What are the ECG criteria for diagnosing supraventricular tachycardia (SVT) with aberrancy?

ECG Criteria for SVT with Aberrancy

When evaluating a wide-complex tachycardia (QRS >120 ms), SVT with aberrancy is suggested when the QRS morphology in tachycardia is identical to the QRS seen during sinus rhythm, indicating pre-existing bundle branch block or rate-related aberrant conduction. 1

Key Diagnostic Features Supporting SVT with Aberrancy

Primary Criteria

QRS morphology comparison is the most reliable criterion:

• QRS complexes in tachycardia that match sinus rhythm strongly suggest SVT with aberrancy 1
• This indicates either pre-existing bundle branch block or rate-dependent aberrant conduction that normalizes when heart rate slows

Specific ECG Patterns

In lead V1 with right bundle branch block (RBBB) morphology:

• rsR' pattern (triphasic) suggests SVT with aberrancy 1
• This classic RBBB pattern is more consistent with supraventricular origin
• Monophasic R wave is NOT valuable for diagnosing VT 2

Absence of VT criteria:

• No AV dissociation (atrial rate slower than ventricular rate)
• No fusion or capture beats
• R-S interval <100 ms in all precordial leads
• QRS width <140 ms (though this alone is not diagnostic) 2
• No concordance (all QRS complexes in precordial leads not uniformly positive or negative)
• R-wave peak time in lead II <50 ms 1

Additional Supporting Features

Rate considerations:

• Tachycardias >190 bpm often lack unequivocal criteria for differentiation 2
• Aberrancy is rate-dependent and should normalize when heart rate decreases

Clinical context matters:

• Younger patients without structural heart disease favor SVT
• Absence of prior myocardial infarction supports SVT diagnosis 3

Critical Pitfalls

Do not rely on single-lead assessment: The MCL1 lead cannot substitute for V1 and shows different QRS morphology in 40% of VT cases 2. Multiple leads are essential for accurate diagnosis.

Approximately 10% of wide-complex tachycardias defy differentiation using standard ECG criteria alone 2, 4. In these cases, invasive electrophysiology study may be necessary 5.

Conventional criteria have reduced sensitivity for idiopathic VT: Standard criteria correctly identify only 82% of idiopathic VT (versus 95% of post-MI VT), particularly when VT originates from septal or Purkinje sites 6. This means some VTs may appear to meet SVT criteria.

Algorithmic Approach

1. Compare tachycardia QRS to sinus rhythm QRS - if identical, strongly favors SVT with aberrancy
2. Assess for AV dissociation - if absent, more consistent with SVT
3. Examine V1 morphology - rsR' pattern supports SVT with RBBB aberrancy
4. Check precordial leads - absence of concordance supports SVT
5. Measure R-S intervals - all <100 ms supports SVT
6. When uncertain, treat as VT - safer approach given that VT accounts for >80% of wide-complex tachycardias 3

Remember: Hemodynamically unstable patients require immediate cardioversion regardless of rhythm diagnosis 1, 7. Diagnostic precision should never delay life-saving treatment.