A 73 yo patient with h/o diabetes, hypertension and heart failure who presented with palpitations. Is this VT or SVT with aberrancy or fixed bundle branch block?
Image 1 - ECG case
This is a ("mostly") regular wide complex tachycardia (WCT) at a rate of about 214 bpm with a left bundle branch block (LBBB) morphology and left axis deviation (LAD).
It is difficult to be certain if there is AV dissociation. There is no capture and fusion beat. If we use the Brugada algorithm, there is an RS complex best seen in V3-V6. The RS interval is less than 100 ms. There is no AV dissociation. This is a LBBB-like WQRST with R wave in leads V1 and V2 less than 30 ms, the RS interval is less than 60 ms and the V6 is rS and not QR,QS or monophasic R. Thus, this favors SVT with aberrant conduction than VT.
Rule-out AV nodal reentry tachycardia and orthodromic reentry tachycardia
At certain points, distinct positive/upright P waves in lead II and III can be seen very close to the QRS (arrows). A positive P wave in the inferior lead will rule out AVN reentry tachycardia (with aberrancy or fixed bundle branch block) and orthodromic AVR because if this was an AVN reentry tachycardia or AVRT, the P waves will be inverted because of retrograde atrial activation.
With 1:1 conduction at a rate of about 214 bpm, the SVT would be atrial tachycardia vs a slow atrial flutter. This is supported by the distinct P waves.
A beta-blocker was given which reduced the rate and revealed 2:1 conduction. At times, you would be mistaken to interpret this as sinus tachycardia with a LBBB and left anterior fascicular block.
Image 2 - ECG case at a slower ventricular rate
At slower ventricular rate, the exta P waves can be seen.
Image 3 - ECG case at even a slower ventricular rate
Thus, the case is atrial tachycardia vs (slow) atrial flutter with 1:1 conduction with LBBB, LAD