How to Tell VT From SVT with Aberrancy – Mattu, Brady, Tabas, Ferguson Teach Us

Written by Alex Chen, MD

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The differential of wide complex tachycardia (WCT) includes ventricular tachycardia (VT) and supraventricular tachycardia with aberrant conduction (SVT-AC). The summary below provides some tips for differentiating the two. However, if you are unsure it is always prudent to assume VT until proven otherwise.

Why does this matter?
It can be tough to tell one from another, but the treatment is drastically different.  Read the tips from the ECG masters to learn more.  And when you’re finished, you have to check out this post on LITFL that unpacks the algorithms in #10 below, gives example ECGs, and even has a quiz to test your knowledge.

Pearls from Mattu, Brady, Tabas, Ferguson:

1. Clinical stability does not differentiate between VT and SVT-AC.
2. History suggestive of VT includes: prior MI, heart failure, recent angina pectoris, or advanced age.
3. Sinus tachycardia may be aberrantly conducted due to bundle branch block (BBB) or toxic/metabolic cause (i.e. hyperkalemia, sodium-channel blockade). There tends to be a more variable QRS duration with toxic/metabolic.
4. AVNRT with aberrant conduction has retrograde P waves in 70%.
5. AF with WPW has beat to beat variation in QRS duration (getting impulses from both bypass tract and AV node). AF with BBB has consistent QRS duration. 
6. Presence of 1st degree heart block on previous EKG means it’s much less likely SVT-AC (unlikely to conduct in a rapid 1:1 pattern); assume VT.
7. Previous BBB on EKG may point you toward SVT-AC, but it is a marker of heart disease and is at higher risk for VT.
8. AV dissociation is present in approximately 50% of VT (absence does not rule out) and may rarely be present in AVNRT.
9. You can get slower rates of monomorphic VT (130-160 bpm) with end-stage heart failure or chronic amiodarone use.
10. There are multiple algorithms (Brugada, Wellens, Vereckei, R wave peak time, etc), but they can still misdiagnose. Assume VT if you are unsure.

Source
The differential diagnosis of wide QRS complex tachycardia.  Am J Emerg Med. 2017 Oct;35(10):1525-1529. doi: 10.1016/j.ajem.2017.07.056. Epub 2017 Jul 17.

Peer reviewed by Thomas Davis, MD and Clay Smith, MD.