Trifascicular Block

Background

• 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

• Anterior MI
• Rheumatic fever
• Myocarditis
• Lyme disease
• Lenegre's disease
• Lev's disease
• SLE
• Systemic sclerosis
• Amyloidosis
• Hemochromatosis
• Sarcoidosis
• Hyperkalemia
• Toxicology
  • Beta blocker toxicity
  • Calcium channel blocker toxicity
  • Digoxin toxicity
  • Amiodarone

Types of second degree AV block

AV blocks

• First degree AV block
• Second degree
  • Second degree AV block type I (Wenkebach)
  • Second degree AV block type II
• Third degree AV block
• AV dissociation without complete heart block

Bundle and Fascicular Blocks

• Right Bundle Branch Block
• Left Bundle Branch Block
• Left Anterior Fascicular Block
• Left Posterior Fascicular Block
• Trifascicular Block

Premature Beats

• Premature atrial contraction
• Premature junctional complex
• Premature ventricular contraction

Evaluation

2nd degree AV Block Type 2 (4:3 conduction)

2nd degree AVB, 2:1 conduction, LBBB with buried p-waves in t-waves

Workup

• Evaluate for underlying pathology
• ECG
• Labs
  • CBC
  • Chemistry
  • Troponin
  • PT/PTT

Diagnosis

• 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

Management

• If symptomatic, standard ACLS guidelines for symptomatic bradycardia to include
  • Atropine 0.5mg IV q3-5min PRN total dose of 3mg
  • Transcutaneous pacing, followed by transvenous pacing
  • Dopamine IV consider for low BP 3mcg/kg/minute titrate up to 20 mcg/kg/minute
  • Dobutamine IV consider for heart failure at 5mcg/kg/minute titrate up to 20mcg/kg/minute if needed for HR and BP augmentation
• Treat underlying etiology
• Avoid AV nodal blocking agents (e.g. β-blockers)

Disposition

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

See Also

• Heart block