Fasciculoventricular pathway causing delta wave

K.V.

and this article:

n continuation of our prior discussion - see this case from Dr. Wellens from this month's Heart Rhythm journal - another cause of delta wave / "pre-excitation":

Young woman with palpitations and preexcitation.

Josephson ME, Wellens HJ.

Heart Rhythm. 2015 Sep;12(9):2041-2. doi: 10.1016/j.hrthm.2015.04.031. Epub 2015 Apr 24. No abstract available. 

Useful diagnostic maneuvers for a fasciculoventricular pathway are those that slow atrioventricular nodal conduction (ie, carotid sinus massage or valsalva, adenosine, or a β-blocker or calcium channel blocker), which would prolong the PR interval and not change the degree of preexcitation.

An electrophysiological study confirmed a fascicoloventricular pathway (fixed, short HV interval, pacing-induced prolongation of atrioventricular nodal conduction with no change in preexcitation). No arrhythmias were induced. Long-term monitoring demonstrated her palpitations were due to sinus tachycardia. Fasciculoventricular pathways are not known to participate in reentrant tachycardias, but they may exist as innocent bystanders during other tachycardias. As such, no attempt to ablate them should be made.