Wide-Complex Tachycardia: VT vs Mimics

Why this matters

Check for a pulse first. Wide-complex tachycardia (WCT) is a high-stakes call and you do not have much time. The safe default is this: unstable regular WCT is treated as ventricular tachycardia (VT). VT is common and dangerous, so that default is the safer start. The mistake is saying “it is just supraventricular tachycardia (SVT) with aberrancy” while the patient is sick, or missing a look-alike such as high potassium that needs a different drug.

Your strip may be messy, the patient may be moving, and you do not have an electrophysiology lab. Follow the default and your protocol. Do not delay care to argue about the name.

Definitions

• Wide-complex tachycardia means a rate typically over 100 and a QRS of 0.12 seconds or more, about 3 small boxes, on teaching criteria. A regular wide rhythm at about 100–110 or faster with poor perfusion is a ventricular tachycardia pathway until proven otherwise. Do not withhold cardioversion or the arrest pathway because the rate is “only 120” or “could be accelerated idioventricular rhythm.” Rate bands overlap. Perfusion and protocol decide. This rate language is a teaching boundary, not a universal cutoff.
• Ventricular tachycardia (VT) starts in the ventricle. It may be monomorphic, the same shape, or polymorphic, a changing shape.
• SVT with aberrancy is supraventricular tachycardia conducted with a bundle-branch block or a rate-related wide QRS. It can look like VT.
• Other mimics include a paced tachycardia, high potassium with a wide or sine-wave QRS, artifact, and pre-excited AF (irregular, very wide, and changing) in WPW (Wolff-Parkinson-White).

Clinical sequence

1. Check for a pulse. If there is none, treat pulseless VT and the arrest pathway. Defibrillate. Do not call it stable WCT.
2. Protect the airway, breathing, and circulation, and judge stability. Hypotension, altered mental status, shock, ischemic pain, or acute heart failure means the unstable pathway. For monomorphic VT with a pulse, that is often synchronized cardioversion per protocol.
3. Say whether it is regular or irregular. Regular monomorphic WCT defaults to VT. Irregular WCT is a warning: polymorphic VT or torsades, AF with aberrancy, or pre-excited AF. Follow protocol.
4. Use the history: prior VT or an ICD, structural heart disease, age, missed dialysis or high-potassium risk, a tricyclic overdose, or known AF.
5. Do not delay treatment to make a fine rhythm distinction if the patient is unstable.

VT Default vs Mimics — Practical Notes

• Start with VT for regular wide-complex tachycardia in adults, especially with a history of heart disease. That is safer when perfusion is poor.
• High potassium: a wide QRS, a slow or sine-wave shape, end-stage kidney disease, missed dialysis, or crush injury. You may need calcium, or another treatment your protocol lists for high potassium, not a VT drug alone.
• Polymorphic VT or torsades changes shape. It is often tied to a long QT. Use magnesium and the defibrillation path per protocol. Do not use the same drug plan as monomorphic VT.
• Adenosine: some protocols allow a trial in regular monomorphic WCT that is stable and meets criteria. Many systems do not. Do not improvise adenosine for irregular WCT or presumed VT.
• Antiarrhythmics such as amiodarone or lidocaine are only for use if you are authorized. Know the cautions on your protocol.

Key points

• Unstable, regular, wide, and a pulse: use the synchronized cardioversion pathway per protocol until proven otherwise.
• Pulseless WCT: defibrillate without sync, per the arrest protocol.
• Expert ECG criteria, such as Brugada or Vereckei scores, are advanced. Do not let a textbook score delay care of an unstable patient.
• Get a 12-lead when the patient is stable enough. It helps the ED and may show a STEMI or a paced rhythm. Never delay a shock for a 12-lead in arrest or unstable VT.
• Write down the rate, regularity, an estimate of QRS width, the stability findings, what you did, and how the patient responded.

Common errors

• Calling it “SVT with aberrancy” because the patient is young. Age is not proof.
• Giving a rate-control drug or an AV-node blocker for irregular wide pre-excited AF. That is dangerous in WPW-related AF.
• Treating a sine wave that looks like high potassium as VT only.
• A long pause to name the rhythm while you do not treat instability.

Practice

Related: Stable vs Unstable Tachycardia, Shockable Arrest: VF & pVT.

Sources & Further Study

Named guidelines for further study. They are not clinical orders and do not replace your protocol or medical direction.

• NASEMSO National Model EMS Clinical Guidelines (2022) — U.S. EMS model language; protocol still wins
• AHA 2025 Part 9: Adult Advanced Life Support — regular monomorphic WCT is VT-first; avoid AV-nodal blockers in irregular wide (possible WPW) patterns
• Regular monomorphic WCT in adults is treated as VT until proven otherwise. Avoid AV-nodal blockers in irregular wide (possible WPW-related) patterns.
• Your cardioversion, antiarrhythmic, and hyperkalemia protocols.