Trifascicular block is a problem with the

electrical conduction Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows ...

of the

heart The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide to t ...

, specifically the three fascicles of the bundle branches that carry electrical signals from the

atrioventricular node The atrioventricular node or AV node electrically connects the heart's atria and ventricles to coordinate beating in the top of the heart; it is part of the electrical conduction system of the heart. The AV node lies at the lower back section of t ...

to the ventricles. The three fascicles are one in the right bundle branch, and two in the left bundle branch the

left anterior fascicle 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 ...

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 Third-degree atrioventricular block (AV block) is a medical condition in which the electrical impulse generated in the sinoatrial node (SA node) in the atrium of the heart can not propagate to the ventricles. Because the impulse is blocked, an ...

: 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 bu ...

(RBBB) and

left bundle branch block Left bundle branch block (LBBB) is a conduction abnormality in the heart that can be seen on an electrocardiogram (ECG). In this condition, activation of the left ventricle of the heart is delayed, which causes the left ventricle to contract late ...

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 A bundle branch block is a defect in one the bundle branches in the electrical conduction system of the heart. Anatomy and physiology The heart's electrical activity begins in the sinoatrial node (the heart's natural pacemaker), which is situat ...

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

PR interval In electrocardiography, the PR interval is the period, measured in milliseconds, that extends from the beginning of the P wave (the onset of atrial depolarization) until the beginning of the QRS complex (the onset of ventricular depolarization ...

( 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

electrophysiology study A cardiac electrophysiology study (EP test or EP study) is a minimally invasive procedure using catheters introduced through a vein or artery to record electrical activity from within the heart. This electrical activity is recorded when the hear ...

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 The bundle of His (BH) or His bundle (HB) ( "hiss"Medical Terminology for Health Professions, Spiral bound Version'. Cengage Learning; 2016. . pp. 129–.) is a collection of heart muscle cells specialized for electrical conduction. As part of t ...

) 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 or permanent pacemaker 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 +

, even in the absence of symptoms (1b) * Bifascicular block + 2nd degree AV Block Type 2, even in the absence of symptoms (1b) * Alternating

s, even in the absence of symptoms (1c) ''Class II'' * Bifascicular block + syncope + alternative causes ruled out (e.g. orthostasis, arrhythmia) (2a) ''Class III'' (i.e. pacemaker not recommended) * Bifascicular block without symptoms * Bifascicular block + 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