VT vs SVT with Aberration: A Quick Interpretation Guide
Introduction Distinguishing ventricular tachycardia (VT) vs supraventricular tachycardia (SVT) with aberrancy is a critical skill in electrophysiology and emergency medicine. Misdiagnosis can lead to inappropriate treatment and adverse outcomes. This blog post provides a structured approach to identifying VT versus SVT with aberration using key electrocardiogram (ECG) features.
Key Features Favoring VT
- Absence of Typical Bundle Branch Block (BBB) Morphology
- Atypical QRS patterns that do not match typical right bundle branch block (RBBB) or left bundle branch block (LBBB) morphology increase the likelihood of VT.
- AV Dissociation
- Independent atrial (P waves) and ventricular (QRS complexes) activity suggest VT.
- Captured and Fusion Beats
- Captured beats: Normal sinus beats occurring within a VT episode.
- Fusion beats: Hybrid beats resulting from simultaneous activation by normal sinus and ventricular impulses.
- Concordance in Precordial Leads
- Positive concordance: All V1-V6 leads show entirely positive (R wave) complexes.
- Negative concordance: All V1-V6 leads show entirely negative (QS) complexes.
Brugada Algorithm for VT vs SVT
The Brugada algorithm is a widely accepted method for distinguishing VT from SVT with aberration:
- Positive or Negative Concordance in Precordial Leads?
- If yes → VT
- If no → Proceed to step 2
- Onset of R to Nadir of S > 100 ms in Any Lead?
- If yes → VT
- If no → Proceed to step 3
- AV Dissociation Present?
- If yes → VT
- If no → Proceed to step 4
- Morphology Criteria for VT in V1 & V6?
- If yes → VT
- If no → SVT
Standard Bundle Branch Block (BBB) Patterns vs VT Morphology
RBBB vs VT with RBBB Morphology
- RBBB Pattern:
- V1: Tall second R wave (R’)
- V6: Broad, deep S wave
- VT with RBBB Morphology:
- V1: Monophasic R, QR, or dominant QS pattern
- V6: R < S (R:S ratio < 1)
- R > R’ (Tall left rabbit ear)
LBBB vs VT with LBBB Morphology
- LBBB Pattern:
- V1: Deep S wave
- V6: Broad, clumsy R wave
- VT with LBBB Morphology:
- V1/V2: Initial r > 30 ms, r to nadir of S > 60 ms, or notched downstroke
- V6: Any q wave, QS, or QR pattern
Axis Deviation Suggesting VT
- Right superior axis (+ve aVR, -ve I, aVF) → VT
- Left axis in presence of RBBB → VT
- Right axis in presence of LBBB → VT
Conclusion
Differentiating VT vs SVT with aberrancy requires a systematic approach. Using the Brugada algorithm, identifying AV dissociation, captured beats, and concordance, and analyzing morphology criteria can significantly improve diagnostic accuracy. Always prioritize VT in unclear cases, as misdiagnosing VT as SVT could result in inappropriate treatment and increased mortality risk.