Case:
A 74-year-old female was admitted due an episode of loss of consciousness with a 3-year history of recurrent syncope and previous loop recorder implant (Medtronic Reveal Linq®). There was no history of coronary artery disease, structural heart disease, or other cardiovascular implantable electronic devices (CIED). Resting echocardiogram and stress testing were normal. Electrocardiogram (ECG) at baseline showed left bundle branch block (LBBB) (Figure 1), with no history of pre-excitation. She was not on antiarrhythmic medications. Interrogation of the device showed multiple episodes of wide complex tachycardia temporally unrelated to the loss of consciousness, with a changing QRS morphology (Figure 2). What are the differential diagnoses for the arrhythmia?