1.5% of patients may have a bifascicular block on the electrocardiogram.
This alteration is a combination of intraventricular conduction disturbances, which can carry a risk of progression to complete atrioventricular block, especially in patients with syncopal symptoms 1.
The 2009 AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram 1 do not recommend the term «bifascicular block» because of the great variation in anatomy and pathology producing such pattern. The committee recommends that each conduction defect be described separately in terms of the structures involved 1.
Anatomy of Bifascicular Block
- 1- AV node and bundle of His
- 2- Right branch of bundle of His
- 3- Left branch of bundle of His
- 4- Anterior fascicle
- 5- Posterior fascicle
The ventricular conduction system can be classified as a three fascicles system. Consisting of the right bundle branch, and the anterior and posterior fascicles of the left bundle branch.
A bifascicular block is the combination of a blockade of two of these branches.
Bifascicular Blocks and complete AV block
In patients with bifascicular block in the electrocardiogram and episodes of syncope, there is the possibility that symptoms are secondary to an unknown advance atrioventricular block.
A more complex cardiology study should be performed in these patients, even, in some cases, it is advisable to perform an electrophysiological study to estimate the Hiss-ventricular interval (HV).
In patients with bifascicular block in the EKG without symptoms, the risk of advance atrioventricular block is low, but is recommended clinical and electrocardiographic monitoring.
Treatment of Bifascicular Block
Bifascicular blocks not require treatment except if the patient had syncope or an advance AV block is detected.
Permanent pacemaker implantation is indicated for complete AV block, or type II second-degree AV block. Also permanent pacemaker implantation is reasonable for syncope when other likely causes have been excluded 3.