This ladder diagram is from the following publication Atrioventricular Block with Narrow and Wide QRS: The Pause That Refreshes. The full article can be accessed here:
https://www.ahajournals.org/doi/full/10.1161/CIRCULATIONAHA.121.055990
The authors present the following differential diagnoses:
1. Sinus Rhythm with PVC's
2. Sinus Rhythm with equal His conduction delay
3. Sinus Rhythm with resolution of LBB refractoriness
