Pulseless Electrical Activity in Cardiac Arrest

Pulseless electrical activity, or PEA, is a form of cardiac arrest in which the heart’s electrical system continues producing organized signals on a monitor, but those signals fail to generate a pulse you can feel. Unlike ventricular fibrillation, where the heart quivers chaotically and can be shocked back into rhythm, PEA cannot be treated with a defibrillator. That distinction makes it one of the more challenging emergencies in medicine, because the treatment depends almost entirely on figuring out why the heart stopped pumping and fixing that specific problem. Roughly a quarter of out-of-hospital cardiac arrests present with PEA as the initial rhythm, and while survival has historically been poor, the numbers have improved over the past two decades as recognition and cause-directed treatment have gotten better.

Not All PEA Is the Same

One of the most clinically meaningful distinctions in PEA is between “true” PEA and “pseudo-PEA.” In true PEA, the heart’s electrical activity carries on but the muscle itself is essentially motionless. In pseudo-PEA, the heart is actually contracting, just too weakly to produce a palpable pulse. Pseudo-PEA patients still have some residual cardiac motion and may even have very low blood pressures that standard pulse checks miss. This matters because pseudo-PEA tends to respond much better to treatment. A pilot study found that thoracic impedance waveforms recorded by defibrillator pads showed fluctuations only in pseudo-PEA patients, hinting at a future tool to tell the two apart in real time without needing an ultrasound probe.¹

Bedside ultrasound is currently the most practical way to separate the two. When a rescuer places an ultrasound probe on the chest during a resuscitation pause, they can see whether the heart is moving at all. A meta-analysis pooling data from over 1,200 patients found that cardiac activity seen on point-of-care ultrasound had a pooled sensitivity of about 86% and specificity of about 64% for predicting return of spontaneous circulation.² In plain terms, if the ultrasound shows a beating heart, there is a reasonable chance the patient can be brought back. If the heart is completely still, the outlook is considerably darker. Ultrasound can also reveal some of the treatable causes of PEA in the first place, such as fluid around the heart or a collapsed lung.

Why the Heart Keeps Firing but Stops Pumping

PEA is not a disease. It is the final common pathway of many different emergencies, all of which either starve the heart of what it needs or physically prevent it from filling and ejecting blood. Emergency medicine uses the classic mnemonic of “Hs and Ts” to organize the search for a reversible cause. The Hs include hypovolemia (severe blood loss or dehydration), hypoxia (lack of oxygen), hydrogen ion excess (severe acidosis), hypo- or hyperkalemia (dangerously low or high potassium), and hypothermia. The Ts include tension pneumothorax, cardiac tamponade, toxins, and thrombosis in the coronary arteries or pulmonary vessels.

Some of these causes come up more often than others. Pulmonary embolism, a large blood clot blocking the lung’s arteries, is strikingly common in unexplained PEA arrests. One study of patients who arrested with PEA as the initial rhythm found that about a third had pulmonary emboli, compared with none of the patients whose arrests presented with other rhythms like asystole or ventricular fibrillation.³ That finding alone has influenced how aggressively clinicians consider clot-busting drugs during PEA arrests when no other cause is obvious.⁴

Tension pneumothorax is another reversible cause that can kill quickly if missed. Air leaks into the space around the lung and progressively compresses the heart and great vessels, strangling blood return. In an animal model, PEA arrest was induced once intrapleural pressure reached about 20 mmHg, reinforcing how rapidly cardiovascular collapse can occur once the pressure tips past a critical threshold.⁵ The treatment is immediate decompression with a needle or chest tube, which can reverse the arrest within seconds.

Cardiac tamponade, where fluid or blood fills the sac around the heart and prevents it from expanding, is a similarly dramatic cause. A case report described a 14-year-old girl who arrested outside a hospital with PEA; an emergency physician’s bedside ultrasound revealed a massive pericardial effusion causing tamponade, and draining the fluid restored circulation.⁶ Severe hyperkalemia, often seen in kidney failure or medication effects, can also widen the heart’s electrical complexes until effective pumping ceases entirely. One case documented a patient with a potassium level of 8 mmol/L who progressed to PEA arrest despite aggressive treatment.⁷

Hypoxia from suffocation or airway obstruction is among the oldest recognized triggers. In animal studies of asphyxiation-induced PEA, a characteristic sequence unfolds: the heart rate initially speeds up, blood pressure rises, then the heart slows dramatically and blood pressure plummets as oxygen runs out and carbon dioxide skyrockets.⁸ Understanding this sequence helps explain why securing the airway and delivering oxygen is a priority during any PEA resuscitation.

Drug-Related Risk Factors

Certain medications appear to tilt the odds toward PEA rather than other arrest rhythms. The Oregon Sudden Unexpected Death Study compared over 300 PEA cases to more than 500 cases of ventricular fibrillation and found that patients taking antipsychotic drugs were roughly two and a half times more likely to arrest with PEA than with a shockable rhythm, even after adjusting for age, sex, and other health conditions. PEA cases in that study also tended to be older and were more frequently women.⁹ The mechanism likely involves these drugs’ effects on the heart’s ion channels, which can disrupt the coupling between electrical signals and mechanical contraction without necessarily triggering the chaotic fibrillation that defibrillators are designed to fix.

Using End-Tidal CO₂ to Guide Resuscitation

During CPR, one of the most useful real-time measurements is end-tidal carbon dioxide, or ETCO₂, the concentration of carbon dioxide in exhaled breath. Because CO₂ production depends on blood flow through the lungs, a rising ETCO₂ during chest compressions suggests that circulation is improving. In PEA arrests specifically, one study found a positive linear relationship between rising ETCO₂ and the likelihood of regaining a pulse, with increases above 20 mmHg being highly specific for return of spontaneous circulation.¹⁰ The practical takeaway for rescuers is straightforward: if ETCO₂ is trending upward, keep going, because the resuscitation may be working even if a pulse is not yet palpable.

ETCO₂ also helps during pulse-check pauses. When compressions stop briefly, ETCO₂ drops rapidly if there is no spontaneous heartbeat, but stays elevated or rises if the heart has restarted on its own.¹¹ This reduces the need for prolonged pauses to check pulses, which themselves interrupt chest compressions and lower the chances of survival.

The Race to Give Epinephrine

Because PEA cannot be defibrillated, the pharmacologic cornerstone of its treatment is epinephrine (adrenaline). Epinephrine constricts blood vessels and redirects blood toward the heart and brain, and the speed with which it is administered turns out to matter considerably. A large study of in-hospital cardiac arrests with nonshockable rhythms found a stepwise decrease in survival for every minute of delay: about 12% of patients survived when epinephrine was given in the first minute, compared with roughly 7% when it was given at seven minutes or later.¹²

A similar pattern holds outside the hospital. An analysis of out-of-hospital cardiac arrests found that each minute from paramedic arrival to epinephrine administration was associated with roughly a 4% decrease in the odds of survival for adults. When epinephrine was given late compared with early, the odds of survival were about 18% lower overall.¹³ The message is consistent across settings: delays cost lives.

Beyond the timing, research on the dynamic effects of epinephrine during PEA arrests showed that the drug markedly increased the rate of transition from PEA to return of spontaneous circulation and slowed the rate of being declared dead. By 20 minutes, about a quarter of patients who received epinephrine had regained a pulse, versus about 15% of those who did not.¹⁴ These are still sobering numbers, but the drug clearly shifts the trajectory in the right direction, buying time for rescuers to identify and treat the underlying cause.

How Common Is PEA, and Are Outcomes Improving?

PEA accounts for a substantial share of cardiac arrests. A 16-year prospective study of sudden cardiac arrests in a large U.S. community found that about 24% presented with PEA as the initial rhythm, compared with roughly 41% with ventricular fibrillation and 35% with asystole. While ventricular fibrillation cases declined over the study period, PEA incidence remained relatively stable.¹⁵

The encouraging trend in that same study was survival. For PEA arrests, survival roughly doubled over the 16 years, climbing from about 6% in the earliest period to nearly 14% in the most recent. Ventricular fibrillation survival also improved, from about 28% to 37%. Asystole survival, by contrast, barely budged and remained under 5%.¹⁶ The gains in PEA survival likely reflect better public awareness, faster emergency response, wider use of bedside ultrasound to find fixable causes, and the emphasis on early epinephrine described above.

An important nuance buried in these numbers is that the electrical rate during PEA matters. One study found that patients whose PEA rhythm was faster than 60 beats per minute had a 30-day survival rate of about 22% and good neurological outcomes in about 15% of cases, rates comparable to patients who arrest with shockable rhythms.¹⁷ A faster electrical rate often indicates that the heart still has some contractile reserve and may be closer to pseudo-PEA. Slow PEA, below 40 beats per minute, carries a much bleaker prognosis and is more likely to represent a dying heart with little mechanical function left.

Long-Term Quality of Life After PEA Arrest

The fear with any cardiac arrest is that even if a patient survives, brain damage from the period without blood flow may leave them severely impaired. For PEA specifically, the data on long-term outcomes is limited but offers some cautious hope. An observational study tracking patients who survived out-of-hospital PEA arrests found that five of seven patients who were alive one year after resuscitation had returned to the same functional level they had before their arrest.¹⁸ The sample is small, but it pushes back against the assumption that PEA survivors are inevitably left with devastating neurological deficits. The key variable seems to be how quickly the underlying cause was reversed and effective circulation restored.

Extracorporeal CPR for Refractory Cases

When standard resuscitation fails, some centers can place patients on extracorporeal membrane oxygenation (ECMO), a machine that takes over the heart’s pumping and the lungs’ gas exchange function. This approach, called extracorporeal CPR or ECPR, is resource-intensive and only available at specialized hospitals, but the results in PEA can be surprisingly encouraging compared with other nonshockable rhythms. One study reported a survival-to-discharge rate of about 24% in patients whose PEA was the initial rhythm at the time ECPR was initiated, while no patients presenting with asystole survived to leave the hospital.¹⁹

A Japanese center developed a novel strategy using a hybrid emergency room equipped with a CT scanner to rapidly diagnose the cause of PEA arrest before committing to ECMO. Of 12 PEA patients evaluated, nine were found by CT to have non-survivable causes like intracranial hemorrhage or aortic rupture, allowing the team to avoid futile ECMO. The remaining three underwent ECPR, and two survived with good neurological outcomes.²⁰ This kind of selective approach illustrates where PEA management is headed: rapid identification of the cause, then matching the intervention to what is actually fixable.

PEA in Children

Pediatric cardiac arrest is mercifully rare, but when it happens, PEA and asystole are far more common initial rhythms than the shockable rhythms that predominate in adult cardiac emergencies. A large registry study of over 9,400 pediatric patients found that about 58% initially presented with PEA and 43% with asystole. Children who arrested in PEA had better odds of regaining a pulse and surviving to hospital admission than those in asystole.²¹

An interesting wrinkle emerged in the age-stratified analysis: the overall survival advantage of PEA over asystole was driven primarily by neonates. In older children, survival to hospital discharge did not differ between the two rhythms once neonatal intensive care patients were excluded.²² This challenges the common convention of lumping PEA and asystole together as “nonshockable rhythms” and treating them as equally grim. At least in neonates, PEA carries a distinctly better prognosis, possibly because the causes in that age group, such as respiratory failure, are more amenable to rapid reversal.

When Paramedics Decide to Stop

One of the hardest decisions in prehospital medicine is when to stop resuscitating a PEA arrest that is not responding. Unlike a shockable rhythm, where each defibrillation attempt gives a concrete yes-or-no signal, PEA can persist unchanged on the monitor for a long time, leaving rescuers in a gray zone. A mixed-methods study of senior paramedics in the field found that their decisions to cease resuscitation were guided by a blend of clinical judgment and contextual factors. They weighed the patient’s pre-existing health, frailty, and age alongside how long the resuscitation had been running and whether any of the known reversible causes could still be addressed.²³

These paramedics described assessing patients as “non-survivable” when continued CPR was considered harmful with no realistic prospect of benefit. The study highlighted how much judgment is involved and how protocols alone do not capture the complexity. A frail 90-year-old with slow PEA and no identifiable reversible cause is a fundamentally different situation from a 40-year-old who arrested after a known drug overdose, even though both display the same rhythm on the monitor. The growing emphasis on point-of-care ultrasound and ETCO₂ monitoring has given these field clinicians better tools for making the call, but the decision remains one of the most ethically charged moments in emergency medicine.

Experimental Therapies on the Horizon

Standard PEA resuscitation has not changed dramatically in its basic framework for years: CPR, epinephrine, find and fix the cause. But researchers are exploring whether pharmacologic agents beyond epinephrine might improve neurological outcomes, which remain poor even when a pulse is restored. One animal study tested a novel peptide administered during PEA resuscitation and found that while return of spontaneous circulation did not differ significantly between groups, fully intact neurological survival was dramatically better in the treatment group. In that study, none of the 12 control animals had intact neurological function at 24 hours, compared with 11 out of 12 in the peptide group.²⁴ This is early-stage work in animals, not humans, and a single study with 24 subjects. But the gap in neurological outcomes was large enough to suggest that protecting the brain during PEA resuscitation, rather than just restarting the heart, is a research avenue worth watching.