Pulseless electrical activity (PEA) is a specific form of cardiac arrest where the heart ceases to pump blood effectively, leading to a loss of circulation. In cardiac arrest, the heart stops its function, but PEA presents a unique and deceptive challenge because the heart’s electrical system remains active. This condition is a medical emergency that requires immediate intervention, as the lack of a palpable pulse means blood is not reaching the brain or other organs. Understanding PEA is paramount because its management differs significantly from other types of cardiac arrest.
Defining Pulseless Electrical Activity
PEA is a physiological paradox where the electrical activity of the heart is present, but the mechanical action of pumping blood is absent. When a patient is monitored, the electrocardiogram (ECG) displays an organized electrical rhythm, which can look deceptively normal or near-normal. This organized electrical rhythm is not strong enough to produce the necessary contraction force, resulting in no detectable pulse or effective blood circulation throughout the body.
This phenomenon is sometimes referred to as electromechanical dissociation, highlighting the uncoupling of the heart’s electrical and mechanical functions. PEA stands in contrast to ventricular fibrillation (V-Fib), where the electrical signals are chaotic and disorganized, or asystole, commonly known as a “flatline,” which shows no electrical activity whatsoever. In some cases, a very weak contraction is present, but it is insufficient to generate a palpable pulse, a state sometimes called “pseudo-PEA”.
Understanding the Reversible Causes
The primary focus in managing PEA is identifying and reversing the underlying cause responsible for the failure of the heart’s mechanical pump despite the electrical trigger. These causes are often categorized using the mnemonic “H’s and T’s,” representing the most common, treatable conditions that lead to this state.
The “H’s” (Fluid, Chemical, and Oxygen Imbalances)
- Hypovolemia (severe volume loss, typically from internal or external bleeding or dehydration).
- Hypoxia (lack of adequate oxygen, often resulting from respiratory failure).
- Hydrogen ion acidosis (profound changes in the body’s acid-base balance).
- Hyper- or hypokalemia (abnormal levels of potassium).
- Hypothermia (core body temperature that is too low).
The “T’s” (Mechanical Obstructions)
Mechanical obstructions physically impede the heart’s function, preventing it from filling with blood or ejecting it effectively. These underlying problems deplete the energy stores needed for muscle fiber shortening, leading to the cardiac arrest.
- Tension pneumothorax (air buildup in the chest cavity compressing the heart and major blood vessels).
- Cardiac tamponade (fluid or blood accumulation around the heart, preventing it from fully expanding).
- Thrombosis (large blood clots in the lungs, pulmonary embolism, or the coronary arteries, myocardial infarction).
Treatment Focus: Addressing the Underlying Problem
Because PEA is not a problem of electrical disorganization, a defibrillator is ineffective and will not restart the heart. The immediate action is high-quality cardiopulmonary resuscitation (CPR), which manually circulates blood to the brain and heart while the medical team searches for the cause. Effective CPR involves chest compressions at a rate of 100 to 120 per minute, minimizing interruptions to maintain the critical flow of blood.
Medications are also administered to help support the heart during the process of diagnosis and reversal. Epinephrine, a potent vasoconstrictor, is given in one-milligram doses intravenously every three to five minutes throughout the resuscitation attempt. This drug primarily works by increasing the pressure in the arteries, which helps drive blood flow to the heart muscle itself and the brain. Simultaneously, the medical team must take specific actions to correct the presumed underlying issue, such as providing intravenous fluids for hypovolemia or performing a procedure to relieve pressure from a tension pneumothorax or cardiac tamponade.
Expected Outcome and Survival Rates
PEA generally carries a more guarded prognosis compared to shockable rhythms like ventricular fibrillation, mainly because it signifies a profound underlying physiological collapse. For out-of-hospital cardiac arrests, the survival rate to hospital discharge for PEA is significantly lower, often reported to be in the low single digits, compared to shockable rhythms.
The chance of survival hinges almost entirely on the speed and accuracy with which the reversible cause is identified and treated. If the cause is quickly corrected, such as relieving a tension pneumothorax, the patient has a much better chance of survival. However, PEA caused by widespread issues like massive thrombosis or prolonged oxygen deprivation has a significantly worse outcome. The prompt reversal of the underlying problem remains the most important determinant.