Version control: This document is current with respect to 2015 American Heart Association® Guidelines for CPR and ECC. These guidelines are current until they are replaced on October 2020. If you are reading this page after October 2020, please contact ACLS Training Center at for an updated document.

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Using the ACLS Tachycardia Algorithm for Managing Unstable Tachycardia

There are two keys to managing patients with unstable tachycardia are. The first is quickly recognizing that the patient has significant symptoms and is unstable. The second is quickly recognizing that the patient's signs and symptoms are caused by the tachycardia. You need to decide if the tachycardia is producing the hemodynamic instability and serious signs and symptoms or if the signs and symptoms are producing the tachycardia—for example, the pain and distress of an acute MI could be causing the tachycardia. Making this decision can be difficult. Generally, a heart rate between 100 bpm and approximately 150 bpm is usually caused by an underlying process that is represented as sinus tachycardia (see Stable Tachycardia module for more information on sinus tachycardia). Heart rates > 150 bpm may be symptomatic. The higher the rate, the more likely the symptoms are a result of the tachycardia. Underlying heart disease or other problems can cause symptoms at lower heart rates. Keep in mind the following considerations:


The ACLS Tachycardia Algorithm is organized around the following questions:

  1. Is the patient stable or unstable?
  2. Is the QRS wide or narrow?
  3. Is the ventricular rhythm regular or irregular?


Does the patient have a pulse? If no, the patient’s rhythm is PEA and should be treated as such.

If yes:

Assess the patient using the primary and secondary surveys:

  1. Check airway, breathing, and circulation.
  2. Give oxygen if the oxygen saturation is less than 94% or the patient is short of breath.
  3. Perform a 12 Lead ECG if the patient is stable.
  4. Identify rhythm.
  5. Check blood pressure.
  6. Identify and treat reversible causes if the rhythm is sinus tachycardia.

Is the patient stable?

Look for altered mental status, ongoing chest pain, hypotension, or other signs of shock.

Remember: Rate-related symptoms are uncommon if heart rate is less than 150 bpm.

If the signs and symptoms continue after you have given oxygen and supported the airway and circulation AND if significant symptoms are due to the tachycardia, then the tachycardia is UNSTABLE and immediate cardioversion is indicated.

If you determine that the patient has an unstable tachycardia, perform immediate synchronized cardioversion. This is not a decision to take lightly as it carries with it a significant risk of stroke.

  1. Start an IV.
  2. Give sedation if the patient is conscious.
  3. Do not delay cardioversion.
  4. Consider expert consultation.

If you determine that the patient has a stable tachycardia, start an IV and obtain a 12-lead ECG

For a patient with a stable tachycardia, decide if the QRS complex is wide or narrow and if the rhythm is regular.

Patient hasTreatment
Narrow (< 0.12 sec) QRS complexTry vagal maneuvers
Regular rhythmGive adenosine 6 mg rapid IV push.
Repeat 12 mg dose once if necessary

Does the patient's rhythm convert? If it does, the rhythm was atrial in origin. The conversion of a rhythm by adenosine is considered diagnostic of atrial arrhythmia. At this point you watch for a recurrence. If the tachycardia resumes, treat with adenosine or longer-acting AV nodal blocking agents such as diltiazem or beta-blockers.

Patient hasTreatment
Narrow (< 0.12 sec) QRS complexConsider expert consultation
Irregular rhythmControl patient's rate with diltiazem or beta-blockers. Use beta-blockers with caution for patients with pulmonary disease or congestive heart failure.

If the rhythm is irregular narrow-complex tachycardia, it is probably atrial fibrillation, possible atrial flutter, or multi-focal atrial tachycardia.

Patient hasTreatment
Wide (>0.12 sec) QRS complexExpert consultation is advised.
Regular rhythmExpert consultation advised.
If patient is in ventricular tachycardia or uncertain rhythmAmiodarone 150 mg IV over 10 min; repeat as needed to maximum dose of 2.2 g in 24 hours. Prepare for elective synchronized cardioversion. The half life of amiodarone is very long. If possible consult a cardiologist before using in a stable patient. Another choice would be to use procainamide.
If patient is in SVT with aberrancyAdenosine 6 mg rapid IV push If no conversion, give 12 mg rapid IV push; may repeat 12 mg dose once
Patient hasTreatment
Wide (> 0.12) QRS complex
Irregular rhythmSeek expert consultation
If pre-excited atrial fibrillation (AF + WPW)Avoid AV nodal blocking agents such as adenosine, digoxin, diltiazem, verapamil.
Consider amiodarone 150 mg IV over 10 min
If recurrent polymorphic VTSeek expert consultation
If torsades de pointesSeek expert consultation

You may not always be able to tell from the ECG whether the rhythm is ventricular or supraventricular. Most wide-complex tachycardias originate in the ventricles (particularly if the patient is older or has underlying heart disease). If the patient does not have a pulse, treat the rhythm as ventricular fibrillation and follow the Pulseless Arrest Algorithm.

If the patient is unstable and has a wide-complex tachycardia, assume the rhythm is VT until you can prove otherwise.