AHA ACLS Algorithms Quick Reference (Cardiac Arrest, Bradycardia, Tachycardia, Post-ROSC)

ACLS providers do not pass the megacode by memorizing the algorithm charts. They pass by knowing the decision points cold. Which branch of the cardiac arrest algorithm am I on right now, shockable or non-shockable. Is this bradycardia stable or unstable. Is this tachycardia regular or irregular, wide or narrow, stable or unstable. The drugs and doses are the easy part. The branches are where the megacode goes sideways.

The American Heart Association updates the ACLS algorithms on a roughly five-year cycle, with focused updates between major releases. The four algorithms tested on every ACLS course remain consistent in structure across editions. Adult Cardiac Arrest. Adult Bradycardia With A Pulse. Adult Tachycardia With A Pulse. Post-Cardiac Arrest Care. This guide walks each one, calls out the decision points, and lists the drug doses from the current AHA Guidelines. Verify against the most recent provider manual before clinical use. Algorithms change. The structure of this post will not change with them.

The cardiac arrest algorithm starts with the BLS sequence. CPR, attach monitor, get a rhythm. Everything that follows branches off the rhythm assessment at the two-minute interval.

Shockable rhythms. Ventricular fibrillation and pulseless ventricular tachycardia. The path is shock, CPR for 2 minutes, rhythm check, shock if still in VF/pVT, CPR, epinephrine 1 mg IV/IO every 3 to 5 minutes starting after the second shock, rhythm check, shock if indicated, CPR, amiodarone 300 mg IV/IO bolus as the first antiarrhythmic dose for refractory VF/pVT, rhythm check, shock, CPR, second dose amiodarone 150 mg IV/IO if still refractory. Lidocaine is an alternative antiarrhythmic where amiodarone is unavailable, at 1 to 1.5 mg/kg first dose and 0.5 to 0.75 mg/kg second dose.

Defibrillation energy. Biphasic at the manufacturer-recommended dose, commonly 120 to 200 joules for the first shock and equivalent or higher for subsequent shocks. Monophasic is 360 joules. Minimize the pause around the shock. Resume compressions immediately, do not stop for a pulse check after the shock.

Non-shockable rhythms. Pulseless electrical activity and asystole. The path is CPR for 2 minutes, epinephrine 1 mg IV/IO as soon as feasible, CPR, rhythm check, CPR, epinephrine every 3 to 5 minutes, continue. There is no defibrillation in PEA or asystole. Confirm asystole in a second lead before calling it. A flat line in one lead with QRS complexes in another is a lead problem, not a rhythm.

Reversible causes, the Hs and Ts. Throughout the arrest you and your team are running through the reversible causes. Hypovolemia, Hypoxia, Hydrogen ion or acidosis, Hypo or hyperkalemia, Hypothermia. Tension pneumothorax, Tamponade cardiac, Toxins, Thrombosis pulmonary, Thrombosis coronary. The patient who is going to survive a cardiac arrest with a reversible cause survives because somebody identified the cause and treated it during the arrest, not after ROSC.

Airway management. High-quality compressions and defibrillation come first. Advanced airway placement should not interrupt compressions. Bag-valve-mask with a good two-person seal is acceptable. Once an advanced airway is in place, switch from cycles to continuous compressions at 100 to 120 per minute with ventilations at 1 every 6 seconds, 10 per minute.

End-tidal CO2. Capnography is your real-time feedback on CPR quality and your earliest indicator of ROSC. A sustained increase in ETCO2 above 35 to 40 mmHg suggests return of circulation. An ETCO2 persistently under 10 mmHg after 20 minutes of high-quality CPR with addressed reversible causes is a reasonable consideration in the decision to terminate.

Bradycardia in ACLS is heart rate under 50 beats per minute. The algorithm asks one question first. Is the patient symptomatic, with bradycardia causing the symptoms?

Asymptomatic bradycardia. Monitor and identify the underlying cause. Reversible causes include hypoxia, hypothermia, medication effect including beta-blockers and calcium channel blockers, electrolyte abnormalities. Address the cause.

Symptomatic bradycardia. Signs and symptoms include hypotension, acutely altered mental status, signs of shock, ischemic chest discomfort, and acute heart failure. If any of these are present and clearly tied to the rate, you treat.

First-line treatment is atropine 1 mg IV/IO bolus, repeated every 3 to 5 minutes to a maximum of 3 mg total. Atropine is unlikely to work in high-grade AV block such as type II second-degree or third-degree block, and in these cases transcutaneous pacing should not be delayed for atropine.

If atropine is ineffective or the patient is in high-grade block, the next steps are transcutaneous pacing, dopamine infusion 5 to 20 mcg/kg/min, or epinephrine infusion 2 to 10 mcg/min. Choose pacing for symptomatic high-grade block. Choose an inotrope infusion for ongoing bradycardia with hypotension after atropine.

Transcutaneous pacing setup. Place pads in anterior-posterior position when possible, start at a rate of 60 to 80 bpm, increase output in 10 mA increments until electrical capture is confirmed on the monitor and mechanical capture is confirmed by a palpable pulse that matches the paced rate. Sedate the patient if they are awake, pacing is painful.

Address the cause throughout. A heart rate of 38 in a patient on a fresh beta-blocker after a known accidental ingestion is not the same problem as a heart rate of 38 in a patient with an inferior MI. The algorithm covers the rate. You still have to treat the patient.

Tachycardia in ACLS is heart rate generally over 150 in adults, with the algorithm activated when the rate is causing or threatening hemodynamic compromise. The first question is stability.

Unstable tachycardia. Signs of instability include hypotension, acutely altered mental status, signs of shock, ischemic chest discomfort, and acute heart failure, with the rhythm clearly the driver. Treatment is synchronized cardioversion. Energy doses are typically 50 to 100 joules biphasic for narrow regular tachycardia such as SVT, 120 to 200 joules biphasic for atrial fibrillation, 100 joules biphasic for atrial flutter or other narrow irregular tachycardia, and 100 joules biphasic for monomorphic wide regular VT with a pulse. Sedate first if the patient is conscious. Do not delay cardioversion in a deteriorating patient for an ideal sedation plan.

Stable tachycardia. Now you have time to think. Get a 12-lead ECG. Determine width and regularity.

Stable narrow regular tachycardia. Most likely supraventricular tachycardia. Try vagal maneuvers first. If unsuccessful, adenosine 6 mg rapid IV push followed by a 20 mL saline flush. If unsuccessful, second dose of adenosine 12 mg rapid IV push. Adenosine has a half-life of seconds, the push must be rapid and immediately followed by the flush, ideally through an IV in the antecubital or larger.

Stable narrow irregular tachycardia. Most likely atrial fibrillation with rapid ventricular response, also atrial flutter with variable conduction or multifocal atrial tachycardia. Rate control with a beta-blocker or diltiazem per local protocol. Do not use adenosine for narrow irregular tachycardia, it will not convert atrial fibrillation and the brief AV block can be diagnostically confusing.

Stable wide regular tachycardia. Treat as ventricular tachycardia until proven otherwise. Amiodarone 150 mg IV over 10 minutes, may repeat. Alternative is procainamide or sotalol per local protocol and contraindications. Adenosine may be considered if the rhythm is suspected to be SVT with aberrancy, but it is not the safest choice if VT is on the differential.

Stable wide irregular tachycardia. Differential includes atrial fibrillation with aberrancy, atrial fibrillation in Wolff-Parkinson-White, and polymorphic VT. Avoid AV nodal blocking agents in suspected WPW with atrial fibrillation, they can accelerate the rate through the accessory pathway. Polymorphic VT with a long QT, torsades de pointes, is treated with magnesium sulfate 1 to 2 grams IV. Defibrillation, not synchronized cardioversion, is used if the patient becomes pulseless.

ROSC is the start of the post-cardiac arrest phase, not the end of the code. The patient who survives to hospital discharge with good neurologic function is the patient whose post-ROSC care was as disciplined as the resuscitation.

Optimize ventilation and oxygenation. Target SpO2 of 92 to 98 percent. Avoid both hypoxia and prolonged hyperoxia. Target ETCO2 of 35 to 45 mmHg. Avoid hyperventilation, which lowers cerebral perfusion.

Treat hypotension. Target systolic blood pressure of at least 90 mmHg and mean arterial pressure of at least 65 mmHg. Use isotonic crystalloid bolus and vasopressors as needed. Common choices are norepinephrine 0.1 to 0.5 mcg/kg/min, epinephrine 2 to 10 mcg/min, or dopamine 5 to 20 mcg/kg/min, titrated to MAP target.

Obtain a 12-lead ECG. STEMI on the post-arrest 12-lead drives the patient to the cath lab. Even without STEMI, coronary angiography is reasonable in select post-arrest patients per current guidelines and clinical context.

Targeted temperature management. Current AHA guidance supports targeted temperature management for comatose adults after ROSC, with the target temperature selected between 32 and 36 degrees Celsius maintained for at least 24 hours, followed by controlled rewarming and active fever prevention through at least 72 hours from ROSC.

Identify and treat the cause. The Hs and Ts work matters as much after ROSC as during the arrest. The patient who arrested from a pulmonary embolism still has a pulmonary embolism. The patient who arrested from hyperkalemia still has hyperkalemia.

Transport to a cardiac arrest receiving center. Where regional systems exist, transport to a hospital capable of cardiac catheterization, targeted temperature management, and post-arrest critical care.

ACLS providers who freeze in the megacode usually know the algorithms intellectually. The freeze happens because they have not run the decision points under verbal pressure enough times. Megacode is not a knowledge test. It is a verbal reflex test.

Practice out loud. The first thing you call on a code should not be the first time you have said it out loud this month. Run mock megacodes with a partner, with a manikin, with a recording app on your phone. Force yourself to verbalize the rhythm interpretation, the next intervention, and the dose. The hand-and-mouth coordination is part of the skill.

Drill the branches harder than the doses. The doses are stable across editions. The decision points are where students get stuck. Stable or unstable. Shockable or non-shockable. Narrow or wide, regular or irregular. Drill those first.

The StruckBox NREMT EMT prep library includes ACLS-aligned scenario questions that drill the algorithm decision points the same way a megacode does. You read the rhythm, you call the intervention, the explanation walks you back through the branch you took and where it sits on the current algorithm. Pair that with hands-on megacode practice and the algorithms become reflex. The branches stop being the bottleneck. Your team becomes the multiplier.