Trifascicular Block

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  • First degree AV block, right bundle branch block, and left anterior hemiblock
  • Conduction disease of all three fascicles: fight bundle branch, and left posterior and left anterior fascicles
  • Trifascicular blocks can deteriorate into high grade blocks

Clinical Features

  • ECG will show a bifascicular block and a prolonged PR interval

Differential Diagnosis

Differential includes ischemic events, electrolyte abnormalities, and medication overdoses in addition to rheumatologic conditions[1][2]

Types of second degree AV block

AV Blocks

Bundle and Fascicular Blocks

Premature Beats


2nd degree AV Block Type 2 (4:3 conduction)
2nd degree AVB, 2:1 conduction, LBBB with buried p-waves in t-waves


  • Evaluate for underlying pathology
  • ECG
  • Labs


  • Prolongation of the PR interval (first degree AV block) AND
    • Right bundle branch block AND
    • Either left anterior fascicular block or left posterior fascicular block
  • ECG will show more atrial complexes than ventricular complex indicating high grade heart block
  • Right budle branch block + extreme left axis deviation (left anterior fascicular block) + atrioventricular heart block



  • Symptomatic patients should be admitted for monitoring and evaluation for a permanent pacemaker
  • Cardiology consult

See Also

External Links


  1. Hampton, JR. The ECG in Practice (5th edition), Churchill Livingstone 2008.
  2. Wagner, GS. Marriott’s Practical Electrocardiography (11th edition), Lippincott Williams & Wilkins 2007.
  3. Sovari AA et al. Second-Degree Atrioventricular Block Treatment & Management. eMedicine. Apr 28, 2014.