Approach to Wide Complex Tachycardia

 

Approach to Wide Complex Tachycardia (WCT): A Practical, Clinician-Focused Guide

Wide complex tachycardia (WCT) is one of the most high-risk arrhythmias encountered in emergency and cardiac care. The default assumption is always VT until proven otherwise, because mistreating VT as SVT can be fatal, while mistreating SVT as VT is usually safer.

This post outlines a simple, stepwise approach to correctly identify the underlying rhythm and choose the right management strategy.

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1. Start With the Basics: What Is Wide Complex Tachycardia?

A rhythm is considered wide complex when:

QRS ≥ 120 ms

Ventricular rate is >100 bpm

The wide QRS indicates either ventricular origin (VT) or supraventricular impulse traveling abnormally (e.g., aberrancy, pre-excitation, paced rhythm).

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2. The First Big Question: Regular or Irregular?

A. Regular WCT

This narrows the diagnosis to:

Ventricular tachycardia (most common)

SVT with aberrancy (e.g., RBBB/LBBB pattern)

Antidromic AVRT (WPW)

Paced rhythm

B. Irregular WCT

Think of:

Atrial fibrillation with aberrancy

AF with pre-excitation (WPW) → dangerous: avoid AV nodal blockers

Polymorphic VT (including TdP)

Often unstable; treat immediately.

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3. Clues Favoring VT (Most Important Section)

Up to 80% of regular wide tachycardias are VT, especially in older adults.

Key features that strongly suggest VT:

Clinical clues

Age > 35–40 years

History of MI, scar, cardiomyopathy

Shock, low BP, or severe symptoms

AV dissociation (P waves independent of QRS)

Capture & fusion beats

ECG clues

Extreme axis (northwest axis)

Very broad QRS > 160 ms

Concordance (all precordial leads uniformly positive or negative)

Morphology that doesn’t match typical LBBB/RBBB

Positive or negative precordial concordance

When in doubt → treat as VT.

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4. Approach When Rhythm Is Regular

Step 1: Compare QRS with baseline ECG

Identical to baseline BBB? → SVT with aberrancy likely

Different QRS? → VT more likely

Step 2: Look for AV relationship

AV dissociation → VT

1:1 AV conduction → SVT with aberrancy or orthodromic AVRT

Step 3: Assess QRS morphology (V1 & V6)

Classic RBBB/LBBB-like patterns → SVT with aberrancy possible

Atypical morphology → VT

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5. Approach When the Rhythm Is Irregular

Irregular + Wide QRS → 3 causes

Condition Key Features Notes

AF with BBB Irregularly irregular, typical RBBB/LBBB morphology Usually stable

AF with WPW Very fast (>200 bpm), bizarre QRS Never give AV nodal blockers (adenosine, β-blocker, verapamil, diltiazem, digoxin)

Polymorphic VT QRS shape changes beat-to-beat Treat immediately as VT

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6. Management Principles

If unstable → Shock immediately (synchronized).

If stable:

If VT is likely

Amiodarone or procainamide

Treat underlying ischemia/electrolytes

Avoid AV nodal blockers

If SVT with aberrancy is suspected

Vagal maneuvers

Adenosine diagnostic trial (regular narrow-like tachy only)

β-blockers or CCBs if AV nodal reentry suspected

If AF with pre-excitation

Use procainamide or ibutilide

Avoid all AV nodal blockers

Consider shock if unstable

If polymorphic VT

Treat like unstable VT

If torsades → magnesium + pacing or isoproterenol

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7. Key Take-Home Messages

Assume VT first—especially in older patients or those with structural heart disease.

Regular vs irregular is the fastest way to narrow diagnosis.

QRS morphology, AV relationship, and clinical history help differentiate VT from SVT.

Avoid AV nodal blockers in AF with WPW.

When uncertain, VT management is safer.