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What is Pulseless electrical activity and explain in detail?
Pulseless electrical activity (PEA) refers to cardiac arrest in which the electrocardiogram shows a heart rhythm that should produce a pulse, but does not. Pulseless electrical activity is found initially in about 55% of people in cardiac arrest.Under normal circumstances, electrical activation of muscle cells precedes mechanical contraction of the heart (known as electromechanical coupling). In PEA, there is electrical activity but insufficient cardiac output to generate a pulse and supply blood to the organs, whether the heart itself is failing to contract or otherwise. While PEA is classified as a form of cardiac arrest, significant cardiac output may still be present, which may be determined and best visualized by bedside ultrasound (echocardiography).
Cardiopulmonary resuscitation (CPR) is the first treatment for PEA, while potential underlying causes are identified and treated. The medication epinephrine (aka adrenaline) may be administered. Survival is about 20%.

Signs and symptoms
Pulseless electrical activity leads to a loss of cardiac output, and the blood supply to the brain is interrupted. As a result, PEA is usually noticed when a person loses consciousness and stops breathing spontaneously. This is confirmed by examining the airway for obstruction, observing the chest for respiratory movement, and feeling the pulse (usually at the carotid artery) for a period of 10 seconds.

Causes
These possible causes are remembered as the 6 Hs and the 6 Ts. See Hs and Ts

Hypovolemia
Hypoxia
Hydrogen ions (Acidosis)
Hyperkalemia or Hypokalemia
Hypoglycemia
Hypothermia
Tablets or Toxins
Cardiac Tamponade
Tension pneumothorax
Thrombosis (e.g., myocardial infarction, pulmonary embolism)
Tachycardia
Trauma (e.g., hypovolemia from blood loss)The possible mechanisms by which the above conditions can cause pulseless in PEA are the same as those recognized as producing circulatory shock states. These are (1) impairment of cardiac filling, (2) impaired pumping effectiveness of the heart, (3) circulatory obstruction and (4) pathological vasodilation causing loss of vascular resistance and excess capacitance. More than one mechanism may be involved in any given case.

Diagnosis
The absence of a pulse confirms a clinical diagnosis of cardiac arrest, but PEA can only be distinguished from other causes of cardiac arrest with a device capable of electrocardiography (ECG/EKG). In PEA, there is organised or semi-organised electrical activity in the heart as opposed to asystole (flatline) or to the disorganised  electrical activity of either ventricular fibrillation or ventricular tachycardia.

Treatment
Cardiac resuscitation guidelines (ACLS/BCLS) advise that cardiopulmonary resuscitation should be initiated promptly to maintain cardiac output until the PEA can be corrected