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Trifascicular block

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Title: Trifascicular block  
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Subject: First-degree atrioventricular block, Bundle branch block, Bundle of His, HACEK endocarditis, Right atrial enlargement
Collection: Cardiac Dysrhythmia
Publisher: World Heritage Encyclopedia

Trifascicular block

Trifascicular heart block
Classification and external resources
ICD-10 I45.3
ICD-9-CM 426.54

Trifascicular block is a problem with the electrical conduction of the heart. It is diagnosed on an electrocardiogram (ECG/EKG) and has three features:[1]


  • Differential diagnosis 1
  • Diagnosis 2
  • Treatment 3
  • References 4
  • External links 5
  • See also 6

Differential diagnosis

Trifascicular block is important to diagnose because it is difficult to tell based on the surface ECG whether the prolonged PR interval is due to disease in the AV node or due to diffuse distal conduction system disease.

  • In the former case, if the block at the AV node level becomes complete, the escape rhythm will originate from the bundle of His, which typically will generate heart rates in the 40s, allowing the individual to survive and complain of symptoms of fatigue or near-syncope to their physician.
  • In the latter case, however, because the conduction system disease is diffuse in nature, the escape rhythm may be fascicular or ventricular, which may be at rates that are life-threateningly low.


The diagnosis of whether the PR prolongation is due to AV nodal disease or diffuse conduction system disease is typically made by an electrophysiology study of the conduction system. In an electrophysiology study, trifascicular block due to AV nodal disease (true trifascicular block does not involve the AV node) block is represented by a prolonged AH interval (denoting prolonged time from impulse generation in the atria and conduction to the bundle of His) with a relatively preserved HV interval (denoting normal conduction from the bundle of His to the ventricles). Trifascicular block due to distal conduction system disease is represented by a normal AH interval and a prolonged HV interval.


The treatment for diffuse distal conduction system disease is insertion of a pacemaker. If the PR prolongation is due to AV nodal disease, a case may be made for observation, as it may never progress to complete heart block with life threateningly low heart rates.

Regardless of where in the conduction system the block is, if the block is believed to be the cause of syncope in an individual, a pacemaker is an appropriate treatment.


  1. ^ 1161101334 at GPnotebook

External links


See also

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