Your patient is stable but has wide complex tachycardia (WCT).  Your attending wants to give adenosine but you are unsure.  Isn’t there a chance this could lead to ventricular fibrillation?  In what circumstances is it safe to diagnose/ treat WCT with adenosine?

Rhythym morphology is key.
Blocking the AV node in the case of afib with an accessory pathway (for example wolff-parkinson-white) can force conduction down the accessory pathway.  (In case you see the term used, this is antidromic/ “backwards” conduction).    Unlike the AV node this pathway lacks a significant refractory period and can unleash the full atrial rate of 300-600 on the ventricles causing VF and death.  Afib with preexcitation will be irregular.
So why does my attending want to give adenosine?  Because your patients has regular/monomorphic WCT.
adenosine is supported in the 2010 AHA ACLS guidlines for use in the diagnosis and treatment of stable AND regular WCT because the underlying rhythm could be SVT (ventricular tachycardia is still more likely).  If WCT is caused by SVT adenosine will:
-terminate reentrant loop arrythmias
-block AV conduction and reveal underlying rhythms
-or do nothing (you patient likely has VT)
Be aware that adenosine can terminate VT!  it probably has something to do with cAMP and automaticity in patients with structural heart disease
Adenosine can have a role in the diagnosis and treatment of regular WCT.  But be careful as it can prove lethal in preexcitation syndromes.  avoid in all irregular or unstable WCT
Arbo, John E., Stephen Ruoss, Geoffrey K. Lighthall, Michael P. Jones, and Joshua Stillman. Decision Making in Emergency Critical Care: An Evidence-based Handbook. N.p.: n.p., n.d. Print.

“2010 ACLS Guidelines-CPR.” Http:// N.p., n.d. Web. 21 Aug. 2015.