Rate Related Bundle Branch Blocks

Case and content by Brandon Fainstad, MD.
Edits and graphics by Yilin Zhang, MD. 


70 yo M presents with sepsis secondary to a presumed skin and soft tissue infection. On presentation, he is febrile to 40C, tachycardic to 145 bpm, BPs 90s/50s.

His EKG on presentation showed the following:

His baseline EKG shows:

How do you explain the change from his baseline EKG? 

What is the significance of this ECG finding?  

  1. Fisher, JD & Aronson, RS. Rate-dependent Bundle Branch Block: Occurrence, Causes, and Clinical Correlation. JACC. 1990;16(1): 240-243.
  2. Denes, P, et al: Electrophysiological observations in patients with rate dependent bundle branch block. Circulation.1975;51:244-250