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.
How do you explain the change from his baseline EKG?
This is a example of rate dependent bundle branch block. There is an incomplete RBBB on the patient’s baseline ECG that becomes more pronounced at higher heart rates. Diseased His-Purkinjie fibers have prolnged refractory periods. So there are instances when a baseline ECG, at a normal rate, will have completely normal QRS morphology but at higher heart rates, impulses are delivered to the ventricular conduction system (His-Purkinjie fibers) before they complete their refractory period, resulting in a bundle branch block. These typically occur at a critical heart rate2.
What is the significance of this ECG finding?
This almost always indicates underlying disease in the conduction system, especially if there is any conduction delay at baseline (as there is in this patient)1. This can also be caused by antiarrhythmic drugs.
- Fisher, JD & Aronson, RS. Rate-dependent Bundle Branch Block: Occurrence, Causes, and Clinical Correlation. JACC. 1990;16(1): 240-243.
- Denes, P, et al: Electrophysiological observations in patients with rate dependent bundle branch block. Circulation.1975;51:244-250