ECG criteria
- The monitor shows organized ventricular electrical activity with discernible QRS complexes (not an isoelectric line, not chaotic VF oscillations, and not VT/VF morphology)
- Palpation of major arteries (carotid, femoral) reveals no pulse
- Clinical signs of circulatory arrest: unresponsiveness, apnea, or agonal gasps only
- The rhythm can be sinus, junctional, atrial, or idioventricular—any organized ventricular rhythm
- QRS width has limited prognostic value and may only guide the search for the etiology; it is not a diagnostic criterion for PEA itself or any specific underlying cause
- The heart rate on the monitor can be normal or even high—this does not rule out PEA
- POCUS sometimes reveals cardiac contractions in the absence of a palpable pulse, referred to as pseudo-PEA; the absence of visible contractions indicates PEA with no detectable mechanical activity. POCUS findings should not delay CPR and do not serve as the sole basis for terminating resuscitation
What it looks like on ECG
PEA is not a morphological ECG pattern, but rather a clinical and electrocardiographic combination: organized (non-chaotic) ventricular electrical activity on the monitor accompanied by the clinical presentation of cardiac arrest (no pulse, unresponsiveness, no effective breathing). The underlying ECG rhythm can be of any type:
| Rhythm variant | What is seen on the ECG |
|---|---|
| Sinus electrical activity | P waves followed by organized QRS complexes; intervals and morphology may be normal or pathologically altered |
| Junctional or idioventricular rhythm | Absent P waves or AV dissociation, narrow/wide QRS |
| Pronounced sinus bradycardia | Infrequent complexes, wide or narrow QRS |
| Wide QRS rhythm | Resembles slow VT or bundle branch block, frequently seen in hyperkalemia, acidosis, and poisonings |
Key point for interpretation: before designating a rhythm as "PEA", it is necessary to rule out asystole and ventricular standstill (an isoelectric line on the screen, or only P waves visible without QRS complexes—atrial electrical activity is preserved, but detectable ventricular depolarization is absent; technical errors must be excluded), as well as VF/VT (chaotic oscillations without discernible complexes or monomorphic/polymorphic ventricular tachycardia). If ventricular QRS complexes are discernible and organized, yet there is no pulse, it is PEA. Always rule out technical errors (disconnected lead, artifact) and verify the rhythm across multiple leads.
QRS width can serve as a guide in searching for the etiology, but it is not a reliable diagnostic sign: a narrow QRS is somewhat more common in mechanical impediments to cardiac filling or outflow (cardiac tamponade, tension pneumothorax, massive PE, severe hypovolemia), whereas a wide QRS occurs in primary myocardial injury or depression (severe myocardial infarction, hyperkalemia, severe acidosis, sodium channel blocker overdose). However, a narrow QRS can also occur in metabolic etiologies, and a wide QRS in mechanical obstruction and ischemia; therefore, the search for reversible causes (5Hs/5Ts) must be conducted regardless of the complex width.
Mechanism
Myocardial electrical activity (depolarization) is preserved but fails to translate into an effective mechanical contraction sufficient to generate a palpable pulse and cardiac output. The dissociation between electrical and mechanical events can occur at several levels: myocardial contraction itself is too weak (severe ischemia, acidosis, hypoxia, cardiodepressant overdose), the heart is unable to fill with blood (tamponade or tension pneumothorax externally compress the chambers, severe hypovolemia prevents adequate filling), or effective output is sharply reduced due to vascular bed obstruction (massive PE causes acute pulmonary vascular bed obstruction and a dramatic increase in right ventricular afterload, leading to acute right heart failure, decreased pulmonary blood flow, and reduced left ventricular preload). The term "electromechanical dissociation" has historically been used as a synonym for PEA, emphasizing this uncoupling between the electrical impulse and mechanical response rather than denoting a separate opposing category.
Causes
Traditionally remembered as the "5Hs and 5Ts" (reversible causes):
- Hypovolemia (massive blood loss, dehydration)
- Hypoxia
- Hydrogen ions (acidosis)
- Hypo-/hyperkalemia and other electrolyte imbalances
- Hypothermia
- Pericardial tamponade
- Tension pneumothorax
- Toxins (drug overdose: tricyclic antidepressants, calcium channel blockers, beta-blockers, digoxin)
- Coronary thrombosis / acute coronary syndrome
- Thrombosis of the pulmonary artery — pulmonary embolism (PE), especially high-risk
Cardiogenic shock as the final progression mechanism of any severe condition (primarily myocardial infarction) can lead to cardiac arrest via a PEA mechanism, but it is not a standalone etiological cause on par with the 5Hs/5Ts.
Additionally: severe sepsis, anaphylaxis, ventricular wall/aortic aneurysm rupture.
Differential diagnosis
Asystole and ventricular standstill — an isoelectric line on the monitor, or only P waves visible without ventricular QRS complexes: atrial electrical activity is preserved, but ventricular depolarization is absent (technical errors must be excluded and confirmed in multiple leads). This differs from PEA, where ventricular QRS complexes are present and organized. Pulseless ventricular fibrillation and ventricular tachycardia — chaotic oscillations (VF) or monomorphic/polymorphic wide complexes at a high rate (VT), require immediate defibrillation, unlike PEA, where defibrillation is not indicated. Severe hypotension with a preserved yet weak pulse is not cardiac arrest; the pulse is palpable, albeit weakly, and management differs. Monitor artifacts (disconnected lead, tremor) can mimic an organized or chaotic rhythm — verified clinically and via another lead/sensor.
Clinical significance and management
PEA is one of the four cardiac arrest rhythms (along with asystole, VF, and pulseless VT) and is classified as a "non-shockable" rhythm: defibrillation is not indicated. Physician action algorithm:
- Immediately initiate high-quality cardiopulmonary resuscitation (chest compressions with minimal interruptions, adequate ventilation)
- Establish venous or intraosseous access as soon as possible and administer epinephrine (per CPR algorithms for non-shockable rhythms — as early as possible, then repeated every 3–5 minutes); vascular access and drug administration must not delay chest compressions
- Actively search for and treat reversible causes using the "5Hs/5Ts" scheme — this dictates the prognosis; without addressing the underlying cause, resuscitation is likely to be ineffective
- If a trained operator is available, point-of-care cardiac ultrasound (POCUS) can be used to assess myocardial contractility, pericardial effusion, signs of right ventricular strain (suggestive of PE), and hypovolemia; the examination is performed with a pre-positioned probe during the scheduled brief pause for rhythm analysis (no more than 10 seconds) and must not delay chest compressions, defibrillation, or drug administration; POCUS findings do not replace clinical evaluation and do not serve as an independent basis for terminating CPR
- For non-traumatic tamponade — emergent pericardiocentesis according to protocol; in traumatic cardiac arrest — immediate surgical decompression/resuscitative thoracotomy within a specialized algorithm, as pericardiocentesis is not always effective in this setting; tension pneumothorax must be immediately decompressed via the preferred available method (needle decompression or chest tube placement based on setting and training), followed by chest tube insertion; for suspected PE — consider thrombolysis per resuscitation protocol; for hypovolemia — simultaneously control the bleeding source and administer blood/blood products, supplemented by balanced crystalloid solutions if necessary; for hyperkalemia — administer appropriate corrective therapy
- Continue CPR with rhythm reassessment every 2 minutes, transitioning to the appropriate algorithm step if VF/VT appears (defibrillation) or if signs of return of spontaneous circulation (ROSC) occur
Prognosis is largely determined by how rapidly the reversible cause is identified and treated.
Common interpretation errors
- Diagnosing PEA based solely on an ECG without clinical pulse assessment — PEA is a clinical and electrocardiographic concept, not a rhythm morphology
- Confusing PEA with slow idioventricular activity in a patient with a palpable pulse — this requires palpation/POCUS, not just a monitor screen
- Wasting time analyzing rhythm morphology at the expense of immediately starting chest compressions
- Attempting to defibrillate an organized rhythm without a pulse — this is not indicated; PEA is a non-shockable rhythm
- Failing to purposefully search for a reversible cause (4H/4T), limiting management to standard compressions and adrenaline alone, or relying too heavily on QRS width as an indicator of a specific cause
4H and 4T: Hypovolemia, Hypoxia, Hydrogen ions (acidosis), Hypo-/hyperkalemia, Hypothermia — Tamponade, Tension pneumothorax, Toxins, Thrombosis (coronary), Thromboembolism (pulmonary)
1. Which sign is mandatory for the diagnosis of PEA?
PEA is diagnosed clinically: organized electrical activity on the monitor with the absence of a palpable pulse; QRS width and rate are not diagnostic criteria.
2. Is defibrillation indicated in PEA?
PEA and asystole are non-shockable cardiac arrest rhythms; defibrillation is indicated only for VF and pulseless VT.
3. What distinguishes PEA from asystole/ventricular standstill when P waves are present without QRS complexes on the monitor?
Isolated P waves without QRS complexes indicate an absence of ventricular electrical activity and correspond to asystole/ventricular standstill rather than PEA, despite preserved atrial activity.
Frequently asked questions
How does PEA differ from asystole?
In asystole, the monitor shows either a flatline or only P waves without ventricular complexes (ventricular standstill) — there is no ventricular electrical activity. In PEA, organized ventricular electrical activity is visible with discernible QRS complexes, but no pulse is palpable. These are different cardiac arrest rhythms, although CPR management is similar.
Can you defibrillate in PEA?
No, PEA is a non-shockable cardiac arrest rhythm. Defibrillation is indicated only for ventricular fibrillation and pulseless ventricular tachycardia. In PEA, the mainstay of treatment is high-quality CPR, timely administration of adrenaline, and searching for a reversible cause.
Is PEA dangerous?
Yes, this is a form of cardiac arrest that is immediately life-threatening. The prognosis depends on the speed of initiating resuscitation and how quickly a reversible cause (tamponade, pneumothorax, PE, electrolyte abnormalities, etc.) is identified and resolved.
How to determine the cause of PEA from an ECG?
A definitive answer cannot be given from a single ECG. QRS width can provide some diagnostic direction: a narrow QRS is somewhat more common in mechanical causes (tamponade, tension pneumothorax, massive PE, severe hypovolemia), while a wide QRS points toward metabolic and toxic causes (hyperkalemia, acidosis, intoxications) or severe myocardial injury. However, this is not a strict rule; exceptions occur, and a clinical search using the 4H/4T mnemonic is mandatory regardless of QRS width.
What heart rate occurs in PEA?
Any — bradycardia, normal rate, or even tachycardia. The rate itself does not define the diagnosis of PEA; the decisive criterion is the absence of a pulse in the presence of an organized rhythm on the monitor.
ECG Course
Interpretation from basics to myocardial infarction — learn to read any ECG using a systematic algorithm.
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ECG Strip Simulator
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Related terms
More in the section "Ventricular Arrhythmias"
Sources
- Goldberger A. Clinical Electrocardiography: A Simplified Approach
- Hampton J. The ECG in Practice
- Clinical guidelines for cardiopulmonary resuscitation (ERC/AHA)
Educational material for medical students and physicians. Does not replace clinical guidelines and physical examination; the ECG must always be interpreted in conjunction with the clinical picture.