ACLS Tachycardia Algorithm Explained (2025 Guidelines)

ACLS Cards · Updated November 3, 2026 · Adult · 2025 guidelines · Clinical review pending

The tachycardia algorithm is a sorting exercise. First: is the patient unstable because of the fast rate? If yes, electricity. If no, sort the rhythm by QRS width and regularity, then pick the matching treatment.

Rate as cause or consequence

The algorithm applies when the heart rate is typically 150/min or more^{pending review, ref T1}. Below that, a fast rate is more often a response to something else: fever, pain, bleeding, hypoxia. The 2025 material puts more emphasis on asking whether the rhythm is causing the problem or is a consequence of it^{pending review, ref T16}. Shocking a sinus tachycardia caused by blood loss fixes nothing.

Unstable: synchronized cardioversion

If the fast rhythm is causing hypotension, altered mental status, signs of shock, ischemic chest discomfort or acute heart failure, perform synchronized cardioversion. Sedate whenever feasible^{pending review, ref T17}, but don't delay for it in a crashing patient.

Rhythm	Starting energy (device-dependent)
Narrow, regular	100 J^{pending review, ref T8}
Monomorphic VT	100 J^{pending review, ref T8}
Atrial fibrillation	≥200 J^{pending review, ref T8}
Atrial flutter	200 J^{pending review, ref T8}
Sustained polymorphic VT	not synchronized: an immediate unsynchronized shock at the defibrillation dose^{pending review, ref T9}

If a repeat shock is needed, check that sync is still on^{pending review, ref T21}; some devices reset after each shock.

Stable: the 2×2 grid

Get a 12-lead ECG. A QRS of 0.12 s or more^{pending review, ref T2} is wide. Then:

	Regular	Irregular
Narrow	Narrow-complex tachycardia (formerly "SVT"). Vagal maneuvers including modified Valsalva^{pending review, ref T15}, then adenosine 6 mg rapid push with a flush, then 12 mg^{pending review, ref T3}. Then rate control.	Usually atrial fibrillation (or flutter with variable block, or multifocal atrial tachycardia). Rate control with a calcium-channel blocker (diltiazem or verapamil) or a β-blocker, dosed per protocol^{pending review, ref T12}.
Wide	Treat as VT unless clearly otherwise. Adenosine only if regular and monomorphic^{pending review, ref T11}. Antiarrhythmic: procainamide or amiodarone (see below). Expert consultation.	Think pre-excited AF, polymorphic VT or torsades. Get expert help. No AV-nodal blockers, digoxin or IV amiodarone in pre-excited AF^{pending review, ref T13}.

Drug notes

Adenosine: avoid in asthma; consider 1 mg with a central line or heart transplant^{pending review, ref T4}.
Procainamide: 20–50 mg/min until the arrhythmia is suppressed, hypotension occurs, the QRS widens by 50%, or 17 mg/kg is given; maintenance 1–4 mg/min; avoid with prolonged QT or heart failure^{pending review, ref T5}.
Amiodarone: 150 mg over 10 min, repeat as needed; then 1 mg/min for the first 6 h^{pending review, ref T6}.
Verapamil/diltiazem in wide-complex tachycardia: harmful; don't^{pending review, ref T11}.
Calcium-channel blockers: avoid in suspected systolic heart failure^{pending review, ref T12}.
Torsades: magnesium 1–2 g IV^{pending review, ref T10}. Not for polymorphic VT with a normal QT^{pending review, ref T10}.
AF or flutter of longer duration: for more than 48 h without anticoagulation, cardioversion carries stroke risk^{pending review, ref T14}, so get expert input.
Don't stack antiarrhythmics without expert advice, and keep the defibrillator attached^{pending review, ref T19}.

What changed in 2025

AF cardioversion starts at ≥200 J and flutter at 200 J^{pending review, ref G1}, rather than escalating up from a low energy.
Sustained polymorphic VT gets an immediate unsynchronized shock^{pending review, ref G2}.
"SVT" is now called narrow-complex tachycardia, sotalol was removed from the algorithm, and there's more emphasis on cause vs consequence^{pending review, ref G10}.

Common mistakes

Synchronized vs unsynchronized. Pulseless VT and polymorphic VT get unsynchronized shocks. Everything else unstable with a pulse gets synchronized.
Giving adenosine to an irregular wide rhythm. It's only for regular, monomorphic rhythms.
Chasing the rate in sinus tachycardia. Treat the cause.
Losing the pulse. No pulse means you're in the cardiac arrest algorithm now.

Previous: the bradycardia algorithm explained.

Source: 2025 Guidelines for CPR and Emergency Cardiovascular Care (Circulation, October 2025), as summarized in the pack's source checklist. Original wording and layout; no guideline figures reproduced.