Supraventricular Tachycardia with abnormal conduction (“aberrancy”) is often difficult to distinguish from Ventricular Tachycardia. The 2015 AHA guidelines on the management of adults with SVT state that the presence of AV dissociation (i.e., the presence of P waves visible among the QRS complexes at a rate slower than the ventricular rate) or fusion/capture beats “provides the diagnosis of ventricular tachycardia.” Other criteria are suggestive, but not confirmatory. Diagnostic algorithms – Brugada or Vereckei for example, are complicated and can be difficult to apply.
Since some treatments for SVT might be deleterious in a case of VT (i.e., calcium channel blockers), the rule of thumb is to err on the side of VT in any ambiguous case. That being said, the 2010 ACLS guidelines state that when the diagnosis is uncertain, adenosine can be given as it would be safe in either case and that it could be both therapeutic and diagnostic. The implication is that SVT may revert with adenosine, but VT would not.
This brings me to the point. During a recent discussion with the residents about the subtleties of SVT with aberrancy vs VT, I mentioned that some cases of VT will convert with adenosine. I was met with an uncomfortable silence and disbelief. So, below I’ll give the reference of some articles that clearly give examples of times when VT is known to convert with adenosine. Now you know. ACLS guidelines to the contrary, conversion of a wide complex, regular tachycardia with adenosine is often consistent with SVT, but is not diagnostic of SVT. If you find yourself in this situation, be aware that you have not necessarily ruled out VT.
https://www.ahajournals.org/doi/epub/10.1161/CIR.0000000000000311
Searcy EM 