Not Your Average Syncope

HPI:  Elderly male with history of HTN, DM, and early dementia presents to ED following a witnessed syncopal event at home.  Family denies seizure activity, trauma, or anticoagulation.  He is now asymptomatic and back at clinical baseline.  Laboratory workup and CXR are unremarkable.  EKG is shown below:

ECG:

ECG Interpretation:
Normal sinus rhythm w/ bifascicular block (RBBB + LAFB).  Unchanged from multiple old ECGs dating back more than 8 years.

Discussion:
Bifascicular block is a combination of Right bundle branch block (RBBB) with either Left anterior fascicular block (LAFB) or Left posterior fascicular block (LPFB).  When present, ventricular conduction is dependent on only the single remaining fascicle.  EKG findings:

·  RBBB, and either
·  Left axis deviation > -45o, or
·  Right axis deviation > +110o

Bifascicular block is a common benign finding.  It is indicative of extensive conducting system disease, but risk of progressing to complete heart block is minimal (<1% per year).  In isolation, no acute treatment is indicated.  HOWEVER, syncope is a red flag!  Despite no change from old ECGs, in a patient with known bifascicular block a new finding of syncope can indicate intermittent 3rd degree AV block.  Patient is at high risk for PEA arrest, ventricular standstill, and sudden cardiac death.

Management:
·  Admit to telemetry-monitored floor
·  Mandatory cardiology consultation
·  Likely will receive permanent implanted pacemaker

By Dr. Blake Johnson

References:
1. McAnulty JH, Rahimtoola SH, Murphy E, DeMots H, Ritzmann L, Kanarek PE, et al. Natural history of “high-risk” bundle-branch block: final report of a prospective study. N Engl J Med. 1982 Jul 15; 307(3):137-43. PMID: 7088050

2. Burns, E. Bifascicular Block [Web log post]. Retrieved July 28, 2015, from http://lifeinthefastlane.com/ecg-library/basics/bifascicular-block/