Case: 55yo homeless man presents to the hospital altered and febrile to 39, seen two weeks ago at OSH for cough where EKG was documented as “normal sinus rhythm”

This EKG was obtained in the ED

(click image to enlarge)

What is the EKG finding and what underlying diagnosis should be at the top of your differential?

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Answer: EKG finding Bifasicular block

underlying condition to worry about: endocarditis with abscess formation


Bifasicular block is defined as RBBB + left anterior fasicular block or left posterior fasicular block. In this state  the ventricles are receiving electrical activity through one remaining fasicle rather than the typical three, aka a sign of extensive conduction system disease. Bifasicular block has several causes (ischemia, hyperkalemia, long standing HTN, congenital disease, primary degenerative disease of conduction system, abscess). In a patient with signs and symptoms of endocarditis and a newly developed bifasicular block you better be looking for an abscess!

diagnosing the LAFB/LPFB portion of bifasicular block

LAFB criteria: left axis deviation, small Q waves/tall R waves in I/L, small R waves/deep S in II/III/F, slightly prolonged QRS, increased QRS voltage in limb leads.

LPFB criteria (less common): right axis deviation, small R/deep S in I/L, small Q/tall R in II/III/F, QRS slightly prolonged, increased QRS in limb leads, no other causes for right axis deviation.

Combine either of these w/ RBBB and you get a bifasicular block.


RBBB +LAFB= bifasicular block.

Given the close proximity of the aortic ring to the conduction system, new conduction system abnormalities in a patient with endocarditis should warrant further investigation into abscess formation. Although EKG findings lack sensitivity (~25%), specificity is >90% for abscess formation. EKG changes most commonly occur with aortic valve disease though can be present with involvement of the other valves.

All manner of conduction disease can be present from first degree AV block to third, either bundle branch blocks, bifasicular or single fasicle blocks.

Overarching point: new EKG changes in somebody who fits the picture for endocarditis warrants investigation for abscess formation.