Editing Trifascicular block

{{Medref|date=February 2021}}
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'''Trifascicular block''' is a problem with the [[Electrical conduction system of the heart|electrical conduction]] of the [[heart]], specifically the three fascicles of the [[bundle branches]] 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]]. 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]] (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 block]]s". 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]] is observed in a patient with a prolonged [[Electrical conduction system of the heart#AV node/Bundles: PR interval|PR interval]] ([[first degree AV block]]).

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.{{cn|date=February 2021}}

==Treatment==
An implantable cardiac [[artificial pacemaker|pacemaker]] or permanent [[artificial pacemaker|pacemaker]] is recommended in the following clinical circumstances. Class 1 recommendation is the strongest recommendation. Level A evidence is the highest level of evidence. {{cn|date=February 2021}}

''Class I''
* [[Bifascicular block]] + [[complete heart block]], even in the absence of symptoms (1b)
* [[Bifascicular block]] + [[Second-degree atrioventricular block|2nd degree AV Block]] Type 2, even in the absence of symptoms (1b)
* Alternating [[bundle branch block]]s, even in the absence of symptoms (1c)

''Class II''
* [[Bifascicular block]] + [[Syncope (medicine)|syncope]] + alternative causes ruled out (e.g. orthostasis, arrhythmia) (2a)

''Class III'' (i.e. [[artificial pacemaker|pacemaker]] not recommended)
* [[Bifascicular block]] without symptoms
* [[Bifascicular block]] + [[First-degree atrioventricular block|1st degree AV Block]], without symptoms

==References==
<references />

==External links==
{{Medical resources
| ICD10           = {{ICD10|I45.3}}
| ICD9            = {{ICD9|426.54}}
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* 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.
{{Circulatory system pathology}}

{{DEFAULTSORT:Trifascicular Block}}
[[Category:Cardiac arrhythmia]]