What are the ECG criteria for ventricular tachycardia?

ECG Criteria for Ventricular Tachycardia

The most reliable ECG criteria for diagnosing ventricular tachycardia (VT) include AV dissociation, fusion complexes, absence of RS complexes in precordial leads, and RS interval >100 ms in any precordial lead. 1, 2

Primary Diagnostic Criteria

AV Dissociation and Fusion Beats

• AV dissociation: Ventricular rate faster than atrial rate - pathognomonic for VT but only visible in about 30% of cases 1, 2
• Fusion complexes: Merger between conducted sinus impulses and ventricular depolarization - pathognomonic for VT 1, 2
• Physical exam signs of AV dissociation: Irregular cannon A waves in jugular venous pulse, variability in first heart sound loudness and systolic blood pressure 1

QRS Morphology (Brugada Criteria)

• Absence of RS complexes in all precordial leads (V1-V6) - indicates VT 1, 2
• RS interval >100 ms (onset of R wave to nadir of S wave) in any precordial lead - indicates VT 1, 2

QRS Width

• QRS width >140 ms with right bundle branch block (RBBB) pattern - suggests VT 1
• QRS width >160 ms with left bundle branch block (LBBB) pattern - suggests VT 1
• Note: QRS width alone is not definitive, as SVT with pre-existing BBB can have wide QRS 1

Additional Diagnostic Criteria

Vereckei Algorithm (aVR Lead)

• Initial R wave in aVR - suggests VT 1, 2
• Initial R or Q wave >40 ms in aVR - suggests VT 1, 2
• Notch on descending limb at onset of predominantly negative QRS - suggests VT 1, 2

Other Morphological Features

• QRS concordance: All positive or all negative QRS complexes across precordial leads - strongly suggests VT 1, 2
• R-wave peak time ≥50 ms in lead II - suggests VT 1, 2
• QR complex in one or more precordial leads V2-V6 - suggests VT 3
• Predominantly negative QRS complexes in leads V4-V6 - suggests VT 3

Algorithmic Approach to Wide Complex Tachycardia

1. First step: Look for AV dissociation or fusion beats (pathognomonic for VT)
2. Second step: Apply Brugada criteria (absence of RS complexes or RS interval >100 ms)
3. Third step: Check QRS width (>140 ms with RBBB or >160 ms with LBBB)
4. Fourth step: Examine aVR lead using Vereckei algorithm
5. Fifth step: Look for QRS concordance across precordial leads

Important Clinical Considerations

• Do not rely on hemodynamic stability to distinguish SVT from VT - stable vital signs can occur in both conditions 1, 2
• When in doubt, treat as VT - especially before administering calcium channel blockers, which can cause hemodynamic collapse in VT 1
• QRS identical to sinus rhythm suggests SVT rather than VT 1
• SVT with pre-existing bundle branch block can be mistaken for VT 2

Pitfalls to Avoid

• Misdiagnosing VT as SVT with aberrancy: This can lead to inappropriate treatment with calcium channel blockers, potentially causing hemodynamic collapse 1
• Overreliance on single criteria: No single criterion is 100% sensitive or specific; use multiple criteria 4
• Ignoring clinical context: Patient history of structural heart disease increases likelihood of VT 3
• Failure to recognize fusion beats: These are subtle but pathognomonic for VT 1

By systematically applying these criteria, clinicians can accurately differentiate VT from SVT with aberrancy in most cases, leading to appropriate treatment decisions that reduce morbidity and mortality.