Wide-Complex Tachycardia: VT vs Mimics

Why This Is Hard

Wide-complex tachycardia (WCT) forces a high-stakes call under time pressure. Most paramedics were taught: unstable regular WCT → treat as VT. That teaching saves lives because VT is common and dangerous. The trap is overconfidence in “it’s just SVT with aberrancy” when the patient is sick — or missing mimics like hyperkalemia that need a different drug path.

Prehospital tools are limited: imperfect strips, motion, no full electrophysiology lab. Your job is safe defaults plus protocol discipline — not winning a rhythm contest.

Definitions (Education)

• Wide-complex tachycardia — rate typically >100 with QRS duration ≥0.12 s (3 small boxes) on teaching criteria.
• Ventricular tachycardia (VT) — ventricular origin; may be monomorphic (same shape) or polymorphic.
• SVT with aberrancy — supraventricular tachycardia conducted with bundle-branch block or rate-related wide QRS — can look like VT.
• Other mimics / special cases — paced tachycardia, hyperkalemia (wide, sine-wave tendency), artifact, and pre-excited AF (irregular, very wide, variable) in WPW-related education topics.

Street Approach

1. Pulse? No pulse → treat as pulseless VT / arrest (defibrillation pathway), not “stable WCT.”
2. ABCs and stability — hypotension, AMS, shock, ischemic pain, acute failure → unstable pathway (often synchronized cardioversion for monomorphic VT with pulse per protocol).
3. Regular or irregular? Regular monomorphic WCT defaults toward VT in EMS education. Irregular WCT is a red-flag category (polymorphic VT/torsades, AF + aberrancy, pre-excited AF) — follow protocol carefully.
4. History clues — prior VT/ICD, structural heart disease, age, missed dialysis/hyperK risk, TCA overdose context, known AF.
5. Do not delay therapy for exotic differentiation if the patient is unstable.

VT Default vs Mimics — Practical Notes

• Default to VT thinking for regular WCT in adults, especially with heart disease history — safer for the unstable patient.
• Hyperkalemia — wide QRS, slow-ish or sine-wave morphology, ESRD/missed dialysis, crush. May need calcium/shift therapies per protocol rather than “VT meds only.”
• Polymorphic VT / torsades — changing morphology; often associated with long QT context; magnesium and defibrillation pathways per protocol — not the same as monomorphic VT drug choices.
• Adenosine — some protocols allow it as a diagnostic/therapeutic trial in regular monomorphic WCT that is stable and meets criteria; many systems restrict it. Irregular WCT and presumed VT are not places to freestyle adenosine.
• Antiarrhythmics (amiodarone, lidocaine, etc.) — only as authorized; know contraindications in your formulary.

Key Points for Paramedics

• Unstable + regular wide + pulse → synchronized cardioversion pathway per protocol until proven otherwise.
• Pulseless WCT → defibrillation (unsynchronized) per arrest protocol.
• Expert ECG criteria (Brugada, Vereckei, etc.) are advanced; do not let textbook criteria delay care in a crashing patient.
• 12-lead when stable enough — helps ED and may show STEMI or paced morphology; never delay shocks for a 12-lead in arrest/unstable VT.
• Document: rate, regularity, QRS width estimate, stability criteria, interventions, response.

Field Pitfalls

• Calling “SVT with aberrancy” because the patient is young — age is not proof.
• Giving rate-control or AV-nodal blockers in irregular wide pre-excited AF (education warning — dangerous in WPW-related AF).
• Treating hyperK-looking sine wave only as VT.
• Long differentiation pauses without treating instability.

Practice

In CardioStrip, pick wide tachycardias and force: pulse → regular/irregular → stable/unstable → default action class. Compare monomorphic vs polymorphic examples if available.

Sources & Further Study

• ACLS WCT / VT education frameworks.
• Your cardioversion, antiarrhythmic, and hyperkalemia protocols.