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Put any two — or three — conditions side by side, adult or pediatric, to spot the look-alike differences fast, row by row.

Cardiac Arrest Rhythms

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In one line

·When the heart stops, it shows up in one of four rhythms on the monitor—two you can shock, two you cannot.

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Normal physiology

·The heart is a four-chamber pump (two on top called atria, two on bottom called ventricles) that runs on electricity. A spark starts at the top in a tiny patch of cells called the SA node (the heart's natural pacemaker). The spark spreads across both atria so they squeeze and fill the ventricles. Then the spark travels down a wire (the AV node and His-Purkinje system) into the thick bottom chambers (ventricles), and they squeeze hard to shoot blood out—left ventricle to the body, right ventricle to the lungs. This cycle repeats sixty to one hundred times every minute, and each squeeze moves about two ounces of blood. For the pump to work, you need three things working together: an electrical spark in the right order, heart muscle strong enough to squeeze, and enough blood inside the heart to push out.

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What goes wrong

·Cardiac arrest means the heart stops doing its job—no organized beat, no blood flow. The four rhythms show different ways the heart can stop. In V-fib and V-tach the electrical system goes haywire; the spark fires so fast and chaotic that the muscle just quivers or beats uselessly. In PEA and asystole the heart is too sick, too empty, too crushed, or too poisoned to beat even if some electrical spark is still there (PEA) or the spark has died completely (asystole).

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Hallmark signs

·No pulse felt anywhere on the body
·No breathing or only gasping breaths (agonal breathing)
·Unresponsive to any stimulus
·Sudden collapse without warning
·Skin turns blue or gray (cyanosis), especially lips and fingertips
·Pupils become wide and do not shrink when light is shined into the eyes
·No normal heart sounds heard with a stethoscope, or very weak disorganized sounds
·Monitor shows ventricular fibrillation (VF): a wild, irregular, squiggly line with no clear beats

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Red flags · escalate now

·No pulse and no breathing—start CPR immediately and call for help; every second without blood flow kills brain cells
·Rhythm on monitor is ventricular fibrillation (VF) or pulseless ventricular a fast heart rate (tachycardia) (VT)—shock with a defibrillator as soon as possible to try to reset the heart
·Flat line (asystole) or PEA rhythm—look for and fix reversible causes fast (low oxygen, low blood volume, heart squeeze from fluid around it, blood clot in lung, heart attack, low potassium or high potassium, overdose, low body temperature, tension in chest from collapsed lung)
·Person collapsed suddenly in front of you—survival depends on immediate high-quality chest compressions and early defibrillation; do not wait for advanced help to start CPR

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Workup

·Arterial blood gas (ABG) during CPR
·Potassium (K⁺) level
·Glucose (blood sugar)
·Lactate level
·Troponin I or T
·Point-of-care ultrasound (POCUS) during CPR
·Core body temperature (rectal or esophageal probe)
·Toxicology screen or drug history

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Treatment

·Start high-quality CPR immediately: push hard and fast on the center of the chest at 100–120 compressions per minute, let the chest come all the way back up after each push, and minimize pauses
·Defibrillate (shock) immediately if the monitor shows VF or pulseless VT — use 120–200 joules biphasic or 360 joules monophasic, then resume CPR for 2 minutes before checking rhythm again
·Give epinephrine 1 mg IV or intraosseous (IO) every 3–5 minutes during the code
·Give amiodarone 300 mg IV or IO (first dose), then 150 mg IV if VF or pulseless VT continues after 2–3 shocks
·Secure the airway with an endotracheal tube (ETT) or supraglottic airway (like an i-gel or King LT), then give breaths at 10 per minute with 100% oxygen while continuing compressions without pausing
·Find and fix the Hs: Hypovolemia (low blood volume — give IV fluids or blood), Low oxygen (Hypoxia) (low oxygen — intubate and give 100% O₂), Hydrogen ion (acidosis — give sodium bicarbonate if pH < 7.1), Hypo/High potassium (Hyperkalemia) (give calcium, insulin + glucose, or potassium), Hypothermia (warm the person to at least 32°C), Low blood sugar (Hypoglycemia) (give D50 IV)
·Find and fix the Ts: Tension pneumothorax (collapsed lung — needle decompression or chest tube), Tamponade (fluid around heart — pericardiocentesis), Toxins (drugs or poisons — give antidotes like naloxone, calcium, sodium bicarbonate, or lipid emulsion), Clot formation (Thrombosis) coronary (heart attack — emergency cardiac cath and stent), Clot formation pulmonary (blood clot in lungs — give tPA 50 mg IV during CPR if confirmed)
·After the heart restarts (return of spontaneous circulation, ROSC), cool the body to 32–36°C for 24 hours (targeted temperature management, also called therapeutic hypothermia)

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NCLEX trap

·Asystole is NOT shockable. The shock paddle only works on two rhythms: VF (ventricular fibrillation – the heart quivers like jelly instead of pumping) and pulseless VT (ventricular a fast heart rate (tachycardia) – the heart beats so fast it cannot fill with blood). For asystole, start CPR immediately and hunt for the six Hs and five Ts (reasons the heart stopped, like low oxygen, too little blood, wrong potassium level, or a blood clot in the lung). Fixing one of those problems is what can restart the heart.
·PEA is a trick rhythm. The monitor shows electrical activity, but when you feel for a pulse there is none – the heart muscle is not squeezing hard enough to push blood. This is cardiac arrest. Start CPR right away and search for the Hs and Ts, because one of them is blocking the heart from pumping even though the electricity is firing.
·Never shock asystole – it does not help and wastes time. While your team does CPR, immediately start hunting for the Hs and Ts: low oxygen (Hypoxia), low blood volume (Hypovolemia), too much or too little potassium (Hydrogen ion/too much acid in the blood (acidosis) or high potassium (hyperkalemia)/low potassium (hypokalemia)), body too cold (Hypothermia), low blood sugar (Hypoglycemia), fluid squeezing the heart (Tamponade), air trapped in the chest (Tension pneumothorax), poison (Toxins), blood clot in the lung (Thrombosis – pulmonary), or clot in a heart artery (Thrombosis – coronary). Fixing the root cause is the only way to restart the heart in asystole.
·VF and pulseless VT are the only two shockable rhythms. Shock FIRST – as fast as possible, ideally within seconds. After the shock, start CPR immediately. Give epinephrine 1 mg IV after 2 minutes of CPR (or after the second shock cycle), then repeat every 3 to 5 minutes. The shock is the single most important treatment in the first moments of VF – drugs come second.
·Getting the pulse back (called ROSC – return of spontaneous circulation) is only step one. The heart may still be weak and barely pumping, the brain may be swelling from lack of oxygen, and the original problem (like a blocked heart artery or a blood clot in the lung) is often still there. Immediately cool the body to 32–36°C (89.6–96.8°F) to protect the brain, get a 12-lead EKG to look for a heart attack, send blood tests (potassium, oxygen, glucose, lactate), and if the EKG shows a heart attack, take the person to the cardiac catheterization lab (cath lab) right away to open the blocked artery. Stay vigilant – the first hour after ROSC is critical.
·Never give up early. VF and pulseless VT often convert to a normal rhythm with early shock and good CPR. Asystole and PEA can improve if you find and fix the Hs and Ts. Keep high-quality CPR going (push hard and fast – at least 2 inches deep, 100 to 120 compressions per minute, allow full chest recoil, minimize interruptions). Some people survive and go home with full brain function, especially if the arrest happened in the hospital or someone started CPR immediately. Follow your hospital's protocol and current ACLS guidelines – many patients have walked out of the hospital after cardiac arrest.

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