Pulseless Electrical Activity (PEA) is a specific classification of cardiac arrest where the heart ceases to pump blood effectively, leading to a sudden loss of function, breathing, and consciousness. PEA is one of the four main rhythms found during cardiac arrest. It is defined by a profound failure of the heart’s mechanical function despite the presence of measurable electrical activity. This means that while a heart monitor may display an organized rhythm, the patient will have no detectable pulse or blood pressure.
Defining Pulseless Electrical Activity
Pulseless Electrical Activity is fundamentally a state of electrical-mechanical dissociation, meaning the heart’s electrical system and its pumping mechanism are uncoupled. The heart muscle receives the electrical signal that tells it to contract, which is visible on an electrocardiogram (ECG) monitor. However, the muscle fibers fail to generate enough force to squeeze the ventricles and push blood out into the body’s circulation.
This failure of mechanical contraction can result from various underlying problems that prevent the muscle cells from responding to the electrical impulse. The electrical circuit is complete, but the mechanical action is absent or too weak to be effective.
The absence of a palpable pulse is the defining clinical feature of PEA, regardless of the tracing shown on the cardiac monitor. In a phenomenon sometimes called “pseudo-PEA,” the heart may be contracting, but the contractions are so weak that they cannot generate a blood pressure sufficient to be felt. In either true or pseudo-PEA, the result is a catastrophic failure of blood flow to the brain and other vital organs.
How PEA Differs from Other Cardiac Arrest Rhythms
PEA is categorized as a non-shockable cardiac rhythm, which differentiates it from the shockable rhythms of ventricular fibrillation (V-fib) and pulseless ventricular tachycardia (pVT). V-fib and pVT involve chaotic or extremely rapid electrical signals that prevent the heart muscle from coordinating a proper beat. In these cases, defibrillation can effectively reset the heart’s electrical system, allowing a normal rhythm to resume.
In contrast, PEA already displays an organized, or at least semi-organized, electrical pattern on the monitor. Because the problem is not a lack of electrical order but a failure of mechanical response, defibrillation is an ineffective treatment. Applying an electric shock would not solve the core issue of the heart muscle’s inability to contract.
PEA is also distinct from asystole, often referred to as a “flatline,” which represents a complete absence of all electrical activity in the heart. While both PEA and asystole are non-shockable rhythms, PEA holds a slightly better prognosis. The presence of electrical activity suggests the heart may be closer to recovery if the underlying mechanical failure can be reversed quickly.
The Critical Underlying Causes of PEA
PEA is rarely a primary electrical disorder of the heart itself; instead, it is almost always a result of a severe, underlying systemic problem. Identifying and correcting this root cause is the immediate focus of medical intervention, as PEA is reversible if the cause is treated in time. These causes are commonly grouped into a mnemonic device known as the “H’s and T’s.”
H’s (Systemic Conditions)
The “H’s” include conditions like Hypovolemia (severe loss of blood or bodily fluids, resulting in a heart that lacks enough volume to pump) and Hypoxia (a profound lack of oxygen, which quickly starves the heart muscle and prevents effective contraction). Hydrogen ion excess, or acidosis, describes a state of high acidity in the blood that impairs the heart muscle’s function.
Electrolyte imbalances, specifically Hypo- or Hyperkalemia (low or high potassium), interfere with the electrical stability needed for contraction. Hypothermia, or a dangerously low body temperature, also slows and weakens the heart muscle significantly.
T’s (Mechanical Issues and Toxins)
The “T’s” cover mechanical issues, such as Tamponade, where fluid builds up around the heart, physically squeezing it and preventing it from filling with blood. Tension pneumothorax involves air leaking into the chest cavity and compressing the lung and heart, impeding blood return.
Thrombosis refers to a blockage, such as a massive pulmonary embolism (clot in the lung arteries) or a widespread coronary artery clot (heart attack), which stops blood flow to or from the heart. Finally, Toxins, including certain drug overdoses, can directly suppress the heart muscle’s ability to contract.
Immediate Medical Response to PEA
The initial immediate medical response to PEA is high-quality cardiopulmonary resuscitation (CPR) to manually circulate blood and oxygen to the vital organs. While CPR is performed, emergency medical teams administer the medication epinephrine, also known as adrenaline, typically one milligram every three to five minutes. Epinephrine helps to increase blood flow to the heart and brain and can help the heart regain a rhythm with an effective pulse.
Since PEA is a non-shockable rhythm, the primary goal shifts away from defibrillation and towards rapidly diagnosing the underlying cause. Medical personnel use various diagnostic tools during the resuscitation effort to pinpoint the reversible “H’s and T’s.” This can involve a quick physical assessment for signs of trauma or fluid loss, as well as point-of-care ultrasound (POCUS) to visualize the heart.
Ultrasound can quickly reveal if the heart is being compressed by fluid (tamponade) or if it is nearly empty due to severe blood loss (hypovolemia). Treating the identified cause becomes the priority, which may involve administering intravenous fluids for hypovolemia, relieving a tension pneumothorax with a needle, or giving specific antidotes for a toxin. This focused, simultaneous treatment of the systemic problem and support of the circulation offers the best chance of reversing PEA and achieving a return of spontaneous circulation.