused the mechanical failure in the first place. Medical teams use a mnemonic device known as the “H’s and T’s” to quickly consider the common, potentially reversible causes of PEA.
Reversible Causes (H’s and T’s)
- Hypovolemia (low blood volume)
- Hypoxia (low oxygen)
- Hydrogen ion excess (acidosis)
- Hypo/Hyperkalemia (potassium imbalance)
- Hypothermia (low body temperature)
- Tension pneumothorax (collapsed lung with pressure)
- Tamponade (fluid around the heart)
- Toxins (poisoning or overdose)
- Thrombosis (pulmonary or coronary blood clot)
Correcting these issues is the only way to restore the heart’s ability to pump effectively. For instance, fluid administration reverses hypovolemia, while a needle decompression can relieve a tension pneumothorax. Without identifying and treating a reversible cause, the outcome for a patient in PEA is poor.