Emergency Medicine Hub / Cardiovascular Emergencies • 3 min read • 3 sections

Wide Complex Tachycardias: VT vs SVT with Aberrancy

Comprehensive emergency evaluation and protocolized resuscitation of regular wide-complex tachycardias (QRS >= 120 ms): Ventricular Tachycardia (VT) vs. Supraventricular Tachycardia with bundle branch block aberrancy or pre-excitation; pathophysiological default rule ('treat all wide-complex tachycardias as VT until proven otherwise'); electrocardiographic criteria (AV dissociation, fusion beats, capture beats, concordance in precordial leads); step-by-step application of the Brugada Algorithm and Vereckei aVR Rule; PROCAMIO trial evidence favoring IV Procainamide over Amiodarone; and emergent synchronized electrical cardioversion.

Resuscitation Quick Actions • First 2 Minutes

High-Acuity

The 80/95% VT Rule

> 80% of all regular wide-complex tachycardias are VT (> 95% in patients with prior MI, CAD, or CHF); treat as VT until proven otherwise

Pathognomonic VT Signs

1) AV Dissociation, 2) Capture Beats (normal narrow beats), 3) Fusion Beats (Dressler hybrid beats), 4) Extreme Northwest Axis (-90° to 180°)

Vereckei aVR Rule Step 1

Look at lead aVR: If there is an INITIAL R WAVE (monophasic R in aVR), it is VENTRICULAR TACHYCARDIA with 98% specificity

PROCAMIO Drug Choice

Procainamide 10–17 mg/kg IV at 20–50 mg/min terminates stable VT faster and with less hypotension than Amiodarone (150 mg IV)

Never Give Verapamil

DO NOT administer IV Verapamil or Diltiazem to undifferentiated wide-complex tachycardia; causes catastrophic cardiovascular collapse in VT

Unstable Shock Energy

Synchronized biphasic cardioversion: 100J -> 200J -> 300J -> 360J (if polymorphic VT or pulseless, switch to UNSYNCHRONIZED DEFIBRILLATION 200J)

Monomorphic Ventricular Tachycardia

Regular wide QRS complexes of uniform morphology. Differentiate from SVT with aberrancy using Brugada and Vereckei algorithms; if hemodynamically stable, treat with Procainamide (10-17 mg/kg IV over 20-30 min) or Amiodarone (150 mg over 10 min).

Bottom-Line Clinical Pearl

In emergency medicine, any regular wide-complex tachycardia (QRS >= 120 ms) must be TREATED AS VENTRICULAR TACHYCARDIA until proven otherwise. Over 80% of all wide-complex tachycardias (and > 95% in patients with a history of prior myocardial infarction or structural heart disease) are Ventricular Tachycardia! Pathognomonic hallmarks of VT on 12-lead ECG include: Atrioventricular (AV) dissociation (P waves marching independently through QRS complexes), Capture beats (normal narrow sinus beat breaking through), Fusion beats ('Dressler beats', hybrid QRS from simultaneous sinus and ventricular depolarization), and Extreme Right Axis Deviation ('northwest axis' between -90° and 180°). For stable VT, the PROCAMIO trial demonstrated that IV Procainamide (10–17 mg/kg) has significantly higher termination efficacy and fewer adverse cardiac events than IV Amiodarone. For unstable VT (hypotension, chest pain, altered mental status), perform immediate Synchronized Electrical Cardioversion (100–200J).

1. The Universal Mandate: Treat All Wide Tachycardias as VT

A wide-complex tachycardia (WCT) is defined as a heart rate $> 100\text{ bpm}$ with a QRS duration $\ge 120\text{ ms}$ (3 small boxes). In the emergency department, 80% of all regular WCTs are Ventricular Tachycardia (VT). In patients aged $> 50\text{ years}$, or those with a documented history of prior myocardial infarction, coronary artery disease, congestive heart failure, or structural cardiomyopathy, over 95% of regular WCTs are VT. Mistaking VT for SVT with aberrancy and administering calcium-channel blockers (verapamil or diltiazem) precipitates acute hemodynamic collapse, refractory shock, and asystolic cardiac arrest.

2. Pathognomonic Electrocardiographic Features of VT

ECG Diagnostic Feature	Electrocardiographic Appearance	Pathophysiologic Rationale & Diagnostic Power
Atrioventricular (AV) Dissociation	Independent, slow, regular P waves marching through the rhythm at a slower rate than the fast wide QRS complexes (best seen in V1, II, or Lewis leads)	100% specific for Ventricular Tachycardia. Demonstrates that the SA node is firing independently while a ventricular focus drives the ventricles.
Capture Beats	An occasional, isolated, perfectly normal narrow QRS complex that occurs amidst the run of wide-complex tachycardia	Virtually 100% specific for VT. A sinus impulse finds the AV node and His-Purkinje system out of their refractory period, conducting normally to 'capture' the ventricles.
Fusion Beats ('Dressler Beats')	A single hybrid QRS complex whose morphology and duration are intermediate between the narrow sinus beat and the wide VT beat	Virtually 100% specific for VT. Occurs when a supraventricular sinus impulse and an ectopic ventricular impulse collide and simultaneously depolarize different parts of the myocardium.
Extreme Right Axis Deviation ('Northwest Axis')	Frontal plane QRS axis between -90° and 180° (QRS predominantly negative in lead I and lead aVF; positive in lead aVR)	Virtually pathognomonic for VT. Depolarization is traveling in an unnatural direction: from the cardiac apex upward toward the base, opposite to normal His-Purkinje activation.
Precordial Concordance	All QRS complexes from V1 through V6 are entirely positive (R waves) OR entirely negative (QS complexes)	Negative concordance is $> 98\%$ specific for VT; positive concordance indicates VT originating in the posterior left ventricular wall.

3. The Vereckei aVR Algorithm

The Vereckei algorithm relies entirely on a single ECG lead—lead aVR—evaluating four sequential questions; answering YES to ANY step establishes the diagnosis of Ventricular Tachycardia:

Step Sequence	Diagnostic Question in Lead aVR	Interpretation If YES
Step 1	Is there an initial R wave (monophasic R, Rs, or notched R)?	YES = Ventricular Tachycardia (98% specific). Normal supraventricular activation travels away from aVR, creating an initial Q wave.
Step 2	Is the width of the initial r or q wave $> 40\text{ ms}$ (1 small box)?	YES = Ventricular Tachycardia. Slow myocardial cell-to-cell conduction produces a broad initial wave.
Step 3	Is there notching on the descending limb of a predominantly negative QRS complex?	YES = Ventricular Tachycardia.
Step 4	Is the ventricular activation-velocity ratio ($v_i/v_t$) $\le 1.0$ (initial depolarization slower than terminal)?	YES = Ventricular Tachycardia.<br>If NO to all 4 steps = SVT with aberrancy.

Critical Pitfall / Contraindication

PROCAMIO TRIAL EVIDENCE: PROCAINAMIDE BEATS AMIODARONE: The landmark multicenter randomized PROCAMIO trial compared IV Procainamide (10 mg/kg over 20 min) against IV Amiodarone (5 mg/kg over 20 min) for regular stable wide-complex tachycardia. Procainamide achieved a significantly higher rate of successful tachycardia termination (67% vs 38%) with a significantly lower rate of major adverse cardiac events (9% vs 41%, primarily severe hypotension requiring cardioversion). Procainamide is the evidence-based first-line chemical antiarrhythmic for stable monomorphic VT.

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