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Differential Diagnosis
When the intrinsic rhythm is sinus:
I. What was the first beat of the tachycardia?
When the intrinsic rhythm is atrial fibrillation:
Artifact
Always consider artifact if:
- SVT with aberrancy (SVT with RBBB or SVT with LBBB)
- Nonsustained VT
- Artifact
- Uncertain (“I don’t know”) – this is a better choice than incorrect guessing!
When the intrinsic rhythm is sinus:
I. What was the first beat of the tachycardia?
- If the first early beat was a PAC (premature P wave in front of the QRS) -> SVT
- If the first early beat was a PVC (no premature P wave in front of the QRS) -> VT
- A-V dissociation present -> VT
- More QRS complexes than P waves -> VT
- Combination QRS morphology (QRS wider than during sinus but narrower than the widest QRS)
- P waves must be present in front of the combination morphology QRS complexes
When the intrinsic rhythm is atrial fibrillation:
- If the WCT is regular -> VT
Artifact
Always consider artifact if:
- It is uncertain which was the first or the last beat of the WCT
- The rate of the tachycardia was excessive
- The patient remained asymptomatic during a long run of a very fast tachycardia
- Intrinsic QRS complexes march through
- “Notches” march through
- Simultaneous hemodynamic tracing indicates regularity
