Dr. Smith's ECG Blog

This was sent by a former resident without any information:

It is obvious what to do (electrical cardioversion), but what is the probable rhythm diagnosis?
My response was:
VT vs. 1:1 flutter with aberrancy.
I wonder if the patient is on flecainide, without an AV nodal blocker.

Show me the post cardioversion ECG.

He sent this, recorded after electrical cardioversion:

Further history:

This patient with a history of atrial fibrillation s/p ablation x 2, presented with palpitations.

He is on flecainide and metoprolol.  Flecainide dose had been increased on the day before