Trifascicular block is a problem with the electrical conduction of the heart, specifically the three fascicles of the

bundle branches The bundle branches, or Tawara branches, are offshoots of the bundle of His in the heart's ventricle. They play an integral role in the electrical conduction system of the heart by transmitting cardiac action potentials from the bundle of His to ...

that carry electrical signals from the atrioventricular node to the ventricles. The three fascicles are one in the right bundle branch, and two in the left bundle branch the left anterior fascicle and the

left posterior fascicle The bundle branches, or Tawara branches, are offshoots of the bundle of His in the heart's Ventricle (heart), ventricle. They play an integral role in the electrical conduction system of the heart by transmitting cardiac action potentials from the ...

. A block at any of these levels can cause an abnormality to show on an electrocardiogram The most literal meaning of trifascicular block is complete heart block: all three fascicles are blocked. A second, and clinically distinct, definition of trifascicular block is a circumstance in which

right bundle branch block A right bundle branch block (RBBB) is a heart block in the right bundle branch of the electrical conduction system. During a right bundle branch block, the right ventricle is not directly activated by impulses travelling through the right bund ...

(RBBB) and left bundle branch block occur in the same patient, but at distinct points in time. For example, a patient that is found to have a RBBB one day and a LBBB another can be said to have "alternating bundle branch blocks". In this context, because all three fascicles show evidence of block at different points in time, the term trifascicular block is often used. Finally, the third meaning of trifascicular block refers to a specific finding on an electrocardiogram in which

bifascicular block Bifascicular block is a conduction abnormality in the heart where two of the three main fascicles of the His/Purkinje system are blocked. Most commonly, it refers to a combination of right bundle branch block (RBBB) and either left anterior fas ...

is observed in a patient with a prolonged PR interval (

first degree AV block First-degree atrioventricular block (AV block) is a disease of the electrical conduction system of the heart in which electrical impulses conduct from the cardiac atria to the ventricles through the atrioventricular node (AV node) more slowly tha ...

). The treatment of trifascicular block is highly dependent on which clinical entity (one of the three above) is being described.

Diagnosis

An electrophysiology study of the conduction system can help discern the severity of conduction system disease. In an electrophysiology study, trifascicular block due to AV nodal disease 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. In the absence of symptoms, a prolonged AH interval is likely benign while a prolonged HV interval is almost always pathologic.

Treatment

An implantable cardiac

pacemaker An artificial cardiac pacemaker (or artificial pacemaker, so as not to be confused with the natural cardiac pacemaker) or pacemaker is a medical device that generates electrical impulses delivered by electrodes to the chambers of the heart eith ...

or permanent

is recommended in the following clinical circumstances. Class 1 recommendation is the strongest recommendation. Level A evidence is the highest level of evidence. ''Class I'' *

Bifascicular block Bifascicular block is a conduction abnormality in the heart where two of the three main fascicles of the His/Purkinje system are blocked. Most commonly, it refers to a combination of right bundle branch block (RBBB) and either left anterior fas ...

+ complete heart block, even in the absence of symptoms (1b) *

+ 2nd degree AV Block Type 2, even in the absence of symptoms (1b) * Alternating bundle branch blocks, even in the absence of symptoms (1c) ''Class II'' *

+ syncope + alternative causes ruled out (e.g. orthostasis, arrhythmia) (2a) ''Class III'' (i.e.

not recommended) *

without symptoms *

+ 1st degree AV Block, without symptoms

References

External links

* http://www.ecglibrary.com/trifas.html * http://circ.ahajournals.org/content/97/13/1325.long - new guidelines in which trifascicular block terminology continues to be used. {{DEFAULTSORT:Trifascicular Block Cardiac arrhythmia